Secondary battery and electric device

Abstract

The invention relates to the technical field of batteries, in particular to a secondary battery and an electric device. Active ions of the secondary battery comprise A ions, the secondary battery comprises electrolyte, the electrolyte comprises fluorine-containing sulfonate and alkali metal ions, the radius of the alkali metal ions is larger than that of the A ions, and the A ions comprise sodium ions or lithium ions. By adopting the secondary battery provided by the invention, interfacial films with low impedance and stable structure can be formed on the surfaces of the positive electrode and the negative electrode, the interfacial side reaction is effectively suppressed, and the transmission path of A ions is expanded, so that the problem of increase of the circulating direct-current internal resistance of the battery caused by the side reaction of the positive electrode material and the electrolyte at the electrode interface is solved, and the cycle performance of the secondary battery is improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a secondary battery and a power utilization device. BACKGROUND

[0002] Secondary batteries such as lithium ion batteries are attracting much attention due to their high specific energy, long cycle life, low self-discharge, good safety performance and other characteristics, and current applications of lithium ion batteries have penetrated into all aspects of daily life such as cameras, notebook computers, electric vehicles and the like.

[0003] With the rapid growth of portable electronic devices, electric vehicles and the like, the demand for power batteries is also growing. Among them, the electrochemical performance of the battery is also increasingly concerned by people.

[0004] The electrolyte is an important component of the secondary battery, and the electrolyte determines the composition and structure of the two-phase interface film on the electrode surface, and has an important influence on the stability of the electrode structure and the cycle life of the secondary battery.

[0005] Improving the cycle life of the battery has always been the pursuit of the industry, but due to the side reaction of the electrolyte at the cathode and anode interface, the comprehensive performance of the battery is poor. SUMMARY

[0006] The main purpose of the present application is to provide a secondary battery, which aims to improve the cycle performance of the battery.

[0007] To achieve the above purpose, the present application provides a secondary battery, the active ion of the secondary battery includes A ion, the secondary battery includes an electrolyte, the electrolyte includes a fluorine-containing sulfonate and an alkali metal ion, the radius of the alkali metal ion is greater than the radius of the A ion, and the A ion includes a sodium ion or a lithium ion.

[0008] The electrolyte includes a fluorine-containing sulfonate, which can improve the insertion and extraction kinetics of ions in the electrode. Specifically, the fluorine-containing sulfonate can provide S-O bonds and S=O bonds. Taking a lithium electrode as an example, it can form an interface film rich in lithium-sulfur oxide (Li2S x O y ) on the positive and negative electrode surfaces to achieve fast Li + insertion / extraction kinetics; on the other hand, it can protect the electrode interface. Specifically, taking a lithium electrode as an example, the fluorine ion and lithium ion in the fluorine-containing sulfonate have similar radii and strong binding energy. During the charging and discharging process of the battery, the fluorine ion and lithium ion are combined to uniformly deposit lithium fluoride that is insoluble in the electrolyte on the surface of the active material, further protecting the electrode interface and inhibiting the decomposition of the subsequent electrolyte.

[0009] Meanwhile, the electrolyte further comprises alkali metal ions, the active ions of the secondary battery comprise A ions, the A ions comprise sodium ions or lithium ions, the radius of the alkali metal ions is greater than the radius of the A ions, the secondary battery comprises a sodium ion battery or a lithium ion battery, that is, when the electrolyte is used in the sodium ion battery, the alkali metal ions comprise ions with a radius greater than that of sodium ions, and when the electrolyte is used in the lithium ion battery, the alkali metal ions comprise ions with a radius greater than that of lithium ions. In this way, the alkali metal ions are embedded in the material layer of the positive electrode and the negative electrode, the layer spacing is expanded, the diffusion of the A ions is facilitated, the A ions are more easily diffused, and the ion migration impedance is smaller. Meanwhile, the addition of the alkali metal ions can reduce the surface static potential, improve the interface stability of the electrolyte and the positive electrode material, and reduce the side reaction at the interface.

[0010] Therefore, by adopting the scheme of the present application, an interface film with low impedance and stable structure can be formed on the surface of the positive and negative electrodes, the interface side reaction can be effectively suppressed, and the transmission path of the A ions is expanded, thereby improving the problem of the increase of the battery cycle direct current resistance (DCR, Directive Current Resistance) caused by the side reaction of the positive electrode material and the electrolyte at the electrode interface, and improving the cycle performance of the secondary battery.

[0011] Optionally, the electrolyte further comprises a fluorine-containing phosphoric acid salt.

[0012] The fluorine-containing phosphoric acid salt can participate in the film formation at the negative electrode interface, and the combination of the fluorine-containing sulfonic acid salt and the fluorine-containing phosphoric acid salt can significantly improve the cycle performance of the battery. It can be understood that the fluorine-containing sulfonic acid salt can participate in the film formation at the positive and negative electrode interfaces, and the fluorine-containing phosphoric acid salt preferentially participates in the film formation at the negative electrode interface. At this time, the fluorine-containing sulfonic acid salt and the fluorine-containing phosphoric acid salt have a competitive relationship at the negative electrode interface. Based on the fact that the fluorine-containing phosphoric acid salt preferentially participates in the film formation at the negative electrode interface, more fluorine-containing sulfonic acid salt participates in the film formation at the positive electrode. It can be understood that, in addition to participating in the film formation at the positive electrode interface, the fluorine-containing sulfonic acid salt can also penetrate into the positive electrode coating and participate in the film formation on the surface of the positive electrode material particles. That is, in the case where more fluorine-containing sulfonic acid salt participates in the film formation at the positive electrode, the fluorine-containing sulfonic acid salt is more likely to form a film on the surface of the positive electrode material particles in the positive electrode coating, which helps to improve the ion insertion and extraction kinetics in the positive electrode coating.

[0013] Optionally, the secondary battery satisfies at least one of the following conditions:

[0014] The mass percentage of the fluorine-containing sulfonic acid salt in the total mass of the electrolyte is x%, and the mass percentage of the fluorine-containing phosphoric acid salt in the total mass of the electrolyte is z%, and 0.01≤x / z≤10, preferably 0.05≤x / z≤5.

[0015] The percentage of the mass of the fluorine-containing phosphate salt in the total mass of the electrolyte is z%, 0.01≤z≤0.5, preferably 0.02≤z≤0.3;

[0016] The cation of the fluorine-containing phosphate salt comprises at least one of lithium, sodium, potassium, magnesium, calcium and barium.

[0017] The fluorine-containing phosphate salt comprises fluorine-containing lithium phosphate, and the fluorine-containing lithium phosphate comprises at least one of lithium difluorophosphate, lithium monofluorophosphate, lithium difluorophosphate bisoxalate and lithium tetrafluorophosphate oxalate.

[0018] In the present application, the percentage of the mass of the fluorine-containing sulfonate in the total mass of the electrolyte is x%, the percentage of the mass of the fluorine-containing phosphate salt in the total mass of the electrolyte is z%, and 0.01≤x / z≤10, preferably 0.05≤x / z≤5.

[0019] If x / z<0.01, i.e. the fluorine-containing sulfonate is relatively less and the fluorine-containing phosphate salt is relatively more, the positive electrode film formation is not enough, the side reaction between the positive electrode and the electrolyte occurs, and the cycle and the cycle DCR increase are deteriorated; in addition, the negative electrode film formation is too thick and the inorganic components are too many, the interface film is unstable, and the cycle performance is also not good.

[0020] If x / z>10, i.e. the fluorine-containing sulfonate is relatively more and the fluorine-containing phosphate salt is relatively less, the conductivity of the electrolyte is affected, which is reflected on the battery as the power is deteriorated.

[0021] Limiting the ratio of the two to the range of 0.01 to 10 can ensure that the influence on the battery power is minimal, while ensuring more excellent cycle life performance.

[0022] The percentage of the mass of the fluorine-containing phosphate salt in the total mass of the electrolyte is z%, 0.01≤z≤0.5, preferably 0.02≤z≤0.3; the fluorine-containing phosphate salt can participate in the formation of the interface film at the negative electrode interface, and the combination of the fluorine-containing sulfonate and the fluorine-containing phosphate salt can significantly improve the cycle performance of the battery. If the fluorine-containing phosphate salt is used too little, it is difficult to effectively further improve the cycle life. If the fluorine-containing phosphate salt is used too much, the inorganic components of the solid-state electrolyte interface film (SEI) formed are too many, and the inorganic matter generally has greater rigidity and no elasticity. During the cycle process, the negative electrode material continuously expands and shrinks, which may cause the SEI film to break, and thus is not conducive to the cycle.

[0023] The cation of the fluorine-containing phosphate salt comprises at least one of lithium, sodium, potassium, magnesium, calcium and barium.

[0024] The fluorine-containing phosphate salt comprises fluorine-containing lithium phosphate, and the fluorine-containing lithium phosphate comprises at least one of lithium difluorophosphate, lithium monofluorophosphate, lithium difluorophosphate bisoxalate and lithium tetrafluorophosphate oxalate.

[0025] Optionally, the secondary battery satisfies at least one of the following conditions:

[0026] The mass percentage of the fluorine-containing sulfonate in the total mass of the electrolyte is x%, and 0.003≤x≤0.15;

[0027] The mass percentage of the alkali metal ion in the total mass of the electrolyte is y%, and 0.001≤y≤0.1;

[0028] The cation of the fluorine-containing sulfonate comprises at least one of lithium, sodium, potassium, iron, aluminum, magnesium, calcium, barium and quaternary ammonium.

[0029] The fluorine-containing sulfonate comprises lithium-containing sulfonate, and the lithium-containing sulfonate comprises at least one of lithium fluorosulfonate, lithium triflate, lithium perfluorobutyl sulfonate, lithium perfluoro-n-octyl sulfonate and lithium 2,3-difluorobenzenesulfinate.

[0030] The alkali metal ion comprises at least one of sodium ion, potassium ion and calcium ion.

[0031] The anion of the alkali metal comprises at least one of PF6 — , FSI — , TFSI — , ClO4 — and BF4 — .

[0032] In the present application, the mass percentage of the fluorine-containing sulfonate in the total mass of the electrolyte is x%, and 0.003≤x≤0.15. It can be understood that if the fluorine-containing sulfonate is added too little, the effect is not obvious; if the fluorine-containing sulfonate is added too much, it will cause the viscosity of the electrolyte to increase, increase the ion migration resistance, worsen the conductivity, and be not conducive to the cycle performance.

[0033] In the present application, the mass percentage of the alkali metal ion in the total mass of the electrolyte is y%, and 0.001≤y≤0.1. Taking lithium ion battery as an example, the alkali metal ion takes sodium ion as an example, that is, the content of sodium ion should not be too high, y≤0.1, because the reduction potential of sodium ion is lower than that of lithium ion, and in the charging process, sodium ion will first be embedded in the graphite negative electrode, and high content of sodium ion will occupy the position of lithium ion embedded in the negative electrode, resulting in the decrease of reversible specific capacity of lithium battery, in addition, the precipitation of sodium ion will also cause the graphite electrode surface to be unable to form an effective passivation layer, and the battery performance will be worsened; at the same time, the content of sodium ion should not be too low, which is helpful for the embedding of sodium ion in the material layer of the positive electrode and the negative electrode, expanding the interlayer spacing and being conducive to the diffusion of lithium ion.

[0034] In the present application, the cation of the fluorine-containing sulfonate comprises at least one of lithium, sodium, potassium, iron, aluminum, magnesium, calcium, barium and quaternary ammonium.

[0035] In the present application, the fluorine-containing sulfonate includes at least one of lithium fluorosulfonate, lithium trifluoromethylsulfonate, lithium perfluorobutylsulfonate, lithium perfluoro-n-octylsulfonate, and lithium 2,3-difluorobenzenesulfinate.

[0036] In the present application, the alkali metal ion includes at least one of a sodium ion, a potassium ion, and a calcium ion.

[0037] In the present application, the anion of the alkali metal includes at least one of PF6 — , FSI — , TFSI — , ClO4 — , BF4 — .

[0038] Optionally, the secondary battery further includes a positive electrode tab, and the positive electrode tab includes a positive electrode active material, and the positive electrode active material includes a low-cobalt positive electrode material, and a structural formula of the low-cobalt positive electrode material is A a Ni b Co c M d N e O f B g , wherein 0.8≤a≤1.3, 0.2≤b≤0.96, 0.03≤c≤0.2, 0.01≤d≤0.6, 0≤e≤0.5, 0≤f≤2, 0≤g≤2, A includes Na or Li, M includes at least one of Mn and Al, N includes at least one of B, W, Si, Ti, Zr, Sr, Sn, Tb, Nb, Sb, Se, Ce, and Te, and B includes at least one of S, N, P, F, Cl, Br, and I.

[0039] It can be understood that, with the increasing requirements for capacity, cycle performance, and safety performance, the positive electrode material is undergoing iterative development of low-cobalt and cobalt-free. The traditional cobalt-free and low-cobalt material has low cobalt content, poor intrinsic conductivity of the material, high electrochemical impedance, high initial impedance in the charging and discharging cycle process, and often accompanied by phenomena such as DCR deterioration. That is, the low-cobalt positive electrode material is the trend of the times, which can reduce the cost and improve the energy density.

[0040] However, low cobalt has some problems. It is known that the cobalt content affects the kinetics of the positive electrode material. Taking a lithium ion battery as an example, on the one hand, the presence of cobalt can effectively inhibit Li / Ni cation mixing and stabilize the layered structure of the ternary positive electrode. With the decrease of the cobalt content, the threshold for the formation of Li / Ni mixing is lowered, and a series of movements such as migration, transport and diffusion of lithium ions in the lattice are restricted. On the other hand, the content of cobalt significantly affects the electrical conductivity of the material. The lower the cobalt content, the worse the electrical conductivity. Therefore, reducing the content of cobalt in the positive electrode material will worsen the kinetics of the material, increase the direct current resistance (DCR) growth rate during the charging and discharging cycle of the battery, and reduce the cycle stability.

[0041] To solve the above problems, a low-cobalt positive electrode material system is applied in the secondary battery of the present application. The above-mentioned secondary battery can improve the problem of battery cycle DCR growth caused by low cobalt and improve the cycle performance of the lithium secondary battery.

[0042] The above-mentioned secondary battery can further reduce the amount of cobalt in the positive electrode material without deteriorating the performance of the battery. Specifically, the positive electrode sheet includes a positive electrode active material, and the positive electrode active material includes a low-cobalt positive electrode material, and the structural formula of the low-cobalt positive electrode material is A a Ni b Co c M d N e O f B g , wherein 0.8≤a≤1.3, 0.2≤b≤0.96, 0.03≤c≤0.2, 0.01≤d≤0.6, 0≤e≤0.5, 0≤f≤2, 0≤g≤2, A includes Na or Li, M includes at least one of Mn and Al, N includes at least one of B, W, Si, Ti, Zr, Sr, Sn, Tb, Nb, Sb, Se, Ce and Te, and B includes at least one of S, N, P, F, Cl, Br and I.

[0043] Optionally, the compaction density of the positive electrode sheet is in the range of 3.0 g / cm 3 to 3.7 g / cm 3 .

[0044] It can be understood that too large or too small compaction density is not conducive to ion intercalation and deintercalation.

[0045] The compaction density of the positive electrode sheet should not be too large, because the larger the compaction density, the greater the degree of extrusion between the particles of the material, the smaller the porosity of the electrode sheet, the worse the performance of the electrode sheet in absorbing electrolyte, the more difficult the electrolyte is to infiltrate, the greater the ion transport resistance, the greater the polarization during the battery cycle, the greater the attenuation, and the more obvious the increase in internal resistance.

[0046] The compaction density of the positive electrode should not be too small, because the smaller the compaction density, the larger the distance between particles and the smaller the contact area between particles, which is not conducive to electronic conductivity, increases discharge polarization, and is also not conducive to battery cycle performance.

[0047] Using the compaction density range specified in this application facilitates the penetration of the electrolyte into the surface of the material particles inside the active layer, forming a low-resistance and stable film on the surface of the material particles, increasing the ion migration rate and reducing side reactions between the material and the electrolyte.

[0048] Optionally, the secondary battery satisfies at least one of the following conditions:

[0049] The mass m1 of the low-cobalt cathode material and the mass m2 of the electrolyte satisfy the following relationship: 15≤m1 / m2≤30;

[0050] The volume average particle size D50 of the low cobalt cathode material ranges from 2 μm to 6 μm.

[0051] The low-cobalt cathode material includes a single-crystal low-cobalt cathode material;

[0052] The positive electrode includes a current collector and a positive electrode coating disposed on at least one side of the current collector, wherein the thickness of the positive electrode coating ranges from 40 μm to 60 μm.

[0053] It is understandable that the mass m1 of the low-cobalt cathode material and the mass m2 of the electrolyte satisfy the above relationship. This helps to form an effective film layer on the surface of the low-cobalt cathode material, improve the problem of DCR growth in battery cycle caused by low cobalt, and improve the cycle performance of the secondary battery.

[0054] Understandably, under certain conditions, smaller particle size leads to better kinetics, but larger specific surface area results in more side reactions under high pressure. The volume average particle size D50 of low cobalt cathode materials meets the above range, which allows for a balance between battery cycle life and DCR growth.

[0055] Optionally, this application also provides an electrical device, which includes a secondary battery as described above.

[0056] The secondary battery disclosed in this application comprises active ions including A ions and an electrolyte including fluorosulfonates and alkali metal ions. The radius of the alkali metal ions is larger than that of the A ions, and the A ions include sodium ions or lithium ions. Fluorosulfonates improve the insertion and extraction kinetics of ions in the electrodes, protecting the electrode interface and inhibiting subsequent electrolyte decomposition. Alkali metal ions expand the interlayer spacing, facilitating the diffusion of A ions and reducing ion migration impedance. Simultaneously, the addition of alkali metal ions improves the interfacial stability between the electrolyte and the positive electrode material, reducing side reactions at the interface. Thus, using the secondary battery of this application, a low-impedance, structurally stable interfacial film can be formed on the positive and negative electrode surfaces, effectively suppressing interfacial side reactions and expanding the transport path of A ions. This alleviates the problem of increased DC internal resistance during battery cycling caused by side reactions between the positive electrode material and the electrolyte at the electrode interface, thereby improving the cycle performance of the secondary battery. Attached Figure Description

[0057] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the structures shown in these drawings without creative effort.

[0058] Figure 1 This is a schematic diagram of a battery cell according to one embodiment of this application;

[0059] Figure 2 yes Figure 1 An exploded view of a battery cell according to an embodiment of this application is shown.

[0060] Figure 3 This is a schematic diagram of a battery module according to one embodiment of this application;

[0061] Figure 4 This is a schematic diagram of a battery pack according to one embodiment of this application;

[0062] Figure 5 yes Figure 4 An exploded view of a battery pack according to an embodiment of this application is shown;

[0063] Figure 6 This is a schematic diagram of an electrical device in which a single battery cell is used as a power source according to one embodiment of this application.

[0064] Explanation of icon numbers:

[0065] Reference Name Reference Name 1 Battery pack 5 Battery cell 2 Upper case 51 Housing 3 Lower case 52 Electrode assembly 4 Battery module 53 Cover plate

[0066] The realization of the objective, functional features and advantages of the present invention will be further explained in conjunction with the embodiments and with reference to the accompanying drawings. Detailed Implementation

[0067] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0068] 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.

[0069] 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.

[0070] Unless otherwise specified, all embodiments and optional embodiments of this application can be combined to form new technical solutions.

[0071] Unless otherwise specified, all technical features and optional technical features of this application may be combined to form new technical solutions.

[0072] Unless otherwise specified, all steps in this application may be performed sequentially or randomly, preferably sequentially. For example, the method includes steps (a) and (b), indicating that the method may include steps (a) and (b) performed sequentially, or it may include steps (b) and (a) performed sequentially. For example, the mention that the method may also include step (c) indicates 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.

[0073] In recent years, secondary batteries have been widely used in energy storage power systems such as hydropower, thermal power, wind power and solar power plants, as well as in many fields such as power tools, electric bicycles, electric motorcycles, electric cars, military equipment, and aerospace.

[0074] The pursuit of high energy density and low cost, for example, the continuous increase in the cutoff voltage of lithium-ion batteries and the decreasing cobalt content in the cathode, leads to a decline in the stability of cathode materials. With the intercalation and deintercalation of lithium ions, the materials may collapse or break down. For instance, newly purchased electric vehicles often have good power performance and fast acceleration from 0 to 100 km / h. However, with the continuous charge and discharge cycles of the secondary battery, side reactions occur between the cathode and the electrolyte, resulting in the loss of active lithium in the cathode active material. During this process, the DC internal resistance (DCR) continuously increases, power performance deteriorates, and user experience is severely affected.

[0075] To address the aforementioned problems, this invention proposes a secondary battery. The active ions in the secondary battery include A ions, and the secondary battery includes an electrolyte containing fluorosulfonate and alkali metal ions. The radius of the alkali metal ions is larger than that of the A ions, and the A ions include sodium ions or lithium ions.

[0076] The performance of the electrolyte itself and the interface between it and the positive and negative electrodes greatly affect the performance of the battery. Choosing a suitable electrolyte can help protect the interface between the positive and negative electrodes, and the electrochemical performance of the battery, such as cycle performance, can be significantly improved.

[0077] The electrolyte includes fluorosulfonates, which, on the one hand, can improve the ion insertion and extraction kinetics in the electrode. Specifically, fluorosulfonates can provide SO bonds and S=O bonds. Taking lithium electrodes as an example, they can form lithium-sulfur oxide (Li₂S₂) rich in sulfide on the positive and negative electrode surfaces. x O y The interface film of ) to achieve rapid Li +Intercalation / extraction kinetics; on the other hand, it can protect the electrode interface. Specifically, taking the lithium electrode as an example, the fluoride ions and lithium ions in the fluorosulfonate have similar radii and strong binding energy. During the battery charging and discharging process, the fluoride ions and lithium ions combine and can uniformly deposit lithium fluoride that is insoluble in the electrolyte on the surface of the active material, further protecting the electrode interface and inhibiting the subsequent decomposition of the electrolyte.

[0078] Meanwhile, the electrolyte also includes alkali metal ions. The active ions in the secondary battery include A ions, which include sodium ions or lithium ions. The radius of the alkali metal ions is larger than that of the A ions. The secondary battery includes sodium-ion batteries or lithium-ion batteries. That is, when the electrolyte is used for sodium-ion batteries, the alkali metal ions include ions with a larger radius than sodium ions. When the electrolyte is used for lithium-ion batteries, the alkali metal ions include ions with a larger radius than lithium ions. This setting helps the alkali metal ions to embed into the material layers of the positive and negative electrodes, expands the interlayer spacing, and facilitates the diffusion of A ions, making the diffusion of A ions easier and reducing the ion migration resistance. At the same time, the addition of alkali metal ions can reduce the surface electrostatic potential, improve the interfacial stability between the electrolyte and the positive electrode material, and reduce side reactions at the interface.

[0079] Therefore, by adopting the solution of this application, an interface film with low impedance and stable structure can be formed on the positive and negative electrode surfaces, effectively suppressing interface side reactions and expanding the transport path of A ions, thereby improving the problem of increased DC internal resistance of the battery during cycling caused by side reactions between the positive electrode material and the electrolyte at the electrode interface, and improving the cycle performance of the secondary battery.

[0080] In one embodiment, the electrolyte further includes fluorinated phosphate.

[0081] Fluorophosphates (PO) x F y a- Fluorosulfonates and fluorinated phosphates can participate in film formation at the negative electrode interface. The combined use of fluorinated sulfonates and fluorinated phosphates can significantly improve the cycle performance of the battery. It is understandable that fluorinated sulfonates can participate in film formation at both the positive and negative electrode interfaces, while fluorinated phosphates preferentially participate in film formation at the negative electrode interface. In this case, fluorinated sulfonates and fluorinated phosphates compete for film formation at the negative electrode interface. Based on the preferential participation of fluorinated phosphates in film formation at the negative electrode interface, more fluorinated sulfonates participate in film formation at the positive electrode. It is understandable that, in addition to participating in film formation at the positive electrode interface, fluorinated sulfonates can also penetrate with the electrolyte into the positive electrode coating and participate in film formation on the surface of the positive electrode material particles. That is, with more fluorinated sulfonates participating in film formation on the positive electrode side, fluorinated sulfonates are more likely to form films on the surface of the positive electrode material particles inside the positive electrode coating, which helps improve the kinetics of ion insertion and extraction within the positive electrode coating.

[0082] In one embodiment, the secondary battery satisfies at least one of the following conditions: the mass percentage of fluorosulfonate in the total mass of the electrolyte is x%, and the mass percentage of fluorophosphate in the total mass of the electrolyte is z%, satisfying 0.01≤x / z≤10, preferably 0.05≤x / z≤5; the mass percentage of fluorophosphate in the total mass of the electrolyte is z%, 0.01≤z≤0.5, preferably 0.02≤z≤0.3; the cation of the fluorophosphate includes at least one of lithium, sodium, potassium, magnesium, calcium, and barium; the fluorophosphate includes lithium fluorophosphate, and lithium fluorophosphate includes at least one of lithium difluorophosphate, lithium monofluorophosphate, lithium difluorobis(oxalate)phosphate, and lithium tetrafluoro(oxalate)phosphate.

[0083] In this application, the percentage of the mass of fluorosulfonate to the total mass of the electrolyte is x%, and the percentage of the mass of fluorophosphate to the total mass of the electrolyte is z%, satisfying 0.01≤x / z≤10, preferably 0.05≤x / z≤5.

[0084] If x / z < 0.01, meaning there is relatively less fluorosulfonate and relatively more fluorophosphate, the positive electrode film protection is insufficient, which will lead to side reactions between the positive electrode and the electrolyte, worsening the cycle and increasing the cycle DCR. In addition, if the negative electrode film is too thick and contains too many inorganic components, the interfacial film will be unstable, which is also not conducive to cycle performance.

[0085] If x / z > 10, meaning there is a relatively high amount of fluorosulfonate and a relatively low amount of fluorophosphate, it will affect the conductivity of the electrolyte, which will result in a deterioration in the battery's power.

[0086] Limiting the ratio of the two to between 0.01 and 10 ensures minimal impact on battery power while guaranteeing superior cycle life performance.

[0087] In the above range of 0.01≤x / z≤10, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0.01, 0.02, 0.03, 0.04, 0.05, 0.08, 0.1, 0.3, 0.5, 0.8, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, etc., as well as the range values ​​between any two of the above point values.

[0088] In this application, the percentage of fluorinated phosphate in the total electrolyte mass is z%, 0.01≤z≤0.5, preferably 0.02≤z≤0.3. Fluorinated phosphate can participate in the formation of the interfacial film at the negative electrode interface. The combined use of fluorosulfonate and fluorinated phosphate can significantly improve the cycle performance of the battery. If too little fluorinated phosphate is used, it is difficult to effectively improve the cycle life. If too much fluorinated phosphate is used, the formed solid electrolyte interphase (SEI) film will have too much inorganic component. Inorganic materials are generally rigid and lack elasticity. During cycling, the continuous expansion and contraction of the negative electrode material may cause the SEI film to break, which is detrimental to cycling.

[0089] In the above 0.01≤z≤0.5, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0.01, 0.02, 0.03, 0.04, 0.05, 0.08, 0.1, 0.2, 0.3, 0.4, 0.5, etc., as well as the range values ​​between any two of the above point values.

[0090] The cations of the fluorinated phosphates in this application include at least one selected from lithium, sodium, potassium, magnesium, calcium, and barium. The fluorinated phosphates in this application include lithium fluorinated phosphate, which includes at least one selected from lithium difluorophosphate, lithium monofluorophosphate, lithium difluorobis(oxalato)phosphate, and lithium tetrafluoro(oxalato)phosphate.

[0091] In one embodiment, the secondary battery satisfies at least one of the following conditions: the mass percentage of fluorosulfonate to the total mass of the electrolyte is x%, 0.003≤x≤0.15; the mass percentage of alkali metal ions to the total mass of the electrolyte is y%, 0.001≤y≤0.1; the cation of the fluorosulfonate includes at least one of lithium, sodium, potassium, iron, aluminum, magnesium, calcium, barium, and quaternary ammonium; the fluorosulfonate includes lithium fluorosulfonate, which includes at least one of lithium fluorosulfonate, lithium trifluoromethylsulfonate, lithium perfluorobutylsulfonate, lithium perfluoron-octylsulfonate, and lithium 2,3-difluorobenzenesulfinate; the alkali metal ion includes at least one of sodium ion, potassium ion, and calcium ion; and the alkali metal anion includes PF6. — FSI — TFSI — ClO4 — BF4 — At least one of them.

[0092] In this application, the percentage of fluorosulfonate in the total mass of the electrolyte is x%, where 0.003 ≤ x ≤ 0.15. It is understood that if too little fluorosulfonate is added, the effect will be insignificant; if too much fluorosulfonate is added, the electrolyte viscosity will increase, increasing ion migration resistance, deteriorating conductivity, and negatively impacting cycle performance.

[0093] In the above range of 0.003≤x≤0.15, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0.003, 0.004, 0.005, 0.008, 0.01, 0.03, 0.05, 0.08, 0.1, 0.12, 0.13, 0.14, 0.15, etc., as well as the range values ​​between any two of the above point values.

[0094] In this application, the percentage of alkali metal ions in the total mass of the electrolyte is y%, 0.001≤y≤0.1. Taking lithium-ion batteries as an example, sodium ions are used as an example of alkali metal ions. That is, the sodium ion content should not be too high, y≤0.1, because sodium ions have a lower reduction potential than lithium ions. During charging, sodium ions will first embed into the graphite anode. A high sodium ion content will compete with lithium ions for embedding positions in the anode, leading to a decrease in the reversible specific capacity of the lithium battery. In addition, the precipitation of sodium ions will also prevent the formation of an effective passivation layer on the graphite electrode surface, deteriorating battery performance. At the same time, the sodium ion content should not be too low, as this helps sodium ions embed into the material layers of the positive and negative electrodes, expanding the interlayer spacing and facilitating the diffusion of lithium ions.

[0095] In the above 0.001≤y≤0.1, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0.001, 0.002, 0.003, 0.004, 0.005, 0.008, 0.01, 0.03, 0.05, 0.08, 0.09, 0.1, etc., as well as the range values ​​between any two of the above point values.

[0096] By controlling the amount of fluorosulfonate in the electrolyte and optimizing the content range of alkali metal ions in the electrolyte, the problem of DCR growth in low-cobalt cathode secondary batteries can be effectively improved.

[0097] In this application, the cation of the fluorosulfonate includes at least one of lithium, sodium, potassium, iron, aluminum, magnesium, calcium, barium, and quaternary ammonium.

[0098] In this application, fluorosulfonates include lithium fluorosulfonates, which include at least one of lithium fluorosulfonate, lithium trifluoromethyl sulfonate, lithium perfluorobutyl sulfonate, lithium perfluoron-octyl sulfonate, and lithium 2,3-difluorobenzenesulfinate.

[0099] In this application, the alkali metal ion includes at least one selected from sodium ions, potassium ions, and calcium ions. In this application, the alkali metal anion includes PF6. — FSI — TFSI —ClO4 — BF4 — At least one of them

[0100] In one embodiment, the secondary battery further includes a positive electrode sheet, which comprises a positive electrode active material, and the positive electrode active material comprises a low-cobalt positive electrode material, the low-cobalt positive electrode material having the structural formula A. a Ni b Co c M d N e O f B g Wherein, 0.8≤a≤1.3, 0.2≤b≤0.96, 0.03≤c≤0.2, 0.01≤d≤0.6, 0≤e≤0.5, 0≤f≤2, 0≤g≤2, A includes Na or Li, M includes at least one of Mn and Al, N includes at least one of B, W, Si, Ti, Zr, Sr, Sn, Tb, Nb, Sb, Se, Ce and Te, and B includes at least one of S, N, P, F, Cl, Br and I.

[0101] Understandably, with increasingly stringent requirements for capacity, cycle life, and safety performance, cathode materials are undergoing iterative development towards low-cobalt and cobalt-free technologies. Traditional cobalt-free and low-cobalt materials, due to their low cobalt content, exhibit poor intrinsic conductivity, high electrochemical impedance, and high initial impedance during charge-discharge cycles, often accompanied by deterioration in discharge coefficient (DCR). Therefore, low-cobalt cathode materials are the inevitable trend, as they can reduce costs and increase energy density.

[0102] However, low cobalt content presents several challenges. It's known that cobalt content affects the kinetics of cathode materials. Taking lithium-ion batteries as an example, on the one hand, the presence of cobalt effectively suppresses Li / Ni cation mixing and stabilizes the layered structure of the ternary cathode. Lowering the cobalt content reduces the threshold for Li / Ni mixing, thus restricting the migration, transport, and diffusion of lithium ions within the crystal lattice. On the other hand, cobalt content significantly impacts the material's conductivity; lower cobalt content results in poorer conductivity. Therefore, reducing the cobalt content in cathode materials will worsen material kinetics, increasing the rate of increase in DC resistance (DCR) during battery charge-discharge cycles and deteriorating cycle stability.

[0103] To address the aforementioned issues, a low-cobalt cathode material system is used in the secondary battery of this application. This secondary battery can mitigate the increase in DCR (discharge rate reduction) during battery cycling caused by low cobalt content, thereby improving the cycle performance of the secondary battery.

[0104] Using the above-mentioned secondary battery, the amount of cobalt in the positive electrode material can be further reduced without degrading battery performance. Specifically, the positive electrode sheet includes a positive electrode active material, which includes a low-cobalt positive electrode material. The structural formula of the low-cobalt positive electrode material is A.a Ni b Co c M d N e O f B g Wherein, 0.8≤a≤1.3, 0.2≤b≤0.96, 0.03≤c≤0.2, 0.01≤d≤0.6, 0≤e≤0.5, 0≤f≤2, 0≤g≤2, A includes Na or Li, M includes at least one of Mn and Al, N includes at least one of B, W, Si, Ti, Zr, Sr, Sn, Tb, Nb, Sb, Se, Ce and Te, and B includes at least one of S, N, P, F, Cl, Br and I.

[0105] In the above 0.8≤a≤1.3, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, as well as 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, etc., and the range values ​​between any two of the above point values.

[0106] In the above 0.2≤b≤0.96, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, as well as 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9, 0.96, etc., and the range values ​​between any two of the above point values.

[0107] In the above 0.03≤c≤0.2, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0.03, 0.05, 0.08, 0.09, 0.1, 0.11, 0.13, 0.15, 0.18, 0.2, etc., as well as the range values ​​between any two of the above point values.

[0108] In the above 0.01≤d≤0.6, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0.01, 0.02, 0.03, 0.05, 0.08, 0.09, 0.1, 0.11, 0.13, 0.15, 0.18, 0.2, 0.3, 0.4, 0.5, 0.6, etc., as well as the range values ​​between any two of the above point values.

[0109] In the above 0≤e≤0.5, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.008, 0.01, 0.03, 0.05, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, etc., as well as the range values ​​between any two of the above point values.

[0110] In the above, 0≤f≤2, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.008, 0.01, 0.03, 0.05, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.5, 1.8, 2, etc., as well as the range values ​​between any two of the above point values.

[0111] In the above 0≤g≤2, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 0, 0.001, 0.002, 0.003, 0.004, 0.005, 0.008, 0.01, 0.03, 0.05, 0.08, 0.09, 0.1, 0.2, 0.3, 0.4, 0.5, 0.8, 0.9, 1.0, 1.1, 1.2, 1.3, 1.5, 1.8, 2, etc., as well as the range values ​​between any two of the above point values.

[0112] In one embodiment, the compaction density of the positive electrode sheet is in the range of 3.0 g / cm³. 3 Up to 3.7 g / cm 3 .

[0113] Understandably, both excessively high and excessively low compaction densities are detrimental to the insertion and extraction of ions.

[0114] The compaction density of the positive electrode should not be too high, because the higher the compaction density, the greater the degree of compression between material particles, the smaller the porosity of the electrode, the worse the electrode's ability to absorb electrolyte, the more difficult it is for the electrolyte to wet, the greater the ion transport resistance, the greater the polarization during battery cycling, the greater the battery degradation, and the more significant the increase in internal resistance.

[0115] The compaction density of the positive electrode should not be too small, because the smaller the compaction density, the larger the distance between particles and the smaller the contact area between particles, which is not conducive to electronic conductivity, increases discharge polarization, and is also not conducive to battery cycle performance.

[0116] Using the compaction density range specified in this application facilitates the penetration of the electrolyte into the surface of the material particles inside the active layer, forming a low-resistance and stable film on the surface of the material particles, increasing the ion migration rate and reducing side reactions between the material and the electrolyte.

[0117] The above 3.0 g / cm 3 Up to 3.7 g / cm 3 In this context, the values ​​include the minimum and maximum values ​​within the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments and 3.0 g / cm³. 3 3.1g / cm 3 3.2g / cm 3 33g / cm 3 3.4g / cm 3 3.5g / cm 3 3.6g / cm 3 3.7g / cm 3 And so on, as well as the range of values ​​between any two of the above point values.

[0118] In one embodiment, the battery satisfies at least one of the following conditions: the mass m1 of the low-cobalt cathode material and the mass m2 of the electrolyte satisfy the relationship: 15≤m1 / m2≤30; the volume average particle size D50 of the low-cobalt cathode material ranges from 2μm to 6μm; the cathode electrode includes a current collector and a cathode coating disposed on at least one side of the current collector, the thickness of the cathode coating ranging from 40μm to 60μm.

[0119] D50 is the particle size at which the cumulative particle size distribution percentage of a sample reaches 50%. Physically, it means that 50% of the particles are larger than D50, and 50% are smaller. D50 is also called the median diameter or median particle size. D50 is often used to represent the average particle size of powders.

[0120] It is understandable that the mass m1 of the low-cobalt cathode material and the mass m2 of the electrolyte satisfy the above relationship. This helps to form an effective film layer on the surface of the low-cobalt cathode material, improve the problem of DCR growth in battery cycle caused by low cobalt, and improve the cycle performance of the secondary battery.

[0121] Understandably, under certain conditions, smaller particle size leads to better kinetics, but larger specific surface area results in more side reactions under high pressure. The volume average particle size D50 of low cobalt cathode materials meets the above range, which allows for a balance between battery cycle life and DCR growth.

[0122] In the above 15≤m1 / m2≤30, the values ​​include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, as well as 15, 16, 18, 20, 21, 23, 25, 28, 29, 30, etc., and the range values ​​between any two of the above point values.

[0123] The values ​​in the range of 2μm to 6μm include the minimum and maximum values ​​of the range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, as well as 2μm, 3μm, 4μm, 5μm, 6μm, etc., and the range values ​​between any two of the above point values.

[0124] The values ​​in the range of 40μm to 60μm include the minimum and maximum values ​​of this range, as well as every value between the minimum and maximum values. Specific examples include, but are not limited to, the point values ​​in the embodiments, and 40μm, 41μm, 43μm, 45μm, 48μm, 50μm, 51μm, 53μm, 55μm, 58μm, 60μm, etc., as well as the range values ​​between any two of the above point values.

[0125] In one embodiment, this application also provides an electrical device, which includes a secondary battery as described above.

[0126] Understandably, secondary batteries include individual battery cells, battery modules, and battery packs.

[0127] In addition, the following description of the battery (cell battery, battery module, battery pack) and electrical device of this application will be made with appropriate reference to the accompanying drawings.

[0128] In one embodiment of this application, a battery cell is provided.

[0129] Typically, a battery cell includes 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 of ions between the positive and negative electrodes. The separator, positioned between the positive and negative electrodes, primarily prevents short circuits between the electrodes while allowing ions to pass through. The separator described above is the improved separator of this application.

[0130] 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.

[0131] 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.

[0132] 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.).

[0133] In some embodiments, when the electrode assembly is a lithium-ion battery, the positive electrode active material may be a positive electrode active material known in the art for lithium-ion batteries. As an example, the positive electrode active material may include at least one of the following materials: lithium phosphates with an olivine structure, lithium transition metal oxides, and their respective modified compounds. However, this application is not limited to these materials, and other conventional materials that can be used as battery positive electrode active materials may also be used. These positive electrode active materials may be used alone or in combination of two or more. Examples of lithium transition metal oxides include, but are not limited to, lithium cobalt oxides (such as LiCoO2), lithium nickel oxides (such as LiNiO2), lithium manganese oxides (such as LiMnO2, LiMn2O4), lithium nickel cobalt oxides, lithium manganese cobalt oxides, lithium nickel manganese oxides, and lithium nickel cobalt manganese oxides (such as LiNi). 1 / 3 Co 1 / 3Mn 1 / 3 O2 (also known as NCM) 333 LiNi 0.5 Co 0.2 Mn 0.3 O2 (also known as NCM) 523 LiNi 0.5 Co 0.25 Mn 0.25 O2 (also known as NCM) 211 LiNi 0.6 Co 0.2 Mn 0.2 O2 (also known as NCM) 622 LiNi 0.8 Co 0.1 Mn 0.1 O2 (also known as NCM) 811 ), lithium nickel cobalt aluminum oxide (such as LiNi) 0.85 Co 0.15 Al 0.05At least one of O2 and its modified compounds. Examples of lithium phosphates with an olivine structure include, but are not limited to, lithium iron phosphate (such as LiFePO4 (also referred to as LFP)), lithium iron phosphate and carbon composites, lithium manganese phosphate (such as LiMnPO4), lithium manganese phosphate and carbon composites, lithium manganese iron phosphate, and lithium manganese iron phosphate and carbon composites.

[0134] During the charging and discharging process of a battery, Li undergoes insertion / extraction and consumption, resulting in varying molar Li content at different discharge states. In the examples of cathode materials in this application, the molar Li content refers to the initial state of the material, i.e., the state before feeding. When the cathode material is applied to the battery system, the molar Li content changes after charge-discharge cycles.

[0135] In the examples of cathode materials in this application, the molar content of O is only a theoretical value. Oxygen release from the crystal lattice will cause changes in the molar content of oxygen, and the actual molar content of O will fluctuate.

[0136] 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.

[0137] 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.

[0138] 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.

[0139] 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, the negative electrode film layer including a negative electrode active material.

[0140] 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.

[0141] 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.).

[0142] In some embodiments, the negative electrode active material may be a 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, 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.

[0143] 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).

[0144] 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.

[0145] In some embodiments, the negative electrode film may optionally include other additives, such as thickeners (e.g., sodium carboxymethyl cellulose (CMC-Na)).

[0146] In some embodiments, the negative electrode sheet can be prepared by dispersing the components used to prepare the negative electrode sheet, such as the negative electrode active material, conductive agent, binder and any other components, in a solvent (e.g., deionized water) to form a negative electrode slurry; coating the negative electrode slurry onto the negative electrode current collector, and then obtaining the negative electrode sheet after drying, cold pressing and other processes.

[0147] The electrolyte acts as a conductor of ions between the positive and negative electrodes. This application does not specify any particular type of electrolyte; it can be selected according to requirements.

[0148] In some embodiments, the electrolyte is an electrolyte solution. The electrolyte solution includes an electrolyte salt and a solvent.

[0149] In some embodiments, the solvent may be selected from at least one of ethylene carbonate, propylene carbonate, methyl ethyl carbonate, diethyl carbonate, dimethyl carbonate, dipropyl carbonate, methyl propyl carbonate, ethyl propyl carbonate, butyl carbonate, fluoroethylene carbonate, methyl formate, methyl acetate, ethyl acetate, propyl acetate, methyl propionate, ethyl propionate, propyl propionate, methyl butyrate, ethyl butyrate, 1,4-butyrolactone, sulfolane, dimethyl sulfone, methyl ethyl sulfone, and diethyl sulfone.

[0150] In some embodiments, the electrolyte may also include additives that can improve certain battery performance, such as additives that improve battery overcharge performance, additives that improve battery high-temperature or low-temperature performance, etc.

[0151] In some embodiments, the battery cell 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.

[0152] In some embodiments, the diaphragm material can be selected from at least one of glass fiber, nonwoven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The diaphragm can be a single-layer film or a multi-layer composite film, without particular limitation. When the diaphragm is a multi-layer composite film, the materials of each layer can be the same or different, without particular limitation.

[0153] In some implementations, the positive electrode, negative electrode, and separator can be fabricated into an electrode assembly using a winding or stacking process.

[0154] In some embodiments, the battery cell may include an outer packaging. This outer packaging can be used to encapsulate the electrode assembly and electrolyte described above.

[0155] In some embodiments, the outer packaging of the battery cell can be a rigid shell, such as a hard plastic shell, an aluminum shell, or a steel shell. The outer packaging of the battery cell can also be a flexible package, such as a pouch. The material of the flexible package can be plastic; examples of plastics include polypropylene, polybutylene terephthalate, and polybutylene succinate.

[0156] This application does not impose any particular limitation on the shape of the battery cell; it can be cylindrical, square, or any other arbitrary shape. For example, Figure 1 The example shown is a square-structured battery cell 5.

[0157] In some implementations, refer to Figure 2The outer packaging may include a housing 51 and a cover 53. The housing 51 may include a base plate and side plates connected to the base plate, the base plate and side plates forming a receiving cavity. The housing 51 has an opening communicating with the receiving cavity, and the cover 53 can be placed over the opening to close the receiving cavity. The positive electrode, negative electrode, 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. Electrolyte is immersed in the electrode assembly 52. ​​The number of electrode assemblies 52 contained in a single battery cell 5 may be one or more, which can be selected by those skilled in the art according to specific practical needs.

[0158] 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.

[0159] Figure 3 This is battery module 4, used as an example. (See reference...) Figure 3 In battery module 4, multiple battery cells 5 can be arranged sequentially along the length of battery module 4. Of course, they can also be arranged in any other manner. Furthermore, these multiple battery cells 5 can be fixed in place using fasteners.

[0160] Optionally, the battery module 4 may also include a housing with a receiving space in which multiple battery cells 5 are received.

[0161] 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.

[0162] Figure 4 and Figure 5 This is battery pack 1 as an example. (See reference...) Figure 4 and Figure 5 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 body 2 and a lower body 3, with the upper body 2 covering the lower body 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.

[0163] In addition, this application also provides an electrical device, which includes at least one of the battery cell, battery module, or battery pack provided in this application. The battery cell, battery module, or battery pack can be used as the power source of the electrical device or as the 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.

[0164] As an electrical device, you can choose individual battery cells, battery modules, or battery packs according to your usage requirements.

[0165] Figure 6 This is an example of an electrical device. The device could be a pure electric vehicle, a hybrid electric vehicle, or a plug-in hybrid electric vehicle. To meet the high power and high energy density requirements of individual battery cells, a battery pack or battery module can be used.

[0166] Another example device could be a mobile phone, tablet, or laptop. These devices typically require a slim and lightweight design and can use a single battery cell as their power source.

[0167] Example

[0168] Example 1

[0169] Electrolyte preparation:

[0170] In an argon-filled glove box (water content <10ppm, oxygen content <1ppm), ethylene carbonate and ethyl methyl carbonate (3:7V / V) are mixed evenly in a certain ratio. Then, an appropriate amount of LiPF6 is slowly added to a non-aqueous organic solvent. After the lithium salt is completely dissolved, a 1mol / L basic electrolyte is obtained.

[0171] The electrolyte is prepared by adding fluorosulfonate (lithium fluorosulfonate, with a content of 0.08% of the total mass of the electrolyte), alkali metal ions (NaPF6, with a sodium ion content of 0.005% of the total mass of the electrolyte), and fluorophosphate (lithium difluorophosphate, with a content of 0.2% of the total mass of the electrolyte) to the above-mentioned basic electrolyte and stirring it evenly.

[0172] Preparation of the positive electrode sheet:

[0173] The positive electrode active material (LiNi) 0.6 Co 0.12 Mn 0.28A positive electrode slurry was prepared in N-methylpyrrolidone (NMP) using O2 (with a D50 of 4 μm), conductive agent Super P, and binder polyvinylidene fluoride (PVDF). The solid content of the positive electrode slurry was 50 wt%, and the solid component consisted of LiNi. 0.6 Co 0.12 Mn 0.28 The mass ratio of O2, Super P, and PVDF is 8:1:1. The positive electrode slurry is coated onto the current collector aluminum foil and dried at 85℃, then cold-pressed. After edge trimming, cutting, and slitting, it is dried under vacuum at 85℃ for 4 hours to produce the positive electrode sheet. The single-sided coating thickness is 50μm, and the compaction density is 3.4g / cm³. 3 .

[0174] Preparation of negative electrode sheet:

[0175] Graphite, used as the negative electrode active material, a certain amount of silicon, and conductive agent Super P, thickener CMC, and binder styrene-butadiene rubber (SBR) are mixed evenly in deionized water to prepare a negative electrode slurry. The solid content of the negative electrode slurry is 30wt%, and the mass ratio of graphite, Super P, CMC, and binder styrene-butadiene rubber (SBR) in the solid components is 80:15:3:2. The negative electrode slurry is coated onto a current collector copper foil and dried at 85℃. Then, it is cold-pressed, trimmed, cut into sheets, and slit. Finally, it is dried under vacuum at 120℃ for 12 hours to prepare the negative electrode sheet.

[0176] Preparation of secondary batteries (lithium-ion batteries):

[0177] A 16μm polyethylene film (PE) is used as the separator. The prepared positive electrode, separator, and negative electrode are stacked in sequence, with the separator positioned between the positive and negative electrodes to isolate them. The cells are then wound to obtain a bare cell, tabs are welded on, and the bare cell is placed in an outer package. The electrolyte prepared above is injected into the dried cell, followed by encapsulation, settling, formation, shaping, and capacity testing to complete the preparation of the lithium-ion battery (the thickness of the soft-pack lithium-ion battery is 4.0mm, the width is 60mm, and the length is 140mm).

[0178] Examples 2 to 17

[0179] Based on Example 1, the content c of cobalt in the positive electrode material, the content and type of fluorosulfonate in the electrolyte, the content of sodium alkali metal ions, the compaction density of the positive electrode sheet, and the type and content of fluorophosphate in the electrolyte were adjusted to obtain Examples 2 to 17 in Table 1.

[0180] Comparative Examples 1 to 3

[0181] Comparative Example 1 was prepared without adding fluorosulfonate and alkali metal sodium ions, as shown in Table 1.

[0182] Comparative Example 2 was prepared without the addition of alkali metal sodium ions, as shown in Table 1.

[0183] Comparative Example 3 was prepared without the addition of fluorosulfonate, as shown in Table 1.

[0184] Performance testing

[0185] Electrolyte composition testing:

[0186] Solvents and additives can be determined by gas chromatography (GC), with quantitative analysis of composition and content based on standard GB / T9722-2006. Electrolyte salts can be quantitatively analyzed by ion chromatography (IC) based on standard JY / T020-1996 to determine the concentration of inorganic components / lithium salts in the electrolyte. Sodium ion content can be quantitatively analyzed by inductively coupled plasma atomic emission spectrometry (ICP) based on standard EPA 6010D-2018.

[0187] Electrode compaction density (PD) test:

[0188] Parameter definition: Mass per unit area of ​​material with a specified thickness.

[0189] Test method: The compaction density (PD) of the negative electrode film is determined by measuring the mass of the negative electrode film per unit area (g / cm³). 2 The density of the negative electrode (PD) is determined by the negative electrode thickness (cm) (number of sampling points > 14). The compaction density of the negative electrode is PD = mass of the negative electrode per unit area (g / cm³). 2 ) / Negative electrode thickness (cm).

[0190] Testing of the cycle capacity retention rate and cycle DCR growth rate of individual battery cells:

[0191] At 45℃, charge the battery cell at a constant current of 0.33C to 4.4V, then charge it at a constant voltage of 4.4V to a current of 0.05C, then discharge it at 0.5C for 1 hour, and discharge it at a current of 4C for 30s. Record the initial voltage V1 at the start of discharge and the voltage V2 after 30s of discharge. The initial DCR = (V1-V2) / I1, where I1 is the current corresponding to 4C.

[0192] Then, the battery cell is charged at a constant current of 0.5C to 4.4V, then charged at a constant voltage of 4.4V to the cutoff current of 0.05C, and then discharged at a constant current of 1C to 2.8V. This constitutes one charge-discharge cycle. The discharge capacity of this cycle is recorded as the discharge capacity of the lithium-ion battery cell in the first cycle. This cycle is repeated for the same battery cell. After 1000 cycles, the discharge capacity of the 1000th cycle is recorded.

[0193] Then, the battery cells were charged at a constant current of 0.33C to 4.4V, then charged at a constant voltage of 4.4V to a current of 0.05C, then discharged at 0.5C for 1 hour, and discharged at a current of 4C for 30 seconds. The initial voltage V3 at the start of discharge and the voltage V4 after 30 seconds of discharge were recorded. The DCR of the 1000th cycle was calculated as (V3-V4) / I2, where I2 is the current corresponding to 4C.

[0194] Cyclic DCR growth rate (%) = (DCR of the 1000th cycle - Initial DCR) / Initial DCR × 100%. Capacity retention rate of a lithium-ion battery cell after 1000 cycles at 45℃ and 0.5C / 1C = Discharge capacity of the 1000th cycle / Discharge capacity of the 1st cycle × 100%.

[0195] Table 1 List of Examples

[0196]

[0197]

[0198]

[0199] Table 2 Performance List

[0200]

[0201]

[0202] As can be seen from the test results in Tables 1 and 2, DCR (Direct Current Resistance) represents the DC resistance. Compared with the cycle DCR growth rate and cycle capacity retention rate obtained from Comparative Examples 1 to 3, the overall performance of Examples 1 to 17 is improved. This indicates that using the secondary battery of this application can reduce the DC resistance of the secondary battery, resulting in a secondary battery with better cycle performance.

[0203] The above are merely preferred embodiments of the present invention and do not limit the scope of the patent. Any equivalent structural transformations made using the contents of the specification and drawings of the present invention under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the scope of patent protection of the present invention.

Claims

1. A secondary battery characterized by comprising: The active ion of the secondary battery includes an A ion, the secondary battery includes an electrolyte, the electrolyte includes a fluorine-containing sulfonate and an alkali metal ion, the alkali metal ion has a radius greater than that of the A ion, and the A ion includes a sodium ion or a lithium ion.

2. The secondary battery according to claim 1, wherein The electrolyte further includes a fluorine-containing phosphate.

3. The secondary battery according to claim 2, wherein At least one of the following conditions is satisfied: A percentage value of a mass of the fluorine-containing sulfonate with respect to a total mass of the electrolyte is x%, and a percentage value of a mass of the fluorine-containing phosphate with respect to the total mass of the electrolyte is z%, and 0.01≤x / z≤10, preferably 0.05≤x / z≤5 is satisfied; A percentage value of a mass of the fluorine-containing phosphate with respect to a total mass of the electrolyte is z%, and 0.01≤z≤0.5, preferably 0.02≤z≤0.3 is satisfied; A cation of the fluorine-containing phosphate includes at least one of lithium, sodium, potassium, magnesium, calcium, and barium; The fluorine-containing phosphate includes lithium fluorophosphate, and the lithium fluorophosphate includes at least one of lithium difluorophosphate, lithium monofluorophosphate, lithium difluorobisoxalate phosphate, and lithium tetrafluorooxalate phosphate.

4. The secondary battery according to any one of claims 1 to 3, wherein At least one of the following conditions is satisfied: A percentage value of a mass of the fluorine-containing sulfonate with respect to a total mass of the electrolyte is x%, and 0.003≤x≤0.15 is satisfied; A percentage value of a mass of the alkali metal ion with respect to a total mass of the electrolyte is y%, and 0.001≤y≤0.1 is satisfied; A cation of the fluorine-containing sulfonate includes at least one of lithium, sodium, potassium, iron, aluminum, magnesium, calcium, barium, and quaternary ammonium; The fluorine-containing sulfonate includes lithium fluorosulfonate, and the lithium fluorosulfonate includes at least one of lithium fluorosulfonate, lithium trifluoromethylsulfonate, lithium perfluorobutylsulfonate, lithium perfluoro-n-octylsulfonate, and lithium 2,3-difluorobenzenesulfinate; The alkali metal ion includes at least one of a sodium ion, a potassium ion, and a calcium ion. The anion of the alkali metal comprises at least one of PF6 — , FSI — , TFSI — , CIO4 — , BF4 — .

5. The secondary battery according to any one of claims 1 to 4, wherein The secondary battery further includes a positive electrode tab including a positive electrode active material, the positive electrode active material including a low-cobalt positive electrode material, the low-cobalt positive electrode material having a structural formula of A a Ni b Co c M d N e O f B g wherein 0.8≤a≤1.3, 0.2≤b≤0.96, 0.03≤c≤0.2, 0.01≤d≤0.6, 0≤e≤0.5, 0≤f≤2, 0≤g≤2, A includes Na or Li, M includes at least one of Mn and Al, N includes at least one of B, W, Si, Ti, Zr, Sr, Sn, Tb, Nb, Sb, Se, Ce and Te, and B includes at least one of S, N, P, F, Cl, Br and I.

6. The secondary battery according to any one of claims 1 to 5, wherein The compacted density of the positive electrode plate ranges from 3.0 g / cm 3 to 3.7 g / cm 3 .

7. The secondary battery according to any one of claims 1 to 6, wherein At least one of the following conditions is satisfied: A mass m1 of the low-cobalt positive electrode material and a mass m2 of the electrolyte satisfy a relationship: 15≤m1 / m2≤30; A volume average particle size D50 of the low-cobalt positive electrode material ranges from 2 μm to 6 μm; The low-cobalt positive electrode material includes a single-crystal low-cobalt positive electrode material; The positive electrode sheet includes a current collector and a positive electrode coating layer disposed on at least one side of the current collector, and a thickness of the positive electrode coating layer ranges from 40 μm to 60 μm.

8. An electrical device, characterized by The power consumption device includes the secondary battery according to any one of claims 1 to 7.

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