Lithium-ion secondary battery and manufacturing method therefor, assembly and electric device

Abstract

A lithium-ion secondary battery and a manufacturing method therefor, an assembly and an electric device. The lithium-ion secondary battery comprises a positive electrode sheet and an electrolyte; the positive electrode sheet comprises a positive electrode active layer, the positive electrode active layer comprises a positive electrode active material, the positive electrode active material comprises a lithium composite metal oxide material, and the lithium composite metal oxide material comprises non-agglomerated primary particles; the electrolyte comprises polycyclic sulfate.

Description

Lithium-ion secondary batteries, their preparation methods, components and electrical devices

[0001] Related applications

[0002] This application claims priority to Chinese patent application No. CN2025101256140, filed on January 27, 2025, entitled "Lithium-ion secondary battery and preparation method thereof, components and power device thereof", the entire contents of which are incorporated herein by reference. Technical Field

[0003] This application relates to the field of lithium-ion secondary battery technology, and further to lithium-ion secondary batteries and their preparation methods, components and electrical devices. Background Technology

[0004] The statements herein are provided only as background information in connection with this application and do not necessarily constitute prior art.

[0005] With the technological advancements in lithium-ion rechargeable batteries, they are increasingly being used in a wide range of fields, including smartphones, tablets, laptops, power tools, electric bicycles, electric motorcycles, electric vehicles, military equipment, and aerospace. They are also widely used in energy storage systems for hydropower, thermal power, wind power, and solar power plants. To meet the ever-increasing demand for longer battery life, the high-voltage performance of lithium-ion rechargeable batteries is receiving increasing attention. By increasing the operating voltage of lithium-ion rechargeable batteries, energy storage can be increased within the same battery volume or weight, thereby extending battery life. As the application of lithium-ion rechargeable batteries at high voltages becomes more widespread, high-temperature scenarios are often unavoidable. Non-limiting examples include high temperatures in summer, exposure to direct sunlight, and high-temperature storage and / or usage environments near the equator. Therefore, the requirements for the high-temperature performance of lithium-ion rechargeable batteries at high voltages are becoming increasingly stringent. Summary of the Invention

[0006] In view of the above problems, this application provides a lithium-ion secondary battery, its preparation method, components, and power application device. This lithium-ion secondary battery exhibits improved high-temperature performance under high voltage.

[0007] In a first aspect of this application, a lithium-ion secondary battery is provided.

[0008] In some embodiments, a lithium-ion secondary battery is provided, comprising a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the separator is disposed between the positive electrode and the negative electrode; the positive electrode includes a positive active layer, the positive active layer includes a positive active material, the positive active material includes a lithium composite metal oxide material, and the lithium composite metal oxide material includes non-agglomerated primary particles;

[0009] The electrolyte comprises an electrolyte salt, a non-aqueous solvent, and an additive; the additive comprises a polycyclic sulfate ester, wherein the polycyclic sulfate ester contains at least two cyclic sulfate ester units in its structural formula.

[0010] For high-voltage lithium-ion secondary batteries, incorporating lithium composite metal oxide (LCMO) materials into the positive electrode active material is beneficial for providing a higher voltage platform. However, the structural stability of LMO materials under high voltage faces certain challenges: during high-voltage cycling and / or storage, the positive electrode active material undergoes significant volume changes due to the extraction or insertion of numerous active ions, resulting in substantial volume stress. This makes the crystal structure of the LMO material susceptible to damage, increasing the risk of particle cracking and exacerbating interfacial side reactions, which in turn worsens the battery's cycle life and / or storage life under high voltage. Furthermore, in high-voltage battery systems operating at high temperatures, the exacerbated interfacial side reactions due to particle cracking in the LMO material are further intensified, severely deteriorating the battery's high-temperature performance. By incorporating non-agglomerated primary particles into the LMO material, compared to secondary particles with interfacial interfaces, these non-agglomerated primary particles can better resist volume stress changes and cracking risks during high-voltage cycling and / or storage, thus providing better structural stability for the LMO material under high voltage. However, for high-voltage applications in high-temperature environments, interfacial side reactions and other side reactions in the battery system are significantly amplified, leading to a sharp increase in the rate of battery capacity decay. When lithium-ion secondary batteries are cycled and / or stored under the dual conditions of high voltage and high temperature, even with non-agglomerated primary particles in lithium composite metal oxide materials, the cycle and / or storage performance of the batteries is still not ideal. Therefore, it is necessary to further improve the high-temperature performance of lithium-ion secondary batteries under high voltage.

[0011] In the lithium-ion secondary battery provided in the first aspect, the positive electrode active material includes a lithium composite metal oxide material, and the positive electrode active material includes non-agglomerated primary particles. In another aspect, by introducing a polycyclic sulfate additive into the electrolyte, under high voltage and high temperature, the polycyclic sulfate can participate in the construction or repair of the solid electrolyte interfacial film (the interfacial film at the positive electrode is denoted as the CEI film, and the interfacial film at the negative electrode is denoted as the SEI film) at the positive and negative electrodes, forming a denser interfacial film, which can significantly and persistently enhance the stability of the CEI film and the SEI film. The improved stability of the CEI film can enhance the performance of the lithium composite metal oxide material. The structural stability of the positive electrode active material, including non-agglomerated primary particles, in the lithium-ion composite metal oxide material at high voltage and high temperature is beneficial for suppressing interfacial side reactions at high voltage and high temperature, and delaying battery capacity decay during cycling or storage at high voltage and high temperature. Furthermore, the introduced polycyclic sulfate additive can absorb moisture that may be present in the electrolyte, reducing the generation of hydrofluoric acid. This significantly reduces the damage of hydrofluoric acid to the CEI and SEI films and the chemical corrosion of the positive electrode active material by hydrofluoric acid at high voltage and high temperature, further improving cycle performance and / or storage performance at high voltage and high temperature. Under high voltage and high temperature conditions, by utilizing the synergistic effect of polycyclic sulfates in the electrolyte in improving the stability of the CEI and SEI films, enhancing the structural stability of non-agglomerated primary particles in lithium-ion composite metal oxide materials, suppressing interfacial side reactions, absorbing moisture, and reducing hydrofluoric acid generation, the high-temperature performance of lithium-ion secondary batteries at high voltage can be significantly improved.

[0012] In addition, by using polycyclic sulfate additives to absorb moisture in the electrolyte, gas production caused by water participating in side reactions can be reduced.

[0013] The improvement described in any part of the context of this application is not intended to be limited to any theory.

[0014] In some embodiments, the structure of the cyclic sulfate unit is shown in formula (I):

[0015] In equation (I), R1 is a covalent bond, -CHQ 11 -or-CHQ 12 -CHQ 13 -; where Q 11 Q 12 and Q 13 Each is independently a H atom, halogen, and C atom. 1-6 Alkyl or C 1-6 Alkyl group.

[0016] In some embodiments, the polycyclic sulfate contains two structures of formula (II):

[0017] Among them, R7 is a hydrogen atom, a halogen, or a carbon atom. 1-6 Alkyl or C 1-6 Alkyl group.

[0018] In some embodiments, the polycyclic sulfate ester satisfies one or more of the following characteristics:

[0019] (ta1) Any cyclic sulfate ester unit is a 5- to 7-membered ring;

[0020] (ta2) Any two adjacent cyclic sulfate units are independently separated by -(CH2). q -、-O- or -(CH2) q1 -O-(CH2) q2 - Connected; where q is an integer selected from 0 to 3, and q1 and q2 are integers selected from 0 to 6 respectively, and 1≤(q1+q2)≤6.

[0021] In some embodiments, in the polycyclic sulfate ester, any two adjacent cyclic sulfate units are independently connected by a covalent bond, C 1-3 Alkylene, -O-, -L 11 -O-、-OL 11 -or-L 21 -OL 22 - Connected together, where L 11 C 1-6 Alkylene, L 21 and L 22 Each independently is C 1-3 Alkylene;

[0022] Optionally, any C 1-3 The alkylene group is independently methylene, 1,2-ethylene, or 1,3-propylene;

[0023] Optionally, any C 1-6 The alkylene group is independently methylene, 1,2-ethylene, 1,3-propylene, butylene, pentylene, or hexylene.

[0024] In some embodiments, the polycyclic sulfate ester satisfies one or more of the following characteristics:

[0025] (tb1) The number of cyclic sulfate units contained in the polycyclic sulfate ester is 2, 3 or 4;

[0026] (tb2) The cyclic sulfate units in the polycyclic sulfate ester are connected in series;

[0027] (tb3) The polycyclic sulfate contains a halogen, wherein the halogen is a fluorine atom;

[0028] (tb4) The polycyclic sulfate contains C 1-6 Alkyl, the C 1-6 Alkyl group is C 1-3 Alkyl group, which may be methyl group;

[0029] (tb5) The polycyclic sulfate contains C 1-6 Alkoxy, the C 1-6 The alkoxy group is C 1-3 Alkoxy, or alternatively methoxy.

[0030] In some embodiments, the polycyclic sulfate comprises a compound with the structural formula shown in formula (III); R 41 and R 42 Each is independently a H atom, halogen, and C atom. 1-6 Alkyl, C 1-6 Alkyl groups or structures represented by formula (IV);

[0031] Among them, R 11 R 12 and R 13 Each is independently a covalent bond, -CHQ 21 -or-CHQ 22 -CHQ 23 -; where Q 21 Q 22 and Q 23 Each is independently a H atom, halogen, and C atom. 1-6 Alkyl or C 1-6 Alkoxy;

[0032] R 71 H atom, halogen, C 1-6 Alkyl or C 1-6 Alkoxy;

[0033] L6 is -(CH2) n -or-(CH2) n1 -O-(CH2) n2 -, n is an integer selected from 0 to 3, n1 and n2 are integers selected from 0 to 3 respectively and 1≤(n1+n2)≤3;

[0034] L3 is -(CH2) q -、-O- or -(CH2) q1 -O-(CH2) q2 -; where q is an integer selected from 0 to 3, and q1 and q2 are integers selected from 0 to 6 respectively, and 1≤(q1+q2)≤6.

[0035] In some embodiments, the polycyclic sulfate includes at least one of the following compounds:

[0036] By adjusting the structure of the polycyclic sulfate, the degree of participation of the polycyclic sulfate in constructing the positive and negative electrode interface films and its water absorption effect can be adjusted under high voltage and high temperature, which is beneficial to better and durably improve the stability of the positive and negative electrode interface films, better absorb water, better improve the structural stability of non-agglomerated primary particles in the lithium composite metal oxide material, and better improve the cycling performance and / or storage performance of the battery under high voltage and high temperature.

[0037] As a non-limiting example, when the cyclic sulfate unit is a 5- to 7-membered ring, it is beneficial to make the polycyclic sulfate have a more appropriate stability by adjusting the ring strain.

[0038] As another non-limiting example, when the number of cyclic sulfate units contained in the polycyclic sulfate is 2, 3, or 4, it is beneficial to better adjust the degree of participation of the polycyclic sulfate in constructing the positive and negative electrode interface films and its water absorption effect under high voltage and high temperature, and further beneficial to better improve the high-temperature performance of the battery under high voltage.

[0039] In some embodiments, in a lithium-ion secondary battery, the mass ratio of the polycyclic sulfate in the electrolyte is denoted as W, satisfying 0 < W ≤ 1%, optionally 0.005% ≤ W ≤ 1%, further optionally 0.01% ≤ W ≤ 1%, and further optionally 0.02% ≤ W ≤ 0.5%.

[0040] By controlling the mass ratio (W) of the polycyclic sulfate in the electrolyte of the lithium-ion secondary battery, under high voltage and high temperature conditions, it is more beneficial to exert the synergistic improvement effects of the polycyclic sulfate in the electrolyte in improving the stability of the CEI film and SEI film, improving the structural stability of non-agglomerated primary particles in the lithium composite metal oxide material, inhibiting interfacial side reactions, absorbing water, reducing the generation of hydrofluoric acid, etc., which can more significantly improve the high-temperature performance of the lithium-ion secondary battery under high voltage, and at the same time is beneficial to control the internal resistance of the battery within a more appropriate range.

[0041] In addition, the higher the mass ratio of the polycyclic sulfate in the electrolyte, the more beneficial it is to reduce the gas generation caused by the participation of water in side reactions.

[0042] In some embodiments, the D v 50 of the lithium composite metal oxide material is 2.5 μm to 5 μm;

[0043] Optionally, the D <000 (should this be v ? Assuming so) 50 of the lithium composite metal oxide material is 3 μm to 4.5 μm.

[0044] By making the D of the lithium composite metal oxide materialv Controlling the particle size distribution of lithium composite metal oxide materials, including non-agglomerated primary particles, within the aforementioned range is beneficial for achieving a more suitable particle size distribution. This can indirectly adjust the contact area between the lithium composite metal oxide material and the electrolyte, which helps to control the interfacial side reactions between the lithium composite metal oxide material and the electrolyte at high voltage and high temperature. It can also take into account the structural stability advantage of the non-agglomerated primary particles in the lithium composite metal oxide material, enabling the lithium composite metal oxide material to better resist volume stress changes and cracking risks at high voltage and high temperature, thus improving the high-temperature performance of the battery at high voltage.

[0045] In some embodiments, the D of the positive electrode active material v 50 is 2.5μm to 5μm.

[0046] In some embodiments, the D of the positive electrode active material v 50 is 3μm to 4.5μm, and can be selected as 3.2μm to 4.2μm.

[0047] By using the D of the positive electrode active material v Controlling the particle size distribution of the positive electrode active material, including non-agglomerated primary particles, within the aforementioned range is beneficial for achieving a more suitable particle size distribution. This can indirectly adjust the contact area between the positive electrode active material and the electrolyte, which helps to control the interfacial side reactions between the positive electrode active material and the electrolyte at high voltage and high temperature. It can also take into account the structural stability advantage of non-agglomerated primary particles, enabling the positive electrode active material to better resist volume stress changes and cracking risks at high voltage and high temperature, thus improving the high-temperature performance of the battery at high voltage.

[0048] In some embodiments, the specific surface area of ​​the positive electrode active material is 0.3 m². 2 / g~1.5m 2 / g.

[0049] In some embodiments, the specific surface area of ​​the positive electrode active material is 0.5 m². 2 / g~1.2m 2 / g.

[0050] By adjusting the specific surface area of ​​the positive electrode active material within the aforementioned range, it is beneficial to ensure that the contact area between the positive electrode active material, including non-agglomerated primary particles, and the electrolyte is within a more suitable range. This helps to control the interfacial side reactions between the positive electrode active material and the electrolyte at high voltage and high temperature, while also taking into account the structural stability advantages of non-agglomerated primary particles. This allows the positive electrode active material to better resist volume stress changes and cracking risks at high voltage and high temperature, thus improving the high-temperature performance of the battery at high voltage.

[0051] By adjusting the D of the positive electrode active material v Having one or two of the parameters, such as 50 and the specific surface area of ​​the positive electrode active material, within the aforementioned range is beneficial for controlling the interfacial side reactions between the positive electrode active material and the electrolyte at high voltage and high temperature. It can also take into account the structural stability advantage of non-agglomerated primary particles, enabling the positive electrode active material to better resist volume stress changes and cracking risks at high voltage and high temperature, which is conducive to better improving the high-temperature performance of the battery at high voltage.

[0052] In some embodiments, the average particle size of the primary particles in the positive electrode active material is 1.1 μm to 3.0 μm.

[0053] In some embodiments, the average particle size of the primary particles in the positive electrode active material is 1.3 μm to 2.5 μm.

[0054] By controlling the average particle size of primary particles in the cathode active material within the aforementioned range, on the one hand, it is beneficial to ensure that the primary particles in the cathode active material have a more suitable size, which can reduce the content of small-sized, large-specific-surface-area non-agglomerated primary particles. Under high voltage and high temperature, this helps to reduce interfacial side reactions and improve the stability of the CEI film. On the other hand, for secondary particles that may exist in the cathode active material, it is also beneficial to increase the contact area between primary particles in the secondary particles, thereby improving the structural stability of secondary particles under high voltage and high temperature. This can better reduce the generation of fresh interfaces and slow down electrolyte consumption and battery capacity decay under high voltage and high temperature. Based on the aforementioned multiple effects, controlling the average particle size of primary particles in the cathode active material within the aforementioned range is beneficial to better improve the high-temperature performance of the battery under high voltage. Furthermore, when the average particle size of the primary particles in the positive electrode active material is relatively large, the solid-phase transport path of active ions becomes longer, which may lead to an increase in the battery's internal resistance. In the lithium-ion secondary battery provided in this application, by introducing polycyclic sulfates into the electrolyte, the battery's internal resistance can be controlled within a suitable range while significantly improving high-temperature performance under high voltage during the initial stage of cycling and / or storage. During the later stage of cycling and / or storage, the dense interfacial film constructed with the participation of polycyclic sulfates enables the positive electrode active material to still resist volume stress changes and cracking risks well after long-term cycling and / or storage, and effectively suppress the increase in impedance during the later stage of cycling and / or storage, thereby significantly improving the battery's internal resistance after long-term cycling and / or storage.

[0055] In some embodiments, the D of the positive electrode active material is... v The ratio of 50 to the average particle size of the primary particles in the positive electrode active material is denoted as B1, which satisfies 1≤B1≤2.5.

[0056] In some implementations, 1.6 ≤ B1 ≤ 2.2.

[0057] By using the D of the positive electrode active material v 50 (can be written as D) v 50 A The ratio of B1 to the average particle size (D1) of the primary particles in the positive electrode active material (B1 = D) v 50 A Controlling / D1) within the aforementioned range helps to make the median particle size of the positive electrode active material particles close to the average particle size of the primary particles, which are the basic unit of particles. This helps to reduce the agglomeration ratio of primary particles in the positive electrode active material and reduce the content of secondary particles as agglomerates of primary particles. Correspondingly, it increases the proportion of non-agglomerated primary particles, which can better resist the risk of particle cracking under high voltage and high temperature. This makes the positive electrode active material have better structural stability under high voltage and high temperature, and is more conducive to improving the high-temperature performance of the battery under high voltage.

[0058] In some embodiments, the positive electrode sheet satisfies one or more of the following characteristics:

[0059] (tc1) In the lithium composite metal oxide material, the proportion of non-agglomerated primary particles is greater than or equal to 70%;

[0060] (tc2) In the positive electrode active material, the proportion of non-agglomerated primary particles is greater than or equal to 65%.

[0061] In some embodiments, the positive electrode sheet satisfies one or more of the following characteristics:

[0062] (tc1') In the lithium composite metal oxide material, the proportion of non-agglomerated primary particles is greater than or equal to 80%;

[0063] (tc2') In the positive electrode active material, the proportion of non-agglomerated primary particles is greater than or equal to 75%.

[0064] By controlling one or both of the following parameters within the aforementioned ranges—the proportion of non-agglomerated primary particles in lithium composite metal oxide materials and the proportion of non-agglomerated primary particles in cathode active materials—it is beneficial to improve the structural stability of cathode active materials under high voltage and high temperature, thereby further improving the high-temperature performance of batteries under high voltage.

[0065] In some embodiments, the lithium composite metal oxide material includes one or more of lithium nickel-based oxides, lithium-rich manganese-based cathode materials, spinel lithium manganese oxide, lithium cobalt oxide, and any of the aforementioned modified forms; wherein the modified forms include one or more of doping modification and coating modification.

[0066] Introducing lithium nickel-based oxides into the positive electrode active material is beneficial to improving the energy density.

[0067] Introducing positive electrode active materials such as lithium-rich manganese-based positive electrode materials, spinel lithium manganate, and lithium cobalt oxide into the positive electrode active material is beneficial to making the positive electrode active material have better structural stability at high voltages and high temperatures, thereby being beneficial to better suppressing the attenuation of the battery capacity at high voltages and high temperatures, and being more beneficial to improving the high-temperature performance of the battery at high voltages.

[0068] In some embodiments, the lithium composite metal oxide material includes lithium nickel-based oxides, the lithium nickel-based oxides contain Li element, non-lithium metal elements, and O element, the non-lithium metal elements include Ni element, and the lithium nickel-based oxides satisfy one or more of the following characteristics:

[0069] (t1) The atomic molar ratio of Ni element to non-lithium metal elements in the lithium nickel-based oxides is q1, where 0.5 ≤ q1 < 1;

[0070] (t2) The lithium nickel-based oxides contain Ni element and Li element with an atomic molar ratio of q2:x2, where 0.5 ≤ q2 < 1 and 0.6 ≤ x2 ≤ 1.2;

[0071] (t3) The lithium nickel-based oxides contain Ni element and O element with an atomic molar ratio of q3:x3, where 0.5 ≤ q3 < 1 and 1.6 ≤ x3 ≤ 2.1.

[0072] In some embodiments, the lithium composite metal oxide material satisfies one or more of the following characteristics:

[0073] (i) 0.5 ≤ q1 ≤ 0.99;

[0074] (ii) 0.5 ≤ q2 ≤ 0.99;

[0075] (iii) 0.5 ≤ q3 ≤ 0.99;

[0076] (iv) The lithium nickel-based oxides contain Co element, and the atomic molar ratio of Co element to non-lithium metal elements in the lithium nickel-based oxides is q4, where 0 < q4 ≤ 0.25, optionally 0.02 ≤ q4 ≤ 0.25;

[0077] (v) The lithium nickel-based oxides contain Mn element, and the atomic molar ratio of Mn element to non-lithium metal elements in the lithium nickel-based oxides is q5, where 0 < q5 ≤ 0.35, optionally 0.1 ≤ q5 ≤ 0.35;

[0078] (vi) The lithium nickel-based oxide accounts for 80% to 100% of the mass of the lithium composite metal oxide material.

[0079] In some embodiments, the lithium composite metal oxide material satisfies one or more of the following characteristics:

[0080] (ti) 0.5 ≤ q1 ≤ 0.8 or 0.8 <q1≤0.99;

[0081] (tii) 0.5 ≤ q2 ≤ 0.8 or 0.8 <q2≤0.99;

[0082] (tiii) 0.8 ≤ x² ≤ 1.1;

[0083] (tiv) 0.5 ≤ q3 ≤ 0.8 or 0.8 <q3≤0.99;

[0084] (tv)1.8≤x3≤2.06;

[0085] (tvi) The lithium nickel-based oxide contains Co, where 0.05 ≤ q4 ≤ 0.2;

[0086] (tvii) The lithium nickel-based oxide contains Mn element, 0.15≤q5≤0.3;

[0087] (tviii) The lithium nickel-based oxide accounts for 90% to 100% of the mass of the lithium composite metal oxide material.

[0088] By controlling the nickel content of the lithium nickel-based oxide in the positive electrode active material, the crystal structure stability of the positive electrode active material is improved under high voltage and high temperature, which is beneficial to the battery having better high-temperature performance under high voltage.

[0089] In some embodiments, the lithium composite metal oxide material includes one or more of lithium nickel cobalt manganese-based oxides and modified forms of lithium nickel cobalt manganese-based oxides, wherein the modified forms include one or more of doping modification and coating modification.

[0090] In lithium nickel cobalt manganese-based oxides, nickel can increase energy density, cobalt can reduce cation mixing, enhance material structural stability and rate performance, and manganese can stabilize the layered structure of lithium nickel cobalt manganese-based oxide materials, but these effects are not limited to those described above.

[0091] In some embodiments, the positive electrode sheet satisfies one or more of the following characteristics:

[0092] (te1) The lithium composite metal oxide material in the positive electrode active layer accounts for 80% to 99% by mass;

[0093] (te2) The lithium composite metal oxide material accounts for 95% to 100% of the mass of the positive electrode active material.

[0094] In some embodiments, the positive electrode sheet satisfies one or more of the following characteristics:

[0095] (te1') The lithium composite metal oxide material in the positive electrode active layer accounts for 90% to 99% by mass;

[0096] (te2') The lithium composite metal oxide material accounts for 96% to 99% of the mass of the positive electrode active material.

[0097] By controlling one or more parameters, such as the mass ratio of lithium composite metal oxide material in the positive electrode active layer and the mass ratio of lithium composite metal oxide material in the positive electrode active material, within the aforementioned range, it is beneficial to better leverage the advantages of the aforementioned lithium composite metal oxide material.

[0098] In some embodiments, the positive electrode active material includes lithium iron phosphate positive electrode materials, which include at least one of lithium iron phosphate and a composite material of lithium iron phosphate and carbon.

[0099] Optionally, the lithium iron phosphate cathode material includes carbon-coated lithium iron phosphate.

[0100] At low SOC (State of Charge), most of the lithium ions in the positive electrode active material are released, and the positive electrode active material approaches the end of its discharge plateau, resulting in a significant drop in the battery's open-circuit voltage. Since the battery's power output is proportional to the terminal voltage, a decrease in voltage directly leads to a decrease in power performance. Furthermore, at low SOC, the lithium ion concentration in the positive electrode active material decreases, leading to a decrease in material conductivity and an increase in diffusion resistance. Based on the aforementioned effects, the battery's voltage and internal resistance are prone to instability at low SOC, affecting the stable power output at low SOC.

[0101] The voltage plateau of lithium iron phosphate cathode materials is relatively low and stable, and they have good voltage matching with lithium composite metal oxide materials. By introducing lithium iron phosphate cathode materials into the cathode active materials including lithium composite metal oxide materials, the discharge current of lithium iron phosphate cathode materials dominates at low SOC, and the cathode active materials have a relatively stable voltage plateau. This allows the battery to maintain a relatively stable voltage at low SOC, improves the stability of the battery's internal resistance, and improves the stability of power output at low SOC.

[0102] By introducing lithium iron phosphate (LFP) cathode materials into the positive electrode active material, the battery can maintain a relatively stable voltage at low SOC, thus improving the stability of the battery's internal resistance. Furthermore, by utilizing the absorption effect of polycyclic sulfates in the electrolyte on water, the decomposition side reaction of water at high voltage and high temperature can be significantly suppressed. This can delay or avoid the consumption of electrolyte by newly introduced water after the introduction of LFP cathode materials, and reduce the generation of hydrofluoric acid after the introduction of LFP cathode materials. Therefore, the adverse effects of introducing LFP cathode materials on high-voltage and high-temperature performance during cycling and / or the initial storage period can be significantly suppressed.

[0103] In some embodiments, the D of the lithium iron phosphate cathode material v 50 is 1μm to 11μm.

[0104] In some embodiments, the D of the lithium iron phosphate cathode material v 50 is 4μm to 9μm.

[0105] By using the D of lithium iron phosphate cathode materials v When the value of 50 is controlled within the aforementioned range, it has good size matching with lithium composite metal oxide materials, which is beneficial for better control of interfacial side reactions of positive electrode active materials. This is also beneficial for lithium-ion secondary batteries, including those using lithium composite metal oxide materials and lithium iron phosphate positive electrode materials, to have better high-temperature performance under high voltage.

[0106] In some embodiments, the positive electrode sheet satisfies one or more of the following characteristics:

[0107] (tf1) The lithium iron phosphate cathode material has a mass percentage of 0.8% to 4.95% in the cathode active layer, and can be selected as 0.9% to 3.96%;

[0108] (tf2) The lithium iron phosphate cathode material accounts for 1% to 5% of the mass of the cathode active material, and can be selected as 1% to 4%.

[0109] By controlling one or both of the following parameters within the aforementioned ranges—the mass ratio of lithium iron phosphate cathode material in the cathode active layer and the mass ratio of lithium iron phosphate cathode material in the cathode active material—it is beneficial to combine the advantages of both lithium composite metal oxide materials and lithium iron phosphate cathode materials under high voltage and high temperature, thereby achieving better high-temperature performance under high voltage.

[0110] In some embodiments, the electrolyte further includes one or both of fluoroethylene carbonate and tris(trimethylsilane) phosphate.

[0111] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0112] (tg1) The mass percentage of fluoroethylene carbonate in the electrolyte is 0.1% to 3%;

[0113] The mass percentage of (tg2) tris(trimethylsilane) phosphate in the electrolyte is 0.1% to 0.5%.

[0114] In some embodiments, the electrolyte satisfies one or more of the following characteristics:

[0115] (tg1') The mass percentage of fluoroethylene carbonate in the electrolyte is 0.1% to 2.5%;

[0116] The mass percentage of (tg2')tris(trimethylsilane)phosphate in the electrolyte is 0.1% to 0.35%.

[0117] By introducing fluoroethylene carbonate (FEC) into the electrolyte, a more stable SEI film can be formed on the surface of the negative electrode, which is beneficial to improving the cycle performance and / or storage performance of the battery under high voltage and high temperature.

[0118] By introducing tris(trimethylsilane) phosphate (TMSP) into the electrolyte, phosphorus-containing components can be introduced into the negative electrode SEI film. The negative electrode SEI film formed with the participation of TMSP has low impedance, which is beneficial to reducing the internal resistance of the battery.

[0119] In some embodiments, the electrolyte comprises lithium bis(fluorosulfonyl)imide.

[0120] In some embodiments, the molar volume concentration of the lithium bis(fluorosulfonyl)imide in the electrolyte is greater than 0 mol / L and less than or equal to 0.3 mol / L.

[0121] In some embodiments, the molar volume concentration of the lithium bis(fluorosulfonyl)imide in the electrolyte is 0.1 mol / L to 0.25 mol / L.

[0122] Lithium bisfluorosulfonylimide (LiFSI) can participate in the formation of a stable solid electrolyte interfacial film at both the positive and negative electrodes. Introducing LiFSI into the electrolyte can improve the stability of the positive and negative electrode interfacial film, which is beneficial for enhancing the stability of the positive and negative electrode active materials under high voltage and high temperature, better suppressing interfacial side reactions in the electrolyte, delaying battery capacity decay under high voltage and high temperature, and improving the battery's cycle and / or storage performance under high voltage and high temperature.

[0123] In addition, compared with traditional lithium hexafluorophosphate, LiFSI has a higher dissociation ability, which is beneficial to improving the liquid phase conductivity and thus reducing the battery internal resistance.

[0124] In some embodiments, the negative electrode sheet includes a negative electrode active layer, and the negative electrode active layer includes the negative electrode active material; the negative electrode active material includes one or more of carbon-based materials and silicon-based materials.

[0125] In some embodiments, the negative electrode active material includes graphite material;

[0126] Optionally, the graphite material accounts for 80% to 100% of the mass of the negative electrode active material, more preferably 90% to 100%, and even more preferably 97% to 100%.

[0127] The negative electrode active material in the negative electrode sheet can be one of the aforementioned types, but is not limited to these.

[0128] In some embodiments, the charging cutoff voltage of the lithium-ion secondary battery is greater than or equal to 4.2V, and can be selected as 4.2V to 4.5V.

[0129] In some embodiments, the charging cutoff voltage of the lithium-ion secondary battery is greater than or equal to 4.3V, and can be selected as 4.3V to 4.5V.

[0130] In a second aspect of this application, a lithium-ion secondary battery assembly is provided.

[0131] In some embodiments, the lithium-ion secondary battery of the first aspect of this application can be prepared by forming the lithium-ion secondary battery assembly of the second aspect of this application.

[0132] In some embodiments, a lithium-ion secondary battery assembly is provided, comprising a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the separator is disposed between the positive electrode and the negative electrode; the positive electrode includes a positive active layer, the positive active layer includes a positive active material, the positive active material includes a lithium composite metal oxide material, and the lithium composite metal oxide material includes non-agglomerated primary particles;

[0133] The electrolyte comprises an electrolyte salt, a non-aqueous solvent, and an additive; the additive comprises a polycyclic sulfate ester, wherein the polycyclic sulfate ester contains at least two cyclic sulfate ester units in its structural formula.

[0134] In the second aspect of the lithium-ion secondary battery assembly, the positive electrode active material includes lithium composite metal oxide material, and the positive electrode active material includes non-agglomerated primary particles; by introducing polycyclic sulfate additives into the electrolyte, polycyclic sulfates can participate in the construction of solid electrolyte interface films at the positive and negative electrodes more quickly during the formation process at high voltage and high temperature, forming a denser interface film, which can significantly enhance the stability of CEI film and SEI film. For the prepared lithium-ion secondary battery, the improved stability of the CEI film can significantly and persistently enhance the structural stability of the positive electrode active material, including non-agglomerated primary particles in the lithium composite metal oxide material, under high voltage and high temperature. It also helps suppress interfacial side reactions under high voltage and high temperature, delaying battery capacity decay during cycling or storage at high voltage and high temperature. Furthermore, the polycyclic sulfate additive can absorb moisture in the electrolyte, reducing the generation of hydrofluoric acid. This significantly reduces the damage of hydrofluoric acid to the CEI and SEI films and the chemical corrosion of the positive electrode active material under high voltage and high temperature, further improving the cycle performance and / or storage performance of the lithium-ion secondary battery under high voltage and high temperature. Using the lithium-ion secondary battery module provided in the second aspect of this application, the prepared lithium-ion secondary battery can exhibit significantly improved high-temperature performance under high voltage.

[0135] In some embodiments, in a lithium-ion secondary battery assembly, the polycyclic sulfate accounts for 0.1% to 3% of the mass of the electrolyte.

[0136] In some embodiments, in a lithium-ion secondary battery assembly, the polycyclic sulfate accounts for 0.2% to 2% of the mass of the electrolyte.

[0137] By controlling the mass percentage (W0) of polycyclic sulfates in the electrolyte of lithium-ion secondary battery components, a denser and more stable interfacial film can be formed during the formation process under high voltage and high temperature conditions. Furthermore, during cycling and / or storage under high voltage and high temperature conditions, polycyclic sulfates in the electrolyte can better exert their synergistic effects in improving the stability of CEI and SEI films, enhancing the structural stability of non-agglomerated primary particles in lithium composite metal oxide materials, suppressing interfacial side reactions, absorbing moisture, and reducing hydrofluoric acid generation. This can significantly improve the high-temperature performance of lithium-ion secondary batteries under high voltage, while also helping to control the battery internal resistance within a suitable range.

[0138] In some embodiments, the lithium-ion secondary battery assembly satisfies one or more of the following characteristics:

[0139] (tj1) The polycyclic sulfate is as defined in the first aspect of this application;

[0140] (tj2) The positive electrode sheet is as defined in the first aspect of this application;

[0141] (tj3) The negative electrode sheet is as defined in the first aspect of this application;

[0142] (tj4) The electrolyte also includes one or two of fluoroethylene carbonate and tris(trimethylsilane) phosphate;

[0143] (tj5) The electrolyte includes lithium difluorosulfonylimide.

[0144] In some embodiments, in the lithium-ion secondary battery assembly, the electrolyte satisfies one or more of the following characteristics:

[0145] (tk1) The electrolyte includes fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate in the electrolyte is 1% to 6%;

[0146] (tk2) The electrolyte includes tris(trimethylsilane) phosphate, and the mass percentage of tris(trimethylsilane) phosphate in the electrolyte is 0.1% to 1%;

[0147] (tk3) The electrolyte includes lithium bis(fluorosulfonyl)imide, and the molar concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is greater than 0 and less than or equal to 0.3 mol / L.

[0148] In some embodiments, in the lithium-ion secondary battery assembly, the electrolyte satisfies one or more of the following characteristics:

[0149] (tm1) The mass percentage of fluoroethylene carbonate in the electrolyte is 1% to 5%;

[0150] The mass percentage of (tm2) tris(trimethylsilane) phosphate in the electrolyte is 0.1% to 0.7%;

[0151] The molar concentration of (tm3) bis(fluorosulfonyl)imide lithium in the electrolyte is 0.1 mol / L to 0.3 mol / L.

[0152] In a third aspect of this application, a method for preparing a lithium-ion secondary battery is provided, which can be used to prepare the lithium-ion secondary battery described in the first aspect of this application.

[0153] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, which includes the following steps:

[0154] An electrode assembly comprising a positive electrode, a separator, and a negative electrode is placed inside a battery casing; wherein the separator is disposed between the positive electrode and the negative electrode.

[0155] An electrolyte is injected into the battery casing to prepare a lithium-ion secondary battery assembly;

[0156] Let it stand and soak; and

[0157] to form;

[0158] The positive electrode sheet includes a positive active layer, the positive active layer includes a positive active material, the positive active material includes a lithium composite metal oxide material, and the lithium composite metal oxide material includes non-agglomerated primary particles.

[0159] The electrolyte comprises an electrolyte salt, a non-aqueous solvent, and an additive; the additive comprises a polycyclic sulfate ester, wherein the polycyclic sulfate ester contains at least two cyclic sulfate ester units in its structural formula.

[0160] In this application, unless otherwise stated, "casing" and "battery casing" have the same meaning and can be used interchangeably.

[0161] The prepared lithium-ion secondary battery can have the advantages of the aforementioned lithium-ion secondary batteries, including significantly improved high-temperature performance at high voltage.

[0162] In some embodiments, the method for preparing the lithium-ion secondary battery satisfies one or more of the following characteristics:

[0163] (tn1) After injecting electrolyte into the battery casing, the lithium-ion secondary battery assembly described in the second aspect of this application is obtained;

[0164] (tn2) In the electrode assembly, the positive electrode is as defined in the first aspect of this application;

[0165] (tn3) In the electrode assembly, the negative electrode is as defined in the first aspect of this application.

[0166] In a fourth aspect of this application, a lithium-ion secondary battery is provided, which is obtained by performing a formation process on the lithium-ion secondary battery assembly described in the second aspect of this application, or by using the lithium-ion secondary battery preparation method described in the third aspect of this application.

[0167] In a fifth aspect of this application, an electrical device is provided, comprising at least one of the lithium-ion secondary battery described in the first aspect of this application, the lithium-ion secondary battery described in the fourth aspect of this application, and a lithium-ion secondary battery prepared using the lithium-ion secondary battery assembly described in the second aspect of this application.

[0168] Details of one or more embodiments or examples of this application are set forth in the following drawings and description. Other features, objects, and advantages of this application will become apparent from the specification, drawings, and claims. Attached Figure Description

[0169] To better describe and illustrate the embodiments, examples, or models provided in this application, reference may be made to one or more accompanying drawings. Additional details or examples used to describe the drawings should not be considered as limiting the scope of any of the disclosed applications, the currently described embodiments, examples, or models, or the best mode of conduct of these applications as currently understood. Furthermore, the same reference numerals denote the same parts throughout the drawings. In the drawings:

[0170] Figure 1 is a schematic diagram of a battery cell according to an embodiment of this application.

[0171] Figure 2 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 1.

[0172] Figure 3 is a schematic diagram of a battery device according to an embodiment of this application.

[0173] Figure 4 is a schematic diagram of a battery pack according to one embodiment of this application.

[0174] Figure 5 is an exploded view of the battery pack of one embodiment of this application shown in Figure 4.

[0175] Figure 6 is a schematic diagram of an electrical device using a lithium-ion secondary battery as a power source according to an embodiment of this application.

[0176] Explanation of reference numerals in the attached drawings: 1, battery pack; 2, upper casing; 3, lower casing; 4, battery assembly; 5, individual battery cell; 51, housing; 52, electrode assembly; 53, cover plate; 6, electrical device. Detailed Implementation

[0177] The following describes in detail, with appropriate reference to the accompanying drawings, some embodiments and examples of the lithium-ion secondary battery and its preparation method, components, and power-consuming device of this application. However, some unnecessary detailed descriptions may be omitted. For example, detailed descriptions of well-known matters and repetitive descriptions of practically identical structures may be omitted. This is to avoid unnecessarily lengthy descriptions and to facilitate understanding by those skilled in the art. Furthermore, the accompanying drawings and the following description are provided to enable those skilled in the art to fully understand this application and are not intended to limit the subject matter of the claims.

[0178] The "range" disclosed in this application can be defined in the form of a lower limit and an upper limit. A given range is defined by selecting a lower limit and an upper limit, which define the boundaries of a particular range. Ranges defined in this way can include or exclude endpoints. Any endpoint can be included or excluded independently and can be combined arbitrarily; that is, any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for a specific parameter, it is expected that ranges of 60-110 and 80-120 are also included. Furthermore, if minimum range values ​​1 and 2 are listed, and maximum range values ​​3, 4, and 5 are also listed, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5. In this application, unless otherwise stated, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0" and "5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when describing a parameter as an integer ≥ 2, it is equivalent to listing integers such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, and 12 for that parameter. For instance, when describing a parameter as an integer selected from "2-10", it is equivalent to listing the integers 2, 3, 4, 5, 6, 7, 8, 9, and 10.

[0179] In this application, the term "numerical value" includes the number itself and its reasonable approximations. The definition of "numerical value" can apply to discrete numerical points or to the endpoints of a numerical range. Unless otherwise specified, the term "approximation" covers a numerical interval based on a reasonable range of fluctuations of the number itself. This reasonable range of fluctuations can vary depending on the type and magnitude of the number. This reasonable range of fluctuations can be reasonably determined based on the accuracy of the testing or measurement method. Therefore, when referring to a numerical value or a numerical range, unless otherwise specified, it should be understood that the numerical value includes its reasonable approximation, and the numerical range includes reasonable approximations at both endpoints. Those skilled in the art will understand that acceptable fluctuation ranges of the relevant approximations can be included within the definition of the numerical value or the numerical range. In this application, unless otherwise specified, "N1" can be reasonably understood as "about N1," and "N1~N2" can be reasonably understood as "about N1 to about N2," where N1 and N2 are two unequal numerical values.

[0180] In this application, unless otherwise specified, "about" means within a reasonable range above and below the stated number, and the range of fluctuation may vary depending on the type and value of the stated number. For example, a range of ±10%, ±5%, ±2%, ±1%, etc., may be allowed. For example, taking "about 20°C" and its approximation as ±1°C, approximate values ​​such as 19°C, 19.5°C, etc., within the approximation range indicated by "about 20°C" should also be included in the range indicated by "about 20°C".

[0181] In this application, the terms "multiple," "various," "multiple items," "several," etc., unless otherwise specified, refer to a quantity greater than or equal to 2. For example, "one or more" means one or more (greater than or equal to) two. It can be understood that when "any number of" items are involved, it refers to any suitable combination of multiple items, that is, a combination of "any number of" items in a manner that does not conflict and enables the implementation of this application.

[0182] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0183] In this document, the term "embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment may be included in at least one embodiment or implementation of this application. The appearance of this phrase in various places throughout the specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment mutually exclusive with other embodiments. It will be explicitly and implicitly understood by those skilled in the art that the embodiments described herein can be combined with other embodiments. The term "implementation" as used herein has a similar understanding.

[0184] In this application, open-ended technical features or solutions described using terms such as "containing," "comprising," or "including" do not exclude additional members beyond those listed unless otherwise specified. They can be considered as providing both closed-ended features or solutions comprised of the listed members and open-ended features or solutions that include additional members beyond the listed members. For example, if 'a' includes a1, a2, and a3, it may also include other members or exclude additional members unless otherwise specified. This can be considered as providing both features or solutions where "a consists of a1, a2, and a3" or "a is selected from a1, a2, and a3," and features or solutions where "a includes not only a1, a2, and a3, but also other members."

[0185] In this application, unless otherwise specified, M (e.g., m1) means that m1 is a non-limiting example of M, and it is understood that M is not limited to m1.

[0186] In this application, "optionally," "optionally," and "optional" mean that something is optional, that is, it is selected from either "with" or "without." If multiple "options" appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "option" is independent. Unless otherwise specified, the descriptions such as "optionally include" and "optionally contain" in this application, taking "optionally include" as an example, mean "may include or not include."

[0187] In this application, unless otherwise specified, the features or solutions corresponding to "and / or" include any one of two or more of the related listed items, as well as any and all combinations of the related listed items. Any and all combinations include any two related listed items, any more related listed items, or a combination of all related listed items. For example, "M and / or N" represents the group consisting of M, N, and "a combination of M and N". "Containing M and / or N" can mean "containing M, containing N, and containing both M and N", or "containing M, containing N, or containing both M and N", and can be appropriately understood according to the context.

[0188] The terms “combinations of,” “any combination of,” and “any combination of” used in this article include all suitable combinations of any two or more of the listed items.

[0189] In this document, the term "suitable" in phrases such as "suitable combination," "suitable method," and "any suitable method" refers to the technical solution that enables the implementation of this application.

[0190] In this document, terms such as "preferred," "better," "more suitable," "ideal," "good," and "superior" are merely descriptions of more effective implementation methods or embodiments, and should be understood not to limit the scope of protection of this application. If multiple "preferred" terms appear in a technical solution, unless otherwise specified and there are no contradictions or mutual constraints, each "preferred" term shall be independent.

[0191] In this application, terms such as "further," "even more," "especially," "for example," "as," "example," and "exemplary" are used for descriptive purposes to indicate differences in content, but should not be construed as limiting the scope of protection of this application.

[0192] In this application, the terms "first aspect," "second aspect," "third aspect," "fourth aspect," and "fifth aspect," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or quantity, nor should they be construed as implicitly indicating the importance or quantity of the indicated technical features. Moreover, "first," "second," "third," "fourth," and "fifth" etc. serve only as a non-exhaustive enumeration and should be understood not to constitute a closed limitation on quantity.

[0193] In the description of this application, it should be understood that the terms "length", "width", "thickness", "height", "upper", "lower", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this application.

[0194] In this application, unless otherwise expressly specified and limited, the terms "connected," "linked," etc., should be interpreted broadly, for example, as a fixed connection, a detachable connection, or an integral part. Those skilled in the art can understand the meaning of the above terms in this application according to the circumstances.

[0195] In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediate medium. In this application, unless otherwise expressly specified and limited, the phrase "above" or "below" the second feature can indicate a horizontal positional relationship, or it can simply indicate the existence of an attachment relationship without specifying a horizontal positional relationship.

[0196] In this application, the term "room temperature" generally refers to 4℃ to 35℃, and may refer to 20℃ ± 5℃. In some embodiments or examples of this application, room temperature refers to 20℃ to 30℃.

[0197] In this application, when a unit is specified for a data range, if it is only followed by the right endpoint, it indicates that the units for the left and right endpoints are the same. For example, 3~5μm or 3-5μm both mean that the units for the left endpoint "3" and the right endpoint "5" are both μm (micrometers), and have the same meaning as 3μm~5μm. Furthermore, similar descriptions of other parameters such as temperature and size are interpreted in the same way.

[0198] In this application, "greater than or equal to", "greater than or equal to", and "≥" have the same meaning and can be used interchangeably; "less than or equal to", "less than or equal to", and "≤" have the same meaning and can be used interchangeably; "greater than" can be equivalently represented as ">", and "less than" can be equivalently represented as "<". In this application, unless otherwise specified, "greater than or equal to" and "≥" can be considered as providing two additional solutions: "greater than" and "equal to". In this application, unless otherwise specified, "less than or equal to" and "≤" can be considered as providing two additional solutions: "less than" and "equal to".

[0199] In this application, the exemplary descriptions such as "in some implementations (or embodiments)" and "in one implementation (or embodiment)" may cover, but are not limited to, the following meanings: these solutions can be combined with other solutions in a suitable manner to form new technical solutions.

[0200] Unless otherwise stated, the improvements described in this application are not intended to be limited to any theoretical constraints.

[0201] With the increasing prevalence of lithium-ion rechargeable batteries, their high-voltage performance is receiving more and more attention in order to meet the ever-growing demand for longer driving ranges. Increasing the operating voltage of lithium-ion rechargeable batteries can increase energy storage while maintaining the same battery volume or weight, thereby extending driving time. As the application of lithium-ion rechargeable batteries at high voltages becomes more widespread, high-temperature scenarios are often unavoidable. Non-limiting examples include high temperatures in summer, exposure to direct sunlight, and high-temperature storage and / or usage environments near the equator. Therefore, the requirements for the high-temperature performance of lithium-ion rechargeable batteries under high voltages are becoming increasingly stringent.

[0202] In this application, unless otherwise specified, "high voltage" is greater than or equal to 4.2V, and can be selected from 4.2V to 4.5V, or any of the following voltages or a range selected from any two of the following voltages: 4.2V, 4.3V, 4.4V, 4.5V, etc.

[0203] In this application, unless otherwise specified, "high temperature" can be 35℃~60℃, optionally 37℃~60℃, further optionally 40℃~60℃, and even further optionally 45℃~60℃, but is not limited thereto.

[0204] In this application, unless otherwise stated, "high-temperature performance under high voltage" may include at least one of high-voltage cycling performance and high-voltage storage performance.

[0205] For high-voltage lithium-ion secondary batteries, incorporating lithium composite metal oxide materials into the positive electrode active material can provide a higher voltage platform. However, the structural stability of lithium composite metal oxide materials at high voltages faces certain challenges: during cycling and / or storage at high voltages, the positive electrode active material undergoes significant ion extraction and insertion, leading to repeated large volume changes in its crystal structure and subjecting it to substantial volume change stress. This makes the crystal structure of the lithium composite metal oxide material prone to damage, increasing the risk of particle cracking and exacerbating interfacial side reactions, which in turn worsens the battery's cycle life and / or storage life at high voltages. Furthermore, in high-voltage battery systems operating at high temperatures, the exacerbated interfacial side reactions due to particle cracking of the lithium composite metal oxide material are further intensified, severely deteriorating the battery's high-temperature performance at high voltages.

[0206] To improve the structural stability of cathode active materials under high voltage and thus enhance battery storage performance at high voltage, non-agglomerated primary particles can be incorporated into lithium composite metal oxide materials. Compared to secondary particles with inter-particle interfaces, non-agglomerated primary particles lack the inter-particle interfaces found in secondary particles. This allows non-agglomerated primary particles to better resist volumetric stress changes and cracking risks during cycling and / or storage at high voltage, resulting in better structural stability of lithium composite metal oxide materials at high voltage.

[0207] However, for high-voltage applications in high-temperature environments, interfacial side reactions and other side reactions in the battery system are significantly amplified, leading to a sharp increase in the rate of battery capacity decay. When lithium-ion secondary batteries are cycled and / or stored under the dual conditions of high voltage and high temperature, even with the inclusion of non-agglomerated primary particles in lithium composite metal oxide materials, the cycle and / or storage performance of the battery is still not ideal. Therefore, it is necessary to further improve the high-temperature performance of lithium-ion secondary batteries under high voltage. When using a single type of additive such as 1,3-propanesulfonyl lactone (PS), 1,3-propenesulfonate lactone (PST), acid anhydride, or siloxane additives to enhance the film formation of the positive and / or negative electrodes, the improvement in cycle life under high voltage and high temperature is still not ideal, and may also introduce other drawbacks, such as environmental issues (e.g., using a single type of PS) and excessive interfacial impedance (e.g., acid anhydride).

[0208] According to various embodiments and examples of this application, this application provides a lithium-ion secondary battery and its preparation method, components, and power application device. This lithium-ion secondary battery exhibits improved high-temperature performance under high voltage.

[0209] In this application, unless otherwise specified, the term "lithium-ion secondary battery" refers to a secondary battery in which the active ions include lithium ions, and "lithium-ion battery cell" refers to a battery cell in which the active ions include lithium ions. Typically, a lithium-ion secondary battery includes a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of ions between the positive and negative electrodes. The separator, placed between the positive and negative electrodes, primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0210] In this application, unless otherwise specified, "electrode active material layer" includes at least one of the positive active material layer of the positive electrode sheet and the negative active material layer of the negative electrode sheet. Depending on the specific circumstances, the electrode active material layer may refer to either the positive active material layer or the negative active material layer. It is understood that the positive active material layer contains positive active material, and the negative active material layer contains negative active material. In this application, "electrode active material layer" may also be referred to as "active material layer," "positive active material layer" may also be referred to as "positive active layer," and "negative active material layer" may also be referred to as "negative active layer."

[0211] In this application, the terms "electrode sheet" and "electrode plate" have the same meaning and can be used interchangeably. An electrode sheet can be a positive electrode sheet or a negative electrode sheet, and the "active material" or "active substance" in the electrode sheet has the ability to reversibly insert and extract active ions.

[0212] In this application, the term "negative electrode sheet" includes a negative electrode active layer, which includes a negative electrode active material. The term "negative electrode active material" refers to a material used in a negative electrode sheet that is capable of reversibly inserting and de-inserting active ions.

[0213] In this application, unless otherwise specified, "negative electrode sheet" includes a negative electrode current collector. A "negative electrode current collector" refers to a structure responsible for collecting and conducting electrons at the negative electrode. In the negative electrode sheet, the negative electrode active layer is located on at least one side of the negative electrode current collector, and may be located on one or both sides of the negative electrode current collector.

[0214] In this application, the term "positive electrode sheet" includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material. The term "positive electrode active material" refers to a material used in a positive electrode sheet that is capable of reversibly extracting and inserting active ions.

[0215] In this application, unless otherwise specified, "positive electrode sheet" includes a positive current collector. A "positive current collector" refers to a structure responsible for collecting and conducting electrons at the positive electrode. In the positive electrode sheet, the positive active layer is located on at least one side of the positive current collector, and may be located on one or both sides of the positive current collector.

[0216] In this application, unless otherwise specified, "separation membrane" and "diaphragm" have the same meaning and can be used interchangeably.

[0217] In a first aspect of this application, a lithium-ion secondary battery is provided, which has improved high-temperature performance at high voltage.

[0218] In some embodiments, a lithium-ion secondary battery is provided, comprising a positive electrode and an electrolyte. The positive electrode includes a positive active layer, which includes a positive active material, which includes a lithium composite metal oxide material comprising non-agglomerated primary particles. The electrolyte comprises a polycyclic sulfate. This lithium-ion secondary battery exhibits improved high-temperature performance at high voltages.

[0219] In some embodiments, a lithium-ion secondary battery is provided, comprising a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the separator is disposed between the positive and negative electrodes; the positive electrode includes a positive active layer, the positive active layer includes a positive active material, the positive active material includes a lithium composite metal oxide material, and the lithium composite metal oxide material includes non-agglomerated primary particles; the electrolyte includes a polycyclic sulfate.

[0220] In some embodiments, the electrolyte includes an electrolyte salt, a non-aqueous solvent, and additives; the additives include polycyclic sulfates.

[0221] In some embodiments, a lithium-ion secondary battery is provided, comprising a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the separator is disposed between the positive and negative electrodes; the positive electrode includes a positive active layer, the positive active layer includes a positive active material, the positive active material includes a lithium composite metal oxide material, and the lithium composite metal oxide material includes non-agglomerated primary particles; the electrolyte includes an electrolyte salt, a non-aqueous solvent, and an additive; the additive includes a polycyclic sulfate, the polycyclic sulfate containing at least two cyclic sulfate units in its structural formula.

[0222] In some embodiments, a lithium-ion secondary battery is provided, which includes a housing and a positive electrode, a separator, a negative electrode and an electrolyte disposed inside the housing, wherein a separator is disposed between the positive electrode and the negative electrode.

[0223] The positive electrode sheet includes a positive electrode active layer, the positive electrode active layer includes a positive electrode active material, the positive electrode active material includes a lithium composite metal oxide material, and the lithium composite metal oxide material includes non-agglomerated primary particles.

[0224] The electrolyte includes electrolyte salts, non-aqueous solvents, and additives, including polycyclic sulfates.

[0225] In this application, unless otherwise specified, "lithium composite metal oxide material" refers to a positive electrode active material comprising lithium, non-lithium metal elements, and oxygen. Typically, the non-lithium metal elements in lithium composite metal oxide materials include transition metal elements; therefore, lithium composite metal oxide materials can also be called "lithium transition metal oxide materials." Non-limitingly, in lithium composite metal oxide materials, the molar percentage of transition metal elements relative to non-lithium metal elements can be 90% to 100%, and can also be any of the following percentages or a range selected from any two of the following percentages: 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0226] In this application, "non-lithium metal element" refers to a metal element that is not lithium.

[0227] In this application, unless otherwise specified, "primary particles" in the positive electrode active material refer to the basic particulate unit of the positive electrode active material. It is understood that primary particles exist in the positive electrode active material. In the positive electrode active material, at least a portion of the primary particles exist in a non-agglomerated state, and a portion may also exist in an agglomerated state. Non-agglomerated primary particles can be referred to as "non-agglomerated primary particles," and aggregates formed by multiple primary particles can be referred to as "secondary particles." It is understood that the positive electrode active material includes at least non-agglomerated primary particles. The positive electrode active material may or may not include secondary particles.

[0228] In this application, unless otherwise specified, "non-agglomerated primary particles" refers to primary particles existing in a non-agglomerated state in the positive electrode active material. Unless otherwise specified, in the lithium-ion secondary battery provided in this application, the lithium composite metal oxide material includes non-agglomerated primary particles. It is understood that the positive electrode active material includes non-agglomerated primary particles, at least a portion of the lithium composite metal oxide material is non-agglomerated primary particles, and the non-agglomerated primary particles in the positive electrode active material include at least a portion of the lithium composite metal oxide material. When the positive electrode active material also contains other types of positive electrode active materials different from the lithium composite metal oxide material, it is understood that the non-agglomerated primary particles in the positive electrode active material may include other types of positive electrode active materials.

[0229] In this application, unless otherwise specified, "electrolyte" includes at least an electrolyte salt and a solvent. The solvent in the electrolyte includes non-aqueous solvents. It is understood that due to factors such as the water content of the raw materials used to prepare the electrode sheets, and the potential introduction of water from the air during electrode sheet preparation and battery assembly, a small or trace amount of water may be present in the electrolyte.

[0230] In the lithium-ion secondary battery provided in this application, it is understood that the positive electrode and the negative electrode are wetted by the electrolyte.

[0231] In this application, unless otherwise specified, "non-aqueous solvent" means a solvent that is not water.

[0232] In the lithium-ion secondary battery provided in this application, the electrolyte may include polycyclic sulfates, such as the lithium-ion secondary battery provided in the first aspect of this application.

[0233] In this application, the term "polycyclic sulfate" refers to a cyclic sulfate compound containing at least two cyclic sulfate units in its structure. Polycyclic sulfates can participate in the formation of solid electrolyte interfacial films by undergoing redox reactions at both the positive and negative electrodes. The interfacial film at the positive electrode can be denoted as a CEI film, and the interfacial film at the negative electrode can be denoted as a SEI film. Furthermore, compared to some traditional film-forming additives, polycyclic sulfates typically preferentially form films, and the resulting films are denser.

[0234] In the lithium-ion secondary battery provided in the first aspect of this application, the positive electrode active material includes a lithium composite metal oxide material, and the positive electrode active material includes non-agglomerated primary particles. On the other hand, by introducing polycyclic sulfate additives into the electrolyte, under high voltage and high temperature, the polycyclic sulfates can participate in the construction or repair of the solid electrolyte interfacial film (the interfacial film at the positive electrode is denoted as the CEI film, and the interfacial film at the negative electrode is denoted as the SEI film) at the positive and negative electrodes, forming a denser interfacial film, which can significantly and persistently enhance the stability of the CEI and SEI films. The improved stability of the CEI film can improve the performance of the lithium composite metal oxide material. The structural stability of the positive electrode active material, including non-agglomerated primary particles in the oxide material, under high voltage and high temperature is beneficial for suppressing interfacial side reactions under high voltage and high temperature, and delaying battery capacity decay during cycling or storage under high voltage and high temperature. Furthermore, the introduced polycyclic sulfate additive can absorb moisture that may be present in the electrolyte, reducing the generation of hydrofluoric acid. This significantly reduces the damage of hydrofluoric acid to the CEI and SEI films and the chemical corrosion of the positive electrode active material under high voltage and high temperature, further improving cycle performance and / or storage performance under high voltage and high temperature. Under high voltage and high temperature conditions, by utilizing the synergistic effect of polycyclic sulfates in the electrolyte in improving the stability of the CEI and SEI films, enhancing the structural stability of non-agglomerated primary particles in lithium composite metal oxide materials, suppressing interfacial side reactions, absorbing moisture, and reducing hydrofluoric acid generation, the high-temperature performance of lithium-ion secondary batteries under high voltage can be significantly improved.

[0235] In addition, by using polycyclic sulfate additives to absorb moisture in the electrolyte, gas production caused by water participating in side reactions can be reduced.

[0236] The improvement described in any part of the context of this application is not intended to be limited to any theory.

[0237] The composition of the positive electrode active material and electrolyte can be controlled by selecting appropriate raw materials or materials.

[0238] Those skilled in the art can identify the components of the electrolyte in a lithium-ion secondary battery using one or more of the following detection methods, including but not limited to: 1H NMR (1H NMR) spectroscopy. 1 Methods such as ¹H NMR, high-performance liquid chromatography (HPLC), matrix-assisted laser desorption / ionization mass spectrometry (MADI-TOF), Fourier transform infrared spectroscopy (FT-IR), and ultraviolet spectroscopy are available. The sample preparation and testing methods for these methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the structure of the material or substance and the characteristics of the sample. As a non-limiting example, FT-IR, ultraviolet spectroscopy, etc., can be used. 1 One or more of the following methods may be used to detect the types and contents of electrolyte components: ¹H NMR, mass spectrometry, MADI-TOF, etc., but not limited to these.

[0239] In some embodiments, the structure of the cyclic sulfate unit is shown in formula (I):

[0240] In equation (I), R1 is a covalent bond, C 1-2 Alkylene or substituted C 1-2 Alkylene. When R1 is a covalent bond, i.e., R1 does not exist, the structural formula of equation (I) is: C 1-2 The alkylene group can be methylene or 1,2-ethylene. Substituted C 1-2 The substituents in the alkylene group can be one or more Q groups, and further, any Q group can independently be a halogen, C, or C. 1-6 Alkyl or C 1-6 Alkyl group. Substituted C 1-2 Non-limiting examples of alkylene groups can be -CHQ 01 -or-CHQ 02 -CHQ 03 -; where Q 01 Q 02 and Q 03 They can each be halogens and C independently. 1-6 Alkyl or C 1-6 Alkyl group.

[0241] In some implementations, in equation (I), R1 is a covalent bond, -CHQ 11 -or-CHQ 12 -CHQ 13 -; where Q 11 Q 12 and Q 13Each is independently a H atom, halogen, and C atom. 1-6 Alkyl or C 1-6 Alkyl group.

[0242] In some implementations, Q 11 Q 12 and Q 13 Each can be independently H, F, methyl, or methoxy.

[0243] In some implementations, Q 11 Q 12 and Q 13 Each is independently H, halogen, or C 1-6 alkyl.

[0244] In some implementations, Q 11 Q 12 and Q 13 Each can be H, F, or methyl independently.

[0245] In some implementations, Q 11 Q 12 and Q 13 Each is independently represented by H.

[0246] In some embodiments, the cyclic sulfate unit shown in formula (I) is a 5-membered ring, a 6-membered ring, or a 7-membered ring, and may further be a 5-membered ring or a 6-membered ring.

[0247] In some embodiments, in formula (I), R1 is a covalent bond, a methylene bond, or a 1,2-ethylene bond.

[0248] In some embodiments, in formula (I), R1 is a covalent bond, a methylene group, or -CHQ. 01 -

[0249] In some implementations, R1 in formula (I) is a covalent bond or a methylene group.

[0250] In some implementations, R1 in equation (I) is a covalent bond, which corresponds to a 5-membered ring.

[0251] In some embodiments, in formula (I), R1 is a methylene group or -CHQ. 01 -, at this point corresponds to a 6-membered ring.

[0252] In some implementations, R1 in formula (I) is a methylene group.

[0253] Unless otherwise stated in this application, the structural formula in This represents the bond attachment point of a covalent bond. Unless otherwise specified, the structural formula contains... This indicates a single bond connection site.

[0254] In this application, unless otherwise specified, the ring structure can be defined according to the number of ring-forming atoms. As an example, a 5-membered ring represents a ring structure with 5 ring-forming atoms, and a 6-membered ring represents a ring structure with 6 ring-forming atoms. The term "ring-forming atom" refers to the constituent atoms of the ring framework. As a non-limiting example, in formula (I), the ring framework is formed by… The S, O, C, and R1 (if R1 is present) are cyclic atoms, while the oxygen atoms corresponding to the two oxygen groups (O=) bonded to the S atom are not considered cyclic atoms. As an example, and It is a 5-membered ring. It is a 6-membered ring.

[0255] In some implementations, non-limiting examples of the structure shown in equation (I) are as follows: wait.

[0256] In some embodiments, the cyclic sulfate unit in the polycyclic sulfate ester can be one or more of the following structures:

[0257] In some embodiments, the polycyclic sulfate contains two structures shown in formula (II):

[0258] Among them, R7 is a hydrogen atom, a halogen, or a carbon atom. 1-6 Alkyl or C 1-6 Alkyl group. Unless otherwise specified, when R7 is a hydrogen atom, it indicates that there is no substituent at that position, and two hydrogen atoms are attached to the corresponding cyclic carbon atom. When R7 is not a hydrogen atom, a substituent is present on the corresponding cyclic carbon atom. The number of substituents can be one, and further, the substituent can be a halogen, carbon, or other chemical compound. 1-6 Alkyl or C 1-6 Alkyl group.

[0259] Non-limiting examples of the structure shown in equation (II) are as follows:

[0260] In this application, unless otherwise specified, "alkyl" means a monovalent residue formed by the loss of a hydrogen atom from a saturated hydrocarbon containing a primary (normal) carbon atom, or a secondary carbon atom, or a tertiary carbon atom, or a quaternary carbon atom, or a combination thereof. Phrases containing this term, such as "C1-6 alkyl," refer to alkyl groups containing 1 to 6 carbon atoms, and each occurrence may independently be C1 alkyl, C2 alkyl, C3 alkyl, C4 alkyl, C5 alkyl, or C6 alkyl. Suitable examples include, but are not limited to: methyl (Me, -CH3), ethyl (Et, -CH2CH3), 1-propyl (n-Pr, n-propyl, -CH2CH2CH3), 2-propyl (i-Pr, i-propyl, -CH(CH3)2), 1-butyl (n-Bu, n-butyl, -CH2CH2CH2CH3), 2-methyl-1-propyl (i-Bu, i-butyl, -CH2CH(CH3)2), 2-butyl (s-Bu, s-butyl, -C H(CH3)CH2CH3), 2-methyl-2-propyl (t-Bu, t-butyl, -C(CH3)3), 1-pentyl (n-pentyl, -CH2CH2CH2CH2CH3), 2-pentyl (-CH(CH3)CH2CH2CH3), 3-pentyl (-CH(CH2CH3)2), 2-methyl-2-butyl (-C(CH3)2CH2CH3), 3-methyl-2-butyl (-CH(CH3)CH(CH3)2), 3-methyl -1-Butyl(-CH2CH2CH(CH3)2), 2-Methyl-1-Butyl(-CH2CH(CH3)CH2CH3), 1-Hexyl(-CH2CH2CH2CH2CH2CH3), 2-Hexyl(-CH(CH3)CH2CH2CH2CH3), 3-Hexyl(-CH(CH2CH3)(CH2CH2CH3)), 2-Methyl-2-pentyl(-C(CH3)2CH2CH2CH3), 3-Methyl-2-pentyl( -CH(CH3)CH(CH3)CH2CH3), 4-methyl-2-pentyl (-CH(CH3)CH2CH(CH3)2), 3-methyl-3-pentyl (-C(CH3)(CH2CH3)2), 2-methyl-3-pentyl (-CH(CH2CH3)CH(CH3)2), 2,3-dimethyl-2-butyl (-C(CH3)2CH(CH3)2) and 3,3-dimethyl-2-butyl (-CH(CH3)C(CH3)3).

[0261] In this application, unless otherwise specified, "alkylene" refers to a hydrocarbon group having two monovalent group centers, which is derived from an alkane by removing two hydrogen atoms (or derived from an alkyl group by removing one more hydrogen atom).

[0262] In this application, the term "alkoxy" refers to a monovalent group formed by the attachment of an alkyl group to -O-. Phrases containing this term include, for example, "C..." 1-6 "Oxaalkyl" refers to an alkoxy group containing 1 to 6 carbon atoms, which can be independently C1 alkoxy, C2 alkoxy, C3 alkoxy, C4 alkoxy, C5 alkoxy, or C6 alkoxy each time it appears. Suitable examples may include, but are not limited to, methoxy (CH3O-), ethoxy (CH3CH2O-), etc.

[0263] In this application, the term "halogen" refers to the elements fluorine, chlorine, bromine, or iodine.

[0264] In this application, in polycyclic sulfates, the term "C" is involved. 1-6 "alkyl" can be C 1-5 Alkyl, C 1-4 Alkyl, C 1-3 Alkyl, C 1-2 Alkyl or methyl. In some embodiments, C 1-6 The alkyl group may be methyl, ethyl, propyl, butyl, pentyl, or hexyl, and may further be methyl. As non-limiting examples, the C group in the structures shown in formula (II), (III), and (IV) is... 1-6 alkyl.

[0265] In this application, in polycyclic sulfates, the term "C" is involved. 1-6 "Alkoxy" can be C 1-5 Alkoxy, C 1-4 Alkoxy, C 1-3 Alkoxy, C 1-2 Alkyl or methoxy. In some embodiments, C 1-6 The alkoxy group may be methoxy, ethoxy, propoxy, butoxy, pentoxy, or hexoxy, and may further be methoxy. As non-limiting examples, the C group in the structures shown in formula (II), (III), and (IV) is... 1-6 Alkyl group.

[0266] In this application, the "halogen" in the polycyclic sulfate ester can be fluorine, chlorine, bromine, or iodine, further can be fluorine, chlorine, or bromine, even further can be fluorine or chlorine, and even further can be fluorine. As non-limiting examples, the halogen in the structures shown in formula (II), formula (III), and formula (IV) are shown.

[0267] In some embodiments, R7 is a H atom, an F atom, a methyl group, or a methoxy group.

[0268] In some implementations, R7 is a H atom, an F atom, or a methyl group.

[0269] In some implementations, R7 is a H atom.

[0270] In some implementations, R7 is an F atom.

[0271] In some implementations, R7 is a methyl group.

[0272] In some embodiments, in the polycyclic sulfate ester, any one of the cyclic sulfate units is a 5-membered to a 7-membered ring. In some of these embodiments, in the polycyclic sulfate ester, any one of the cyclic sulfate units is a 5-membered, 6-membered, or 7-membered ring.

[0273] In some embodiments, in the polycyclic sulfate ester, any one of the cyclic sulfate ester units is a 5-membered ring or a 6-membered ring.

[0274] In some embodiments, in the polycyclic sulfate ester, any one of the cyclic sulfate ester units is a 5-membered ring.

[0275] In some embodiments, in the polycyclic sulfate ester, any one of the cyclic sulfate ester units is a 6-membered ring.

[0276] As a non-limiting example, when the cyclic sulfate unit is a 5- to 7-membered ring, it is advantageous to adjust the ring strain to give the polycyclic sulfate a more suitable stability.

[0277] In some embodiments, any two adjacent cyclic sulfate units are independently separated by -(CH2). q -、-O- or -(CH2) q1 -O-(CH2) q2 - Connected; where q is an integer selected from 0 to 3, and q1 and q2 are integers selected from 0 to 6 respectively, and 1≤(q1+q2)≤6.

[0278] In some implementations, q is 0, 1, 2, or 3. When q is 0, two adjacent cyclic sulfate units are connected by a covalent bond.

[0279] In some implementations, q1 and q2 are 0, 1, 2, 3, 4, 5 or 6, and 1≤(q1+q2)≤6.

[0280] In some implementations, (q1+q2) is 1, 2, 3, 4, 5, or 6.

[0281] In some embodiments, the polycyclic sulfate ester satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0282] (ta1) Any cyclic sulfate ester unit is a 5- to 7-membered ring;

[0283] (ta2) Any two adjacent cyclic sulfate units are independently separated by -(CH2). q -、-O- or -(CH2) q1 -O-(CH2) q2 - Connected; where q is an integer selected from 0 to 3, and q1 and q2 are integers selected from 0 to 6 respectively, and 1≤(q1+q2)≤6.

[0284] In some embodiments, in polycyclic sulfates, any two adjacent cyclic sulfate units are independently connected by a covalent bond, C 1-3 Alkylene, -O-, -L 11 -O-、-OL 11 -or-L 21 -OL 22 - Connected together, where L 11 C 1-6 Alkylene, L 21 and L 22 Each independently is C 1-3 Alkylene.

[0285] In some embodiments, in polycyclic sulfates, L 11 It can be methylene, 1,2-ethylene, 1,3-propylene, butylene, pentylene, or hexylene, and may further be methylene, 1,2-ethylene, 1,3-propylene, 1,4-butylene, 1,5-pentylene, or 1,6-hexylene, each independently.

[0286] In some embodiments, in polycyclic sulfates, L 21 and L 22 Each is independently methylene, 1,2-ethylene, or 1,3-propylene.

[0287] In some embodiments, in polycyclic sulfates, each time "C" is involved 1-3 "alkylene" can be methylene, 1,2-ethylene, or 1,3-propylene, respectively.

[0288] In some embodiments, in polycyclic sulfates, each time "C" is involved 1-6 "alkylene" can be methylene, 1,2-ethylene, 1,3-propylene, butylene, pentylene, or hexylene independently, and can further be methylene, 1,2-ethylene, 1,3-propylene, 1,4-butylene, 1,5-pentylene, or 1,6-hexylene independently.

[0289] In some embodiments, the polycyclic sulfate ester contains 2, 3, or 4 cyclic sulfate units. Examples of polycyclic sulfate esters containing 2 cyclic sulfate units are compounds H1, H2, H3, H4, and H5, as shown below. Examples of polycyclic sulfate esters containing 3 cyclic sulfate units are compounds H6 and H7, as shown below. An example of polycyclic sulfate esters containing 5 cyclic sulfate units is compound H8, as shown below.

[0290] When the number of cyclic sulfate units in a polycyclic sulfate ester is 2, 3, or 4, it is beneficial to better regulate the degree to which the polycyclic sulfate ester participates in the construction of the positive and negative electrode interface film and its absorption of moisture under high voltage and high temperature, thereby improving the high-temperature performance of the battery under high voltage.

[0291] In some embodiments, the cyclic sulfate units in the polycyclic sulfate ester are connected in series, in which case the cyclic sulfate units are not nested on the ring skeleton of the cyclic sulfate units.

[0292] In some embodiments, the polycyclic sulfate contains a halogen, and more specifically, the halogen is a fluorine atom.

[0293] In some embodiments, polycyclic sulfates contain C 1-6 Alkyl, further, C 1-6 Alkyl group is C 1-3 Alkyl, which may be methyl.

[0294] In some embodiments, polycyclic sulfates contain C 1-6 Alkoxy, further, C 1-6 The alkoxy group is C 1-3 Alkoxy, or alternatively methoxy.

[0295] In some embodiments, the polycyclic sulfate ester satisfies one or more of the following characteristics:

[0296] (tb1) The number of cyclic sulfate units contained in polycyclic sulfate esters is 2, 3 or 4;

[0297] (tb2) The cyclic sulfate units in polycyclic sulfate esters are connected in series;

[0298] (tb3) Polycyclic sulfates contain halogens, and further, the halogens are fluorine atoms;

[0299] (tb4) Polycyclic sulfates contain C 1-6 Alkyl, further, C 1-6 Alkyl group is C 1-3 Alkyl group, which may be methyl group;

[0300] (tb5) Polycyclic sulfates contain C 1-6 Alkoxy, further, C 1-6 The alkoxy group is C 1-3 Alkoxy, or alternatively methoxy.

[0301] In some embodiments, the polycyclic sulfate ester comprises a compound with the structural formula shown in formula (III); R 41 and R 42 Each is independently a H atom, halogen, and C atom. 1-6 Alkyl, C 1-6 Alkyl groups or structures represented by formula (IV);

[0302] Among them, R 11 R 12 and R 13 Each is independently a covalent bond, -CHQ 21 -or-CHQ 22 -CHQ 23 -; where Q 21 Q 22 and Q 23 Each is independently a H atom, halogen, and C atom. 1-6 Alkyl or C 1-6 Alkoxy;

[0303] R 71 H atom, halogen, C 1-6 Alkyl or C 1-6 Alkoxy;

[0304] L6 is -(CH2) n -or-(CH2) n1 -O-(CH2) n2 -, n is an integer selected from 0 to 3, n1 and n2 are integers selected from 0 to 3 respectively and 1≤(n1+n2)≤3;

[0305] L3 is -(CH2) q -、-O- or -(CH2) q1 -O-(CH2) q2 -; where q is an integer selected from 0 to 3, and q1 and q2 are integers selected from 0 to 6 respectively, and 1≤(q1+q2)≤6.

[0306] In some implementations, Q 21 Q 22 and Q 23 Each can be independently H, F, methyl, or methoxy.

[0307] In some implementations, Q 21 Q 22 and Q 23Each is independently H, halogen, or C 1-6 alkyl.

[0308] In some implementations, Q 21 Q 22 and Q 23 Each can be H, F, or methyl independently.

[0309] In some implementations, Q 21 Q 22 and Q 23 Each is independently represented by H.

[0310] In some implementations, R 11 R 12 and R 13 Each is independently a covalent bond, methylene or 1,2-ethylene.

[0311] In equation (III), R 41 or R 42 When R is an H atom, it indicates that there is no substituent at that position, and two H atoms are attached to the corresponding cyclic carbon atom. 41 or R 42 When the atom is not an H atom, a substituent exists on the corresponding cyclic carbon atom. The number of substituents can be one, and furthermore, the substituents can be halogens, C atoms, etc. 1-6 Alkyl, C 1-6 Alkoxy or the structure shown in formula (IV).

[0312] In some implementations, R 41 and R 42 Each is independently a H atom, F atom, methyl, methaneoxy or the structure shown in formula (IV), and may be selected as a H atom, F atom, methyl or the structure shown in formula (IV).

[0313] When R 41 and R 42 When all are structures as shown in equation (IV), R 41 and R 42 They can be the same or different. In some implementations, the two L6s are the same. In some implementations, the two Rs are different. 71 Same. In some implementations, R 41 and R 42 same.

[0314] In some implementations, R 11 R 12 and R 13 Each is independently a covalent bond or a methylene group.

[0315] In equation (IV), R 71When R is an H atom, it indicates that there is no substituent at that position, and two H atoms are attached to the corresponding cyclic carbon atom. 71 When the atom is not an H atom, a substituent exists on the corresponding cyclic carbon atom. The number of substituents can be one, and furthermore, the substituents can be halogens, C atoms, etc. 1-6 Alkyl or C 1-6 Alkyl group.

[0316] In some implementations, R 71 It can be a H atom, an F atom, a methyl group, or a methoxy group, and can be selected as a H atom, an F atom, or a methyl group.

[0317] In some implementations, L6 is a covalent bond, corresponding to the aforementioned -(CH2). n - The case where n is 0. Non-restrictive examples include compounds H6 and H8.

[0318] In some implementations, L6 is a covalent bond or -O-.

[0319] In some implementations, L6 is -O-. A non-limiting example is compound H7.

[0320] In some implementations, L3 is a covalent bond or -O-.

[0321] In some embodiments, the polycyclic sulfate includes at least one of the following compounds:

[0322] By adjusting the structure of polycyclic sulfates, the extent to which polycyclic sulfates participate in the construction of the positive and negative electrode interface films and their absorption of moisture can be controlled under high voltage and high temperature. This is beneficial for better and more sustained improvement of the stability of the positive and negative electrode interface films under high voltage and high temperature, better absorption of moisture, better improvement of the structural stability of non-agglomerated primary particles in lithium composite metal oxide materials, and better improvement of the cycle performance and / or storage performance of batteries under high voltage and high temperature.

[0323] In this application, the mass percentage of polycyclic sulfate in the electrolyte in a lithium-ion secondary battery is denoted as W.

[0324] In some embodiments, 0 < W ≤ 1%, further optionally, 0.01% ≤ W ≤ 1%, and further optionally, 0.02% ≤ W ≤ 0.5%. Without limitation, W can also be any one of the following percentages or a range composed of any two of the following percentages: 0.001%, 0.002%, 0.004%, 0.005%, 0.006%, 0.008%, 0.01%, 0.015%, 0.016%, 0.018%, 0.02%, 0.04%, 0.05%, 0.06%, 0.08%, 0.1%, 0.12%, 0.15%, 0.16%, 0.18%, 0.2%, 0.25%, 0.3%, 0.4%, 0.5%, 0.52%, 0.54%, 0.55%, 0.56%, 0.58%, 0.6%, 0.65%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, etc. W can also be selected from any one of the following ranges: 0.001% - 1%, 0.005% - 1%, 0.004% - 0.9%, 0.005% - 0.9%, 0.005% - 0.8%, 0.005% - 0.7%, 0.005% - 0.6%, 0.01% - 0.7%, 0.015% - 0.6%, 0.016% - 0.6%, 0.018% - 0.6%, 0.015% - 0.55%, 0.018% - 0.55%, etc.

[0325] By controlling the mass ratio (W) of the polycyclic sulfate in the electrolyte of the lithium-ion secondary battery, under high-voltage and high-temperature conditions, it is more conducive to exerting the synergistic improvement effects of the polycyclic sulfate in the electrolyte in one or more aspects such as improving the stability of the CEI film and SEI film, improving the structural stability of the non-agglomerated primary particles in the lithium composite metal oxide material, suppressing interfacial side reactions, absorbing moisture, and reducing the generation of hydrofluoric acid, which can more significantly improve the high-temperature performance of the lithium-ion secondary battery under high voltage, and at the same time, it is also conducive to controlling the internal resistance of the battery within a more appropriate range.

[0326] In addition, the higher the mass ratio of the polycyclic sulfate in the electrolyte, the more conducive it is to reducing the gas generation caused by the participation of water in side reactions.

[0327] In some embodiments, the D of the lithium composite metal oxide material v 50 is 2.5 μm to 5 μm, optionally 3 μm to 4.5 μm, and further optionally 3.2 μm to 4.2 μm. Without limitation, the D of the lithium composite metal oxide material v50 can be any of the following values ​​or a range consisting of any two of the following values: 2.5μm, 2.6μm, 2.8μm, 3μm, 3.2μm, 3.3μm, 3.4μm, 3.5μm, 3.6μm, 3.7μm, 3.8μm, 3.9μm, 4μm, 4.1μm, 4.2μm, 4.3μm, 4.4μm, 4.5μm, 4.6μm, 4.8μm, 5μm, etc. The D of the positive electrode active material... v 50 can also be selected from any of the following ranges: 3.5μm to 4.5μm, etc.

[0328] By using lithium composite metal oxide materials D v Controlling the particle size distribution of lithium composite metal oxide materials, including non-agglomerated primary particles, within the aforementioned range is beneficial for achieving a more suitable particle size distribution. This can indirectly adjust the contact area between the lithium composite metal oxide material and the electrolyte, which helps to control the interfacial side reactions between the lithium composite metal oxide material and the electrolyte at high voltage and high temperature. It can also take into account the structural stability advantage of the non-agglomerated primary particles in the lithium composite metal oxide material, enabling the lithium composite metal oxide material to better resist volume stress changes and cracking risks at high voltage and high temperature, thus improving the high-temperature performance of the battery at high voltage.

[0329] In some embodiments, the D of the positive electrode active material v The thickness of 50 is 2.5 μm to 5 μm, optionally 3 μm to 4.5 μm, and further optionally 3.2 μm to 4.2 μm. Non-limitingly, the D of the positive electrode active material... v 50 can be any of the following values ​​or a range consisting of any two of the following values: 2.5μm, 2.6μm, 2.8μm, 3μm, 3.2μm, 3.3μm, 3.4μm, 3.5μm, 3.6μm, 3.7μm, 3.8μm, 3.9μm, 4μm, 4.1μm, 4.2μm, 4.3μm, 4.4μm, 4.5μm, 4.6μm, 4.8μm, 5μm, etc. The D of the positive electrode active material... v 50 can also be selected from any of the following ranges: 3.5μm to 4.5μm, etc.

[0330] In the context of this application, the volumetric cumulative distribution particle size D can be used. v N (where N represents any value selected from 0 to 100) is used to characterize the particle size of the material. It refers to the particle size corresponding to the cumulative volume distribution percentage of the material reaching N%, where the particle size is less than or equal to D. v N's volume percentage is N%. D v N can be obtained from the volumetric cumulative distribution curve of the material particles. Unless otherwise specified, the volumetric cumulative distribution curve is accumulated from zero on the smaller particle size side. Let D...v Taking 50 as an example for illustration. In this application, unless otherwise stated, D v 50 refers to the particle size corresponding to a cumulative volume distribution percentage of 50% in the material. This parameter indicates that the particle size of 50% of the material's volume is less than or equal to D. v 50, and particles accounting for 50% of the material volume have a particle size greater than D. v 50. Those skilled in the art will understand D v The meaning of 50 can be determined using instruments and methods known in the field. For example, it can be conveniently determined using a laser particle size analyzer, such as the Mastersizer 2000E laser particle size analyzer or the LS-909 laser particle size analyzer from Malvern Instruments Ltd. (UK). Furthermore, for equipment models such as the Malvern 2000 laser particle size analyzer, the standard procedure GB / T19077-2016 / ISO 13320:2009 can be referenced for testing.

[0331] It's understandable, various D v N is a statistical parameter representing the particle size of dispersible particles in a material. One non-agglomerated primary particle and one secondary particle are each denoted as a dispersible particle.

[0332] By using the D of the positive electrode active material v Controlling the particle size distribution of the positive electrode active material, including non-agglomerated primary particles, within the aforementioned range is beneficial for achieving a more suitable particle size distribution. This can indirectly adjust the contact area between the positive electrode active material and the electrolyte, which helps to control the interfacial side reactions between the positive electrode active material and the electrolyte at high voltage and high temperature. It can also take into account the structural stability advantage of non-agglomerated primary particles, enabling the positive electrode active material to better resist volume stress changes and cracking risks at high voltage and high temperature, thus improving the high-temperature performance of the battery at high voltage.

[0333] In some implementations, the D of the positive electrode active material can be tested using the following method. v50. A Malvern 2000 (MasterSizer 2000) laser particle size analyzer was used, following the standard procedure: GB / T19077-2016 / ISO 13320:2009. The detailed test procedure included: taking an appropriate amount of the sample to be tested, adding 20mL to 30mL of solvent (to ensure the sample concentration in the injection cell meets the light-blocking requirement of 8% to 12%), and sonicating for 5 minutes (53kHz / 120W) to fully disperse the sample; adding the ultrasonically dispersed sample to the injection cell, and starting the test after the sample has stabilized for 5 to 10 seconds; recording the data after the test. Non-limiting examples of solvents include deionized water and pure water. To avoid agglomeration during the drying process affecting the particle size test, the dispersion test was performed using a washed and moistened sample, which could be washed with anhydrous ethanol.

[0334] In some embodiments, the specific surface area of ​​the positive electrode active material is 0.3 m². 2 / g~1.5m 2 / g, optional 0.5m 2 / g~1.2m 2 / g. Without limitation, the specific surface area of ​​the positive electrode active material may also be any of the following values ​​or selected from a range consisting of any two of the following values: 0.3m² 2 / g, 0.4m 2 / g, 0.5m 2 / g, 0.6m 2 / g, 0.7m 2 / g, 0.8m 2 / g, 0.9m 2 / g, 1.0m 2 / g, 1.1m 2 / g, 1.2m 2 / g, 1.3m 2 / g, 1.4m 2 / g, 1.5m 2 / g etc.

[0335] In this application, unless otherwise specified, the "specific surface area" of the positive electrode active material has a commonly known meaning in the art. It can be tested using nitrogen adsorption specific surface area analysis and calculated using the BET (Brunauer Emmett Teller) method. Nitrogen adsorption specific surface area analysis can be performed using a Tri Star II specific surface area and porosity analyzer from Micromeritics, USA. The test procedures can refer to GB / T 19587-2004. Detailed steps are as follows: Using nitrogen as the adsorbent gas, calculate the specific surface area of ​​the material using the BET method; add the sample to be tested into a BET test tube until it reaches 2 / 3 of the bottom bulb, degas the sample, and heat it; after cooling to room temperature, refill with nitrogen to remove the vacuum, and plug the sample tube opening with a stopper, recording the sample weight; remove the stopper, add a filling rod, install the sample tube onto the instrument analysis station, input the sample weight, and begin the test. Before testing, the sample can be dried.

[0336] By adjusting the specific surface area of ​​the positive electrode active material within the aforementioned range, it is beneficial to ensure that the contact area between the positive electrode active material, including non-agglomerated primary particles, and the electrolyte is within a more suitable range. This helps to control the interfacial side reactions between the positive electrode active material and the electrolyte at high voltage and high temperature, while also taking into account the structural stability advantages of non-agglomerated primary particles. This allows the positive electrode active material to better resist volume stress changes and cracking risks at high voltage and high temperature, thus improving the high-temperature performance of the battery at high voltage.

[0337] By adjusting the D of the positive electrode active material v Having one or two of the parameters, such as 50 and the specific surface area of ​​the positive electrode active material, within the aforementioned range is beneficial for controlling the interfacial side reactions between the positive electrode active material and the electrolyte at high voltage and high temperature. It can also take into account the structural stability advantage of non-agglomerated primary particles, enabling the positive electrode active material to better resist volume stress changes and cracking risks at high voltage and high temperature, which is conducive to better improving the high-temperature performance of the battery at high voltage.

[0338] In some embodiments, the average particle size of the primary particles in the positive electrode active material is 1.1 μm to 3.0 μm, optionally 1.3 μm to 2.5 μm. Non-limitingly, the average particle size of the primary particles in the positive electrode active material may also be any of the following values ​​or a range selected from any two of the following values: 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm, 1.5 μm, 1.6 μm, 1.8 μm, 2 μm, 2.2 μm, 2.4 μm, 2.5 μm, etc.

[0339] In this application, the "average particle size of primary particles in the positive electrode active material" can be denoted as D1.

[0340] The particle morphology of the positive electrode active material can be used to statistically determine the particle size of the primary particles in the positive electrode active material, thereby obtaining the average particle size of the primary particles in the positive electrode active material. The particle morphology of the positive electrode active material can be obtained using scanning electron microscopy (SEM) results (e.g., ZEISS Sigma 300, JEOL SEM, Axia Chemi SEM, etc.). The sample to be tested can be obtained by laying a powder sample of the positive electrode active material on conductive adhesive, or by performing SEM testing on the cross-section of the positive electrode sheet. Non-limitingly, SEM testing can refer to JY / T(001)-1996. One or more regions are randomly selected in the sample to be tested for scanning, and based on the SEM image at a certain magnification, the particle size of each primary particle in the scanned region and the frequency of occurrence of different particle sizes are statistically analyzed, thereby calculating the average particle size of each statistically analyzed primary particle. Non-limitingly, the magnification of a single scanned region can be, for example, 1000X, but is not limited to this. To improve the accuracy of the statistical results, multiple regions can be randomly selected for scanning. The number of particles counted in a single operation can be several hundred, or even more than or equal to 1,000, or more than or equal to 2,000. Increasing the number of particles counted in a single operation improves the accuracy of the statistical results.

[0341] In this application, unless otherwise specified, the maximum diameter of the primary particles in each direction in the SEM morphology image is referred to as the "particle size of the primary particles in the positive electrode active material".

[0342] By controlling the average particle size of primary particles in the cathode active material within the aforementioned range, on the one hand, it is beneficial to ensure that the primary particles in the cathode active material have a more suitable size, which can reduce the content of small-sized, large-specific-surface-area non-agglomerated primary particles. Under high voltage and high temperature, this helps to reduce interfacial side reactions and improve the stability of the CEI film. On the other hand, for secondary particles that may exist in the cathode active material, it is also beneficial to increase the contact area between primary particles in the secondary particles, thereby improving the structural stability of secondary particles under high voltage and high temperature. This can better reduce the generation of fresh interfaces and slow down electrolyte consumption and battery capacity decay under high voltage and high temperature. Based on the aforementioned multiple effects, controlling the average particle size of primary particles in the cathode active material within the aforementioned range is beneficial to better improve the high-temperature performance of the battery under high voltage. Furthermore, when the average particle size of the primary particles in the positive electrode active material is relatively large, the solid-phase transport path of active ions becomes longer, which may lead to an increase in the battery's internal resistance. In the lithium-ion secondary battery provided in this application, by introducing polycyclic sulfates into the electrolyte, the battery's internal resistance can be controlled within a suitable range while significantly improving high-temperature performance under high voltage during the initial stage of cycling and / or storage. During the later stage of cycling and / or storage, the dense interfacial film constructed with the participation of polycyclic sulfates enables the positive electrode active material to still resist volume stress changes and cracking risks well after long-term cycling and / or storage, and effectively suppress the increase in impedance during the later stage of cycling and / or storage, thereby significantly improving the battery's internal resistance after long-term cycling and / or storage.

[0343] In this application, the test sample of the "positive electrode active material" in the positive electrode sheet of a lithium-ion secondary battery can be obtained by disassembling the battery, removing the positive electrode sheet, and extracting the positive electrode active material from the positive electrode active layer of the positive electrode sheet using methods such as solvent washing, ultrasonic dispersion, centrifugation, and fractional sedimentation. The extracted powder sample is then dried to obtain a powder sample. The obtained powder sample can be used for SEM testing or other tests, such as laser particle size analysis. Furthermore, the powder material extracted from the positive electrode active layer can be sintered to remove organic components, thereby obtaining a powder sample of the positive electrode active material.

[0344] For example, the preparation of powder samples of positive electrode active materials can be carried out by the following method: disassemble the battery, take out the positive electrode sheet, soak and clean it with a solvent such as dimethyl carbonate to remove residual electrolyte; scrape the powder material of the positive electrode active layer, soak the powder material extracted from the positive electrode active layer with a solvent (such as N-methylpyrrolidone (NMP) etc.) to dissolve organic components such as binders in the solvent (ultrasonic dispersion and other methods can also be combined to promote dissolution), wash and filter, collect the solid phase, and then use density difference to centrifuge to separate the relatively low-density conductive agent from the suspension, collect the centrifuged precipitate to obtain the test powder of positive electrode active material.

[0345] In this application, the D of the positive electrode active material is... v 50 (can be written as D) v 50 A The ratio of the particle size of the primary particles to the average particle size (D1) in the positive electrode active material is denoted as B1. Therefore, B1 = D... v 50 A / D1.

[0346] In some implementations, 1 ≤ B1 ≤ 2.5, and may be selected as 1.6 ≤ B1 ≤ 2.2. Non-limitingly, B1 may also be any of the following values ​​or a range selected from any two of the following values: 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.0, 2.1, 2.2, 2.4, 2.5, etc.

[0347] By using the D of the positive electrode active material v The ratio of 50 to the average particle size of primary particles in the positive electrode active material (B1 = D) v 50 A Controlling / D1) within the aforementioned range helps to make the median particle size of the positive electrode active material particles close to the average particle size of the primary particles, which are the basic unit of particles. This helps to reduce the agglomeration ratio of primary particles in the positive electrode active material and reduce the content of secondary particles as agglomerates of primary particles. Correspondingly, it increases the proportion of non-agglomerated primary particles, which can better resist the risk of particle cracking under high voltage and high temperature. This makes the positive electrode active material have better structural stability under high voltage and high temperature, and is more conducive to improving the high-temperature performance of the battery under high voltage.

[0348] In some implementations, the positive electrode sheet satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0349] (tc1) In lithium composite metal oxide materials, the proportion of non-agglomerated primary particles is greater than or equal to 70%, and can be selected as greater than or equal to 80%.

[0350] (tc2) In the positive electrode active material, the proportion of non-agglomerated primary particles is greater than or equal to 65%, which can be selected as greater than or equal to 80%.

[0351] In some implementations, the positive electrode sheet satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0352] (tc1') In lithium composite metal oxide materials, the proportion of non-agglomerated primary particles is greater than or equal to 80%;

[0353] (tc2') In the positive electrode active material, the proportion of non-agglomerated primary particles is greater than or equal to 75%.

[0354] In this application, the proportion of non-agglomerated primary particles in the lithium composite metal oxide material is denoted as F1, and the proportion of non-agglomerated primary particles in the cathode active material is denoted as F0. F1 reflects the content of non-agglomerated primary particles in the lithium composite metal oxide material; a higher F1 value indicates more non-agglomerated primary particles and fewer secondary particles. Similarly, F0 reflects the content of non-agglomerated primary particles in the cathode active material; a higher F0 value indicates more non-agglomerated primary particles and fewer secondary particles.

[0355] In some implementations, F1 is greater than or equal to 70%, and optionally, F1 is greater than or equal to 80%. Non-limitingly, F1 can also be any of the following percentages, or greater than or equal to any of the following percentages, or greater than or equal to any of the following percentages and less than or equal to 100%, or a range selected from any two of the following percentages: 70%, 75%, 80%, 85%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, etc. Non-limiting examples of F1 can be 90% to 98%, etc.

[0356] In some implementations, F0 is greater than or equal to 65%, optionally, F0 is greater than or equal to 70%, F0 is greater than or equal to 75%, further optionally, and even more optionally, F0 is greater than or equal to 80%. Non-limitingly, F0 can also be any of the following percentages, or greater than or equal to any of the following percentages, or greater than or equal to any of the following percentages and less than or equal to 100%, or a range selected from any two of the following percentages: 35%, 40%, 45%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 96%, 97%, 98%, etc. Non-limiting examples of F0 can be 87% to 96%, etc.

[0357] Non-limitingly, the "proportion of non-agglomerated primary particles in the cathode active material (F0)" can be obtained through statistical analysis of SEM scan images of the cathode active material. One or more regions are randomly selected for scanning tests, and the number of non-agglomerated primary and secondary particles within the scanned region is counted. The proportion of non-agglomerated primary particles is calculated as the test value of the "proportion of non-agglomerated primary particles in the cathode active material". The magnification of a single scanned region can be, for example, 1000X to 3000X, such as 1000X, 2000X, 3000X, etc., but is not limited to this. The total number of non-agglomerated primary and secondary particles counted in the cathode active material can be greater than or equal to 500, further greater than or equal to 1000, and even further greater than or equal to 2000, but is not limited to the aforementioned numbers. A similar statistical analysis of the "proportion of non-agglomerated primary particles in lithium composite metal oxide materials" can be performed by combining SEM and EDS.

[0358] By controlling one or both of the following parameters within the aforementioned ranges: the proportion of non-agglomerated primary particles in lithium composite metal oxide materials (F1) and the proportion of non-agglomerated primary particles in cathode active materials (F0), it is beneficial to improve the structural stability of cathode active materials under high voltage and high temperature, thereby further improving the high-temperature performance of batteries under high voltage.

[0359] In some embodiments, the positive electrode active material includes a lithium composite metal oxide material. In some embodiments, the lithium composite metal oxide material includes one or more of lithium nickel-based oxides, lithium-rich manganese-based positive electrode materials, spinel lithium manganese oxide, lithium cobalt oxide, and any of the foregoing modified forms; wherein the modification forms include one or more of doping modification and coating modification.

[0360] Introducing lithium nickel-based oxides into the positive electrode active material can help improve energy density.

[0361] By introducing lithium-rich manganese-based cathode materials, spinel lithium manganese oxide, lithium cobalt oxide, and other cathode active materials into the cathode active materials, it is beneficial to enable the cathode active materials to have better structural stability under high voltage and high temperature, thereby better suppressing battery capacity decay under high voltage and high temperature and improving the high-temperature performance of the battery under high voltage.

[0362] In this application, unless otherwise specified, "a modified form of a certain positive electrode active material" includes the positive electrode active material itself and the modifying element. Furthermore, the modifying element may exist as a dopant element, as a coating element, or as a combination of a dopant element and a coating element. Unless otherwise specified, "a modified form of a certain positive electrode active material" still falls within the scope of positive electrode active materials.

[0363] In this application, unless otherwise specified, "doping element" in positive electrode active material refers to a modifying element doped into the positive electrode active material; unless otherwise specified, "coating element" in positive electrode active material refers to a positive electrode active material comprising a positive electrode active particle body and a coating layer located on at least a portion of the surface of the positive electrode active particle body, wherein the coating element is a modifying element located in the coating layer. As a non-limiting example, in positive electrode active material, "the modifying element exists in a combination of doping element and coating element" means that the positive electrode active material comprises a positive electrode active particle body and a coating layer located on at least a portion of the surface of the positive electrode active particle body, at least a portion of the modifying element is doped into the positive electrode active material body, and at least a portion of the modifying element is also contained in the coating layer. The positive electrode active particle body can be a positive electrode active material itself or a doped and modified form of a positive electrode active material. In some embodiments, the doping element may include one or more of Na, K, Ca, Ba, Sb, Ti, Zr, W, Sr, Nb, Mo, Si, Mg, B, Cr, Ta, etc. In some implementations, the coating element may include one or more of Al, Ti, Mg, Zr, Y, Li, W, and Na.

[0364] In this application, unless otherwise specified, "lithium nickel-based oxide" refers to a positive electrode active material comprising lithium, nickel, and oxygen. It is understood that lithium nickel-based oxide is a lithium complex metal oxide, in which case the non-lithium metal element in the lithium complex metal oxide includes nickel. Non-limitingly, lithium nickel-based oxide may include one or more of lithium nickel cobalt manganese-based oxides and lithium nickel cobalt aluminum-based oxides. Unless otherwise specified, lithium nickel-based oxides have a layered structure.

[0365] In some embodiments, lithium nickel-based oxides include lithium nickel cobalt-based oxides. In this application, unless otherwise specified, "lithium nickel cobalt-based oxide" refers to a lithium composite metal oxide comprising lithium, nickel, cobalt, and oxygen, specifically a lithium nickel-based oxide containing cobalt. The non-lithium metal elements included are at least nickel and cobalt. The introduced cobalt element can reduce cation mixing, enhance material structural stability, and improve rate performance.

[0366] In some embodiments, lithium nickel-based oxides include those with the chemical formula Li x (Ni a Co b M' c M” d )O 2-eThe positive electrode active material, where 0.6 ≤ x ≤ 1.2, 0 < a < 1, 0 < b < 1, 0 < c < 1, 0 ≤ d < 1 (optionally, 0 < d < 1), a + b + c + d = 1, -0.1 ≤ e ≤ 0.4 (optionally, -0.1 ≤ e ≤ 0.1). M' may include at least one of Mn and Al. M'' may include one or more of Na, K, Ca, Ba, Sb, Ti, Zr, W, Sr, Nb, Mo, Si, Mg, B, Cr, and Ta. Without limitation, the value or range of x may refer to the value or range of x2. The value of a may refer to the value or range of q1, q2, or q3. Without limitation, the value of b may refer to the value or range of q4. Without limitation, the value of c may refer to the value or range of q5. Without limitation, (2 - e) may refer to the value or range of x3. In some embodiments, M' is the Mn element.

[0367] In this application, unless otherwise specified, "lithium-rich manganese-based cathode material" refers to a positive electrode active material containing Li2MnO3, and may also optionally contain LiMO2, where M is a transition metal element. Without limitation, M may include one or more of transition metal elements such as Ni, Co, Mn, Cr, Fe, Al, Nb, Zr, Mo, Ta, etc. The layered lithium-rich manganese-based cathode material has advantages such as high specific capacity, high voltage platform, and easy synthesis. In some embodiments, the chemical formula of the layered lithium-rich manganese-based cathode material is y(Li2MnO3)·(1 - y)(LiMO2), where 0 < y ≤ 1, optionally, 0 < y < 1. In some embodiments, the lithium-rich manganese-based cathode material is a layered lithium-rich manganese-based cathode material.

[0368] In this application, unless otherwise specified, "spinel lithium manganate" refers to LiMn2O4 with a spinel structure, which has a three-dimensional tunnel structure, can provide a fast diffusion channel for lithium ions, and has advantages such as good rate performance and low cost, and can operate under some high voltage conditions.

[0369] In some embodiments, the lithium composite metal oxide material includes lithium nickel-based oxides. It can be understood that the lithium nickel-based oxides contain Li element, non-lithium metal elements, and O element, and the non-lithium metal elements include Ni element. In some of these embodiments, the lithium nickel-based oxides may satisfy one or more of the following characteristics (any numerical parameter in the following characteristics may also be selected from any suitable value or range in the context):

[0370] (t1) The atomic molar ratio of Ni element to non-lithium metal elements in the lithium nickel-based oxide is q1, where 0.5 ≤ q1 < 1;

[0371] (t2) The lithium nickel-based oxide contains Ni and Li elements with an atomic molar ratio of q2:x2, where 0.5 ≤ q2 < 1 and 0.6 ≤ x2 ≤ 1.2;

[0372] (t3) The lithium nickel-based oxide contains Ni and O elements with an atomic molar ratio of q3:x3, where 0.5 ≤ q3 < 1 and 1.6 ≤ x3 ≤ 2.1.

[0373] In some embodiments, the lithium composite metal oxide material satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable value or range in the context):

[0374] (i) 0.5 ≤ q1 ≤ 0.99;

[0375] (ii) 0.5 ≤ q2 ≤ 0.99;

[0376] (iii) 0.5 ≤ q3 ≤ 0.99;

[0377] (iv) The lithium nickel-based oxide contains Co element, and the atomic molar ratio of Co element to non-lithium metal elements in the lithium nickel-based oxide is q4, where 0 < q4 ≤ 0.25, optionally, 0.02 ≤ q4 ≤ 0.25;

[0378] (v) The lithium nickel-based oxide contains Mn element, and the atomic molar ratio of Mn element to non-lithium metal elements in the lithium nickel-based oxide is q5, where 0 < q5 ≤ 0.35, optionally, 0.1 ≤ q5 ≤ 0.35;

[0379] (vi) The mass percentage of the lithium nickel-based oxide in the lithium composite metal oxide material is 80% - 100%.

[0380] In some embodiments, the lithium composite metal oxide material satisfies one or more of the following characteristics (any numerical parameter in the following characteristics can also be selected from any suitable value or range in the context): <照

[0381] (ti) 0.5 ≤ q1 ≤ 0.99, optionally, 0.5 ≤ q1 ≤ 0.8 or 0.8 < q1 ≤ 0.99;

[0382] (tii) 0.5 ≤ q2 ≤ 0.99, optionally, 0.5 ≤ q2 ≤ 0.8 or 0.8 < q2 ≤ 0.99;

[0383] (tiii) 0.6 ≤ x2 ≤ 1.2, optionally, 0.8 ≤ x2 ≤ 1.1;

[0384] (tiv) 0.5 ≤ q3 ≤ 0.99, optionally, 0.5 ≤ q3 ≤ 0.8 or 0.8 < q3 ≤ 0.99;

[0385] (tv) 1.6 ≤ x3 ≤ 2.1, optionally, 1.8 ≤ x3 ≤ 2.06;

[0386] (tvi) The lithium nickel-based oxide contains Co element, 0 < q4 ≤ 0.25, optionally, 0.02 ≤ q4 ≤ 0.25, further optionally, 0.05 ≤ q4 ≤ 0.2;

[0387] (tvii) The lithium nickel-based oxide contains Mn element, 0 < q5 ≤ 0.35, optionally, 0.1 ≤ q5 ≤ 0.35, further optionally, 0.15 ≤ q5 ≤ 0.3;

[0388] (tviii) The mass percentage of the lithium nickel-based oxide in the lithium composite metal oxide material is 80% - 100%, optionally 90% - 100%.

[0389] Non-limitingly, q1, q2, and q3 can each independently be any one of the following values, or be selected from the range formed by any two of the following values: 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, etc. <​​​​​​​​​​​​In some embodiments, 0.5 ≤ q1 ≤ 0.8. In some of these embodiments, 0.5 ≤ q1 ≤ 0.7.

[0395] In some embodiments, 0.5 ≤ q2 ≤ 0.8. In some of these embodiments, 0.5 ≤ qz ≤ 0.7.

[0396] In some embodiments, 0.5 ≤ q3 ≤ 0.8. In some of these embodiments, 0.5 ≤ q3 ≤ 0.7.

[0397] By controlling the nickel content of the lithium nickel-based oxide in the positive electrode active material to be as described above, the crystal structure stability of the positive electrode active material at high voltage and high temperature is better, which is conducive to making the battery have better high-temperature performance at high voltage.

[0398] In some embodiments, 0.7 < q1 ≤ 0.99. In some of these embodiments, 0.8 < q1 ≤ 0.99.

[0399] In some embodiments, 0.7 < q2 ≤ 0.99. In some of these embodiments, 0.8 < q2 ≤ 0.99.

[0400] In some embodiments, 0.7 < q4 ≤ 0.99. In some of these embodiments, 0.8 < q3 ≤ !.99.

[0401] When the lithium nickel-based oxide in the positive electrode active material has the aforementioned higher nickel content, the improvement effect of introducing polycyclic sulfate on the high-temperature performance at high voltage is more obvious.

[0402] In some embodiments, the lithium composite metal oxide material includes one or more of lithium nickel cobalt manganese-based oxides and modified forms of lithium nickel cobalt manganese-based oxides. It can be understood that at this time, the lithium composite metal oxide material includes lithium nickel-based oxides. Non-limitingly, the modified forms include one or more of doping modification and coating modification; both the doping modification method and the coating modification method can adopt or refer to the existing modification methods in the art, including but not limited to the selection of element types, doping amounts, and coating amounts.

[0403] In some embodiments, the lithium nickel cobalt manganese-based oxide optionally includes a modifying element. Further, the modifying element can exist in the form of a doping element, in the form of a coating element, or in a combination form of a doping element and a coating element.

[0404] In some embodiments, the lithium nickel cobalt manganese-based oxide optionally includes doping elements. Further, the doping elements can include one or more of Na, K, Ca, Ba, Sb, Ti, Zr, W, Sr, Nb, Mo, Si, Mg, B, Cr, Ta, etc.

[0405] In this application, unless otherwise specified, "lithium nickel cobalt manganese-based oxide" refers to a positive electrode active material comprising lithium, nickel, cobalt, manganese, and oxygen. It is understood that lithium nickel cobalt manganese-based oxide is a lithium composite metal oxide, and more specifically, a lithium nickel-based oxide. The non-lithium metal elements in lithium nickel cobalt manganese-based oxide include nickel, cobalt, and manganese. In this application, unless otherwise specified, lithium nickel cobalt manganese-based oxides used as positive electrode active materials typically have a layered structure.

[0406] In lithium nickel cobalt manganese-based oxides, nickel can increase energy density, cobalt can reduce cation mixing, enhance material structural stability and rate performance, and manganese can stabilize the layered structure of lithium nickel cobalt manganese-based oxide materials, but these effects are not limited to those described above.

[0407] An example of cation mixing is the Li / Ni mixing.

[0408] In lithium nickel cobalt manganese-based oxides, the ratio of the atomic molar ratio of nickel to the sum of the atomic molar ratios of nickel, cobalt, and manganese is denoted as R. Ni / NCM The ratio of the atomic molar ratio of cobalt to the sum of the atomic molar ratios of nickel, cobalt, and manganese is denoted as R. Co / NCM The ratio of the atomic molar ratio of manganese to the sum of the atomic molar ratios of nickel, cobalt, and manganese is denoted as R. Mn / NCM .

[0409] Without limitation, R Ni / NCM It can also be any of the following values, or greater than or equal to any of the following values ​​and less than 1, or selected from a range consisting of any two of the following values: 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, etc. In some embodiments, 0.5 ≤ R Ni / NCM <1. R Ni / NCM For numerical values ​​and the range of options, please refer to q1.

[0410] Without limitation, R Co / NCM It can also be any of the following values, or a range selected from any two of the following values: 0.02, 0.03, 0.04, 0.05, 0.06, 0.07, 0.08, 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, 0.22, 0.24, 0.25, etc. R Co / NCM For numerical values ​​and the range of options, please refer to q4.

[0411] Without limitation, R Mn / NCMIt can also be any of the following values, or a range selected from any two of the following values: 0.1, 0.12, 0.14, 0.15, 0.16, 0.18, 0.2, 0.22, 0.24, 0.25, 0.26, 0.28, 0.3, 0.32, 0.34, 0.35, etc. R Mn / NCM For numerical values ​​and the range of options, please refer to q5.

[0412] By controlling one or more of the nickel, cobalt, and manganese content in the lithium nickel cobalt manganese-based oxide in the positive electrode active material within the aforementioned range, the crystal structure stability of the positive electrode active material is improved under high voltage and high temperature, which is beneficial for the battery to obtain better high-temperature performance under high voltage.

[0413] In some embodiments, the lithium composite metal oxide material is a ternary cathode material. In this application, the "ternary cathode material" is composed of Li, nickel, cobalt, M2, and oxygen; wherein, M2 can be manganese or aluminum. When M2 is manganese (Mn), the ternary cathode material is lithium nickel cobalt manganese oxide, which can be denoted as NCM; when M2 is aluminum (Al), the ternary cathode material is lithium nickel cobalt aluminum oxide, which can be denoted as NCA.

[0414] In some embodiments, in lithium nickel cobalt manganese-based oxides, the ratio of the sum of the atomic molar ratios of nickel, cobalt, and manganese to the sum of the atomic molar ratios of non-lithium metal elements is denoted as R. NCM .

[0415] Without limitation, R NCM It can be 0.9 to 1, can be selected from 0.95 to 1, or can be any of the following values ​​or a range composed of any two of the following values: 0.9, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1, etc.

[0416] Non-limitingly, the mass percentage of lithium nickel cobalt manganese-based oxide in lithium composite metal oxide material is 80% to 100%, optionally 90% to 100%, or any of the following percentages or selected from any two of the following percentages: 80%, 85%, 90%, 95%, 96%, 97%, 98%, 99%, 100%, etc.

[0417] Understandably, lithium (Li) is intercalated and deintercalated during the charging and discharging process of a battery, and the Li content in the positive electrode varies depending on the state of discharge. In the exemplary descriptions of positive electrode active materials and substances in this application, unless otherwise specified, the Li content can be the initial state of the material or a non-initial state after charge-discharge cycles. When a positive electrode active material or substance is applied to the positive electrode in a battery system, the Li content in the positive electrode active material or substance at the positive electrode typically changes after charge-discharge cycles. The Li content can be measured using atomic molar content, but is not limited to this. Regarding "Li content in the initial state of the material," the initial state of the material refers to the state before it is formed into the positive electrode active layer. It is understood that new materials or substances obtained by appropriate modification based on the listed positive electrode active materials are also within the scope of positive electrode active materials. The aforementioned appropriate modification refers to acceptable modification methods for positive electrode active materials, and non-limiting examples include one or more of coating modification and doping modification.

[0418] In the exemplary description of the positive electrode active material in this application, the oxygen (O) content is only a theoretical value. Lattice oxygen release will cause changes in the atomic molar content of oxygen, and the actual O content will fluctuate. The O content can be measured in atomic molar content, but is not limited to this.

[0419] In some implementations, the positive electrode sheet satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0420] (te1) The mass percentage of lithium composite metal oxide material in the positive electrode active layer is 80% to 99%, and can be selected as 90% to 99%;

[0421] The mass percentage of (te2) lithium composite metal oxide materials in the positive electrode active material is 95% to 100%, and can be selected as 96% to 99%.

[0422] In some implementations, the positive electrode sheet satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0423] The mass percentage of (te1') lithium composite metal oxide material in the positive electrode active layer is 90% to 99%;

[0424] (te2')Lithium composite metal oxide materials account for 96% to 99% of the mass of the positive electrode active material.

[0425] Non-limitingly, the mass percentage of the lithium composite metal oxide material in the positive electrode active layer can be 80%, 81%, 82%, 83%, 84%, 85%, 86%, 87%, 88%, 89%, 90%, 91%, 92%, 93%, 94%, 95%, 96%, 97%, 98%, 99%, etc., or can be within any of the aforementioned percentage ranges. In some embodiments, the mass percentage of the lithium composite metal oxide material in the positive electrode active layer is 80% to 99%, optionally 90% to 99%, further optionally 90% to 98%, and even more preferably 90% to 97%.

[0426] Non-limitingly, the mass percentage of the lithium composite metal oxide material in the positive electrode active material can be 95%, 96%, 97%, 98%, 99%, 100%, etc., or within any of the aforementioned percentage ranges. In some embodiments, the mass percentage of the lithium composite metal oxide material in the positive electrode active material is 95% to 100%. In some other embodiments, the mass percentage of the lithium composite metal oxide material in the positive electrode active material is 96% to 99%.

[0427] By controlling one or more parameters, such as the mass ratio of lithium composite metal oxide material in the positive electrode active layer and the mass ratio of lithium composite metal oxide material in the positive electrode active material, within the aforementioned range, it is beneficial to better leverage the advantages of the aforementioned lithium composite metal oxide material.

[0428] At low SOC (State of Charge), most of the lithium ions in the positive electrode active material are released, and the positive electrode active material approaches the end of its discharge plateau, resulting in a significant drop in the battery's open-circuit voltage. Since the battery's power output is proportional to the terminal voltage, a decrease in voltage directly leads to a decrease in power performance. Furthermore, at low SOC, the lithium ion concentration in the positive electrode active material decreases, leading to a decrease in material conductivity and an increase in diffusion resistance. Based on the aforementioned effects, the battery's voltage and internal resistance are prone to instability at low SOC, affecting the stable power output at low SOC.

[0429] In some embodiments, the positive electrode active material includes lithium iron phosphate-based positive electrode materials. Further, the lithium iron phosphate-based positive electrode material may include at least one of lithium iron phosphate and a composite material of lithium iron phosphate and carbon.

[0430] In this application, unless otherwise specified, "lithium iron phosphate cathode material" refers to a class of cathode active materials containing lithium iron phosphate components. Unless otherwise specified, "lithium iron phosphate cathode material" may have an olivine structure.

[0431] In some embodiments, the composite material of lithium iron phosphate and carbon is carbon-coated lithium iron phosphate.

[0432] In some implementations, lithium iron phosphate cathode materials include carbon-coated lithium iron phosphate.

[0433] In this application, the term "carbon-coated lithium iron phosphate" includes a lithium iron phosphate body and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate body, wherein the lithium iron phosphate body comprises lithium iron phosphate. Non-limitingly, the carbon coating layer may include one or more of soft carbon, hard carbon, and amorphous carbon. Non-limitingly, the mass percentage of the carbon coating layer in the lithium iron phosphate cathode material may be 1% to 1.5%, optionally 1.4% to 1.5%.

[0434] The carbon coating layer in carbon-coated lithium iron phosphate can improve the conductivity of the lithium iron phosphate bulk surface.

[0435] "Soft carbon" and "hard carbon" have well-known meanings in the art. Soft carbon can be graphitized by further high-temperature treatment, while hard carbon is difficult to graphitize even with further high-temperature treatment. In this application, unless otherwise specified, "amorphous carbon" refers to transitional carbon materials with a very low degree of graphitization and crystallization, which are approximately amorphous (or have no fixed shape and periodic structural regularity).

[0436] In some embodiments, lithium iron phosphate cathode materials include lithium iron phosphate-based cathode materials. Lithium iron phosphate-based cathode materials refer to a class of cathode active materials containing lithium iron phosphate. In some embodiments, the lithium iron phosphate bulk material includes lithium iron phosphate.

[0437] In some embodiments, the lithium iron phosphate-based cathode material includes carbon-coated lithium iron phosphate. In this case, the carbon-coated lithium iron phosphate comprises carbon-coated lithium iron phosphate.

[0438] In this application, the term "carbon-coated lithium iron phosphate" includes lithium iron phosphate and a carbon coating layer located on at least a portion of the surface of the lithium iron phosphate. Further, the carbon coating layer may include one or more of soft carbon, hard carbon, and amorphous carbon.

[0439] In some embodiments, the carbon coating layer includes soft carbon. In some of these embodiments, the carbon coating layer is a soft carbon coating layer, in which case the carbon-coated lithium iron phosphate can be referred to as soft carbon-coated lithium iron phosphate. "Soft carbon coating layer" refers to a coating layer mainly composed of soft carbon, where the mass percentage of soft carbon in the coating layer can be close to 100%. The mass percentage of soft carbon in the soft carbon coating layer within the carbon-coated lithium iron phosphate can be 1% to 1.5%, optionally 1.4% to 1.5%, but is not limited thereto.

[0440] The voltage plateau of lithium iron phosphate cathode materials is relatively low and stable, and they have good voltage matching with lithium composite metal oxide materials. By introducing lithium iron phosphate cathode materials into the cathode active materials including lithium composite metal oxide materials, the discharge current of lithium iron phosphate cathode materials dominates at low SOC, and the cathode active materials have a relatively stable voltage plateau. This allows the battery to maintain a relatively stable voltage at low SOC, improves the stability of the battery's internal resistance, and improves the stability of power output at low SOC.

[0441] By introducing lithium iron phosphate (LFP) cathode materials into the positive electrode active material, the battery can maintain a relatively stable voltage under low SOC conditions, thus improving the stability of the battery's internal resistance. Furthermore, by utilizing the absorption effect of polycyclic sulfates in the electrolyte on water, the decomposition side reaction of water under high voltage and high temperature can be significantly suppressed. This can delay or avoid the consumption of electrolyte by newly introduced water after the introduction of LFP cathode materials, and reduce the generation of hydrofluoric acid after the introduction of LFP cathode materials. Therefore, the adverse effects of introducing LFP cathode materials on high-voltage and high-temperature performance during cycling and / or the initial storage period can be significantly suppressed.

[0442] The elemental composition of the positive electrode active material in the positive electrode active layer can be analyzed using methods known in the art, including but not limited to the following: inductively coupled plasma atomic emission spectrometry (ICP), X-ray diffraction (XRD), single-crystal X-ray diffraction (SCXRD), and energy dispersive spectroscopy (EDS). The sample preparation and testing methods for these methods are known to those skilled in the art, and the test parameters can be appropriately adjusted according to the sample characteristics. ICP can be used for quantitative analysis of the component content in the positive electrode active material.

[0443] The detection of positive electrode active material in the positive electrode active layer can be carried out by disassembling the battery after it is fully discharged, removing the positive electrode plate, scraping off the material of the positive electrode active layer, and using elemental analysis methods such as inductively coupled plasma (ICP) spectroscopy to test and analyze the types and proportions of elements, thereby confirming the elemental composition and chemical formula of the positive electrode active material.

[0444] In some embodiments, the positive electrode active material includes a positive electrode active body and a coating layer located on the positive electrode active body.

[0445] For cathode active materials that include a coating layer (e.g., a carbon coating layer), a cross-section can be obtained using FIB (Focused Ion Beam) and the particle cross-sectional morphology can be observed under TEM (Transmission Electron Microscopy). A clear boundary can be observed at the coating interface, and the thickness and average thickness of the coating layer can be calculated based on the TEM image. Further analysis using one or more methods such as energy-dispersive spectroscopy (EDS) and Raman spectroscopy can identify the types of substances in both the coating layer and the cathode active material.

[0446] In some implementations, the D of lithium iron phosphate cathode materials v 50 is 1μm to 11μm, can be selected from 4μm to 9μm, and can also be any of the following values ​​or a range composed of any two of the following values: 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, etc.

[0447] By using the D of lithium iron phosphate cathode materials v When the value of 50 is controlled within the aforementioned range, it has good size matching with lithium composite metal oxide materials, which is beneficial for better control of interfacial side reactions of positive electrode active materials. This is also beneficial for lithium-ion secondary batteries, including those using lithium composite metal oxide materials and lithium iron phosphate positive electrode materials, to have better high-temperature performance under high voltage.

[0448] In some implementations, the positive electrode sheet satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0449] (tf1) The mass percentage of lithium iron phosphate cathode material in the cathode active layer is 0.8% to 4.95%, which can be selected as 0.9% to 3.96%, and further selected as 0.9% to 3.9%;

[0450] (tf2) The mass percentage of lithium iron phosphate cathode material in the cathode active material is 1% to 5%, and can be selected as 1% to 4%.

[0451] Non-limitingly, the mass percentage of lithium iron phosphate cathode material in the cathode active layer can be 0.8%, 0.9%, 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 3.9%, 4%, 4.2%, 4.25%, 4.4%, 4.5%, 4.8%, 4.9%, 4.95%, etc., or can be within any of the aforementioned percentage ranges. In some embodiments, the mass percentage of lithium iron phosphate cathode material in the cathode active layer is 0.8% to 4.95%, optionally 0.9% to 4.95%, further optionally 0.9% to 4.9%, even more optionally 0.9% to 3.96%, and still more optionally 0.9% to 3.9%.

[0452] Non-limitingly, the mass percentage of lithium iron phosphate cathode material in the cathode active material can be 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, 5%, etc., or can be within any of the aforementioned percentage ranges. In some embodiments, the mass percentage of lithium iron phosphate cathode material in the cathode active material is 1% to 5%, optionally 1% to 4%.

[0453] By controlling one or both of the following parameters within the aforementioned ranges—the mass ratio of lithium iron phosphate cathode material in the cathode active layer and the mass ratio of lithium iron phosphate cathode material in the cathode active material—it is beneficial to combine the advantages of both lithium composite metal oxide materials and lithium iron phosphate cathode materials under high voltage and high temperature, thereby achieving better high-temperature performance under high voltage.

[0454] In some embodiments, the electrolyte in a lithium-ion secondary battery further includes one or both of fluoroethylene carbonate and tris(trimethylsilane) phosphate.

[0455] In some embodiments, in lithium-ion secondary batteries, the electrolyte satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0456] (tg1) The mass percentage of fluoroethylene carbonate in the electrolyte is 0.1% to 3%, and can be selected as 0.1% to 2.5%;

[0457] The mass percentage of (tg2) tris(trimethylsilane) phosphate in the electrolyte is 0.1% to 0.5%, and can be selected as 0.1% to 0.35%.

[0458] In some embodiments, in lithium-ion secondary batteries, the electrolyte satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0459] (tg1') The mass percentage of fluoroethylene carbonate in the electrolyte is 0.1% to 2.5%;

[0460] The mass percentage of (tg2')tris(trimethylsilane)phosphate in the electrolyte is 0.1% to 0.35%.

[0461] Non-limitingly, in lithium-ion secondary batteries, the mass percentage of fluoroethylene carbonate in the electrolyte can be 0.1% to 3%, optionally 0.1% to 2.5%, or any of the following percentages or a range selected from any two of the following percentages: 0.1%, 0.2%, 0.3%, 0.4%, 0.5%, 0.6%, 0.8%, 0.9%, 1%, 1.2%, 1.5%, 1.6%, 1.75%, 1.8%, 2%, 2.2%, 2.25%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, etc.

[0462] By introducing fluoroethylene carbonate (FEC) into the electrolyte, a more stable SEI film can be formed on the surface of the negative electrode, which is beneficial to improving the cycle performance and / or storage performance of the battery under high voltage and high temperature.

[0463] Non-limitingly, in lithium-ion secondary batteries, the mass percentage of tris(trimethylsilane)phosphate in the electrolyte can be 0.1% to 0.5%, optionally 0.1% to 0.35%, or any of the following percentages or a range selected from any two of the following percentages: 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.5%, etc.

[0464] By introducing tris(trimethylsilane) phosphate (TMSP) into the electrolyte, phosphorus-containing components can be introduced into the negative electrode SEI film. The negative electrode SEI film formed with the participation of TMSP has low impedance, which is beneficial to reducing the internal resistance of the battery.

[0465] In some embodiments, the electrolyte in the lithium-ion secondary battery optionally includes lithium bisfluorosulfonylimide. Non-limitingly, the molar concentration of lithium bisfluorosulfonylimide in the electrolyte in the lithium-ion secondary battery can be 0 to 0.3 mol / L, optionally greater than 0 mol / L and less than or equal to 0.3 mol / L, further optionally 0.1 mol / L to 0.3 mol / L, and even more preferably 0.1 mol / L to 0.25 mol / L. In lithium-ion secondary batteries, the molar concentration of lithium bis(fluorosulfonyl)imide in the electrolyte can also be any of the following concentrations or a range selected from any two of the following concentrations: 0 mol / L, 0.001 mol / L, 0.01 mol / L, 0.02 mol / L, 0.05 mol / L, 0.1 mol / L, 0.12 mol / L, 0.15 mol / L, 0.16 mol / L, 0.18 mol / L, 0.2 mol / L, 0.24 mol / L, 0.25 mol / L, 0.26 mol / L, 0.28 mol / L, 0.3 mol / L, etc.

[0466] In some embodiments, the electrolyte in the lithium-ion secondary battery includes lithium bisfluorosulfonylimide. In some embodiments, the molar volume concentration of lithium bisfluorosulfonylimide in the electrolyte in the lithium-ion secondary battery can be greater than 0 mol / L and less than or equal to 0.3 mol / L, and is optionally 0.1 mol / L to 0.25 mol / L.

[0467] Lithium bisfluorosulfonylimide (LiFSI) can participate in the formation of a stable solid electrolyte interfacial film at both the positive and negative electrodes. Introducing LiFSI into the electrolyte can improve the stability of the positive and negative electrode interfacial film, which is beneficial for enhancing the stability of the positive and negative electrode active materials under high voltage and high temperature, better suppressing interfacial side reactions in the electrolyte, delaying battery capacity decay under high voltage and high temperature, and improving the battery's cycle and / or storage performance under high voltage and high temperature.

[0468] In addition, compared with traditional lithium hexafluorophosphate, LiFSI has a higher dissociation ability, which is beneficial to improving the liquid phase conductivity and thus reducing the battery internal resistance.

[0469] In some embodiments, the negative electrode includes a negative electrode active layer, which includes a negative electrode active material; the negative electrode active material includes one or more of carbon-based and silicon-based materials. In some embodiments, the negative electrode active material includes graphite. Non-limitingly, the mass percentage of graphite in the negative electrode active material can be 80% to 100%, optionally 90% to 100%, further optionally 97% to 100%, and can also be any of the following percentages or a range selected from any two of the following percentages: 80%, 85%, 90%, 95%, 97%, 98%, 99%, 100%, etc.

[0470] In this application, "graphite material" refers to a negative electrode active material containing graphite, and the graphite material includes at least a graphite matrix. The graphite material may include one or more of artificial graphite and natural graphite. In some embodiments, the negative electrode active material is a graphite material.

[0471] In some embodiments, the negative electrode active material includes graphite, and further, the graphite may include one or more of artificial graphite and natural graphite.

[0472] The negative electrode active material in the negative electrode sheet can be one of the aforementioned types, but is not limited to these.

[0473] In some embodiments, the charging cutoff voltage of the lithium-ion secondary battery is greater than or equal to 4.2V, and can be selected from 4.2V to 4.5V. It can also be any of the following voltages or a range selected from any two of the following voltages: 4.2V, 4.3V, 4.4V, 4.5V, etc.

[0474] In some embodiments, the charging cutoff voltage of the lithium-ion secondary battery is greater than or equal to 4.3V, and can be selected from 4.3V to 4.5V, or any of the following voltages or a range selected from any two of the following voltages: 4.3V, 4.4V, 4.5V, etc.

[0475] In this application, unless otherwise specified, the "charging cut-off voltage" of a secondary battery has a well-known meaning in the art and is usually marked on battery products. Secondary battery products can operate at voltages equal to or lower than the charging cut-off voltage. Taking a lithium-ion secondary battery as an example, as charging progresses, the battery voltage continuously rises; when the charging cut-off voltage is reached, it indicates that the distribution of lithium ions in the positive and negative electrode materials and the electrochemical equilibrium inside the battery have reached a specific state. If charging continues at a high current, exceeding the charging cut-off voltage, irreversible chemical reactions can easily occur inside the battery.

[0476] The following is a description of the positive electrode sheet.

[0477] The positive electrode includes a positive current collector and a positive active layer disposed on at least one surface of the positive current collector, the positive active layer including a positive active material.

[0478] Without limitation, the weight percentage of the positive electrode active material in the positive electrode active layer may be greater than or equal to 80 wt%, further greater than or equal to 90 wt%, and even further greater than or equal to 92 wt%.

[0479] As a non-limiting example, the positive current collector has two surfaces that are opposite to each other in its own thickness direction, and the positive active layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0480] In some embodiments, the positive electrode current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. In the positive electrode current collector, the composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. In the positive electrode current collector, the composite current collector may be obtained by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the positive electrode current collector may include at least one of aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver, and silver alloy. Non-limitingly, in the positive electrode current collector, the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0481] The types of positive electrode active materials can be found above. Positive electrode active materials may also include other types of positive electrode active materials known in the art for use in lithium-ion secondary batteries. A single positive electrode active material may be used alone, or two or more may be used in combination.

[0482] In some embodiments, the positive electrode active material includes a lithium transition metal oxide. Examples of lithium transition metal oxides include, but are not limited to, one or more of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, lithium nickel cobalt oxide, lithium manganese cobalt oxide, lithium nickel manganese oxide, lithium nickel cobalt manganese oxide, lithium nickel cobalt aluminum oxide, and their modified compounds. Non-limiting examples of lithium cobalt oxide may include LiCoO2; non-limiting examples of lithium nickel oxide may include LiNiO2; non-limiting examples of lithium manganese oxide may include LiMnO2, LiMn2O4, etc.; non-limiting examples of lithium nickel cobalt manganese oxide may include LiNi 1 / 3 Co 1 / 3 Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 Examples of lithium nickel cobalt aluminum oxides include LiNi, etc. 0.80 Co 0.15 Al 0.05 O2.

[0483] In some embodiments, the positive electrode active layer optionally includes a binder. As a non-limiting example, the binder may include one or more of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resins. Typically, the binder may be present in the positive electrode active layer at a weight percentage of 0–10 wt%, more commonly 0–8 wt%, and even more commonly 1 wt%–5 wt%, based on the total weight of the positive electrode active layer.

[0484] In some embodiments, the positive electrode active layer optionally includes a conductive agent. As a non-limiting example, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Typically, the weight percentage of the conductive agent in the positive electrode active layer can be 0–10 wt%, more commonly 0–8 wt%, and even more commonly 0–5 wt%, based on the total weight of the positive electrode active layer.

[0485] In some embodiments, the positive electrode sheet can be prepared by dispersing the components used to prepare the positive electrode sheet, such as the positive active material, conductive agent, binder, and any other components, in a solvent to form a positive electrode slurry. Further, the positive electrode slurry is coated onto at least one surface of the positive current collector, and after drying, cold pressing, and other processes, the positive electrode sheet is obtained. Cold pressing can be performed using a cold rolling mill. The solvent in the positive electrode slurry can be, but is not limited to, any of the solvents described in the foregoing embodiments, for example, N-methylpyrrolidone (NMP), and more specifically, NMP. The surface of the positive current collector coated with the positive electrode slurry can be a single surface of the positive current collector or both surfaces of the positive current collector. The solid content of the positive electrode slurry can be 40 wt% to 80 wt%. The viscosity of the positive electrode slurry at room temperature can be adjusted to 5000 mPa·s to 25000 mPa·s. When coating the positive electrode slurry, the single-sided coating surface density (excluding solvent) can be 15 mg / cm³. 2 ~20mg / cm 2 The optional value is (0.25~0.29)g / 1540.25mm. 2 The compaction density of the positive electrode sheet can be 3.2 g / cm³. 3 ~3.5g / cm 3 3.25g / cm³ is an optional value. 3 ~3.35g / cm 3 .

[0486] The term "compacted density" as used in this application has a meaning well-known in the art and is one of the reference indicators for material energy density. In this application, unless otherwise specified, the compacted density of an electrode sheet refers to the ratio of the mass of the electrode active layer to its volume. The compacted density of a positive electrode sheet refers to the ratio of the mass of the positive active layer to its volume, and the compacted density of a negative electrode sheet refers to the ratio of the mass of the negative active layer to its volume.

[0487] The following is a description of the negative electrode plate.

[0488] The negative electrode sheet includes a negative current collector and a negative active layer disposed on at least one surface of the negative current collector, the negative active layer including a negative active material.

[0489] Without limitation, the weight percentage of the negative electrode active material in the negative electrode active layer may be greater than or equal to 80 wt%, and may further be greater than or equal to 90 wt%.

[0490] As a non-limiting example, the negative electrode current collector has two surfaces that are opposite to each other in its own thickness direction, and the negative electrode active layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0491] In some embodiments, the negative electrode current collector may be a metal foil or a composite current collector. For example, copper foil may be used as the metal foil. In the negative electrode current collector, the composite current collector may include a polymer material substrate and a metal layer formed on at least one surface of the polymer material substrate. In the negative electrode current collector, the composite current collector may be formed by forming a metal material on the polymer material substrate. Non-limiting examples of the metal material in the negative electrode current collector may include one or more of copper, copper alloys, nickel, nickel alloys, titanium, titanium alloys, silver, and silver alloys. Non-limitingly, in the negative electrode current collector, the polymer material substrate may include one or more of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), and polyethylene (PE).

[0492] In some embodiments, the types of negative electrode active materials are as described above. Negative electrode active materials may also include other types of negative electrode active materials known in the art for use in lithium-ion secondary batteries. As a non-limiting example, negative electrode active materials may include one or more of the following materials: artificial graphite, natural graphite, soft carbon, hard carbon, silicon-based materials, tin-based materials, and lithium titanate, etc. Silicon-based materials may include one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may include one or more of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials or substances, and other conventional materials that can be used as battery negative electrode active materials may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0493] In some embodiments, the negative electrode active material includes carbon-based materials and silicon-based materials. Non-limitingly, the total mass percentage of the carbon-based and silicon-based materials in the total mass of the negative electrode active material can be ≥80%, optionally ≥90%, further optionally ≥95%, even more optionally ≥96%, and even more optionally 100%. Non-limitingly, the mass percentage of the carbon-based material in the negative electrode active material can also be any of the following percentages, or greater than or equal to any of the following percentages and less than or equal to 100%, or selected from any two of the following percentages: 80%, 82%, 83%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, 99%, etc. Non-limitingly, the carbon-based material can include, but is not limited to, one or more of graphite, soft carbon, hard carbon, etc. Graphite can include one or more of artificial graphite and natural graphite. Carbon-based materials may include, and may further include, graphite materials, but are not limited to these.

[0494] In some embodiments, the negative electrode active material includes graphite material and silicon-based material. Non-limitingly, the percentage of the total mass of graphite material and silicon-based material in the total mass of the negative electrode active material can also be any of the following percentages, or a range selected from any two of the following percentages: 80%, 82%, 83%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, 99%, 100%, etc.

[0495] In some embodiments, the negative electrode active material includes a carbon-based material. Non-limitingly, the mass percentage of the carbon-based material in the negative electrode active material can be ≥80%, optionally ≥90%, further optionally ≥95%, even more optionally ≥96%, and even more optionally 100%. The mass percentage of the carbon-based material in the negative electrode active material can also be any of the following percentages, or greater than or equal to any of the following percentages and less than or equal to 100%, or selected from a range consisting of any two of the following percentages: 80%, 82%, 83%, 84%, 85%, 86%, 88%, 90%, 92%, 94%, 95%, 96%, 98%, 99%, etc. The definition of carbon-based material can be found above; for example, the carbon-based material can be graphite.

[0496] In some embodiments, the negative electrode active layer optionally includes a binder. Non-limitingly, the binder may include one or more of styrene-butadiene rubber (SBR), polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyacrylamide (PAM), polyvinyl alcohol (PVA), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). Non-limitingly, the weight percentage of the binder in the negative electrode active layer may be 0 wt% to 20 wt%, more further 0 wt% to 10 wt%, even further 0 to 5 wt%, even further 1 wt% to 5 wt%, and even more preferably 1 wt% to 3 wt%.

[0497] In some embodiments, the negative electrode active layer optionally includes a conductive agent. Non-limitingly, the conductive agent may include one or more of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. Non-limitingly, the weight percentage of the conductive agent in the negative electrode active layer may be 0 wt% to 15 wt%, more preferably 0 wt% to 10 wt%, and even more preferably 0 wt% to 5 wt%.

[0498] In some embodiments, the negative electrode active layer may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)). Non-limitingly, the weight percentage of other additives in the negative electrode active layer may be 0 wt% to 15 wt%, more preferably 0 wt% to 10 wt%, even more preferably 0 wt% to 5 wt%, even more preferably 0 wt% to 3 wt%, and even more preferably 0 wt% to 2 wt%.

[0499] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder, and any other components, in a solvent (a non-limiting example of a solvent is deionized water) to form a negative electrode slurry. Further, the negative electrode slurry is coated onto at least one surface of the negative electrode current collector, and after drying, cold pressing, and other processes, the negative electrode sheet is obtained. Cold pressing can be performed using a cold rolling mill. The surface of the negative electrode current collector coated with the negative electrode slurry can be a single surface of the negative electrode current collector or both surfaces of the negative electrode current collector. The solid content of the negative electrode slurry can be 30wt% to 70wt%, optionally 40wt% to 60wt%. The viscosity of the negative electrode slurry at room temperature can be adjusted to 2000 mPa·s to 10000 mPa·s, optionally 3000 mPa·s to 10000 mPa·s. When coating the negative electrode slurry, the coating surface density (excluding solvent) can be 75 g / m² on a dry weight basis. 2 ~220g / m 2 The optional value is (0.12~0.2)g / 1540.25mm.2 Based on the surface density of the coating on one side, the compacted density of the negative electrode sheet can be 1.0 g / cm³. 3 ~2.0g / cm 3 1.0g / cm can be selected. 3 ~1.8g / cm 3 .

[0500] The electrolyte is described below as an example.

[0501] In this application, unless otherwise specified, a lithium-ion secondary battery includes an electrolyte, which includes a liquid electrolyte. "Liquid electrolyte" is also known as a liquid electrolyte. The electrolyte serves to conduct ions between the positive and negative electrode plates. In some embodiments, the electrolyte is a liquid electrolyte. The liquid electrolyte includes an electrolyte salt and a solvent.

[0502] In some embodiments, the electrolyte is a non-aqueous electrolyte, also known as a non-aqueous electrolyte solution. In this case, the solvent is a non-aqueous solvent.

[0503] The concentration of electrolyte salts in the electrolyte solution is typically 0.5 mol / L to 5 mol / L.

[0504] In some embodiments, the electrolyte salt includes an electrolyte lithium salt. Non-limitingly, the electrolyte lithium salt may include one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluorophosphate (LiPO2F2), lithium difluorooxalate borate (LiDFOB), lithium dioxalate borate (LiBOB), lithium difluorodioxalate phosphate (LiDFOP), and lithium tetrafluorooxalate phosphate (LiTFOP).

[0505] In some embodiments, the solvent in the non-aqueous electrolyte may include ethylene carbonate (EC). ), propylene carbonate (PC, propylene carbonate) ), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC). One or more of the following: fluoroethylene carbonate (FEC), methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0506] The types of additives in the electrolyte can also be found in the description within the context of this application. Non-limitingly, other types of additives may also be introduced into the electrolyte. These other types of additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0507] The following is an exemplary description of the separator membrane.

[0508] In some embodiments, the lithium-ion secondary battery further includes a separator. This application does not impose any particular limitation on the type of separator; any known porous separator with good chemical and mechanical stability can be selected.

[0509] In some embodiments, the material of the separator may include one or more of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator may be a single-layer film or a multi-layer composite film, without particular limitation. When the separator is a multi-layer composite film, the materials of each layer may be the same or different, without particular limitation.

[0510] In some embodiments, the thickness of the separator is 6 μm to 40 μm, and optionally 6 μm to 20 μm.

[0511] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0512] In some implementations, a lithium-ion secondary battery includes a single battery cell.

[0513] In this application, unless otherwise specified, "cell battery" refers to the basic unit capable of converting chemical energy into electrical energy, and typically includes at least a positive electrode, a negative electrode, an electrolyte, and a separator. During battery charging and discharging, active ions repeatedly insert and extract between the positive and negative electrodes. The electrolyte acts as a conductor of active ions between the positive and negative electrodes. A separator is disposed between the positive and negative electrodes; the separator primarily prevents short circuits between the positive and negative electrodes while allowing ions to pass through.

[0514] In some embodiments, the lithium-ion secondary battery may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0515] In some embodiments, the outer packaging of the lithium-ion secondary battery can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the lithium-ion secondary battery can also be a soft pack, such as a pouch. The soft pack can be made of plastic; further, non-limiting examples of plastic may include one or more of polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0516] A lithium-ion secondary battery includes at least one battery cell. A lithium-ion secondary battery may include one or more battery cells.

[0517] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 shows a square battery cell 5 as an example.

[0518] In some embodiments, referring to FIG2, the outer packaging may include a housing 51 and a cover plate 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover plate 53 can be placed over the opening to close the receiving cavity. The positive electrode sheet, negative electrode sheet, and separator may be formed into an electrode assembly 52 by a winding process or a stacking process. The electrode assembly 52 is encapsulated within the receiving cavity. The electrode assembly 52 is immersed in an electrolyte. The number of electrode assemblies 52 contained in the battery cell 5 may be one or more, which can be selected by those skilled in the art according to actual needs.

[0519] In some implementations, the electrolyte injection coefficient is greater than or equal to 1.6 g / Ah.

[0520] The lithium-ion secondary battery can be a battery device 4 or a battery pack 1.

[0521] The battery device includes at least one battery cell. The number of battery cells in the battery device can be one or more, and those skilled in the art can select an appropriate number according to the application and capacity of the battery device.

[0522] Figure 3 shows a battery device 4 as an example. Referring to Figure 3, in the battery device 4, multiple battery cells 5 can be arranged sequentially along the length of the battery device 4. Of course, they can also be arranged in any other arbitrary way. Furthermore, the multiple battery cells 5 can be fixed in place by fasteners.

[0523] Optionally, the battery device 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0524] In some embodiments, the battery devices described above can also be assembled into a battery pack, and the number of battery devices contained in the battery pack can be one or more. Those skilled in the art can select an appropriate number according to the application and capacity of the battery pack.

[0525] Figures 4 and 5 show a battery pack 1 as an example. Referring to Figures 4 and 5, the battery pack 1 may include a battery compartment and multiple battery devices 4 disposed within the battery compartment. The battery compartment includes an upper compartment 2 and a lower compartment 3, the upper compartment 2 covering the lower compartment 3 to form a closed space for accommodating the battery devices 4. The multiple battery devices 4 can be arranged in any manner within the battery compartment.

[0526] In a second aspect of this application, a lithium-ion secondary battery assembly is provided, which can be used to manufacture lithium-ion secondary batteries.

[0527] In some embodiments, the lithium-ion secondary battery of the first aspect of this application can be prepared by forming the lithium-ion secondary battery assembly of the second aspect of this application.

[0528] In some embodiments, a lithium-ion secondary battery assembly is provided, which includes a positive electrode, a separator, a negative electrode, and an electrolyte, wherein a separator is disposed between the positive electrode and the negative electrode; the positive electrode includes a positive active layer, the positive active layer includes a positive active material, the positive active material includes a lithium composite metal oxide material, and the lithium composite metal oxide material includes non-agglomerated primary particles.

[0529] The electrolyte includes polycyclic sulfates.

[0530] For a definition of polycyclic sulfates, please refer to the first aspect of this application.

[0531] In some embodiments of lithium-ion secondary battery assemblies, the electrolyte includes an electrolyte salt and a polycyclic sulfate.

[0532] In some embodiments of lithium-ion secondary battery components, the electrolyte includes an electrolyte salt, a non-aqueous solvent, and an additive; the additive includes a polycyclic sulfate, and further, the polycyclic sulfate contains at least two cyclic sulfate units in its structural formula.

[0533] In some implementations, the lithium-ion secondary battery assembly may correspond to the state before formation treatment.

[0534] In some embodiments, the lithium-ion secondary battery assembly includes a housing. In some embodiments, an electrode assembly is placed inside the housing and an electrolyte is injected to obtain the lithium-ion secondary battery assembly.

[0535] In the second aspect of the lithium-ion secondary battery assembly, the positive electrode active material includes lithium composite metal oxide material, and the positive electrode active material includes non-agglomerated primary particles; by introducing polycyclic sulfate additives into the electrolyte, polycyclic sulfates can participate in the construction of solid electrolyte interface films at the positive and negative electrodes more quickly during the formation process at high voltage and high temperature, forming a denser interface film, which can significantly enhance the stability of CEI film and SEI film. For the prepared lithium-ion secondary battery, the improved stability of the CEI film can significantly and persistently enhance the structural stability of the positive electrode active material, including non-agglomerated primary particles in the lithium composite metal oxide material, under high voltage and high temperature. It also helps suppress interfacial side reactions under high voltage and high temperature, delaying battery capacity decay during cycling or storage at high voltage and high temperature. Furthermore, the polycyclic sulfate additive can absorb moisture in the electrolyte, reducing the generation of hydrofluoric acid. This significantly reduces the damage of hydrofluoric acid to the CEI and SEI films and the chemical corrosion of the positive electrode active material under high voltage and high temperature, further improving the cycle performance and / or storage performance of the lithium-ion secondary battery under high voltage and high temperature. Using the lithium-ion secondary battery module provided in the second aspect of this application, the prepared lithium-ion secondary battery can exhibit significantly improved high-temperature performance under high voltage.

[0536] In this application, the mass percentage of polycyclic sulfate in the electrolyte of a lithium-ion secondary battery assembly can be denoted as "W0".

[0537] In some embodiments, WO is 0.1% to 3%, optionally 0.1% to 2.5%, further optionally 0.2% to 2%, and may also be any of the following percentages or a range selected from any two of the following percentages: 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, etc. W0 can also be selected from any of the following ranges: 0.15% to 0.25%, 0.16% to 0.24%, 0.18% to 0.22%, 0.19% to 2.1%, etc.

[0538] By controlling the mass percentage (W0) of polycyclic sulfates in the electrolyte of lithium-ion secondary battery components, a denser and more stable interfacial film can be formed during the formation process under high voltage and high temperature conditions. Furthermore, during cycling and / or storage under high voltage and high temperature conditions, polycyclic sulfates in the electrolyte can better exert their synergistic effects in improving the stability of CEI and SEI films, enhancing the structural stability of non-agglomerated primary particles in lithium composite metal oxide materials, suppressing interfacial side reactions, absorbing moisture, and reducing hydrofluoric acid generation. This can significantly improve the high-temperature performance of lithium-ion secondary batteries under high voltage, while also helping to control the battery internal resistance within a suitable range.

[0539] Those skilled in the art will understand that the content of some additive components in the electrolyte may change after formation treatment. As a non-limiting example, for instance, the content of some film-forming additive components decreases due to their participation in the formation of the solid electrolyte interface film of the positive and / or negative electrodes. As a non-limiting example, the content of polycyclic sulfates in the electrolyte typically decreases after formation treatment compared to the electrolyte before formation treatment.

[0540] In some embodiments, after formation treatment, the content of each additive in the prepared lithium-ion secondary battery can be referred to the first aspect of this application.

[0541] In some embodiments, after the formation treatment, the mass percentage of polycyclic sulfate in the electrolyte can be less than 1%, optionally 0.01% to 1%, more preferably 0.02% to 0.5%, or any of the following percentages or a range selected from any two of the following percentages: 0.001%, 0.002%, 0.004%, 0.005%, 0.006%, 0.008%, 0.01%, 0.02%, 0.04%, 0.05%, 0.06%, 0.08%, 0.1%, 0.15%, 0.2%, 0.25%, 0.3%, 0.4%, 0.5%, 0.6%, 0.7%, 0.75%, 0.8%, 0.85%, 0.9%, 0.95%, 1%, etc.

[0542] In lithium-ion secondary battery components, the types of electrolyte lithium salts and solvents in the electrolyte are described in the first aspect of this application. After formation treatment, the mass ratios of electrolyte lithium salts and solvents in the electrolyte may change.

[0543] In some implementations, the lithium-ion secondary battery assembly satisfies one or more of the following characteristics:

[0544] (tj1) Polycyclic sulfates as defined in the first aspect of this application;

[0545] (tj2) The positive electrode is as defined in the first aspect of this application;

[0546] (tj3) The negative electrode is as defined in the first aspect of this application;

[0547] (tj4) The electrolyte also includes one or two of fluoroethylene carbonate and tris(trimethylsilane) phosphate;

[0548] (tj5) The electrolyte includes lithium difluorosulfonylimide.

[0549] In some embodiments, in a lithium-ion secondary battery assembly, the electrolyte satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0550] (tk1) The electrolyte includes fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate in the electrolyte is 1% to 6%, which can be 1% to 5%.

[0551] (tk2) The electrolyte includes tris(trimethylsilane) phosphate, and the mass percentage of tris(trimethylsilane) phosphate in the electrolyte is 0.1% to 1%, which can be 0.1% to 0.7%;

[0552] (tk3) The electrolyte includes lithium bis(fluorosulfonyl)imide, and the molar concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is greater than 0 and less than or equal to 0.3 mol / L, which can be selected as 0.1 mol / L to 0.3 mol / L.

[0553] In some embodiments, in a lithium-ion secondary battery assembly, the electrolyte satisfies one or more of the following characteristics (any numerical parameter of the following characteristics may also be selected from any suitable value or range in the context):

[0554] (tm1) The mass percentage of fluoroethylene carbonate in the electrolyte is 1% to 5%;

[0555] The mass percentage of (tm2)tris(trimethylsilane)phosphate in the electrolyte is 0.1% to 0.7%;

[0556] The molar concentration of (tm3) bis(fluorosulfonyl)imide lithium in the electrolyte is 0.1 mol / L to 0.3 mol / L.

[0557] In some embodiments, the electrolyte in the lithium-ion secondary battery assembly further includes one or both of fluoroethylene carbonate and tris(trimethylsilane) phosphate.

[0558] In some embodiments, the electrolyte in the lithium-ion secondary battery assembly includes fluoroethylene carbonate (FEC). Non-limitingly, in the lithium-ion secondary battery assembly, the mass percentage of FEC in the electrolyte can be 1% to 6%, optionally 1% to 5%, or any of the following percentages or a range selected from any two of the following percentages: 1%, 1.2%, 1.4%, 1.5%, 1.6%, 1.8%, 2%, 2.2%, 2.4%, 2.5%, 2.6%, 2.8%, 3%, 3.5%, 4%, 4.5%, 5%, 5.5%, 6%, etc.

[0559] In some embodiments, the electrolyte in the lithium-ion secondary battery assembly comprises tris(trimethylsilane)phosphate (TMSP). Non-limitingly, in the lithium-ion secondary battery, the mass percentage of TMSP in the electrolyte can be 0.1% to 1%, optionally 0.1% to 0.7%, or any of the following percentages or a range selected from any two of the following percentages: 0.1%, 0.12%, 0.15%, 0.16%, 0.18%, 0.2%, 0.25%, 0.3%, 0.35%, 0.4%, 0.45%, 0.48%, 0.5%, 0.6%, 0.7%, 0.8%, 0.9%, 1%, etc.

[0560] In some embodiments, the electrolyte in the lithium-ion secondary battery assembly optionally includes lithium bisfluorosulfonylimide (LiFSI). Non-limitingly, in the lithium-ion secondary battery assembly, the molar concentration of LiFSI in the electrolyte can be 0–0.3 mol / L, optionally 0.1–0.3 mol / L, or any of the following concentrations or a range selected from any two of the following concentrations: 0 mol / L, 0.001 mol / L, 0.01 mol / L, 0.02 mol / L, 0.05 mol / L, 0.1 mol / L, 0.12 mol / L, 0.15 mol / L, 0.16 mol / L, 0.18 mol / L, 0.2 mol / L, 0.24 mol / L, 0.25 mol / L, 0.26 mol / L, 0.28 mol / L, 0.3 mol / L, etc.

[0561] In some embodiments of the lithium-ion secondary battery assembly, the electrolyte includes lithium bisfluorosulfonylimide (LiFSI). Further, the molar concentration of LiFSI in the electrolyte can be greater than 0 mol / L and less than or equal to 0.3 mol / L, and can be selected as 0.1 to 0.3 mol / L.

[0562] In lithium-ion secondary battery modules, the material composition and dimensions of the positive electrode, negative electrode, and separator can be found in the first aspect of this application. The dimensions of the positive electrode, negative electrode, and separator in the lithium-ion secondary battery module may differ somewhat from those in the lithium-ion secondary battery of the first aspect.

[0563] In a third aspect of this application, a method for preparing a lithium-ion secondary battery is provided, which can be used to prepare the lithium-ion secondary battery described in the first aspect of this application.

[0564] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, which includes the following steps: immersing an electrode assembly, including a positive electrode, a separator, and a negative electrode, in an electrolyte to form a battery.

[0565] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, which includes the following steps:

[0566] An electrode assembly, including a positive electrode, a separator, and a negative electrode, is placed inside a battery casing; wherein a separator is disposed between the positive and negative electrode.

[0567] Inject electrolyte into the battery casing;

[0568] Let it stand and soak; and

[0569] formed.

[0570] In some embodiments, a method for preparing a lithium-ion secondary battery is provided, which includes the following steps:

[0571] An electrode assembly, including a positive electrode, a separator, and a negative electrode, is placed inside a battery casing; wherein a separator is provided between the positive electrode and the negative electrode.

[0572] An electrolyte is injected into the battery casing to prepare a lithium-ion secondary battery assembly.

[0573] Let it stand and soak; and

[0574] formed.

[0575] In some embodiments, the positive electrode includes a positive active layer, the positive active layer includes a positive active material, the positive active material includes a lithium composite metal oxide material, and the lithium composite metal oxide material includes non-agglomerated primary particles; the electrolyte includes a polycyclic sulfate.

[0576] For a definition of polycyclic sulfates, please refer to the first aspect of this application.

[0577] In some embodiments, in a lithium-ion secondary battery assembly, the electrolyte includes an electrolyte salt, a non-aqueous solvent, and an additive; the additive includes a polycyclic sulfate, and further, the polycyclic sulfate contains at least two cyclic sulfate units in its structural formula.

[0578] The prepared lithium-ion secondary battery can have the advantages of the aforementioned lithium-ion secondary batteries, including significantly improved high-temperature performance at high voltage.

[0579] The formation temperature can be 45°C, but is not limited to this.

[0580] In some embodiments, the formation can be performed at 45°C using a method comprising the following steps (steps S1, S2, S3, and S4 are performed sequentially):

[0581] S1) Charge at 0.05C for 14 minutes to 3V, then let stand for 10 minutes;

[0582] S2) Charge to 3.4V at 0.1C and let stand for 10 minutes;

[0583] S3) Charge to 3.65V at 0.2C and let stand for 10 minutes;

[0584] S4) Charge to 3.75V at 0.2C and let stand for 10 minutes;

[0585] The transformation has ended.

[0586] In some embodiments, the method for preparing a lithium-ion secondary battery satisfies one or more of the following characteristics:

[0587] (tn1) After injecting electrolyte into the battery casing, the lithium-ion secondary battery assembly described in the second aspect of this application is obtained;

[0588] (tn2) In the electrode assembly, the positive electrode is as defined in the first aspect of this application;

[0589] (tn3) In the electrode assembly, the negative electrode is as defined in the first aspect of this application.

[0590] D of positive electrode active material v 50. The specific surface area and the average particle size of primary particles can be controlled by selecting raw materials with appropriate sizes for the positive electrode active material.

[0591] Positive electrode active materials can be prepared using known methods. Taking the preparation of lithium composite metal oxide materials as an example, a solid precursor can be prepared according to the target chemical formula of the lithium composite metal oxide material using known methods (such as co-precipitation). Then, the solid precursor of the positive electrode active material, the lithium source, and optional additives are sintered. Combined with one or more methods such as crushing, sieving and classification, and mixing raw materials of specific particle sizes in the required proportions, the D-type positive electrode active material can be obtained. v 50. Control of one or more parameters, including specific surface area and average particle size of primary particles. During sintering, multiple sintering and multiple crushing methods can be employed. For example, a first sintering and a first crushing can be performed at temperature T1, followed by a second sintering and a second crushing at temperature T2, where T1 is not equal to T2. In some embodiments, T1 is greater than T2. ​​In some embodiments, the temperature T1 for the first sintering is 900°C to 980°C. Non-limitingly, the temperature T1 for the first sintering can also be any of the following temperatures or a range selected from any two of the following temperatures: 900°C, 910°C, 920°C, 930°C, 940°C, 950°C, 960°C, 970°C, 980°C, etc. In some embodiments, the temperature T2 for the second sintering is 700°C to 800°C. The first sintering process can lithium-ionize the solid precursor to form the target crystal structure of the positive electrode active material. The first crushing process can reduce particle agglomeration. The second sintering process can repair particle morphology, reduce defects, and promote the fusion of fine particles. The second crushing process can further reduce particle agglomeration. By controlling the process conditions of multiple sintering and multiple crushing processes, the desired positive electrode active material can be obtained.

[0592] For cathode active materials containing doped elements, dopant materials can be introduced during sintering. "Dopant materials" refers to raw materials that can provide dopant elements.

[0593] For positive electrode active materials containing coating elements, the aforementioned method can be used to prepare a positive electrode active body with the target element composition, and then the positive electrode active body and the coating material can be physically and / or chemically coated using known methods in the art.

[0594] In a fourth aspect of this application, a lithium-ion secondary battery is provided, which is obtained by performing a formation process on the lithium-ion secondary battery assembly described in the second aspect of this application, or by preparing it using the lithium-ion secondary battery preparation method described in the third aspect of this application.

[0595] In a fifth aspect of this application, an electrical device is provided, comprising at least one of the lithium-ion secondary battery described in the first aspect of this application, the lithium-ion secondary battery described in the fourth aspect of this application, and a lithium-ion secondary battery prepared using the lithium-ion secondary battery assembly described in the second aspect of this application.

[0596] In some embodiments, the electrical device includes a lithium-ion secondary battery according to any of the embodiments provided in this application.

[0597] Lithium-ion secondary batteries can be used as a power source for electrical devices or as an energy storage unit for electrical devices. Electrical devices can include, but are not limited to, mobile devices, electric vehicles, electric trains, ships and satellites, energy storage systems, etc. Mobile devices can include, for example, mobile phones and laptops; electric vehicles can include, for example, pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, electric motorcycles, power tools, etc., but are not limited to these. This type of electrical device can also be applied to military equipment, aerospace, and other fields, as well as to energy storage power systems such as hydroelectric, thermal, wind, and solar power plants.

[0598] As an electrical device, lithium-ion rechargeable batteries can be selected according to its usage requirements.

[0599] Figure 6 shows an example of an electrical device 6. This electrical device is a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle, etc. To meet the high power and high energy density requirements of the lithium-ion secondary battery for this electrical device, a battery device or battery pack can be used.

[0600] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a lithium-ion rechargeable battery as their power source.

[0601] The polycyclic sulfates involved in this application are commercially available or synthesized using existing methods in the field of organic chemical synthesis. Once the structural formula of the polycyclic sulfate is selected, those skilled in the art can choose a suitable organic synthesis method to prepare the target compound; furthermore, those skilled in the art can also identify the structure of the prepared polycyclic sulfates using one or more of the following detection methods, including but not limited to: 1H NMR spectroscopy (…). 1 Methods include 1H NMR, high performance liquid chromatography (HPLC), matrix-assisted laser desorption / ionization mass spectrometry (MADI-TOF), and Fourier transform infrared spectroscopy (FT-IR).

[0602] Taking H6 of compounds H1 to H8 as an example, the following method can be used for synthesis and structural confirmation.

[0603] The mass percentage of additives in the electrolyte can be determined using nuclear magnetic resonance (NMR) spectroscopy. An Oxford Instruments X-Pulse benchtop NMR spectrometer can be used for this purpose. The testing procedure is as follows: In a nitrogen-filled glove box, add 500 μL of deuterated reagent to the NMR tube, then add 100 μL of the non-aqueous electrolyte sample to the NMR tube. Shake the NMR tube to dissolve the non-aqueous electrolyte in the deuterated reagent. Because the non-aqueous electrolyte is very sensitive to moisture, both the NMR test and sample preparation must be performed under a nitrogen atmosphere (H₂O content less than 0.1 ppm, O₂ content less than 0.1 ppm). Simultaneously, all instruments used in the test must be pre-washed with pure water and dried in a vacuum environment at 60°C for at least 48 hours. The deuterated reagent was prepared as follows: Deuterated dimethyl sulfoxide (DMSO-d6), deuterated acetonitrile, and trifluoromethylbenzene were dried using a 4A molecular sieve at a temperature above 25°C for at least 3 days, ensuring that the water content of all reagents was less than 3 ppm. A Metrohm 831KF coulometric moisture analyzer was used for moisture testing. Then, 10 mL of dried DMSO-d6 and 300 μL of dried internal standard trifluoromethylbenzene were mixed thoroughly in a nitrogen-filled glove box to obtain the first solution. Another 10 mL of dried deuterated acetonitrile and 300 μL of dried internal standard trifluoromethylbenzene were mixed thoroughly to obtain the second solution. The first and second solutions were then mixed thoroughly to obtain the deuterated reagent.

[0604] Taking polycyclic sulfuric acid ester H6 as an example, it can be determined according to... 1 The mass percentage of polycyclic sulfate in the electrolyte was calculated by referring to the area of ​​the four characteristic peaks at 4.8–5.5 ppm in the 1H NMR spectrum and comparing them with the proportion of the characteristic peak area of ​​the internal standard trifluoromethylbenzene.

[0605] In this application, unless otherwise specified, the numerical range described by "above" includes the stated number. For example, "48 hours or more" means greater than or equal to 48 hours.

[0606] The following describes some embodiments of this application. The described embodiments are only a part of the embodiments of this application, and not all of them. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application and its applications. Based on the embodiments in this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0607] In the following examples, room temperature refers to 20°C to 30°C.

[0608] I. Preparation of Lithium-ion Secondary Batteries

[0609] The polycyclic sulfate additives used in the following examples were obtained commercially or prepared by organic synthesis.

[0610] Unless otherwise specified in the examples, the procedures described above, or those described in the literature in this field, or those described in the product instructions, shall be followed. Reagents or instruments whose manufacturers are not specified are all commercially available conventional products, or products that can be synthesized using conventional methods from commercially available products.

[0611] As examples, in the lithium composite metal oxide materials used to prepare the positive electrode sheets of each embodiment in Examples 1-23, the proportion of non-agglomerated primary particles is in the range of 90% to 98%. In the positive electrode active materials used to prepare the positive electrode sheets of each embodiment, the proportion of non-agglomerated primary particles is in the range of 87% to 96%.

[0612] Example 1.

[0613] (1) Positive electrode plate

[0614] LiNi, a ternary cathode material 0.65 Co 0.1 Mn 0.25 O2 (which can be denoted as Ni65), conductive carbon black (Super P), binder polyvinylidene fluoride (PVDF), and lithium iron phosphate cathode material are mixed uniformly in N-methylpyrrolidone (NMP) solvent at a mass ratio of 94:2:1:3, with a solid content of 72wt%, to obtain a cathode slurry. The cathode slurry is then coated onto both sides of the cathode current collector aluminum foil, with a coating density of 0.27 g / 1540.25 mm² on each side. 2 The positive electrode sheet is obtained through processes such as drying, cold pressing, slitting, and cutting. The compacted density of the positive electrode sheet is 3.31 g / cm³. 3 The total mass percentage of the positive electrode active material in the positive electrode active layer is 97%.

[0615] In this example, the positive electrode active material is a combination of lithium composite metal oxide material and lithium iron phosphate positive electrode material, and the D of the positive electrode active material is... v The thickness of 50 is 3.8 μm, and the specific surface area (BET) is 0.9 m². 2 / g, the average particle size of the primary particles is approximately 2μm. The lithium composite metal oxide material is LiNi. 0.65 Co 0.1 Mn 0.25O2, which is a ternary cathode material NCM, can be denoted as Ni65. Lithium iron phosphate cathode materials are lithium iron phosphate-based cathode materials, further classified as soft carbon-coated lithium iron phosphate. Soft carbon-coated lithium iron phosphate includes lithium iron phosphate and a soft carbon coating layer on the surface of the lithium iron phosphate, with the soft carbon coating layer accounting for approximately 1.46% of the mass of the soft carbon-coated lithium iron phosphate.

[0616] In this example, the D of the ternary cathode material Ni65 in the cathode active material... v 50 is 3.7μm, and the D of lithium iron phosphate cathode materials in positive electrode active materials v 50 is 4μm.

[0617] In this example, the lithium composite metal oxide material Ni65 accounts for 94% of the mass of the positive electrode active layer, and the lithium composite metal oxide material Ni65 accounts for 96.9% of the mass of the positive electrode active material.

[0618] In this example, for lithium composite metal oxide materials, non-agglomerated primary particles account for approximately 95% of the total number of particles; for positive electrode active materials, non-agglomerated primary particles account for approximately 92%.

[0619] (2) Negative electrode plate

[0620] Artificial graphite (anode active material), carbon black (Super P) (conductive agent), styrene-butadiene rubber (SBR) (binder), and sodium carboxymethyl cellulose (CMC-Na) were mixed uniformly in deionized water at a mass ratio of 97:0.55:1.15:1.3, with a solid content of 50 wt%, to obtain a cathode slurry. The cathode slurry was then coated onto both sides of a copper foil current collector, with a coating density of 0.16 g / 1540.25 mm² on each side. 2 The negative electrode sheet is obtained through drying, cold pressing, slitting, and cutting processes. The compacted density of the negative electrode sheet is 1.7 g / cm³. 3 .

[0621] (3) Separating membrane

[0622] A polyethylene (PE) film with a thickness of 13 μm is used.

[0623] (4) Electrolyte

[0624] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) were mixed at a mass ratio of 30:70 to obtain an organic solvent. Polycyclic sulfuric acid additive H6 was added to the organic solvent and mixed evenly. Then, fully dried lithium hexafluorophosphate (LiPF6) electrolyte salt was added and mixed thoroughly to ensure that the lithium electrolyte salt was fully dissolved, thus preparing an electrolyte solution with a LiPF6 molar concentration of 0.9 mol / L.

[0625] In this example, the concentration of polycyclic sulfate in the electrolyte is 0.2%, which can be recorded as the initial concentration in the electrolyte as a mass percentage.

[0626] (5) Preparation of lithium-ion secondary batteries

[0627] The positive electrode, separator, and negative electrode are stacked and wound in sequence to obtain an electrode assembly. The electrode assembly is placed in an outer packaging, dried, and then injected with electrolyte to obtain a lithium-ion secondary battery assembly. After vacuum sealing, standing, formation, and shaping, a lithium-ion secondary battery is obtained.

[0628] In this example, the formation parameters are as follows: formation temperature is 45℃, and formation steps are as follows: charge at 0.05C for 14 minutes to 3V, let stand for 10 minutes, then charge at 0.1C to 3.4V and let stand for 10 minutes, then charge at 0.2C to 3.65V and let stand for 10 minutes, then charge at 0.2C to 3.75V and let stand for 10 minutes. The formation is then complete.

[0629] Examples 2-6 were prepared using essentially the same method as in Example 1, the difference being the amount of polycyclic sulfate additive H1 used, as shown in Table 1. In Examples 2-6, the initial concentrations of polycyclic sulfate additive H6 in the electrolyte were 0.5% (Example 2), 1% (Example 3), 2% (Example 4), 0.1% (Example 5), and 3% (Example 6), respectively, by mass percentage.

[0630] Examples 7-13 were prepared using essentially the same method as in Example 3, the difference being the different types of polycyclic sulfate additives used (see Table 1). Examples 7-13 used polycyclic sulfate additives H2 to H5, H1, H7, and H8 respectively, with an initial concentration of 1% of the polycyclic sulfate in the electrolyte.

[0631] Examples 14-15 were prepared using the same method as in Example 3, except that the types of ternary cathode materials in the cathode active materials were different, as shown in Table 1.

[0632] The polycyclic sulfuric acid (PSA) additive used in Examples 1-6 and 14-15 is H1; the PSA additive used in Example 7 is H2; the PSA additive used in Example 8 is H3; the PSA additive used in Example 9 is H4; the PSA additive used in Example 10 is H5; the PSA additive used in Example 11 is H6; the PSA additive used in Example 12 is H7; the PSA additive used in Example 13 is H8; and the ternary cathode material used in Example 14 is LiNi. 0.5 Co 0.2 Mn 0.3O2, the ternary cathode material used in Example 15 is LiN i0.7 Co 0.1 Mn 0.2 O2.

[0633] Example 16 uses the same method as Example 3 to prepare a lithium-ion secondary battery, except that the composition of the additives in the electrolyte is different, and the types of additives added are fluoroethylene carbonate (FEC) and tris(trimethylsilane) phosphate (TMSP).

[0634] In Example 16, the additives in the electrolyte were changed to polycyclic sulfate H1 with an initial concentration of 2%, FEC with an initial concentration of 6%, and TMSP with an initial concentration of 1%, all expressed as mass percentages. In Example 16, the solvent composition was the same as in Example 1, and the type and molar concentration of the electrolyte lithium salt in the electrolyte were the same as in Example 1. The electrolyte lithium salt was LiPF6 with an initial concentration of 0.9 mol / L.

[0635] Example 17 prepared a lithium-ion secondary battery using essentially the same method as Example 16, except that the composition of the additives in the electrolyte was different, with the addition of lithium bis(fluorosulfonyl)imide (LiFSI). The initial concentration of LiFSI in the electrolyte was 0.3 mol / L. In Example 17, the solvent composition was the same as in Example 1, and the initial concentration of LiPF6 in the electrolyte (0.9 mol / L) was the same as in Example 1.

[0636] Example 18 uses essentially the same method as Example 3 to prepare a lithium-ion secondary battery, the difference being that only the ternary cathode material LiNi is used as the positive electrode active material. 0.65 Co 0.1 Mn 0.25 O2 (i.e., Ni65), which omits lithium iron phosphate cathode materials; in the cathode slurry, the cathode active material LiNi 0.65 Co 0.1 Mn 0.25 The mass ratio of O2 (ternary cathode material Ni65), conductive agent carbon black (Super P), and binder polyvinylidene fluoride (PVDF) is the same as in Example 1.

[0637] Examples 19-20 prepared lithium-ion secondary batteries using essentially the same method as in Example 3, the difference being that the ternary cathode material in the positive electrode active material was replaced with a different D... v 50% of the raw materials.

[0638] Example 19 modified to use D v 50 is a ternary cathode material N65 with a thickness of 3.2 μm.

[0639] Example 20 modified with D v50 is a ternary cathode material N65 with a thickness of 4.2 μm.

[0640] Examples 21-22 used essentially the same method as Example 3 to prepare lithium-ion secondary batteries, the difference being that the D of the ternary cathode material was adjusted. v 50 causes the average particle size of the primary particles in the positive electrode active material to be different.

[0641] In Example 21, the average particle size of the primary particles in the positive electrode active material is 1.15 μm.

[0642] In Example 22, the average particle size of the primary particles in the positive electrode active material is 2.93 μm.

[0643] Example 23 uses essentially the same method as Example 3 to prepare a lithium-ion secondary battery, the difference being that the lithium iron phosphate cathode material in the cathode active material is replaced with a different D... v 50% of the raw materials.

[0644] Example 23 uses D v The 50 is a 9μm soft carbon coated lithium iron phosphate, and the soft carbon coating layer accounts for approximately 1.47% of the mass of the soft carbon coated lithium iron phosphate.

[0645] Comparative Example 1 uses a method that is basically the same as that used in Example 1 to prepare a lithium-ion secondary battery, except that no polycyclic sulfuric acid ester additive is added to the electrolyte.

[0646] Comparative Example 2 prepared a lithium-ion secondary battery using essentially the same method as Example 1, except that the type of additive was different, with polycyclic sulfates being replaced by monocyclic sulfates. (Ethylene sulfate).

[0647] Comparative Example 3 uses the same method as Example 18 to prepare a lithium-ion secondary battery, except that no polycyclic sulfuric acid ester additive is added to the electrolyte.

[0648] Comparative Example 4 prepared a lithium-ion secondary battery using essentially the same method as Example 18, the difference being that the type of additive was different, and polycyclic sulfates were replaced with monocyclic sulfates.

[0649] Comparative Example 5 uses a method that is basically the same as that used in Example 19 to prepare a lithium-ion secondary battery, except that no polycyclic sulfuric acid ester additive is added to the electrolyte.

[0650] Comparative Example 6 uses the same method as Example 20 to prepare a lithium-ion secondary battery, except that no polycyclic sulfuric acid ester additive is added to the electrolyte.

[0651] The relevant parameters of the positive electrode active material raw materials and electrolyte additives in the lithium-ion secondary battery components used in Examples 1-23 and Comparative Examples 1-6 can be found in Tables 1 and 3. The residual concentration of electrolyte additives in the lithium-ion secondary batteries prepared in some examples can be found in Table 2. In the lithium-ion secondary batteries prepared in Examples 1-23, the mass percentage of polycyclic sulfates in the electrolyte is less than or equal to 1%, and most are in the range of 0.01% to 1%.

[0652] Table 1.

[0653] In Table 1, the concentrations of polycyclic sulfates, FEC, and TMSP in the electrolyte of lithium-ion secondary battery components are expressed as mass percentages.

[0654] Table 2.

[0655] In Table 2, the concentrations of polycyclic sulfates, FEC, and TMSP in the electrolyte of the prepared lithium-ion secondary batteries are expressed as mass percentages.

[0656] Table 3.

[0657] In Table 3, Ni65 uses LiNi. 0.65 Co 0.1 Mn 0.25 O2, Ni50 uses LiNi 0.5 Co 0.2 Mn 0.3 O2, Ni70 uses LiNi 0.7 Co 0.1 Mn 0.2 O2.

[0658] In Table 3, B1 is the ratio of Dv50 of the positive electrode active material to the average particle size D1 of the primary particles in the positive electrode active material.

[0659] II. Testing and Analysis

[0660] (I) Testing and Analysis Methods

[0661] 1. Material Characterization

[0662] (1) Lithium composite metal oxide materials, lithium iron phosphate cathode materials, and cathode active materials D v 50

[0663] The Malvern 2000 (MasterSizer 2000) laser particle size analyzer was used.

[0664] Preparation of the positive electrode active material test sample: Lithium composite metal oxide material and lithium iron phosphate positive electrode material are mixed according to the mass ratio used in preparing positive electrode slurry to obtain the positive electrode active material test sample.

[0665] The reference standard procedure is GB / T19077-2016 / ISO 13320:2009. The detailed test procedure includes: taking an appropriate amount of the sample to be tested, adding 20 mL of deionized water (sample concentration controlled at 8%–12% opacity), and sonicating for 5 min (53 kHz / 120 W) to fully disperse the sample. Then, the sample is measured according to GB / T19077-2016 / ISO 13320:2009. The ultrasonically dispersed sample is added to the injection cell, and testing begins after the sample has stabilized for 5–10 s. After the sample is poured into the injection tower, it circulates with the solution to the test optical path system. Under the irradiation of the laser beam, the particle size distribution characteristics can be obtained by receiving and measuring the energy distribution of the scattered light. Based on the test data, a volumetric cumulative distribution map of the particle size is plotted, and D is obtained from the distribution map. v 50. To avoid agglomeration during the drying process affecting particle size testing, a dispersion test can be performed on a sample that has been washed with anhydrous ethanol and then moistened.

[0666] The test results can be found in Table 3.

[0667] (2) Specific surface area BET of positive electrode active material

[0668] Sample to be tested: Raw material for positive electrode active material.

[0669] Testing instrument: Tri Star II specific surface area and porosity analyzer from Micromeritics, USA.

[0670] The test procedure can be referred to GB / T 19587-2004. Nitrogen is used as the adsorbent gas, and the specific surface area of ​​the material is calculated by the BET method. The sample to be tested is added into the BET test tube until it reaches 2 / 3 of the bottom bulb, and the sample is degassed and heated. After cooling to room temperature, nitrogen is backfilled to remove the vacuum, and the sample tube opening is plugged with a stopper. The sample weight is recorded. The stopper is removed, a filling rod is added, the sample tube is installed on the instrument analysis station, the sample weight is entered, and the test begins.

[0671] The test results can be found in Table 3.

[0672] 2. Analysis based on scanning electron microscope (SEM) images

[0673] Characterization parameters: morphological observation of the positive electrode active material; average particle size of primary particles in the positive electrode active material, proportion of non-agglomerated primary particles in lithium composite metal oxide materials, and proportion of non-agglomerated primary particles in the positive electrode active material, etc.

[0674] SEM testing parameters include: JEOL scanning electron microscope, Axia Chemi SEM scanning electron microscope, and ZEISS Sigma 300 scanning electron microscope. SEM testing can be referenced in JY / T010-1996. Magnification ranges from 1000X to 3000X.

[0675] Test method: The powder material to be tested is laid and adhered to conductive adhesive. The sample is placed on the stage of a scanning electron microscope. The sample is imaged under the bombardment of the electron beam generated by the electron gun, and the SEM microstructure of the sample is obtained.

[0676] Analysis equipment: LIBMAS intelligent microscopic analysis system for lithium-ion battery materials.

[0677] (1) Average particle size of primary particles in positive electrode active material

[0678] The maximum diameter of the primary particles in each direction in the SEM morphology image is denoted as the "particle size of the primary particles in the positive electrode active material".

[0679] The statistical scope of "primary particles in positive electrode active materials" includes non-agglomerated primary particles and primary particles in secondary particles as shown in SEM morphology images.

[0680] Analytical Method: One to three regions are randomly selected from the sample to be tested for scanning. The particle size of each primary particle is statistically analyzed at an appropriate magnification, and the average particle size is calculated. The magnification ranges from 1000X to 3000X. The number of primary particles counted is ≥2000.

[0681] The test results can be found in Table 3.

[0682] (2) The proportion of non-agglomerated primary particles in lithium composite metal oxide materials (denoted as F1)

[0683] Lithium-based composite metal oxide materials were used as the test samples.

[0684] Analysis Method: One to three regions were randomly selected for scanning tests. The number of non-agglomerated primary and secondary particles was counted, and the proportion of non-agglomerated primary particles was calculated as the test value for "the proportion of non-agglomerated primary particles in lithium composite metal oxide materials". Magnification ranged from 1000X to 3000X. The number of particles in the test material was ≥1000.

[0685] (3) The proportion of non-agglomerated primary particles in the positive electrode active material (denoted as F0).

[0686] Preparation of the test sample of the positive electrode active material: The lithium composite metal oxide material and the lithium iron phosphate positive electrode material are mixed according to the mass ratio used in the preparation of the positive electrode slurry to obtain the test sample of the positive electrode active material.

[0687] Analysis Method: Randomly select 1-3 regions for scanning tests, count the number of non-agglomerated primary and secondary particles, and calculate the proportion of non-agglomerated primary particles as the test value of "the proportion of non-agglomerated primary particles in the positive electrode active material". Magnification ranges from 1000X to 3000X. The number of particles in the test material is ≥1000.

[0688] 3. Test method for the residual amount of electrolyte additives in lithium-ion secondary batteries prepared by formation.

[0689] Disassemble the battery cell and extract the electrolyte as a sample for testing.

[0690] Method for testing the residual amount of polycyclic sulfates after formation: The test was performed using an Oxford Instruments X-Pulse benchtop nuclear magnetic resonance spectrometer.

[0691] Using proton nuclear magnetic resonance spectroscopy (NMR spectroscopy) 1 The mass percentage of additives in the electrolyte was determined by H NMR.

[0692] The testing procedure is as follows: 500 μL of deuterated reagent is added to the NMR tube in a nitrogen-filled glove box, and 100 μL of non-aqueous electrolyte sample is added to the NMR tube. The NMR tube is shaken to dissolve the non-aqueous electrolyte into the deuterated reagent. Since the non-aqueous electrolyte is very sensitive to moisture, both the NMR test and the sample preparation are carried out in a nitrogen atmosphere (H2O content less than 0.1 ppm, O2 content less than 0.1 ppm). At the same time, the instruments related to the test also need to be washed with pure water and dried in a vacuum environment at 60°C for more than 48 hours.

[0693] The deuterated reagent was prepared as follows: Deuterated dimethyl sulfoxide (DMSO-d6), deuterated acetonitrile, and trifluoromethylbenzene were dried using a 4A molecular sieve at a temperature above 25°C for at least 3 days, ensuring that the water content of all reagents was less than 3 ppm. A Metrohm 831KF coulometric moisture analyzer was used for moisture testing. Then, 10 mL of dried DMSO-d6 and 300 μL of dried internal standard trifluoromethylbenzene were mixed thoroughly in a nitrogen-filled glove box to obtain the first solution. 10 mL of dried deuterated acetonitrile and 300 μL of dried internal standard trifluoromethylbenzene were then mixed thoroughly to obtain the second solution. The first and second solutions were then mixed thoroughly to obtain the deuterated reagent.

[0694] Taking polycyclic sulfuric acid ester H6 as an example, it can be determined according to... 1The mass percentage of polycyclic sulfate in the electrolyte was calculated by referring to the area of ​​the four characteristic peaks at 4.8–5.5 ppm in the 1H NMR spectrum and comparing them with the proportion of the characteristic peak area of ​​the internal standard trifluoromethylbenzene.

[0695] 4. Battery performance test

[0696] (1) High voltage and high temperature cycling performance test (45℃ cycling test)

[0697] At 45℃, a lithium-ion secondary battery is charged at a constant current of 1C to 4.4V, then charged at a constant voltage of 4.4V to a cutoff current of 0.05C, left to rest for 10 minutes, and then discharged at a constant current of 1C to 2.5V, left to rest for 5 minutes. This constitutes one charge-discharge cycle. The discharge capacity at this point is recorded as C0. This charge-discharge cycle is repeated for the same lithium-ion secondary battery, and the discharge capacity C of the 1st, 2nd, ... nth cycles is recorded. n The number of cycles must be at least 500.

[0698] Record the battery's cycle capacity retention rate P500 = C after 500 cycles. 500 / C0×100%.

[0699] (2) High-voltage high-temperature storage performance test (storage at 60℃)

[0700] At 25°C, the lithium-ion secondary battery was charged to 4.4V at a constant current of 1C, then charged to the cutoff current of 0.05C at a constant voltage of 4.308V, left to stand for 10 minutes, and then discharged to 2.5V at a constant current of 1C. The discharge capacity D0 at this time was recorded.

[0701] The lithium-ion rechargeable battery was charged at a constant current of 1C to 4.308V, then charged at a constant voltage of 4.308V until the cutoff current reached 0.05C. The battery was then stored at 60°C for 50 days. Afterward, the lithium-ion rechargeable battery was removed and cooled to a surface temperature of 25°C.

[0702] Subsequently, at 25°C, it was discharged at a constant current of 1C to 2.5V, then charged at a constant current of 1C to 4.4V, and then charged at a constant voltage of 4.4V to the cutoff current of 0.05C. After resting for 10 minutes, it was discharged at a constant current of 1C to the termination voltage of 2.5V, thus obtaining the discharge capacity D1 after high-temperature storage at 60°C.

[0703] High-temperature storage capacity retention rate after 50 days at 60℃ = (D1 / D0) × 100%.

[0704] (3) Testing of battery internal resistance DCR

[0705] At 25°C, the lithium-ion secondary battery was charged at a constant current of 1C to 4.4V, then charged at a constant voltage of 4.4V to the cutoff current of 0.05C, allowed to stand for 30 minutes, and then discharged at a constant current of 1C for 0.5 hours (approximately 50% SOC), allowed to stand for 30 minutes, and the voltage V1 after standing was recorded. Subsequently, it was discharged at 4C for 30 seconds, with sampling intervals of 0.1 seconds, and the voltage V2 at the end of the discharge was recorded.

[0706] The initial DCR0 of the battery is (V1-V2) / I, where I is the current corresponding to a 4C rate; at this point, the DCR is the DCR of the cell at approximately 50% SOC.

[0707] The DCR2 was tested using the "high voltage high temperature cycling performance test (45℃ cycling test)" method for 500 cycles. The DCR growth rate after 500 cycles at 45℃ was calculated as (DCR2-DCR0) / DCR0×100%.

[0708] (II) Test Result Analysis

[0709] The performance test results of the lithium-ion secondary batteries prepared in Examples 1-23 and Comparative Examples 1-6 can be found in Tables 4, 5 and 6.

[0710] The lithium-ion secondary batteries prepared in Examples 1-23 all exhibit significantly improved high-temperature performance under high voltage, with significantly enhanced high-temperature cycling performance (45°C) and high-temperature storage performance (60°C) under high voltage. For example, Example 3 can be compared with Comparative Examples 1-2, Example 18 with Comparative Examples 3-4, and Examples 19-20 with Comparative Examples 5-6.

[0711] Compared to Examples 1-6, 18, 19, and 20, Comparative Examples 1, 3, 5, and 6 omit polycyclic sulfates; compared to Examples 1-6 and 18, Comparative Examples 2 and 4 replace polycyclic sulfates with monocyclic sulfates; the high-temperature performance under high voltage in Comparative Examples 1-6 is significantly worse, with a significant decrease in capacity retention after 500 cycles at 45°C and capacity retention after 50 days of storage at 60°C.

[0712] Furthermore, the lithium-ion secondary batteries prepared in Examples 1-23 exhibited significantly improved high-temperature performance at high voltages, while the initial internal resistance of the batteries did not change significantly compared to the comparative examples without the addition of polycyclic sulfates. For example, see Tables 4-5, such as Examples 1-6 compared to Comparative Example 1, Example 18 compared to Comparative Example 3, Example 19 compared to Comparative Example 5, and Example 20 compared to Comparative Example 6. However, in the later stages of cycling and / or storage, the rate of increase in internal resistance of the batteries prepared in Examples 1-23 decreased significantly compared to the comparative examples without polycyclic sulfates or those replaced with monocyclic sulfates. For example, the DCR rate of increase after 500 cycles at 45°C can be seen in Table 6, such as Examples 1 and 3 compared to Comparative Examples 1-2.

[0713] By way of example, comparing Examples 3 and 18 with Comparative Examples 1 and 3, after introducing lithium iron phosphate cathode material into Example 18, the degree of decrease in high-temperature performance under high voltage in Example 3 is much lower than the degree of decrease in Comparative Example 1 after introducing lithium iron phosphate cathode material into Comparative Example 3. In lithium-ion secondary batteries with electrolyte containing polycyclic sulfates, further introducing lithium iron phosphate cathode material into the cathode active material including lithium composite metal oxide material can significantly suppress the adverse effects on high-temperature performance under high voltage that may occur during cycling and / or the initial storage period after introducing lithium iron phosphate cathode material.

[0714] Furthermore, when 1,3-propanesulfonyl lactone (PS), 1,3-propenesulfonyl lactone (PST), or acid anhydride (such as succinic anhydride) were used as single-type additives to replace the polycyclic sulfate in Example 3, the capacity retention rate after 500 cycles at 45°C and the capacity retention rate after 50 days of storage at 60°C both decreased significantly. Moreover, the use of acid anhydride also resulted in larger DCR0 (initial internal resistance) and DCR2 (battery internal resistance after 500 cycles at 45°C).

[0715] Table 4.

[0716] Table 5.

[0717] Table 6.

[0718] The descriptions of the various implementation methods and embodiments above tend to emphasize the differences between them. Similarities or resemblances can be referenced interchangeably, and for the sake of brevity, they will not be repeated here. The technical features of the implementation methods and embodiments described above can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combinations of these technical features do not contradict each other, they should be considered within the scope of this specification.

[0719] It should be noted that this application is not limited to the above-described embodiments and examples. The above-described embodiments and examples are merely examples, and any embodiments and examples that have the same structure and achieve the same effect as the technical concept within the scope of this application are included in the technical scope of this application. The embodiments and examples described above only illustrate several embodiments and examples of this application, and although the descriptions are relatively detailed, they should not be construed as limiting the scope of the patent. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments or examples, and other ways of constructing embodiments or examples by combining some of the constituent elements of the embodiments or examples, are also included in the scope of this application without departing from the spirit of this application.

Claims

1. A lithium-ion secondary battery, comprising a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the separator is disposed between the positive electrode and the negative electrode; the positive electrode comprises a positive active layer, the positive active layer comprises a positive active material, the positive active material comprises a lithium composite metal oxide material, and the lithium composite metal oxide material comprises non-agglomerated primary particles; The electrolyte comprises an electrolyte salt, a non-aqueous solvent, and an additive; the additive comprises a polycyclic sulfate ester, wherein the polycyclic sulfate ester contains at least two cyclic sulfate ester units in its structural formula.

2. The lithium-ion secondary battery according to claim 1, wherein The structure of the cyclic sulfate unit is shown in formula (I): In equation (I), R1 is a covalent bond, -CHQ 11 -or-CHQ 12 -CHQ 13 -; where Q 11 Q 12 and Q 13 Each is independently a H atom, halogen, and C atom. 1-6 Alkyl or C 1-6 Alkyl group.

3. The lithium-ion secondary battery according to claim 2, wherein The polycyclic sulfate contains two structures as shown in formula (II): wherein R7is an H atom, a halogen, a C 1-6 alkyl group or a C 1-6 alkoxy group.

4. The lithium-ion secondary battery according to any one of claims 1 to 3, wherein The polycyclic sulfate ester satisfies one or more of the following characteristics: (ta1) Any cyclic sulfate ester unit is a 5- to 7-membered ring; (ta2) Any two adjacent cyclic sulfate units are independently separated by -(CH2). q -、-O- or -(CH2) q1 -O-(CH2) q2 - Connected; where q is an integer selected from 0 to 3, and q1 and q2 are integers selected from 0 to 6 respectively, and 1≤(q1+q2)≤6.

5. The lithium-ion secondary battery according to claim 4, wherein In the polycyclic sulfate ester, any two adjacent cyclic sulfate units are independently connected by a covalent bond, C 1-3 Alkylene, -O-, -L 11 -O-、-OL 11 -or-L 21 -OL 22 - Connected together, where L 11 C 1-6 Alkylene, L 21 and L 22 Each independently is C 1-3 Alkylene; Optionally, any C 1-3 The alkylene group is independently methylene, 1,2-ethylene, or 1,3-propylene; Optionally, any one of C 1-6 Alkylene is independently methylene, 1,2-ethylidene, 1,3-propylidene, butylidene, pentylidene, or hexylidene.

6. The lithium-ion secondary battery according to any one of claims 1 to 5, wherein The polycyclic sulfate ester satisfies one or more of the following characteristics: (tb1) The number of cyclic sulfate units contained in the polycyclic sulfate ester is 2, 3 or 4; (tb2) The cyclic sulfate units in the polycyclic sulfate ester are connected in series; (tb3) The polycyclic sulfate contains a halogen, wherein the halogen is a fluorine atom; (tb4) The polycyclic sulfate contains C 1-6 Alkyl, the C 1-6 Alkyl group is C 1-3 Alkyl group, which may be methyl group; (tb5) the polycyclic sulfate contains C 1-6 alkoxy, said C 1-6 alkoxy is C 1-3 alkoxy, which can be methoxy.

7. The lithium-ion secondary battery according to any one of claims 1 to 4, wherein said polycyclic sulfate comprises a compound having a structural formula as shown in Formula (III); R 41 and R 42 each independently is an H atom, a halogen, a C 1-6 alkyl group, a C 1-6 alkoxy group, or a structure shown in Formula (IV); Among them, R 11 R 12 and R 13 Each is independently a covalent bond, -CHQ 21 -or-CHQ 22 -CHQ 23 -; where Q 21 Q 22 and Q 23 Each is independently a H atom, halogen, and C atom. 1-6 Alkyl or C 1-6 Alkoxy; R 71 is H atom, halogen, C 1-6 alkyl or C 1-6 alkoxy; L6 is -(CH2) n - or -(CH2) n1 - O-(CH2) n2 -, n is an integer selected from 0 to 3, n1 and n2 are respectively an integer selected from 0 to 3 and 1 ≤ (n1 + n2) ≤ 3; L3 is -(CH2) q -,-O- or -(CH2) q1 -O-(CH2) q2 -; wherein q is an integer selected from 0 to 3, q1 and q2 are integers selected from 0 to 6 respectively and 1 ≤ (q1 + q2) ≤ 6.

8. The lithium-ion secondary battery according to any one of claims 1 to 7, wherein The polycyclic sulfate includes at least one of the following compounds:

9. The lithium-ion secondary battery according to any one of claims 1 to 8, wherein Let W be the mass percentage of the polycyclic sulfate in the electrolyte, satisfying 0. <W≤1%。 10. The lithium-ion secondary battery according to claim 9, wherein 0.01％≤W≤1％。 11. The lithium-ion secondary battery according to claim 9, wherein 0.02％≤W≤0.5％。 12. The lithium-ion secondary battery according to any one of claims 1 to 11, wherein D50 of the lithium complex metal oxide material v 50 is 2.5 to 5 μm; Optionally, the lithium complex metal oxide material has a D v 50 is 3 to 4.5 μm.

13. The lithium-ion secondary battery according to any one of claims 1 to 12, wherein The positive electrode active material D v 50 is 2.5μm to 5μm; optionally, the D of the positive electrode active material is... v 50 is 3μm to 4.5μm, and can be further selected as 3.2μm to 4.2μm.

14. The lithium-ion secondary battery according to any one of claims 1 to 13, wherein The specific surface area of the positive electrode active material is 0.3 m 2 / g ~ 1.5 m 2 / g.

15. The lithium-ion secondary battery according to claim 14, wherein The specific surface area of the positive electrode active material is 0.5 m 2 / g to 1.2 m 2 / g.

16. The lithium-ion secondary battery according to any one of claims 1 to 15, wherein In the positive electrode active material, the average particle size of the primary particles is 1.1 μm to 3.0 μm.

17. The lithium-ion secondary battery according to claim 16, wherein In the positive electrode active material, the average particle size of the primary particles is 1.3 μm to 2.5 μm.

18. The lithium-ion secondary battery according to any one of claims 1 to 17, wherein The D v 50The ratio with respect to the average particle diameter of primary particles in the positive electrode active material is denoted as B1, and satisfies 1≤B1≤2.

5.

19. The lithium-ion secondary battery according to claim 18, wherein, 1.6≤B1≤2.2。 20. The lithium-ion secondary battery according to any one of claims 1 to 18, wherein The positive electrode sheet satisfies one or more of the following characteristics: (tc1) In the lithium composite metal oxide material, the proportion of non-agglomerated primary particles is greater than or equal to 70%; (tc2) In the positive electrode active material, the proportion of non-agglomerated primary particles is greater than or equal to 65%.

21. The lithium-ion secondary battery according to claim 20, wherein, The positive electrode sheet satisfies one or more of the following characteristics: (tc1') In the lithium composite metal oxide material, the proportion of non-agglomerated primary particles is greater than or equal to 80%; (tc2') In the positive electrode active material, the proportion of non-agglomerated primary particles is greater than or equal to 75%.

22. The lithium-ion secondary battery according to any one of claims 1 to 21, wherein The lithium composite metal oxide material includes one or more of lithium nickel-based oxides, lithium-rich manganese-based cathode materials, spinel lithium manganese oxide, lithium cobalt oxide, and any of the aforementioned modified forms; wherein the modified forms include one or more of doping modification and coating modification.

23. The lithium-ion secondary battery according to claim 22, wherein, The lithium composite metal oxide material includes a lithium nickel-based oxide, which contains Li, a non-lithium metal element, and O, wherein the non-lithium metal element includes Ni; the lithium nickel-based oxide satisfies one or more of the following characteristics: (t1) The atomic molar ratio of Ni to the non-lithium metal element in the lithium nickel-based oxide is q1, where 0.5 ≤ q1 < 1; (t2) The lithium nickel-based oxide contains Ni and Li elements in an atomic molar ratio of q2:x2, wherein 0.5≤q2<1 and 0.6≤x2≤1.2; (t3) The lithium nickel-based oxide contains Ni and O elements in an atomic molar ratio of q3:x3, wherein 0.5≤q3<1 and 1.6≤x3≤2.

1.

24. The lithium-ion secondary battery according to claim 23, wherein, The lithium composite metal oxide material satisfies one or more of the following characteristics: (i) 0.5 ≤ q1 ≤ 0.99; (ii) 0.5 ≤ q2 ≤ 0.99; (iii) 0.5 ≤ q3 ≤ 0.99; (iv) The lithium nickel-based oxide contains Co element, and the atomic molar ratio of Co element to non-lithium metal elements in the lithium nickel-based oxide is q4, where 0 < q4 ≤ 0.25, optionally, 0.02 ≤ q4 ≤ 0.25; (v) The lithium nickel-based oxide contains Mn element, and the atomic molar ratio of Mn element to non-lithium metal elements in the lithium nickel-based oxide is q5, where 0 < q5 ≤ 0.35, optionally, 0.1 ≤ q5 ≤ 0.35; (vi) The mass ratio of the lithium nickel-based oxide in the lithium composite metal oxide material is 80% - 100%.

25. The lithium-ion secondary battery according to claim 24, wherein, The lithium composite metal oxide material satisfies one or more of the following characteristics: (ti) 0.5 ≤ q1 ≤ 0.8 or 0.8 < q1 ≤ 0.99; (tii) 0.5 ≤ q2 ≤ 0.8 or 0.8 < q2 ≤ 0.99; (tiii) 0.8 ≤ x2 ≤ 1.1; (tiv) 0.5 ≤ q3 ≤ 0.8 or 0.8 < q3 ≤ 0.99; (tv) 1.8 ≤ x3 ≤ 2.06; (tvi) The lithium nickel-based oxide contains Co element, 0.05 ≤ q4 ≤ 0.2; (tvii) The lithium nickel-based oxide contains Mn element, 0.15 ≤ q5 ≤ 0.3; (tviii) The mass ratio of the lithium nickel-based oxide in the lithium composite metal oxide material is 90% - 100%.

26. The lithium-ion secondary battery according to any one of claims 22 to 25, wherein The lithium composite metal oxide material includes one or more of lithium nickel cobalt manganese-based oxides and modified forms of lithium nickel cobalt manganese-based oxides, and the modified forms include one or more of doping modification and coating modification.

27. The lithium-ion secondary cell according to any one of claims 1 to 26, wherein The positive electrode sheet satisfies one or more of the following characteristics: (te1) The mass ratio of the lithium composite metal oxide material in the positive electrode active layer is 80% - 99%; (te2) The mass ratio of the lithium composite metal oxide material in the positive electrode active material is 95% - 100%.

28. The lithium-ion secondary battery according to claim 27, wherein The positive electrode sheet satisfies one or more of the following characteristics: (te1’) The mass ratio of the lithium composite metal oxide material in the positive electrode active layer is 90% - 99%; (te2’) The mass ratio of the lithium composite metal oxide material in the positive electrode active material is 96% - 99%.

29. The lithium-ion secondary cell according to any one of claims 1 to 28, wherein The positive electrode active material includes lithium iron phosphate-based positive electrode materials, and the lithium iron phosphate-based positive electrode materials include at least one of lithium iron phosphate and a composite material of lithium iron phosphate and carbon.

30. The lithium-ion secondary battery according to claim 29, wherein, The lithium iron phosphate-based positive electrode materials include carbon-coated lithium iron phosphate.

31. The lithium-ion secondary battery according to claim 29 or 30, wherein D of the iron lithium phosphate-based positive electrode material v 50 is 1 to 11 μm.

32. The lithium-ion secondary battery according to claim 31, wherein D of the iron lithium phosphate-based positive electrode material v 50 is 4 to 9 μm.

33. The lithium-ion secondary cell according to any one of claims 29 to 32, wherein, The positive electrode sheet satisfies one or more of the following characteristics: (tf1) The mass ratio of the lithium iron phosphate-based positive electrode material in the positive electrode active layer is 0.8% - 4.95%, optionally 0.9% - 3.96%; (tf2) The lithium iron phosphate cathode material accounts for 1% to 5% of the mass of the cathode active material, and can be selected as 1% to 4%.

34. The lithium-ion secondary cell according to any one of claims 1 to 33, wherein The electrolyte also includes one or both of fluoroethylene carbonate and tris(trimethylsilane) phosphate.

35. The lithium-ion secondary battery according to claim 34, wherein, The electrolyte satisfies one or more of the following characteristics: (tg1) The mass percentage of fluoroethylene carbonate in the electrolyte is 0.1% to 3%; The mass percentage of (tg2) tris(trimethylsilane) phosphate in the electrolyte is 0.1% to 0.5%.

36. The lithium-ion secondary battery according to claim 35, wherein The electrolyte satisfies one or more of the following characteristics: (tg1') The mass percentage of fluoroethylene carbonate in the electrolyte is 0.1% to 2.5%; The mass percentage of (tg2')tris(trimethylsilane)phosphate in the electrolyte is 0.1% to 0.35%.

37. The lithium-ion secondary cell according to any one of claims 1 to 36, wherein, The electrolyte includes lithium difluorosulfonylimide.

38. The lithium-ion secondary battery according to claim 37, wherein, The molar volume concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is greater than 0 mol / L and less than or equal to 0.3 mol / L.

39. The lithium-ion secondary battery according to claim 38, wherein, The molar concentration of lithium difluorosulfonylimide in the electrolyte is 0.1 mol / L to 0.25 mol / L.

40. The lithium-ion secondary cell according to any one of claims 1 to 39, wherein, The negative electrode sheet includes a negative electrode active layer, and the negative electrode active layer includes the negative electrode active material; the negative electrode active material includes one or more of carbon-based materials and silicon-based materials.

41. The lithium-ion secondary battery according to claim 40, wherein, The negative electrode active material includes graphite material; Optionally, the graphite material accounts for 80% to 100% of the mass of the negative electrode active material, optionally 90% to 100%, and further optionally 97% to 100%.

42. The lithium-ion secondary cell according to any one of claims 1 to 41, wherein, The charging cutoff voltage of the lithium-ion secondary battery is greater than or equal to 4.2V, and can be selected as 4.2V to 4.5V.

43. The lithium-ion secondary battery according to claim 42, wherein, The charging cutoff voltage of the lithium-ion secondary battery is greater than or equal to 4.3V, and can be selected as 4.3V to 4.5V.

44. A lithium-ion secondary battery assembly, wherein, The device includes a positive electrode, a separator, a negative electrode, and an electrolyte, wherein the separator is disposed between the positive electrode and the negative electrode; the positive electrode includes a positive active layer, the positive active layer includes a positive active material, the positive active material includes a lithium composite metal oxide material, and the lithium composite metal oxide material includes non-agglomerated primary particles; The electrolyte comprises an electrolyte salt, a non-aqueous solvent, and an additive; the additive comprises a polycyclic sulfate ester, wherein the polycyclic sulfate ester contains at least two cyclic sulfate ester units in its structural formula.

45. The lithium-ion secondary battery assembly of claim 44, wherein, The polycyclic sulfate ester accounts for 0.1% to 3% of the mass of the electrolyte.

46. The lithium-ion secondary battery assembly of claim 45, wherein, The polycyclic sulfate ester accounts for 0.2% to 2% of the mass of the electrolyte.

47. The lithium-ion secondary battery assembly according to any one of claims 44 to 46, wherein it satisfies one or more of the following characteristics: (tj1) The polycyclic sulfate ester as defined in any one of claims 2 to 8; (tj2) The positive electrode plate is as defined in any one of claims 12 to 33; (tj3) The negative electrode sheet is as defined in claim 40 or 41; (tj4) The electrolyte also includes one or two of fluoroethylene carbonate and tris(trimethylsilane) phosphate; (tj5) The electrolyte includes lithium difluorosulfonylimide.

48. The lithium-ion secondary battery assembly of claim 47, wherein, The electrolyte satisfies one or more of the following characteristics: (tk1) The electrolyte includes fluoroethylene carbonate, and the mass percentage of fluoroethylene carbonate in the electrolyte is 1% to 6%; (tk2) The electrolyte includes tris(trimethylsilane) phosphate, and the mass percentage of tris(trimethylsilane) phosphate in the electrolyte is 0.1% to 1%; (tk3) The electrolyte includes lithium bis(fluorosulfonyl)imide, and the molar concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is greater than 0 and less than or equal to 0.3 mol / L.

49. The lithium-ion secondary battery assembly of claim 48, wherein, The electrolyte satisfies one or more of the following characteristics: (tm1) The mass percentage of fluoroethylene carbonate in the electrolyte is 1% to 5%; The mass percentage of (tm2) tris(trimethylsilane) phosphate in the electrolyte is 0.1% to 0.7%; The molar concentration of (tm3) bis(fluorosulfonyl)imide lithium in the electrolyte is 0.1 mol / L to 0.3 mol / L.

50. A method for preparing a lithium-ion secondary battery, comprising the following steps: An electrode assembly including a positive electrode sheet, a separator, and a negative electrode sheet is disposed in a battery case; wherein The separator is provided between the positive electrode and the negative electrode; An electrolyte is injected into the battery casing to prepare a lithium-ion secondary battery assembly; Let it stand and soak; and to form; The positive electrode sheet includes a positive active layer, the positive active layer includes a positive active material, the positive active material includes a lithium composite metal oxide material, and the lithium composite metal oxide material includes non-agglomerated primary particles. The electrolyte comprises an electrolyte salt, a non-aqueous solvent, and an additive; the additive comprises a polycyclic sulfate ester, wherein the polycyclic sulfate ester contains at least two cyclic sulfate ester units in its structural formula.

51. The method for preparing a lithium-ion secondary battery according to claim 50, wherein it satisfies one or more of the following characteristics: (tn1) After injecting electrolyte into the battery casing, the lithium-ion secondary battery assembly as described in any one of claims 44 to 49 is obtained; (tn2) In the electrode assembly, the positive electrode is defined as in any one of claims 12 to 33; (tn3) In the electrode assembly, the negative electrode is defined as in claim 40 or 41.

52. A lithium-ion secondary battery, obtained by performing a formation process on the lithium-ion secondary battery assembly according to any one of claims 44 to 49, or prepared by the method for preparing a lithium-ion secondary battery according to claim 50 or 51.

53. An electrical device comprising at least one of the lithium-ion secondary batteries according to any one of claims 1 to 43 and 52, and a lithium-ion secondary battery prepared using the lithium-ion secondary battery assembly according to any one of claims 44 to 49.

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