Secondary battery and electric device

Abstract

A secondary battery and an electric device, relating to the technical field of lithium batteries. On one hand, a second positive electrode active material is used for positive electrode lithium supplementation to improve the cycle performance of the secondary battery. On the other hand, because a carbon layer on the surface of the second positive electrode active material has a certain catalytic effect on a phosphate ester film-forming additive, the carbon layer can reduce the decomposition potential of the phosphate ester film-forming additive on the surface of the second positive electrode active material, thereby causing part of the phosphate ester film-forming additive to preferentially form a CEI film on the surface of the second positive electrode active material at a relatively low voltage, which can effectively suppress active sites of the carbon layer, and can suppress side reactions between the second positive electrode active material and a solvent at the relatively low voltage. During formation, the remaining phosphate ester film-forming additive preferentially forms a CEI film on the surface of a first positive electrode active material before decomposition of the solvent, isolating the solvent from being in contact with the first positive electrode active material, suppressing the occurrence of side reactions, and improving the cycle performance.

Description

Secondary batteries and electrical appliances

[0001] Cross-references

[0002] This application claims priority to Chinese Patent Application No. 202510213370.1, filed on February 25, 2025, entitled “Secondary Battery and Electrical Device”, the entire contents of which are incorporated herein by reference. Technical Field

[0003] High-voltage battery systems, such as LNMO battery systems, have high energy density but poor cycle performance. Background Technology

[0004] This application is made in view of the above-mentioned problems, and its purpose is to provide a secondary battery and an electrical device to alleviate the problem of poor cycle performance of high-voltage battery systems. Summary of the Invention

[0005] The first aspect of this application provides a secondary battery, which includes a positive electrode sheet and a non-aqueous electrolyte. The positive electrode sheet includes a positive active material layer, which includes a first positive active material and a second positive active material. The first positive active material has a delithiation voltage greater than 4.2V and includes a lithium nickel manganese oxide type active material. The second positive active material has a delithiation voltage lower than that of the first positive active material. The surface of the second positive active material is coated with a carbon layer.

[0006] Non-aqueous electrolytes include positive electrode film-forming additives and solvents. The oxidation decomposition voltage of the positive electrode film-forming additives is lower than that of the solvent. Positive electrode film-forming additives include phosphate ester film-forming additives.

[0007] Therefore, in the secondary battery provided in this application, firstly, by combining the second positive electrode active material and the first positive electrode active material, lithium replenishment is performed using the second positive electrode active material to improve the cycle performance of the secondary battery. Secondly, by introducing phosphate ester film-forming additives into the non-aqueous electrolyte, on the one hand, since the film-forming voltage of phosphate ester film-forming additives is lower than the oxidation decomposition voltage of the solvent, that is, phosphate ester film-forming additives can preferentially form a CEI film before the solvent is oxidized and decomposed by the positive electrode active material, preventing the solvent and the positive electrode active material from contacting and causing side reactions. On the other hand, the carbon layer on the surface of the second positive electrode active material has a certain catalytic effect on the phosphate ester film-forming additives. This process reduces the decomposition potential of phosphate ester film-forming additives on the surface of the second positive electrode active material, resulting in some phosphate ester film-forming additives preferentially forming a CEI film on the surface of the second positive electrode active material at a lower voltage. This effectively inhibits the active sites of the carbon layer and suppresses side reactions between the second positive electrode active material and the solvent at lower voltages, thus improving cycle performance. The remaining phosphate ester film-forming additives react with residual alkali on the surface of lithium nickel manganese oxide active materials during formation, inhibiting alkali metal dissolution and forming a CEI film on the surface of the first positive electrode active material. This isolates the solvent from contact with the first positive electrode active material, suppresses side reactions, and improves cycle performance.

[0008] In any embodiment, the phosphate ester film-forming additive has a mass content of 0.1% to 3% in the non-aqueous electrolyte.

[0009] By controlling the mass content of phosphate ester film-forming additives in the non-aqueous electrolyte to 0.1%~3%, a CEI film can be formed, effectively isolating the solvent from contact with the positive electrode active materials (first positive electrode active material and second positive electrode active material), improving cycle performance, and resulting in lower positive electrode impedance.

[0010] In any embodiment, the positive electrode film-forming additive further includes a low-potential film-forming additive, wherein the film-forming reaction voltage of the low-potential film-forming additive is less than that of the phosphate ester film-forming additive, and the film-forming reaction voltage of the low-potential film-forming additive is less than or equal to the delithiation voltage of the second positive electrode active material.

[0011] Since phosphate ester film-forming additives primarily react with residual alkali on the surface of lithium nickel manganese oxide (LiMO) active materials, they are more suitable for film formation on these materials. However, the second cathode active material has a carbon layer, and its surface properties differ from those of LiMO active materials. Therefore, to improve film formation on the second cathode active material and suppress active sites in the carbon layer, a low-potential film-forming additive is introduced. Because the film-forming reaction voltage of the low-potential additive is lower than that of the phosphate ester additive, it preferentially reacts, allowing for better coating of the second cathode active material's surface and suppression of carbon layer active sites. Furthermore, since the film-forming reaction voltage of the low-potential additive is less than or equal to the delithiation voltage of the second cathode active material, it can isolate the second cathode active material from the solvent before the delithiation voltage, reducing side reactions caused by contact and further improving cycle performance.

[0012] In any embodiment, the mass content of the low-potential film-forming additive in the non-aqueous electrolyte is 0.01% to 5%.

[0013] Controlling the mass content of low-potential film-forming additives in non-aqueous electrolytes within the above-mentioned range is beneficial for them to preferentially form a film on the surface of the second positive electrode active material compared with phosphate ester film-forming additives, thus isolating both from contact with the solvent and improving cycle performance.

[0014] In any embodiment, the low-potential film-forming additive includes at least one of lithium tetrafluoroborate, tetramethylene sulfone, 1,3-propane sulfonyl lactone, 1,3-propene sulfonyl lactone, and vinyl sulfate.

[0015] The aforementioned low-potential film-forming additives have a strong ability to form films on the second positive electrode active material, which is beneficial for suppressing the side reactions of carbon layer catalysis. At the same time, even if a small amount of the aforementioned low-potential film-forming additives form films on the surface of lithium nickel manganese oxide active material, it will not have a negative impact on the lithium nickel manganese oxide active material.

[0016] In any embodiment, the phosphate ester film-forming additive includes at least one of triallyl phosphate, tris(trimethylsilane) phosphate, bis(trimethylsilyl)vinyl phosphate, diethyltrimethylsilyl phosphite, trimethylsilyl dihydrogen phosphate, and mono(trimethylsilyl) phosphite.

[0017] The aforementioned phosphate ester film-forming additives are more suitable for forming films on the surface of the first positive electrode active material. Therefore, the aforementioned phosphate ester film-forming additives can form a CEI film on the surface of the first positive electrode active material during the first charge, suppressing the side reactions of the first positive electrode active material and non-aqueous electrolyte under high voltage or fully charged conditions. They can also reduce the decomposition voltage on the surface of the second positive electrode active material under carbon layer catalysis, forming a certain CEI film on the surface of the second positive electrode active material at a lower voltage, thus suppressing the generation of side reactions catalyzed by the carbon layer.

[0018] In any embodiment, the non-aqueous electrolyte includes a solvent comprising a first fluorinating agent and a second fluorinating agent, the first fluorinating agent comprising fluoroethylene carbonate, and the second fluorinating agent comprising at least one of trifluoroethyl methyl carbonate, trifluoromethyl ethyl sulfone, and trifluoromethyl propyl sulfone.

[0019] The introduction of the first and second fluorinating agents helps to improve the oxidation resistance and pressure resistance of the electrolyte.

[0020] In any embodiment, the first fluorinating agent has a volume percentage of 35% to 55% in the solvent, and / or the second fluorinating agent has a volume percentage of 25% to 45% in the solvent.

[0021] The above settings help improve the electrolyte's resistance to oxidation and pressure.

[0022] In any embodiment, the solvent further includes a chain carbonate, the chain carbonate comprising 15% to 30% by volume in the solvent, and / or the chain carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, and diethyl carbonate.

[0023] In any embodiment, the non-aqueous electrolyte includes a lithium salt additive, which includes LiPO2F2.

[0024] The addition of LiPO2F2 not only improves the conductivity of the electrolyte, but also allows it to preferentially reduce on the negative electrode surface during the formation process to form a low-resistance and dense protective film, thereby reducing the impedance of the SEI film, lowering the internal resistance of the secondary battery, and improving the cycle performance of the secondary battery.

[0025] In any embodiment, the mass content of the lithium salt additive in the non-aqueous electrolyte is 0.1% to 2%. Controlling the mass content of the lithium salt additive in the non-aqueous electrolyte within the above range can, on the one hand, regulate the composition of the negative electrode SEI film, so that the SEI film has a lower impedance, and on the other hand, make the non-aqueous electrolyte have a lower viscosity, thereby enabling lithium ions to have a higher migration rate in the non-aqueous electrolyte.

[0026] In any embodiment, the non-aqueous electrolyte also includes a negative electrode film-forming additive, the mass content of which is 0.5% to 3%.

[0027] By adding a negative electrode film-forming additive to the non-aqueous electrolyte, a better SEI film can be formed on the negative electrode, preventing further reduction and decomposition of the electrolyte on the negative electrode surface and alleviating battery gas generation. A higher mass percentage of the negative electrode film-forming additive in the non-aqueous electrolyte is more beneficial for reducing gas generation in the secondary battery, while a lower mass percentage is more beneficial for controlling the DCR (discharge rate reduction) of the secondary battery. Therefore, controlling the mass percentage of the negative electrode film-forming additive in the non-aqueous electrolyte within the above range is beneficial for achieving both low gas generation and low DCR in the secondary battery.

[0028] In any embodiment, the negative electrode film-forming additive includes at least one of vinylene carbonate and vinyl sulfate.

[0029] Optionally, the negative electrode film-forming additive includes vinylene carbonate and vinyl sulfate, with a mass ratio of vinylene carbonate to vinyl sulfate of 1:1 to 3.

[0030] Vinylene carbonate can form a dense SEI film on the negative electrode surface, alleviating battery gas generation, but its electrochemical performance is poor under high-temperature conditions. Ethylene sulfate, as a low-impedance additive, forms oligomers containing sulfate ions, modifying the SEI film composition on the negative electrode surface and increasing the relative content of sulfur and oxygen atoms. Since both contain lone pairs of electrons, they can attract lithium ions, thus accelerating the shuttle speed of lithium ions in the SEI film, thereby reducing the impedance of the battery interface and improving battery cycle performance. Therefore, compounding vinylene carbonate and ethylene sulfate while controlling the mass ratio within the aforementioned range is beneficial for improving the cycle performance of high-voltage battery systems.

[0031] In any embodiment, the non-aqueous electrolyte includes a sulfur-containing additive, at least one of the sulfur-containing additives 1,3-propanesulfonate lactone and propenyl-1,3-sulfonate lactone; and / or,

[0032] The sulfur-containing additive constitutes 0.5% to 3% of the mass of the non-aqueous electrolyte; and / or,

[0033] The mass percentage of 1,3-propanesulfonic acid lactone in the non-aqueous electrolyte is 0.5% to 1.5%; and / or,

[0034] The mass percentage of propylene-1,3-sulfonyl lactone in the non-aqueous electrolyte is 0.5% to 1.5%.

[0035] If the amount of sulfur-containing additive is too small, a dense SEI film cannot be formed on the negative electrode; if it is too large, excessive film formation will occur, leading to a decrease in cycle performance. Therefore, controlling the mass ratio of sulfur-containing additive, 1,3-propanesulfonate lactone, and propenyl-1,3-sulfonate lactone in the non-aqueous electrolyte is beneficial to improving cycle performance.

[0036] In any embodiment, the non-aqueous electrolyte includes an electrolyte, which includes a lithium salt;

[0037] Wherein, the Rct of the lithium salt is ≤20 ohm; and / or,

[0038] Lithium salts include lithium hexafluorophosphate; and / or,

[0039] The content of electrolyte salts in the non-aqueous electrolyte is 0.8 mol / L to 2 mol / L.

[0040] In any embodiment, the mass ratio of the second positive electrode active material to the first positive electrode active material is (2:98) to (50:50); and / or,

[0041] The average particle size of the primary particles of the first positive electrode active material is 1μm~10μm, and the average particle size of the primary particles of the second positive electrode active material is ≤400nm.

[0042] Generally, the improvement effect of lithium replenishment is directly proportional to the amount added. The more the second positive electrode active material is added, the better the effect of replenishing the active lithium consumption. However, at the same time, it will also reduce the content of the first positive electrode active material, resulting in a decrease in the secondary battery capacity. Therefore, controlling the mass ratio of the second positive electrode active material to the first positive electrode active material to be (2:98)~(50:50) is beneficial to achieve better cycle performance while maintaining a good secondary battery capacity.

[0043] By matching the particle sizes of the two materials, the compaction density of the electrode sheet can be effectively improved, thus increasing the energy density. At the same time, it is beneficial for the delithiated second positive electrode active material to form an inorganic protective layer on the surface of the first positive electrode active material, thereby stabilizing the positive electrode material structure and improving the cycle performance of the secondary battery.

[0044] In any embodiment, the lithium nickel manganese oxide active material includes Li a Ni 0.5-x Mn 1.5-y M x+y O4, wherein M includes at least one of Mg, Zn, Ti, Zr, W, Nb, Al, B, P, Mo, V or Cr, 0.9≤a≤1.1, -0.2≤x≤0.2, -0.02≤y≤0.3, and x+y≥0.

[0045] In any embodiment, the second positive electrode active material includes at least one of lithium phosphate, lithium nickel cobalt aluminum oxide, lithium nickel oxide, lithium selenide, and their respective modifiers.

[0046] In any embodiment, the second positive electrode active material includes a lithium phosphate, which includes LiMPO4, M includes Fe and optionally a non-Fe element, the non-Fe element including one or both of the first doping element and the second doping element.

[0047] The first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Co, Ga, Sn, Sb, Nb, and Ge; and / or,

[0048] The second doping element includes one or more of B, S, Si, and N.

[0049] In any embodiment, the lower limit of the voltage range of the secondary battery is greater than the lithium intercalation voltage of the second positive electrode active material; and / or,

[0050] The upper limit of the voltage range of the secondary battery shall not exceed 5V; and / or,

[0051] The voltage range of the secondary battery is 3.5V to 4.9V.

[0052] A second aspect of this application also provides an electrical device comprising the secondary battery provided in the first aspect of this application. Attached Figure Description

[0053] Figure 1 shows the EIS test results of a symmetrical battery with 50% SOC cathode material.

[0054] Figure 2 is a schematic diagram of a battery cell according to one embodiment of this application.

[0055] Figure 3 is an exploded view of a battery cell according to an embodiment of this application shown in Figure 2.

[0056] Figure 4 is a schematic diagram of a battery module according to one embodiment of this application.

[0057] Figure 5 is a schematic diagram of a battery pack according to one embodiment of this application.

[0058] Figure 6 is an exploded view of the battery pack of one embodiment of this application shown in Figure 5.

[0059] Figure 7 is a schematic diagram of an electrical device using a secondary battery as a power source according to an embodiment of this application.

[0060] Explanation of reference numerals in the attached figures:

[0061] 1-Battery pack; 2-Upper housing; 3-Lower housing; 4-Battery module; 5-Battery cell; 51-Housing; 52-Electrode assembly; 53-Top cover assembly. Embodiments of the present invention

[0062] The embodiments of the secondary battery and power-consuming device of this application are hereby disclosed in detail with appropriate reference to the accompanying drawings. However, 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 making the following description unnecessarily lengthy 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.

[0063] The "range" disclosed in this application is defined by 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 and can be arbitrarily combined; 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 ​​of 1 and 2 are listed, and if maximum range values ​​of 3, 4, and 5 are 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 "0-5" have been listed in this article; "0-5" is simply a shortened representation of these numerical combinations. Furthermore, when a parameter is stated as an integer ≥2, it is equivalent to disclosing that the parameter is, for example, an integer such as 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, etc.

[0064] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0065] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0066] Unless otherwise specified, all steps of this application may be performed sequentially or randomly, preferably sequentially. For example, if the method includes steps (a) and (b), it means that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, if the method may also include step (c), it means that step (c) may be added to the method in any order. For example, the method may include steps (a), (b), and (c), or it may include steps (a), (c), and (b), or it may include steps (c), (a), and (b), etc.

[0067] Unless otherwise specified, the terms "comprising" and "including" as used in this application can be open-ended or closed-ended. For example, "comprising" and "including" can mean that other components not listed may also be included, or that only the listed components may be included.

[0068] Unless otherwise specified, the term "or" is inclusive in this application. For example, the phrase "A or B" means "A, B, or both A and B". More specifically, the condition "A or B" is satisfied by any of the following conditions: A is true (or exists) and B is false (or does not exist); A is false (or does not exist) and B is true (or exists); or both A and B are true (or exist).

[0069] High-voltage battery systems, such as LNMO battery systems, have high energy density but poor cycle performance.

[0070] Based on this, the first aspect of the present application provides a secondary battery, which includes a positive electrode sheet and a non-aqueous electrolyte. The positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material. The delithiation voltage of the first positive electrode active material is greater than 4.2V. The first positive electrode active material includes a lithium nickel manganese oxide active material. The delithiation voltage of the second positive electrode active material is lower than that of the first positive electrode active material. The surface of the second positive electrode active material is coated with a carbon layer.

[0071] Non-aqueous electrolytes include positive electrode film-forming additives and solvents. The oxidation decomposition voltage of the positive electrode film-forming additives is lower than that of the solvent. Positive electrode film-forming additives include phosphate ester film-forming additives.

[0072] For example, the delithiation voltage of the first positive electrode active material is greater than 4.2V and less than 5V. For example, the delithiation voltage of the first positive electrode active material is any value of 4.21V, 4.3V, 4.4V, 4.5V, 4.6V, 4.7V, 4.8V, or 4.9V, or between any two values.

[0073] Understandably, because the second positive electrode active material requires lithium replenishment during formation, its delithiation voltage is lower than that of the first positive electrode active material. The second positive electrode active material only needs to be a lithium replenishment compound that can preferentially delithilate before the first positive electrode active material during charging in the battery system; it does not need to intercalate lithium during discharge. In other words, the electrochemical delithiation of the second positive electrode active material can be irreversible. The delithiation voltage refers to the plateau voltage of the delithiation voltage, while the intercalation voltage refers to the plateau voltage of the intercalation voltage.

[0074] In this application, the determination of the components and contents of the electrolyte can be performed using the following method: 500 μl of deuterated reagent is added to an NMR tube in a nitrogen-filled glove box. 100 μl of the non-aqueous electrolyte sample is then added to the NMR tube. The NMR tube is shaken to dissolve the non-aqueous electrolyte in the deuterated reagent. The NMR is then performed using an Oxford Instruments X-Pulse benchtop NMR spectrometer. Because the non-aqueous electrolyte is highly sensitive to moisture, both the NMR tests and sample preparation are conducted in a nitrogen atmosphere (H₂O content less than 0.1 ppm, O₂ content less than 0.1 ppm). Simultaneously, all instruments used in the tests 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 831 KF coulometric moisture analyzer was used for moisture testing. Then, in a nitrogen-filled glove box, 10 ml of dried DMSO-d6 and 300 μl of dried internal standard trifluoromethylbenzene were mixed thoroughly 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.

[0075] The reasons for poor cycle performance in high-voltage battery systems include: Reason 1: During the initial charge of a rechargeable battery, an SEI layer forms on the negative electrode side, and side reactions occur during cycling. Repeated damage and growth of the SEI film consume a large number of lithium ions, resulting in poor cycle performance. Reason 2: The reaction between the positive electrode active material and the solvent of the non-aqueous electrolyte leads to solvent oxidation and decomposition, gas generation, and affects the structural stability of the positive electrode material, resulting in microcrack formation. These problems cause increased internal resistance and irreversible capacity loss, affecting the cycle performance of the high-voltage battery system.

[0076] Regarding reason 1, this application uses a combination of a second positive electrode active material and a first positive electrode active material. Since the delithiation voltage of the second positive electrode active material is lower than that of the first positive electrode active material, during the first charge, the second positive electrode active material can preferentially undergo delithiation and embedding / storage in the negative electrode, compensating for the active lithium consumption during SEI film formation. Simultaneously, the lithium intercalation potential of the second positive electrode active material is lower than that of the first positive electrode active material; therefore, no lithium will be generated during discharge. + The lithium is reinserted into the second positive electrode active material. That is, after formation, the lithium extracted from the first positive electrode active material in this application is no longer reinserted, but participates in the lithium extraction and insertion of the first positive electrode active material to achieve a lithium replenishment effect, thereby improving cycle performance.

[0077] Regarding reason 2, since the formation voltage of the high-voltage battery system is higher than the delithiation voltage of the second positive electrode active material, and the carbon layer on the surface of the second positive electrode active material has a certain catalytic effect on the solvent, the side reactions on the surface of the second positive electrode active material are intense during formation. Therefore, by introducing phosphate ester film-forming additives into the non-aqueous electrolyte, on the one hand, because the film-forming voltage of phosphate ester film-forming additives is lower than the oxidation decomposition voltage of the solvent, that is, phosphate ester film-forming additives can preferentially form a CEI film before the solvent is oxidized and decomposed by the positive electrode active material, preventing the solvent and positive electrode active material from contacting and causing side reactions, thus improving cycle performance. On the other hand, the second positive electrode... The carbon layer on the surface of the active material has a certain catalytic effect on phosphate ester film-forming additives, thereby reducing the decomposition potential of phosphate ester film-forming additives on the surface of the second cathode active material. As a result, some phosphate ester film-forming additives will preferentially form a CEI film on the surface of the second cathode active material at a lower voltage, effectively suppressing the active sites of the carbon layer and inhibiting the side reactions between the second cathode active material and the solvent at a lower voltage as early as possible. The remaining phosphate ester film-forming additives can also form a CEI film on the surface of the first cathode active material during formation, isolating the solvent from contact with the first cathode active material, suppressing the occurrence of side reactions, and improving cycle performance.

[0078] In summary, the secondary battery provided in this application firstly improves the cycle performance of the secondary battery by compounding a second positive electrode active material with a first positive electrode active material and using the second positive electrode active material for positive electrode lithium replenishment. Secondly, by introducing phosphate ester film-forming additives into the non-aqueous electrolyte, on the one hand, because the film-forming voltage of phosphate ester film-forming additives is lower than the oxidation decomposition voltage of the solvent, that is, phosphate ester film-forming additives can preferentially form a CEI film before the solvent is oxidized and decomposed by the positive electrode active material, preventing the solvent and positive electrode active material from contacting and causing side reactions. On the other hand, the carbon layer on the surface of the second positive electrode active material is more effective against phosphoric acid. Ester-based film-forming additives have a certain catalytic effect, thereby reducing the decomposition potential of phosphate-based film-forming additives on the surface of the second cathode active material. As a result, some phosphate-based film-forming additives will preferentially form a CEI film on the surface of the second cathode active material at a lower voltage, effectively suppressing the active sites of the carbon layer. This can inhibit the side reactions between the second cathode active material and the solvent at a lower voltage as early as possible, thus improving cycle performance. The remaining phosphate-based film-forming additives can form a CEI film on the surface of the first cathode active material during formation, isolating the solvent from contact with the first cathode active material, suppressing the occurrence of side reactions, and improving cycle performance.

[0079] In some embodiments, the phosphate ester film-forming additive has a mass content of 0.1% to 3% in the non-aqueous electrolyte.

[0080] It is understandable that the mass content of phosphate ester film-forming additives in the non-aqueous electrolyte here refers to the content before formation. It is also understandable that phosphate ester film-forming additives can be consumed to form a film during formation and will also be consumed during aging and other processes. Therefore, after the battery cell is formed, the mass proportion of phosphate ester film-forming additives in the non-aqueous electrolyte is reduced or even completely disappeared due to the consumption of film formation. That is, the mass content of phosphate ester film-forming additives in the non-aqueous electrolyte of the battery cell is 0~0.5%.

[0081] Since a higher mass percentage of film-forming additives in the non-aqueous electrolyte is beneficial for the formation of a CEI film and for the high-temperature cycle life of the secondary battery, a higher addition amount results in a thicker CEI film, leading to increased positive electrode impedance, severe polarization, and capacity decay. Therefore, by controlling the mass content of phosphate ester film-forming additives in the non-aqueous electrolyte to 0.1%~3%, a CEI film can be formed, effectively isolating the solvent from contact with the positive electrode active materials (first positive electrode active material and second positive electrode active material), improving cycle performance, and resulting in lower positive electrode impedance.

[0082] For example, the mass content of phosphate ester film-forming additives in the non-aqueous electrolyte is any one of 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, or between any two values.

[0083] In some embodiments, the positive electrode film-forming additive further includes a low-potential film-forming additive, wherein the film-forming reaction voltage of the low-potential film-forming additive is less than that of the phosphate ester film-forming additive, and the film-forming reaction voltage of the low-potential film-forming additive is less than or equal to the delithiation voltage of the second positive electrode active material.

[0084] In other words, positive electrode film-forming additives include phosphate ester film-forming additives and low-potential film-forming additives.

[0085] Since phosphate ester film-forming additives mainly react with the residual alkali on the surface of lithium nickel manganese oxide active materials, they are more suitable for forming films on the surface of lithium nickel manganese oxide active materials. However, the surface of the second positive electrode active material has a carbon layer, and its surface properties are different from those of lithium nickel manganese oxide active materials. Therefore, in order to better form films on the surface of the second positive electrode active material and suppress the active sites of the carbon layer, low-potential film-forming additives are introduced.

[0086] Because the film-forming reaction voltage of low-potential film-forming additives is lower than that of phosphate ester film-forming additives, low-potential film-forming additives can preferentially undergo film-forming reactions compared to phosphate ester film-forming additives. This allows them to better coat the surface of the second cathode active material and suppress carbon layer active sites. Furthermore, since the film-forming reaction voltage of low-potential film-forming additives is less than or equal to the delithiation voltage of the second cathode active material, they can also isolate the second cathode active material from the solvent as early as possible before the delithiation voltage, reducing side reactions caused by contact and further improving cycle performance.

[0087] In some embodiments, the mass content of the low-potential film-forming additive in the non-aqueous electrolyte is 0.01% to 5%.

[0088] It is understandable that the mass content of low-potential film-forming additives in the non-aqueous electrolyte here refers to the content before formation. It is also understandable that low-potential film-forming additives can be consumed to form a film during formation and will also be consumed during aging and other processes. Therefore, after the battery cell is formed, the mass proportion of low-potential film-forming additives in the non-aqueous electrolyte is reduced or even completely disappeared due to the consumption of film formation. That is, the mass content of low-potential film-forming additives in the non-aqueous electrolyte of the battery cell is 0~0.5%.

[0089] Controlling the mass content of low-potential film-forming additives in non-aqueous electrolytes within the above-mentioned range is beneficial for forming a CEI film on the surface of the second positive electrode active material, isolating both from the solvent and improving cycle performance.

[0090] In some embodiments, the low-potential film-forming additive includes at least one of lithium tetrafluoroborate, tetramethylene sulfone, 1,3-propane sulfonyl lactone, 1,3-propene sulfonyl lactone, and vinyl sulfate.

[0091] The aforementioned low-potential film-forming additives have a strong ability to form films on the second positive electrode active material, which is beneficial for suppressing the side reactions of carbon layer catalysis. At the same time, even if a small amount of the aforementioned low-potential film-forming additives form films on the surface of lithium nickel manganese oxide active material, it will not have a negative impact on the lithium nickel manganese oxide active material.

[0092] In some embodiments, the phosphate ester film-forming additives include at least one of triallyl phosphate, tris(trimethylsilane) phosphate, bis(trimethylsilyl)vinyl phosphate, diethyltrimethylsilyl phosphite, trimethylsilyl dihydrogen phosphate, and mono(trimethylsilyl) phosphite.

[0093] The aforementioned phosphate ester film-forming additives are more suitable for forming films on the surface of the first positive electrode active material. Therefore, the aforementioned phosphate ester film-forming additives can form a CEI film on the surface of the first positive electrode active material during the first charge, suppressing the side reactions of the first positive electrode active material and non-aqueous electrolyte under high voltage or fully charged conditions. At the same time, the aforementioned phosphate ester film-forming additives can also reduce the decomposition voltage on the surface of the second positive electrode active material under carbon layer catalysis, forming a certain CEI film on the surface of the second positive electrode active material at a lower voltage, suppressing the generation of side reactions catalyzed by carbon layer.

[0094] In some embodiments, the solvent includes a first fluorinating agent and a second fluorinating agent, the first fluorinating agent including fluoroethylene carbonate, and the second fluorinating agent including at least one of trifluoroethylmethyl carbonate, trifluoromethylethyl sulfone, and trifluoromethylpropyl sulfone.

[0095] The introduction of the first and second fluorinating agents helps to improve the oxidation resistance and pressure resistance of the electrolyte.

[0096] In some embodiments, the first fluorinating agent has a volume percentage of 35% to 55% in the solvent, and / or the second fluorinating agent has a volume percentage of 25% to 45% in the solvent.

[0097] The above settings help improve the electrolyte's resistance to oxidation and pressure.

[0098] In some embodiments, the solvent further includes a chain carbonate, which accounts for 15% to 30% of the volume of the solvent, and / or the chain carbonate includes at least one of dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, dipropyl carbonate, and diethyl carbonate.

[0099] The aforementioned chain carbonates have low viscosity and excellent flowability, which facilitates lithium-ion migration.

[0100] For example, the first fluorinating agent has a volume percentage of 40% in the solvent, the second fluorinating agent has a volume percentage of 30% in the solvent, and the chain carbonate has a volume percentage of 30% in the solvent.

[0101] For example, the first fluorinating agent has a volume percentage of 50% in the solvent, the second fluorinating agent has a volume percentage of 30% in the solvent, and the chain carbonate has a volume percentage of 20% in the solvent.

[0102] For example, the first fluorinating agent has a volume percentage of 40% in the solvent, the second fluorinating agent has a volume percentage of 40% in the solvent, and the chain carbonate has a volume percentage of 20% in the solvent.

[0103] In some embodiments, the non-aqueous electrolyte includes a lithium salt additive, which includes LiPO2F2.

[0104] The addition of LiPO2F2 not only improves the conductivity of the electrolyte, but also allows it to preferentially reduce on the negative electrode surface during the formation process to form a low-resistance and dense protective film, thereby reducing the impedance of the SEI film, lowering the internal resistance of the secondary battery, and improving the cycle performance of the secondary battery.

[0105] In some embodiments, the lithium salt additive has a mass content of 0.1% to 2% in the non-aqueous electrolyte.

[0106] It is understandable that the mass content of lithium salt additives in the non-aqueous electrolyte here refers to the content before formation. It is also understandable that lithium salt additives can be consumed to form a film during formation. Therefore, after the battery cell is formed, the mass proportion of lithium salt additives in the non-aqueous electrolyte is reduced or even completely disappeared due to the consumption of film formation.

[0107] By controlling the mass content of lithium salt additives in the non-aqueous electrolyte within the above-mentioned range, on the one hand, the composition of the negative electrode SEI film can be adjusted to make the SEI film have a lower impedance; on the other hand, the non-aqueous electrolyte can have a lower viscosity, thereby enabling lithium ions to have a higher migration rate in the non-aqueous electrolyte.

[0108] For example, the mass content of lithium salt additive in the non-aqueous electrolyte is any one of 0.1%, 0.2%, 0.5%, 0.7%, 1.0%, 1.2%, 1.5%, 1.7%, 2.0% or between any two values.

[0109] In some embodiments, the non-aqueous electrolyte also includes a negative electrode film-forming additive, the mass content of which is 0.5% to 3%.

[0110] It is understandable that the film-forming voltage of the negative electrode film-forming additive is less than the oxidative decomposition voltage of the solvent.

[0111] By adding a negative electrode film-forming additive to the non-aqueous electrolyte, a better SEI film can be formed on the negative electrode, preventing further reduction and decomposition of the electrolyte on the negative electrode surface and alleviating battery gas generation. A higher mass percentage of the negative electrode film-forming additive in the non-aqueous electrolyte is more beneficial for reducing gas generation in the secondary battery, while a lower mass percentage is more beneficial for controlling the DCR (discharge rate reduction) of the secondary battery. Therefore, controlling the mass percentage of the negative electrode film-forming additive in the non-aqueous electrolyte within the above range is beneficial for achieving both low gas generation and low DCR in the secondary battery.

[0112] For example, the mass content of the negative electrode film-forming additive in the non-aqueous electrolyte is any one of 0.5%, 0.7%, 1.0%, 1.2%, 1.5%, 1.7%, 2.0%, 2.2%, 2.5%, 2.7%, 3.0% or between any two values.

[0113] In some embodiments, the negative electrode film-forming additive includes at least one of vinylene carbonate and vinyl sulfate.

[0114] Optionally, the negative electrode film-forming additive includes vinylene carbonate and vinyl sulfate, with a mass ratio of vinylene carbonate to vinyl sulfate of 1:1 to 3.

[0115] Vinyl carbonate (VC), as a negative electrode film-forming additive, undergoes a polymerization reaction on the surface of the negative electrode of a lithium-ion battery to form a dense SEI film. This prevents further reduction and decomposition of the electrolyte on the negative electrode surface, alleviating battery gas generation. However, its electrochemical performance is poor under high-temperature conditions. In contrast, vinyl sulfate (DTD), as a low-impedance additive, forms oligomers containing sulfate ions, modifying the SEI film components on the negative electrode surface and increasing the relative content of sulfur and oxygen atoms. Since both sulfur and oxygen atoms contain lone pairs of electrons, they can attract lithium ions, thus accelerating the shuttle speed of lithium ions in the SEI film. This reduces the impedance of the battery interface and improves the battery cycle performance.

[0116] Therefore, blending vinylene carbonate and vinyl sulfate in a mass ratio within the aforementioned range is beneficial for improving the cycle performance of high-voltage battery systems.

[0117] For example, the mass ratio of vinylene carbonate to vinyl sulfate is any one of 1:1.0, 1:1.2, 1:1.5, 1:1.7, 1:2.0, 1:2.2, 1:2.5, 1:2.7, 1:3.0 or between any two values.

[0118] In some embodiments, the non-aqueous electrolyte includes a sulfur-containing additive, which includes at least one of 1,3-propanesulfonate lactone and propenyl-1,3-sulfonate lactone.

[0119] The addition of 1,3-propanesulfonate lactone and propenyl-1,3-sulfonate lactone is beneficial for the formation of a dense SEI film on the negative electrode, effectively isolating the negative electrode active material and solvent, and improving electrolyte gas production.

[0120] Furthermore, the sulfur-containing additive constitutes 0.5% to 3% of the mass of the non-aqueous electrolyte; and / or,

[0121] The mass percentage of 1,3-propanesulfonic acid lactone in the non-aqueous electrolyte is 0.5% to 1.5%; and / or, the mass percentage of propenyl-1,3-sulfonic acid lactone in the non-aqueous electrolyte is 0.5% to 1.5%.

[0122] If the amount of sulfur-containing additive is too small, a dense SEI film cannot be formed on the negative electrode; if it is too large, excessive film formation will occur, leading to a decrease in cycle performance. Therefore, controlling the mass ratio of sulfur-containing additive, 1,3-propanesulfonate lactone, and propenyl-1,3-sulfonate lactone in the non-aqueous electrolyte is beneficial to improving cycle performance.

[0123] In some embodiments, the non-aqueous electrolyte includes an electrolyte, which includes a lithium salt with an Rct ≤ 20 ohms.

[0124] The lithium salt includes, but is not limited to, at least one of LiPF6 (lithium hexafluorophosphate), LiBF4 (lithium tetrafluoroborate), LiAsF6 (lithium hexafluoroarsenate), LiFSI (lithium bis(fluorosulfonyl)imide), LiTFSI (lithium bis(trifluoromethanesulfonyl)imide), LiTFS (lithium trifluoromethanesulfonate), LiDFOB (lithium difluorooxalate borate), LiPO2F2 (lithium difluorophosphate), LiDFOP (lithium difluorodioxalate phosphate), LiSO3F (lithium fluoroxanate), NDFOP (difluorodioxalate), LiF(SO2N)2SO2F, KFSI, CsFSI, Ba(FSI)2, and LiFSO2ASO2CH2CH2CF3, wherein A is a metal ion of the salt, for example, Li can be selected as one of them. + Na + K + 、Rb + Cs + .

[0125] Furthermore, lithium salts include lithium hexafluorophosphate.

[0126] Furthermore, the content of electrolyte salts in the non-aqueous electrolyte is 0.8 mol / L to 2 mol / L.

[0127] For example, the content of electrolyte salts in the non-aqueous electrolyte is any value among 0.8 mol / L, 0.9 mol / L, 1.0 mol / L, 1.2 mol / L, 1.5 mol / L, 1.7 mol / L, and 2.0 mol / L, or between any two values.

[0128] In some embodiments, the mass ratio of the second positive electrode active material to the first positive electrode active material is (2:98) to (50:50).

[0129] The testing method for the mass ratio of the second positive electrode active material to the first positive electrode active material includes: discharging the lithium-ion battery to the battery discharge cutoff voltage (e.g., for high-voltage positive electrode active materials, lithium nickel manganese oxide, the battery discharge cutoff voltage is 3.5V) and disassembling it to separate the positive electrode sheet. A cross-section polisher (model IB-09010CP) is used to cut and polish the positive electrode sheet using a high-energy ion beam. The obtained cross-sectional sample is observed under a scanning electron microscope (SEM). The types of elements measured by EDS are used to identify the particles of the second and first positive electrode active materials. Different regions are selected for testing; for example, the mass ratio of the second and first positive electrode active material particles in three regions is tested, and the average value is obtained as the mass ratio of the second and first positive electrode active material particles.

[0130] For example, the mass ratio of the second positive electrode active material to the first positive electrode active material is (5:95) to (40:60).

[0131] Generally, the improvement effect of lithium replenishment is directly proportional to the amount added. The more second positive electrode active material is added, the better the replenishment effect on active lithium consumption. However, it will also reduce the content of the first positive electrode active material, resulting in a decrease in the secondary battery capacity. Therefore, controlling the mass ratio of the second positive electrode active material to the first positive electrode active material to be (2:98) to (30:70) is beneficial to achieve good cycle performance while maintaining a good secondary battery capacity. For example, the mass ratio of the second positive electrode active material to the first positive electrode active material can be any value of 2:98, 5:95, 10:90, 15:85, 20:80, 25:75, 30:70, 35:65, or 40:60, or between any two values.

[0132] Furthermore, the mass ratio of the second positive electrode active material to the first positive electrode active material is (5:95) to (30:70).

[0133] In some embodiments, the average particle size of the primary particles of the first positive electrode active material is 1 μm to 10 μm, and the average particle size of the primary particles of the second positive electrode active material is ≤400 nm.

[0134] In this application, the testing method for the average particle size of the primary particles of the first positive electrode active material and the second positive electrode active material includes: discharging the lithium-ion battery to the battery discharge cutoff voltage (e.g., for high-voltage positive electrode active materials, lithium nickel manganese oxide, the battery discharge cutoff voltage is 3.5V) and disassembling it to separate the positive electrode sheet. A cross-section polisher (model IB-09010CP) is used to cut and polish the positive electrode sheet using a high-energy ion beam. The obtained cross-sectional sample is observed under a scanning electron microscope (SEM). Based on the elemental types measured by EDS, the lithium-replenishing compound particles and high-voltage positive electrode active material particles are identified. Different regions are selected for testing, and the test is performed three times, for example, testing the particle size of 50 or 100 primary particles of the first / second positive electrode active material. The average value is then obtained as the average particle size of the primary particles of the first / second positive electrode active material in the sample.

[0135] By matching the particle sizes of the two materials, the compaction density of the electrode sheet can be effectively improved, thus increasing the energy density. At the same time, it is beneficial for the delithiated second positive electrode active material to form an inorganic protective layer on the surface of the first positive electrode active material, thereby stabilizing the positive electrode material structure and improving the cycle performance of the secondary battery.

[0136] For example, the average particle size of the primary particles of the first positive electrode active material is any value of 1μm, 2μm, 3μm, 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm or between any two values.

[0137] For example, the average particle size of the primary particles of the second positive electrode active material is any value of 30 nm, 50 nm, 80 nm, 100 nm, 130 nm, 150 nm, 180 nm, 200 nm, 230 nm, 250 nm, 270 nm, 300 nm, 330 nm, 350 nm, 370 nm, or 400 nm, or between any two values.

[0138] Furthermore, the average particle size of the primary particles of the second positive electrode active material is ≤200nm.

[0139] Furthermore, the average particle size of the primary particles of the second positive electrode active material is ≤100nm.

[0140] In some embodiments, lithium nickel manganese oxide-based active materials include Li a Ni 0.5-x Mn 1.5-y M x+yO4, wherein M includes at least one of Mg, Zn, Ti, Zr, W, Nb, Al, B, P, Mo, V or Cr, 0.9≤a≤1.1, -0.2≤x≤0.2, -0.02≤y≤0.3, and x+y≥0.

[0141] For example, lithium nickel manganese oxide-based active materials can be LiNi 0.5 Mn 1.5 O4, Li a Ni 0.4 Mn 1.4 Mg 0.2 O4, Li a Ni 0.3 Mn 1.4 Mg 0.3 O4, Li a Ni 0.3 Mn 1.3 Mg 0.4 O4, Li a Ni 0.4 Mn 1.4 Al 0.2 O4, Li a Ni 0.3 Mn 1.4 Al 0.3 O4, Li a Ni 0.3 Mn 1.3 Al 0.4 O4, etc.

[0142] Furthermore, the upper limit voltage of the second positive electrode active material is less than 3.5V.

[0143] Since the upper limit voltage of the second positive electrode active material is less than 3.5V, when it is used in conjunction with lithium nickel manganese oxide active materials, the lithium replenishment compound can preferentially delithilate the high-voltage positive electrode active material during the first charging process, and the second positive electrode active material preferentially intercalates lithium during the discharge process, thereby replacing the compensation for the active lithium consumption of the first positive electrode active material and playing a lithium replenishment role.

[0144] In some embodiments, the second positive electrode active material includes at least one of lithium phosphate, lithium nickel cobalt aluminum oxide, lithium nickel oxide, lithium selenide, and their respective modifiers.

[0145] The second positive electrode active material undergoes only delithiation during formation, and its structure is stable after delithiation. Therefore, the particle size of the primary particles of the lithium replenishment residue after formation is basically unchanged compared to the lithium replenishment compound before formation. This is beneficial to improving the compaction density of the electrode sheet after formation. At the same time, the delithiation residue of the above three lithium replenishment compounds has a stable structure after delithiation, which is beneficial to further improving the cycle performance of the secondary battery.

[0146] In some embodiments, the second positive electrode active material includes a lithium phosphate, which includes LiMPO4, M includes Fe, and optionally a non-Fe element, which includes one or both of the first dopant element and the second dopant element.

[0147] It is understandable that M including Fe and optionally non-Fe elements means that M includes Fe, or M includes both Fe and non-Fe elements.

[0148] Further, the first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Co, Ga, Sn, Sb, Nb, and Ge; and / or,

[0149] The second doping element includes one or more of B, S, Si, and N.

[0150] That is, the first doping element is iron site doping, and the second doping element is phosphorus site doping.

[0151] Lithium-containing phosphates can replenish lithium in the first positive electrode active material, and the residual products (phosphates) after lithium-containing phosphates are delithiated have high voltage stability and will not decompose under high voltage, thus preventing battery gas generation and failure, thereby improving the safety and cycle performance of secondary batteries.

[0152] In some embodiments, the lithium-replenishing compound includes a lithium-containing phosphate, which includes Li 1+x Fe 1-y A y P 1-z R z O4, where x is any value in the range of -0.100 to 0.100, y is any value in the range of 0.001 to 0.500, z is any value in the range of 0.001 to 0.100, A includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Co, Ga, Sn, Sb, Nb and Ge, and R includes one or more elements selected from B, S, Si and N.

[0153] In some embodiments of the technical solutions of this application, the compound Li 1+x Fe 1-y A y P 1-z R z The method for preparing O4 may include the following steps:

[0154] (1) Dissolve and stir the iron source, the iron site doped element A source and acid in a solvent to generate a suspension of iron salt doped with element A. Filter the suspension and dry the filter cake to obtain iron salt doped with element A.

[0155] (2) The lithium source, phosphorus source, element R source, solvent and iron salt doped with element A obtained in step (1) are added to the reaction vessel, ground and mixed to obtain a slurry;

[0156] (3) The slurry obtained in step (2) is transferred to a spray drying equipment for spray drying and granulation to obtain granules;

[0157] (4) The particles obtained in step (3) are sintered to obtain the positive electrode active material.

[0158] In any embodiment, the iron source may be an iron-containing substance known in the art that can be used to prepare lithium iron phosphate, such as one or a combination of elemental iron, ferrous oxide, ferric phosphate, ferric oxalate, and ferric carbonate.

[0159] The acid is selected from one or more of hydrochloric acid, sulfuric acid, nitric acid, phosphoric acid, and organic acids such as oxalic acid, for example, oxalic acid. The source of element R is selected from at least one of sulfates, borates, nitrates, and silicates of element R. The source of element A is selected from at least one of the elemental form, oxide, phosphate, oxalate, carbonate, and sulfate of A.

[0160] In some embodiments, the lithium-containing phosphate includes Li a A e Fe 1-f B f P 1-g C g O 4-n D n Wherein, A includes one or more elements selected from Zn, Al, Na, K, Mg, Nb, Mo, and W; B includes one or more elements selected from Ti, V, Zr, Fe, Ni, Mg, Co, Ga, Sn, Sb, Nb, and Ge; C includes one or more elements selected from B, S, Si, and N; D includes one or more elements selected from S, F, Cl, and Br; a is selected from the range of 0.9 to 1.1, e is selected from the range of 0.001 to 0.1, f is selected from the range of 0.001 to 0.5, g is selected from the range of 0.001 to 0.1, and n is selected from the range of 0.001 to 0.1.

[0161] It should be noted that Li a A e Fe 1-f B f P 1-g C g O 4-n D n The compound is actually a specific LiMPO4 material. Its preparation method can be found in the Li... 1+x Fe 1-y A y P1-z R z O4 is not specified here.

[0162] In the enumeration of positive electrode active materials in this application, the molar content of Li refers to the initial state of the material, i.e. the state before feeding. When the positive electrode active material is applied to the battery system, the molar content of Li will change after charge-discharge cycles.

[0163] Furthermore, due to differences in material preparation processes and conditions, the molar content of oxygen is usually not strictly the same as the coefficient of oxygen in the chemical formula, and fluctuations may occur. For example, in Li... 1+x Fe 1-y A y P 1-z R z The molar content of O in O4 is not strictly 4.

[0164] For example, lithium phosphates can be LiFePO4 or LiMn. 0.1 Fe 0.9 PO4, LiMn 0.2 Fe 0.8 PO4, LiMn 0.3 Fe 0.7 PO4, LiMn 0.4 Fe 0.6 PO4, LiMn 0.5 Fe 0.5 PO4, LiMn 0.6 Fe 0.4 PO4, LiMn 0.7 Fe 0.3 PO4, LiMn 0.8 Fe 0.2 PO4, LiMn 0.9 Fe 0.1 PO4, etc.

[0165] In LiMPO4, M includes both Fe and non-Fe elements. The non-Fe elements include one or both of the first and second doping elements. The first doping element is an iron-site dopant, and the second doping element is a phosphorus-site dopant. The first doping element includes one or more of Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Co, Ga, Sn, Sb, Nb, and Ge. The second doping element includes one or more of B, S, Si, and N.

[0166] It should be noted that the above list of second positive electrode active materials is only intended to illustrate the feasibility of this solution and is not intended to limit the solution.

[0167] In some embodiments, the morphology of the second positive electrode active material includes spherical, sheet-like, rod-like, linear, or other irregular morphologies. That is, the morphology of the lithium-supplementing compound is not limited and can be used in the scheme of this application.

[0168] In some embodiments, the lower limit of the voltage range of the secondary battery is greater than the lithium intercalation voltage of the second positive electrode active material; and / or,

[0169] The upper limit of the voltage range of the secondary battery shall not exceed 5V; and / or,

[0170] The voltage range of the secondary battery is 3.5V to 4.9V. It should be noted that by limiting the voltage range of the secondary battery to 3.5V to 4.9V, since the lower limit of the voltage range of the secondary battery is greater than the lithium intercalation voltage of the second positive electrode active material, the second positive electrode active material is used as a lithium replenishment compound and is delithiated only during the first charge, and does not undergo lithium intercalation during subsequent operation of the secondary battery.

[0171] A second aspect of this application provides an electrical device that includes the secondary battery provided in the first aspect of this application.

[0172] In addition, the secondary battery and power-consuming device of this application will be described below with appropriate reference to the accompanying drawings.

[0173] [Rechargeable Battery]

[0174] The second aspect of this application provides a secondary battery. This application does not particularly limit the type of secondary battery; for example, the secondary battery can be a lithium-ion battery, etc.

[0175] Typically, a secondary battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. During charging and discharging, active ions move back and forth between the positive and negative electrodes, inserting and releasing. The electrolyte acts as a conductor between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits while allowing ions to pass through.

[0176] [Positive electrode plate]

[0177] The positive electrode includes a positive current collector and a positive electrode film layer disposed on at least one surface of the positive current collector, the positive electrode film layer including the positive electrode active material of the first aspect of this application.

[0178] As an example, the positive current collector has two surfaces opposite each other in its own thickness direction, and the positive electrode film layer is disposed on either or both of the two opposite surfaces of the positive current collector.

[0179] In some embodiments, the positive current collector may be a metal foil or a composite current collector. For example, aluminum foil may be used as the metal foil. The composite current collector may include a polymer substrate and a metal layer formed on at least one surface of the polymer substrate. The composite current collector may be formed by forming a metal material (aluminum, aluminum alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0180] In some embodiments, the positive electrode film layer may optionally include a binder. As an example, the binder may include at least one of polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), PVDF-tetrafluoroethylene-propylene terpolymer, PVDF-hexafluoropropylene-tetrafluoroethylene terpolymer, tetrafluoroethylene-hexafluoropropylene copolymer, and fluorinated acrylate resin.

[0181] In some embodiments, the positive electrode film may optionally include a conductive agent. As an example, the conductive agent may include at least one selected from superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0182] In some embodiments, the positive electrode sheet can be prepared by dispersing the above-mentioned components for preparing the positive electrode sheet, such as positive active material, conductive agent, binder and any other components, in a solvent (e.g., N-methylpyrrolidone) to form a positive electrode slurry; coating the positive electrode slurry onto the positive electrode current collector, and then obtaining the positive electrode sheet after drying, cold pressing and other processes.

[0183] [Negative electrode plate]

[0184] In some embodiments, the negative electrode sheet includes a negative current collector and a negative electrode film layer disposed on at least one surface of the negative current collector.

[0185] As an example, the negative electrode current collector has two surfaces opposite each other in its own thickness direction, and the negative electrode film layer is disposed on either or both of the two opposite surfaces of the negative electrode current collector.

[0186] 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. 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. The composite current collector may be formed by forming a metal material (copper, copper alloy, nickel, nickel alloy, titanium, titanium alloy, silver and silver alloy, etc.) on a polymer material substrate (such as a substrate of polypropylene (PP), polyethylene terephthalate (PET), polybutylene terephthalate (PBT), polystyrene (PS), polyethylene (PE), etc.).

[0187] In some embodiments, the negative electrode film layer includes a negative electrode active material. The negative electrode active material may be any negative electrode active material known in the art for use in batteries. As an example, the negative electrode active material may include at least one 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 be selected from at least one of elemental silicon, silicon oxide compounds, silicon-carbon composites, silicon-nitrogen composites, and silicon alloys. Tin-based materials may be selected from at least one of elemental tin, tin oxide compounds, and tin alloys. However, this application is not limited to these materials, and other conventional materials that can be used as negative electrode active materials for batteries may also be used. These negative electrode active materials may be used alone or in combination of two or more.

[0188] In some embodiments, the negative electrode film layer may optionally include a binder. The binder may be selected from at least one 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).

[0189] In some embodiments, the negative electrode film may optionally include a conductive agent. The conductive agent may be selected from at least one of superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0190] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0191] In some embodiments, the negative electrode sheet can be prepared by dispersing the above-mentioned components for preparing the negative electrode sheet, such as negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto a negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0192] In other embodiments, the current collector of the negative electrode sheet typically includes a current collector body and a base coating. The base coating can be disposed on at least one side of the current collector body. The base coating basically does not contain negative electrode active material, and may include a small amount of carbon material. However, the carbon material forms a thin coating and cannot function as a negative electrode active material. In this embodiment, the negative electrode sheet can be an electrode sheet without a negative electrode active material layer. For a negative electrode sheet without a negative electrode active material layer, when the current collector of the negative electrode sheet does not contain a base coating, the film layer can be disposed on the surface of at least one side of the current collector; when the current collector of the negative electrode sheet includes a base coating, the film layer can be disposed on the surface of the base coating away from the current collector.

[0193] In some embodiments, the membrane layer may also include a binder for fixing the additive to the negative electrode sheet. The type of binder is not particularly limited, and those skilled in the art can choose flexibly according to actual needs.

[0194] Electrolyte

[0195] The electrolyte plays a role in conducting ions between the positive and negative electrode plates.

[0196] The electrolyte used is the aforementioned non-aqueous electrolyte.

[0197] [Isolation membrane]

[0198] In some embodiments, the secondary battery also 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.

[0199] In some embodiments, the material of the separator can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator can 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 can be the same or different, without particular limitation.

[0200] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0201] In some embodiments, the secondary battery may include an outer packaging. This outer packaging may be used to encapsulate the electrode assembly and electrolyte described above.

[0202] In some embodiments, the outer packaging of the secondary battery can be a hard shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the secondary battery can also be a soft pack, such as a pouch. The material of the soft pack can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0203] In this application, a secondary battery can refer to a single battery cell, or it can refer to a single physical module comprising multiple battery cells to provide higher voltage and capacity, and it can take the form of a battery pack, battery module, etc.

[0204] 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 2 shows a square battery cell 5 as an example.

[0205] In some embodiments, referring to FIG3, the outer packaging may include a housing 51 and a top cover assembly 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 top cover assembly 53 can cover 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. A non-aqueous electrolyte is immersed in the electrode assembly 52. ​​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 specific practical needs.

[0206] In some implementations, individual battery cells can be assembled into a battery module. The number of individual battery cells contained in a battery module can be one or more, and the specific number can be selected by those skilled in the art based on the application and capacity of the battery module.

[0207] Figure 4 shows a battery module 4 as an example. Referring to Figure 4, in the battery module 4, multiple battery cells 5 can be arranged sequentially along the length of the battery module 4. Of course, they can also be arranged in any other manner. Furthermore, the multiple battery cells 5 can be fixed in place using fasteners.

[0208] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0209] In some embodiments, the battery modules described above can also be assembled into a battery pack, and the number of battery modules contained in the battery pack can be one or more, the specific number of which can be selected by those skilled in the art according to the application and capacity of the battery pack.

[0210] Figures 5 and 6 show a battery pack 1 as an example. Referring to Figures 5 and 6, the battery pack 1 may include a battery box and multiple battery modules 4 disposed within the battery box. The battery box includes an upper box 2 and a lower box 3, with the upper box 2 covering the lower box 3 to form a closed space for accommodating the battery modules 4. The multiple battery modules 4 can be arranged in any manner within the battery box.

[0211] In addition, this application also provides an electrical device, which includes a secondary battery (at least one of a battery cell, battery module, or battery pack) provided in this application. The secondary battery can be used as a power source for the electrical device or as an energy storage unit of the electrical device. The electrical device may include, but is not limited to, mobile devices (e.g., mobile phones, laptops, etc.), electric vehicles (e.g., pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc.), electric trains, ships and satellites, energy storage systems, etc.

[0212] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0213] Figure 7 shows an example of an electrical device. This 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 secondary battery for this device, a battery pack or battery module can be used.

[0214] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a rechargeable battery as their power source.

[0215] The following describes embodiments of this application. The embodiments described below are exemplary and are only used to explain this application, and should not be construed as limiting this application. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in this field or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all conventional products that can be obtained commercially.

[0216] Example 1

[0217] The positive electrode active material, conductive carbon black, binder polyvinylidene fluoride (PVDF), and polyacrylonitrile dispersant were added to N-methylpyrrolidone (NMP) in a mass ratio of 95.1:3:1.8:0.1 and stirred to obtain a coating slurry. The slurry was then uniformly coated on both sides of the positive electrode current collector aluminum foil, dried, rolled, and then die-cut to obtain the positive electrode sheet.

[0218] Among them, the positive electrode active material is lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 The cathode active material is composed of lithium iron phosphate (LiFePO4, LNMO) and carbon-coated lithium iron phosphate (LiFePO4, LFP), with the mass ratio of carbon-coated lithium iron phosphate to lithium nickel manganese oxide being 30:70, meaning that the mass proportion of carbon-coated lithium iron phosphate in the cathode active material is 30%.

[0219] Preparation of the negative electrode sheet

[0220] The negative electrode active material graphite, conductive agent carbon black, binder styrene-butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dissolved in deionized water at a mass ratio of 96.2:0.8:1.8:1.2 and mixed evenly to prepare a slurry (kneaded solids content of 62% and total solids content of 50%). The slurry is uniformly coated onto the negative electrode current collector copper foil once or multiple times, and then dried, cold-pressed, and slit to obtain the negative electrode sheet.

[0221] Preparation of Electrolyte

[0222] In an argon atmosphere glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), organic solvents fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and trifluoroethyl methyl carbonate (FEMC) were mixed evenly in a mass ratio of 4:3:3. LiPF6, LiPO2F2, tris(trimethylsilane) phosphate (TMSP), vinylene carbonate (VC), and vinyl sulfate (DTD) were then added and mixed evenly to obtain a non-aqueous electrolyte.

[0223] The concentration of LiPF6 is 1 mol / L, the mass content of LiPO2F2 in the non-aqueous electrolyte is 1%, the mass content of tris(trimethylsilane)phosphate in the non-aqueous electrolyte is 0.3%, the mass content of vinylene carbonate in the non-aqueous electrolyte is 0.5%, and the mass content of vinyl sulfate in the non-aqueous electrolyte is 1%.

[0224]

Isolation Film

[0225] A polyethylene film with a thickness of 12 μm was used as the separator.

[0226] [Preparation of Lithium-ion Batteries]

[0227] The positive electrode, separator, and negative electrode are stacked in sequence, with the separator acting as a separator between the positive and negative electrodes. The resulting cells are then wound to obtain a bare cell. Tabs are welded onto the bare cell, which is then placed in an aluminum casing and baked at 80°C to remove moisture. Electrolyte is then injected and the casing is sealed, resulting in a non-charged battery. The non-charged battery then undergoes a series of processes including settling, hot and cold pressing, formation (the cell is settling at 45°C for 5 minutes, then charged at 0.02C to 4.5V, settling for 5 minutes, and then charged at 0.1C to 4.65V), shaping, and capacity testing to obtain the lithium-ion battery product.

[0228] Examples 2-14 and Comparative Examples 1-2

[0229] The only difference between each embodiment and the comparative example and Example 1 is the choice of electrolyte.

[0230] The only difference between Comparative Example 1 and Example 1 is that Comparative Example 1 is a base electrolyte composed of an organic solvent and LiPF6. The organic solvent is obtained by mixing fluoroethylene carbonate (FEC), methyl ethyl carbonate (EMC), and trifluoroethyl methyl carbonate (FEMC) in a volume ratio of 4:3:3, and the concentration of LiPF6 is 1 mol / L.

[0231] The only difference between Comparative Example 2 and Example 1 is that the electrolyte is composed of an organic solvent, LiPF6 and tetramethylene sulfone. The organic solvent is obtained by mixing fluoroethylene carbonate (FEC), methyl ethyl carbonate (EMC) and trifluoroethyl methyl carbonate (FEMC) in a volume ratio of 4:3:3. The concentration of LiPF6 is 1 mol / L and the mass content of tetramethylene sulfone in the electrolyte is 1%.

[0232] The differences in the electrolytes used in each embodiment and comparative example are shown in Table 1:

[0233] Table 1. Differences between the various embodiments and comparative examples

[0234]

[0235] In Table 1, solvent 1 consists of FEC, EMC, and FEMC in a volume ratio of 4:3:3; solvent 2 consists of FEC, EMC, and FEMC in a volume ratio of 5:2:3; and solvent 3 consists of FEC, EMC, and FEMC in a mass ratio of 4:2:4.

[0236] The secondary batteries provided in each embodiment and comparative example were tested, including:

[0237] A 25℃ cycle test was conducted, and the cycle capacity retention rate was calculated: At 25℃, the battery was charged at a constant current rate of 0.5 C to the cutoff voltage of 4.9 V, then charged at a constant voltage until the current ≤ 0.05 C, and allowed to stand for 30 min. The battery capacity at this point was recorded as C0. Then, the battery was discharged at a constant current rate of 1 C to the discharge cutoff voltage of 3.5 V, and allowed to stand for 30 min. The battery capacity at this point was recorded as D0. This method was repeated for 207 charge-discharge cycles. The battery capacity after 207 cycles was recorded as D1. The cycle capacity retention rate after 207 charge-discharge cycles at 25℃ can be calculated using the formula D1 / D0 × 100%.

[0238] A 45℃ cycle test was conducted, and the cycle capacity retention rate was calculated: At 45℃, the battery was charged at a constant current rate of 0.5 C to the cutoff voltage of 4.9 V, then charged at a constant voltage until the current ≤ 0.05 C, and allowed to stand for 30 min. The battery capacity at this point was recorded as C0. Then, the battery was discharged at a constant current rate of 1 C to the discharge cutoff voltage of 3.5 V, and allowed to stand for 30 min. The battery capacity at this point was recorded as D0. This method was repeated 282 times. The battery capacity after 282 cycles was recorded as D1. The cycle capacity retention rate after 282 charge-discharge cycles at 45℃ can be calculated using the formula D1 / D0 × 100%.

[0239] The test results are shown in Table 2.

[0240] Table 2 Test Results

[0241]

[0242] As can be seen from Tables 1 and 2, the battery provided in this application embodiment has both a good 25°C cycle capacity retention rate and a good 45°C cycle capacity retention rate, that is, the battery provided in this application has good cycle performance.

[0243] As can be seen from Examples 4, 1, and 2, the introduction of positive electrode film-forming additives can enhance the cycle performance of the battery. Among them, phosphate ester additives can effectively improve the cycle performance of the battery provided in this application.

[0244] As can be seen from Examples 1-3, the mass content of phosphate ester film-forming additives in non-aqueous electrolytes affects the cycle performance, and the range of 0.5%-1.5% shows good cycle capacity retention.

[0245] As can be seen from Examples 1 and 6-7, phosphate ester film-forming additives combined with low-potential film-forming additives can effectively improve the cycle performance of batteries compared to phosphate ester film-forming additives alone.

[0246] As can be seen from Examples 1 and 8-12, adding lithium salt additives and / or negative electrode film-forming additives to the electrolyte is beneficial to improving the cycle performance of the battery.

[0247] As can be seen from Examples 1 and 13-14, different ratios of the organic solvents fluoroethylene carbonate (FEC), ethyl methyl carbonate (EMC), and trifluoroethyl methyl carbonate (FEMC) in the solvent can also affect the cycle performance of the battery to a certain extent.

[0248] Test case

[0249] Prepare the basic electrolyte, electrolyte 1, and electrolyte 2.

[0250] The basic battery solution is composed of LiPF6 and an organic solvent, wherein the concentration of LiPF6 in the basic electrolyte is 1M, and the organic solvent is composed of EC and EMC in a volume ratio of 3:7.

[0251] Electrolyte 1 is the electrolyte shown in Example 6.

[0252] Electrolyte 2 is composed of LiPF6 and organic solvents, wherein the concentration of LiPF6 in the base electrolyte is 1M, and the organic solvents are composed of FEC, EMC and FEMC in a volume ratio of 5:2:3.

[0253] The preparation of the Base positive electrode sheet involves adding the positive electrode active material, conductive agent carbon black, binder polyvinylidene fluoride (PVDF), and polyacrylonitrile dispersant to N-methylpyrrolidone (NMP) at a mass ratio of 95.1:3:1.8:0.1, and stirring to obtain a uniform coating slurry. The slurry is then uniformly coated onto both sides of the positive electrode current collector aluminum foil, followed by drying, rolling, and die-cutting to obtain the positive electrode sheet. The positive electrode active material is composed of lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 Composed of O4, LNMO.

[0254] Preparation of 30% LFP positive electrode sheet: Positive electrode active material, conductive agent carbon black, binder polyvinylidene fluoride (PVDF), and polyacrylonitrile dispersant were added to N-methylpyrrolidone (NMP) at a mass ratio of 95.1:3:1.8:0.1 and stirred until uniformly mixed to obtain a coating slurry. The slurry was then uniformly coated onto both sides of the positive electrode current collector aluminum foil, followed by drying, rolling, and die-cutting to obtain the positive electrode sheet. The positive electrode active material is composed of lithium nickel manganese oxide (LiNi). 0.5 Mn 1.5 The cathode active material is composed of lithium iron phosphate (LiFePO4, LNMO) and carbon-coated lithium iron phosphate (LiFePO4, LFP), with the mass ratio of carbon-coated lithium iron phosphate to lithium nickel manganese oxide being 30:70, meaning that the mass proportion of carbon-coated lithium iron phosphate in the cathode active material is 30%.

[0255] The above-mentioned positive electrode and electrolyte were assembled into a battery according to the method of Example 1.

[0256] Symmetrical cell EIS test: Each cell charged to 50% SOC is disassembled, and two positive electrodes at 50% SOC are assembled into a stack. Using the CHI660D electrochemical workstation from Shanghai Chenhua Company, a sinusoidal voltage signal with a frequency of W1 and a small amplitude is applied to the battery system. The system will generate a sinusoidal current response with a frequency of W2. The change in the ratio of excitation voltage to response current is the impedance spectrum of the electrochemical system. In the AC impedance test, the frequency range is 10 mHz to 100 kHz, and the amplitude is 5 mV.

[0257] The results are shown in Figure 1. Figure 1 shows the EIS test results of a symmetrical battery with 50% SOC cathode material. In Figure 1, Base-electrolyte 1@cathode refers to the battery composed of Base cathode and electrolyte 1, and the test results of the stacked battery formed after the above treatment. 30%LFP-electrolyte 1@cathode refers to the battery composed of 30%LFP cathode and electrolyte 1, and the test results of the stacked battery formed after the above treatment. Similarly, Base-electrolyte 2@cathode, Base-basic electrolyte@cathode, 30%LFP-electrolyte 2@cathode, and 30%LFP-basic electrolyte@cathode can be obtained, which will not be elaborated here.

[0258] As shown in Figure 1, the doping of LFP increases the lithium-ion diffusion and migration of the cathode material through the resistance Rsei and charge transfer resistance Rct of the SEI film. The impedance can be significantly reduced by introducing electrolyte additives.

[0259] It should be noted that this application is not limited to the above-described embodiments. The above embodiments are merely examples, and any embodiments with the same structure and effect as the technical concept within the scope of this application are included in the technical scope of this application. Furthermore, various modifications that can be conceived by those skilled in the art to the embodiments, and other ways of constructing by combining some of the constituent elements of the embodiments, without departing from the spirit of this application, are also included in the scope of this application.

Claims

1. A secondary battery, wherein, The device includes a positive electrode sheet and a non-aqueous electrolyte. The positive electrode sheet includes a positive active material layer, which includes a first positive active material and a second positive active material. The first positive active material has a delithiation voltage greater than 4.2V and includes a lithium nickel manganese oxide active material. The second positive active material has a delithiation voltage lower than that of the first positive active material. The surface of the second positive active material is coated with a carbon layer. The non-aqueous electrolyte includes a positive electrode film-forming additive and a solvent. The oxidative decomposition voltage of the positive electrode film-forming additive is lower than that of the solvent. The positive electrode film-forming additive includes phosphate ester film-forming additives.

2. The secondary battery according to claim 1, wherein, The phosphate ester film-forming additive has a mass content of 0.1%-3% in the non-aqueous electrolyte.

3. The secondary battery according to claim 1 or 2, wherein, The positive electrode film-forming additive also includes a low-potential film-forming additive, wherein the film-forming reaction voltage of the low-potential film-forming additive is lower than that of the phosphate ester film-forming additive, and the film-forming reaction voltage of the low-potential film-forming additive is less than or equal to the delithiation voltage of the second positive electrode active material.

4. The secondary battery according to claim 3, wherein, The low-potential film-forming additive has a mass content of 0.01%-5% in the non-aqueous electrolyte.

5. The secondary battery according to claim 3 or 4, wherein, The low-potential film-forming additive includes at least one of lithium tetrafluoroborate, tetramethylene sulfone, 1,3-propane sulfonyl lactone, 1,3-propene sulfonyl lactone, and vinyl sulfate.

6. The secondary battery according to any one of claims 1 to 5, wherein, The phosphate ester film-forming additives include at least one of triallyl phosphate, tris(trimethylsilane) phosphate, bis(trimethylsilyl)vinyl phosphate, diethyltrimethylsilyl phosphite, trimethylsilyl dihydrogen phosphate, and mono(trimethylsilyl) phosphite.

7. The secondary battery according to any one of claims 1 to 6, wherein, The non-aqueous electrolyte includes a solvent, which includes a first fluorinating agent and a second fluorinating agent. The first fluorinating agent includes fluoroethylene carbonate, and the second fluorinating agent includes at least one of trifluoroethyl methyl carbonate, trifluoromethyl ethyl sulfone, and trifluoromethyl propyl sulfone.

8. The secondary battery according to claim 7, wherein, The first fluorinating agent has a volume percentage of 35% to 55% in the solvent, and / or the second fluorinating agent has a volume percentage of 25% to 45% in the solvent.

9. The secondary battery according to claim 7 or 8, wherein, The solvent further includes chain carbonates, the chain carbonates comprising 15% to 30% by volume in the solvent, and / or the chain carbonates include at least one of dimethyl carbonate, methyl ethyl carbonate, methyl propyl carbonate, dipropyl carbonate, and diethyl carbonate.

10. The secondary battery according to any one of claims 7 to 9, wherein, The non-aqueous electrolyte includes a lithium salt additive, which includes LiPO2F2.

11. The secondary battery according to claim 10, wherein, The lithium salt additive has a mass content of 0.1% to 2% in the non-aqueous electrolyte.

12. The secondary battery according to any one of claims 7 to 11, wherein, The non-aqueous electrolyte also includes a negative electrode film-forming additive, and the mass content of the negative electrode film-forming additive in the non-aqueous electrolyte is 0.5% to 3%.

13. The secondary battery according to claim 12, wherein, The negative electrode film-forming additive includes at least one of vinylene carbonate and vinyl sulfate; Optionally, the negative electrode film-forming additive includes vinylene carbonate and vinyl sulfate, wherein the mass ratio of vinylene carbonate to vinyl sulfate is 1:1 to 3.

14. The secondary battery according to any one of claims 1 to 13, wherein, The non-aqueous electrolyte includes a sulfur-containing additive, which includes at least one selected from 1,3-propanesulfonate lactone and propenyl-1,3-sulfonate lactone; and / or, The sulfur-containing additive accounts for 0.5% to 3% of the mass of the non-aqueous electrolyte; and / or, The 1,3-propanesulfonic acid lactone has a mass percentage of 0.5% to 1.5% in the non-aqueous electrolyte; and / or, The propylene-1,3-sulfonyl lactone has a mass percentage of 0.5% to 1.5% in the non-aqueous electrolyte.

15. The secondary battery according to any one of claims 1 to 14, wherein, The non-aqueous electrolyte includes an electrolyte, which includes a lithium salt; Wherein, the lithium salt has an Rct ≤ 20 ohm; and / or, The lithium salt includes lithium hexafluorophosphate; and / or, The content of electrolyte salts in the non-aqueous electrolyte is 0.8 mol / L to 2 mol / L.

16. The secondary battery according to any one of claims 1 to 15, wherein, The mass ratio of the second positive electrode active material to the first positive electrode active material is (2:98) to (50:50); and / or, The average particle size of the primary particles of the first positive electrode active material is 1μm~10μm, and the average particle size of the primary particles of the second positive electrode active material is ≤400nm.

17. The secondary battery according to any one of claims 1 to 16, wherein, The lithium nickel manganese oxide active material includes Li a Ni 0.5-x Mn 1.5-y M x+y O4, wherein M includes at least one of Mg, Zn, Ti, Zr, W, Nb, Al, B, P, Mo, V or Cr, 0.9≤a≤1.1, -0.2≤x≤0.2, -0.02≤y≤0.3, and x+y≥0.

18. The secondary battery according to any one of claims 1 to 17, wherein, The second positive electrode active material includes at least one of lithium phosphate, lithium nickel cobalt aluminum oxide, lithium nickel oxide, lithium selenide, and their respective modifiers.

19. The secondary battery according to any one of claims 1 to 18, wherein, The second positive electrode active material includes a lithium phosphate, wherein the lithium phosphate includes LiMPO4, M includes Fe and optionally a non-Fe element, wherein the non-Fe element includes one or both of the first doping element and the second doping element; Wherein, the first doping element includes one or more elements selected from Zn, Al, Na, K, Mg, Mo, W, Ti, V, Zr, Mn, Ni, Co, Ga, Sn, Sb, Nb, and Ge; and / or, The second doping element includes one or more elements selected from B, S, Si, and N.

20. The secondary battery according to any one of claims 1 to 19, wherein, The lower limit of the voltage range of the secondary battery is greater than the lithium intercalation voltage of the second positive electrode active material; and / or, The upper limit of the voltage range of the secondary battery is no higher than 5V; and / or, The voltage range of the secondary battery is 3.5V to 4.9V.

21. An electrical appliance, wherein, Includes the secondary battery as described in any one of claims 1 to 20.

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