Lithium-ion battery and electric device

Abstract

A lithium-ion battery and an electric device. The lithium-ion battery comprises a positive electrode sheet and an electrolyte. An active material in the positive electrode sheet comprises a lithium phosphate positive electrode material and lithium nickel cobalt manganese oxide. The electrolyte comprises a positive electrode film-forming agent, a negative electrode film-forming agent and a lithium salt, wherein the lithium salt includes lithium hexafluorophosphate and lithium bisfluorosulfonylimide. The lithium-ion battery satisfies the following equation: 0.1≤(I)≤0.59, where NL is the mass ratio of lithium nickel cobalt manganese oxide to the lithium phosphate positive electrode material, Salt is the numerical value of the sum of the molar concentrations of lithium hexafluorophosphate and lithium bisfluorosulfonylimide in the electrolyte with the unit being mol / L, and Add is the mass ratio of the positive electrode film-forming agent to the negative electrode film-forming agent.

Description

Lithium-ion batteries and electrical equipment

[0001] This application claims priority to Chinese Patent Application No. 202411629583.4, filed on November 14, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of battery technology, specifically to a lithium-ion battery and an electrical device. Background Technology

[0003] As people's demands for environmental protection and energy conservation increase, the upgrading of power battery materials is becoming increasingly urgent. New materials combining ternary materials with lithium manganese iron phosphate (LFP) or vice versa will become an important future development direction. The advantages of these materials are mainly reflected in their higher energy density compared to pure LFP or pure LFP, and their higher safety and lower cost compared to pure ternary materials. As the blending ratio of ternary materials increases, the rate performance and energy density of the battery improve further. Invention Overview

[0004] However, this setup negatively impacts the battery's cycle performance.

[0005] This application provides a lithium-ion battery comprising a positive electrode and an electrolyte. The active material in the positive electrode comprises lithium phosphate positive electrode material and lithium nickel cobalt manganese oxide. The electrolyte comprises a positive electrode film-forming agent, a negative electrode film-forming agent, and a lithium salt. The lithium salt comprises lithium hexafluorophosphate and lithium difluorosulfonylimide salt. The lithium-ion battery satisfies the following formula:

[0006] 0.1≤ ≤0.59, where NL is the mass ratio of the nickel-cobalt-manganese oxide lithium to the lithium phosphate cathode material, and S alt A is the sum of the molar concentrations of the lithium hexafluorophosphate and the lithium difluorosulfonylimide salt in the electrolyte, expressed in mol / L. dd The mass ratio of the positive electrode film-forming agent to the negative electrode film-forming agent.

[0007] This application also provides an electrical device that includes the aforementioned lithium-ion battery. Beneficial effects

[0008] The lithium-ion battery provided in this application improves the cycle performance of the battery by controlling the relationship between the mass ratio of lithium phosphate cathode material and lithium nickel cobalt manganese oxide, the molar concentration of lithium hexafluorophosphate and lithium difluorosulfonylimide in the electrolyte, and the mass ratio of cathode film-forming agent to anode film-forming agent. This allows for the adjustment of the ratio of cathode and anode film-forming agents and the ratio of high-heat-resistant lithium salts based on the mixing ratio of lithium manganese iron phosphate or lithium iron phosphate when doping with ternary materials. Embodiments of the present invention

[0009] As the proportion of ternary materials in lithium manganese iron phosphate and / or lithium iron phosphate increases, the rate performance and energy density of the battery improve, but this also has an adverse impact on the battery's safety performance.

[0010] The technical solution of this application is as follows:

[0011] In a first aspect, embodiments of this application provide a lithium-ion battery, including a positive electrode and an electrolyte. The active material in the positive electrode includes lithium phosphate positive electrode material and lithium nickel cobalt manganese oxide (NCM). The electrolyte includes a positive electrode film-forming agent, a negative electrode film-forming agent, and a lithium salt. The lithium salt includes lithium hexafluorophosphate (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI). The lithium-ion battery satisfies the following formula:

[0012] 0.1≤ ≤0.59, where NL is the mass ratio of lithium nickel cobalt manganese oxide to lithium phosphate cathode material, and S alt A represents the sum of the molar concentrations of lithium hexafluorophosphate and lithium difluorosulfonylimide in the electrolyte, expressed in mol / L. dd This is the mass ratio of the positive electrode film-forming agent to the negative electrode film-forming agent.

[0013] In this application, by controlling the relationship between the mass ratio of lithium phosphate cathode material and lithium nickel cobalt manganese oxide, the molar concentrations of lithium hexafluorophosphate and lithium difluorosulfonyl imide salt in the electrolyte, and the mass ratio of cathode film-forming agent to anode film-forming agent in a lithium-ion battery, the ratio of cathode and anode film-forming agents and the ratio of high-heat-resistant lithium salt can be adjusted according to the mixing ratio of the two materials when doping ternary materials into lithium phosphate cathode material. This improves both the rate performance and energy density of the battery, as well as its cycle performance. A higher mixing ratio of lithium nickel cobalt manganese oxide in the cathode sheet (i.e., a larger NL) allows for a reduction in the anode film-forming agent and an increase in the cathode film-forming agent, thus increasing A. dd This solves the problem that NCM has poorer thermal stability than lithium phosphate cathode materials, and at the same time can reduce the lithium salt concentration, as high-concentration lithium salt is more likely to cause thermal runaway than low-concentration lithium salt.

[0014] The concentrations of lithium hexafluorophosphate and lithium difluorosulfonylimide in the electrolyte refer to the sum of their concentrations in the electrolyte before formation at the time of battery filling. The mass ratio of the positive electrode film-forming agent to the negative electrode film-forming agent refers to the mass ratio of the positive electrode film-forming agent to the negative electrode film-forming agent in the electrolyte before formation at the time of battery filling. 0.1 ≤ ≤0.59, The values ​​can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.59, etc.

[0015] In some embodiments, the lithium-ion battery satisfies: 0.1 ≤ ≤0.57, The values ​​can be 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.57, etc.

[0016] In some embodiments, the lithium phosphate cathode material includes one or more of lithium manganese iron phosphate and lithium iron phosphate.

[0017] In some embodiments, NL is 0.05~0.43, for example, it can be 0.05, 0.1, 0.15, 0.2, 0.25, 0.3, 0.35, 0.4, 0.43, etc. This can improve the battery's energy density and rate performance while ensuring battery safety and long-cycle performance. Adding lithium nickel cobalt manganese oxide (NCM) to lithium manganese iron phosphate and / or lithium iron phosphate can have varying effects. Excessive NCM addition can negatively impact battery safety, while insufficient NCM addition results in only a small increase in energy density and rate performance.

[0018] In some embodiments, NL is 0.1 to 0.3, for example, it can be 0.1, 0.12, 0.15, 0.17, 0.2, 0.22, 0.25, 0.27, 0.3, etc.

[0019] In some embodiments, NL and A dd Satisfy: A dd =a·NL-0.588, where a is 7.1~13.8, for example, it can be 7.1, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5, 12.0, 12.5, 13.0, 13.5, 13.8, etc. Thus, the larger NL is, the more lithium nickel cobalt manganese oxide (NCM) content there is in the positive electrode, and the less lithium manganese iron phosphate and / or lithium iron phosphate content there is, the corresponding A... ddThe larger the concentration of the positive electrode film-forming agent, the more active agent is added to the electrolyte, and the less active agent is added to the negative electrode. This allows the amount of active agent added to increase with the increase of the nickel-cobalt-manganese (NCM) oxide content, while the amount of active agent added to decrease with the decrease of the lithium manganese iron phosphate and / or lithium iron phosphate content. This strengthens the protection of the positive electrode and controls the thickness of the negative electrode film, thereby controlling the battery impedance. If the content of lithium manganese iron phosphate and / or lithium iron phosphate decreases, but the amount of active agent added to the negative electrode remains the same, the active agent will be excessive, resulting in a thicker negative electrode film and increased impedance.

[0020] In some embodiments, a is 7.35 to 8.66, for example, it can be 7.4, 7.5, 7.6, 7.7, 7.8, 7.9, 8.0, 8.1, 8.2, 8.3, 8.4, 8.5, 8.6, etc.

[0021] In some embodiments, A dd The value can range from 0.1 to 3.1, for example, 0.1, 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.1, etc. This provides protection for both the positive and negative electrodes. For example, A... dd If it is too small, the protection effect on the positive electrode will be insufficient, such as A. dd If the diameter is too large, it will not provide sufficient protection for the negative electrode, and the unstable film formation of the positive and negative electrodes will deteriorate the cycle performance of the battery.

[0022] In some embodiments, A dd The value can be between 0.3 and 2.0, for example, it can be 0.3, 0.5, 0.7, 1.0, 1.2, 1.5, 1.7, 2.0, etc.

[0023] In some embodiments, the mass percentage of the positive electrode film-forming agent in the electrolyte is 0.2% to 2.5%, for example, it can be 0.2%, 0.5%, 0.7%, 1%, 1.2%, 1.5%, 1.7%, 2%, 2.2%, 2.5%, etc. This provides sufficient protection for the positive electrode.

[0024] In some embodiments, the mass percentage of the positive electrode film-forming agent in the electrolyte is 0.5% to 2.0%, for example, it can be 0.5%, 0.7%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2.0%, etc. This provides sufficient protection for the positive electrode.

[0025] In some embodiments, the mass percentage of the negative electrode film-forming agent in the electrolyte is 0.8% to 2.0%, for example, it can be 0.8%, 0.9%, 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, 1.9%, 2.0%, etc. This provides sufficient protection for the negative electrode.

[0026] In some embodiments, the mass percentage of the negative electrode film-forming agent in the electrolyte is 1.0% to 1.8%, for example, it can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, etc.

[0027] In some embodiments, the positive electrode film-forming agent includes one or more of 1,3-propanesulfonate lactone (PS), lithium difluorooxalate borate (LiDFOB), lithium bis(oxalate)borate (LiBOB), tris(trimethylsilane)phosphite (TMSP), methane disulfonate methylene ester (MMDS), tris(trimethylsilane)borate ester (TMSB), and hexanetricarbonyl (HTCN). This allows for the effective formation of a cathode electrolyte interphase (CEI) film on the surface of the positive electrode, covering the active sites, reducing the contact between the electrolyte and the electrode, minimizing the decomposition of the electrolyte and positive electrode material in high-potential regions, maintaining the stability of the positive electrode material, and improving battery capacity and cycle performance.

[0028] In some embodiments, the negative electrode film-forming agent includes one or more of vinylene carbonate (VC), fluoroethylene carbonate (FEC), lithium difluorophosphate (LiPO2F2), lithium tetrafluoroborate (LiBF4), and vinyl sulfate (DTD). This allows a stable solid electrolyte interface (SEI) film to be formed on the surface of the negative electrode, providing excellent electronic insulation, allowing only lithium ions to pass through, and preventing further reaction between the electrolyte and the electrode material. This protects the electrode material, extends the battery's cycle life, and improves battery safety.

[0029] In some embodiments, NL and S alt Satisfy: S alt =b·NL+1.124, where b is -0.750 to -0.456, for example, -0.456, -0.500, -0.550, -0.600, -0.650, -0.700, -0.750, etc. Thus, the larger NL is, the higher the content of lithium nickel cobalt manganese oxide (NCM) in the positive electrode, and the lower the content of lithium manganese iron phosphate and / or lithium iron phosphate, the lower the corresponding S. alt A lower total lithium salt concentration improves battery thermal stability and thus enhances battery safety. High lithium salt concentrations can cause thermal runaway, leading to a drop in battery temperature; therefore, controlling the lithium salt concentration is crucial.

[0030] In some embodiments, b is -0.639 to -0.690, for example, it can be -0.639, -0.640, -0.640, -0.650, -0.660, -0.670, -0.680, -0.690, etc.

[0031] In some embodiments, S alt The concentration can be between 0.85 and 1.10, for example, 0.85, 0.87, 0.90, 0.92, 0.95, 0.97, 1.00, 1.02, 1.05, 1.07, 1.10, etc. This allows control over the lithium salt concentration in the electrolyte, thereby reducing the probability of thermal runaway caused by high lithium salt concentrations and improving battery safety.

[0032] In some embodiments, S alt The value can be between 0.90 and 1.05, for example, it can be 0.90, 0.91, 0.92, 0.93, 0.94, 0.95, 0.96, 0.97, 0.98, 0.99, 1.00, 1.01, 1.02, 1.03, 1.04, 1.05, etc.

[0033] In some embodiments, the molar ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the electrolyte decreases as NL increases. Thus, a higher NL, meaning a higher content of lithium nickel cobalt manganese oxide (NCM) and a lower content of lithium manganese iron phosphate and / or lithium iron phosphate in the positive electrode, increases the proportion of LiFSI in the lithium salt and decreases the proportion of LiPF6, thereby improving the battery's thermal stability and safety. Increased NCM content in the battery decreases its thermal stability; LiFSI has better thermal stability than LiPF6, so increasing the proportion of LiFSI can improve the battery's thermal stability.

[0034] In some embodiments, the molar ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the electrolyte is 0.7 to 3.4, for example, it can be 0.7, 1.0, 1.2, 1.5, 1.7, 2.0, 2.2, 2.5, 2.7, 3.0, 3.4, etc.

[0035] In some embodiments, the concentration ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the electrolyte is 1.0 to 2.5, for example, it can be 1.0, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, 1.7, 1.8, 1.9, 2.0, 2.1, 2.2, 2.3, 2.4, 2.5, etc.

[0036] In some embodiments, the concentration of lithium hexafluorophosphate in the electrolyte is 0.35 mol / L to 0.85 mol / L, for example, 0.35 mol / L, 0.45 mol / L, 0.55 mol / L, 0.65 mol / L, 0.75 mol / L, 0.85 mol / L, etc. This allows LiPF6 to passivate the aluminum foil, reducing the corrosion of the aluminum foil by LiFSI, and simultaneously reducing the probability of LiPF6 hydrolyzing to generate HF, thereby improving the stability of the battery.

[0037] In some embodiments, the concentration of lithium hexafluorophosphate in the electrolyte is 0.45 mol / L to 0.75 mol / L, for example, it can be 0.45 mol / L, 0.50 mol / L, 0.55 mol / L, 0.60 mol / L, 0.65 mol / L, 0.70 mol / L, 0.75 mol / L, etc.

[0038] In some embodiments, the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.25 mol / L to 0.50 mol / L, for example, 0.25 mol / L, 0.3 mol / L, 0.35 mol / L, 0.4 mol / L, 0.45 mol / L, 0.5 mol / L, etc. This allows for control of LiFSI corrosion of the aluminum foil, improving battery cycle performance, and simultaneously enhancing the stability and conductivity of the electrolyte.

[0039] In some embodiments, the concentration of lithium bis(fluorosulfonyl)imide in the electrolyte is 0.30 mol / L to 0.45 mol / L, for example, it can be 0.30 mol / L, 0.31 mol / L, 0.32 mol / L, 0.33 mol / L, 0.34 mol / L, 0.35 mol / L, 0.36 mol / L, 0.37 mol / L, 0.38 mol / L, 0.39 mol / L, 0.40 mol / L, 0.41 mol / L, 0.42 mol / L, 0.43 mol / L, 0.44 mol / L, 0.45 mol / L, etc.

[0040] In some embodiments, the areal density of the positive electrode sheet on one side is 200 g / m². 2 ~260g / m 2 For example, it can be 200g / m 2 210g / m 2 220g / m 2 230g / m 2 240g / m 2 250g / m 2 260g / m 2This allows the battery to have a high energy density, but excessive areal density can affect lithium-ion transport, increase battery impedance, and deteriorate battery cycle performance.

[0041] In some embodiments, the areal density of the positive electrode sheet on one side is 210 g / m². 2 ~250g / m 2 For example, it can be 210g / m 2 220g / m 2 230g / m 2 240g / m 2 250g / m 2 wait.

[0042] In some embodiments, the compaction density of the positive electrode sheet is 2.0 g / cm³. 3 ~2.6g / cm 3 For example, it can be 2.0 g / cm³. 3 2.1g / cm 3 2.2g / cm 3 2.3g / cm 3 2.4g / cm 3 2.5g / cm 3 2.6g / cm 3 This can result in a battery with a high energy density, but excessive compaction can crush the particles and destroy the effectiveness of the active materials.

[0043] In some embodiments, the compaction density of the positive electrode sheet is 2.1 g / cm³. 3 ~2.5g / cm 3 For example, it can be 2.1 g / cm³. 3 2.2g / cm 3 2.3g / cm 3 2.4g / cm 3 2.5g / cm 3 wait.

[0044] In some embodiments, the electrolyte injection ratio of the lithium-ion battery is 3.0 g / Ah to 5.0 g / Ah, for example, 3.0 g / Ah, 3.2 g / Ah, 3.5 g / Ah, 3.8 g / Ah, 4.0 g / Ah, 4.2 g / Ah, 4.5 g / Ah, 4.8 g / Ah, 5.0 g / Ah, etc. This can improve battery performance. Too much electrolyte will lead to more side reactions and increase battery cost, while too little electrolyte will lead to insufficient electrode wetting, increased interfacial impedance, and deterioration of battery cycle performance.

[0045] In some embodiments, the electrolyte injection coefficient of the lithium-ion battery is 3.5 g / Ah to 4.5 g / Ah, for example, it can be 3.5 g / Ah, 3.6 g / Ah, 3.7 g / Ah, 3.8 g / Ah, 3.9 g / Ah, 4.0 g / Ah, 4.1 g / Ah, 4.2 g / Ah, 4.3 g / Ah, 4.4 g / Ah, 4.5 g / Ah, etc.

[0046] In some embodiments, the lithium-ion battery further includes a negative electrode, the active material of which is graphite. This can improve battery performance. Graphite is low in cost and has high specific energy, good chemical stability, and long cycle life.

[0047] In some embodiments, the areal density of the negative electrode sheet on one side is 80 g / m². 2 ~110g / m 2 For example, it can be 80g / m 2 90g / m 2 100g / m 2 110g / m 2 This allows the battery to have a high energy density, but excessive areal density can affect lithium-ion transport, increase battery impedance, and deteriorate battery cycle performance.

[0048] In some embodiments, the compaction density of the negative electrode sheet is 1.55 g / cm³. 3 ~1.75g / cm 3 For example, it can be 1.55 g / cm³. 3 1.57g / cm 3 1.6g / cm 3 1.62g / cm 3 1.65g / cm 3 1.67 g / cm 3 1.7g / cm 3 1.72g / cm 3 1.75g / cm 3 This can result in a battery with a high energy density, but excessive compaction can crush the particles and destroy the effectiveness of the active materials.

[0049] This application also provides an electrical device, including the lithium-ion battery described above.

[0050] Example 1

[0051] A lithium-ion battery (a soft-pack battery of model 505070) wherein the active material in the positive electrode is lithium manganese iron phosphate and lithium nickel cobalt manganese oxide (NCM), and the mass ratio (NL) of lithium nickel cobalt manganese oxide to lithium manganese iron phosphate is 0.25%; the positive electrode film-forming agent is methylene disulfonate (MMDS), whose mass percentage in the electrolyte before formation is 1.5%; the negative electrode film-forming agent is vinylene carbonate (VC), whose mass percentage in the electrolyte before formation is 1.2%; the concentration of lithium hexafluorophosphate (LiPF6) in the electrolyte is 0.55 mol / L; and the concentration of lithium difluorosulfonyl imide (LiFSI) in the electrolyte is 0.4 mol / L.

[0052] Example 2

[0053] This embodiment is basically the same as Embodiment 1, except that the mass ratio (NL) of lithium nickel cobalt manganese oxide and lithium manganese iron phosphate in this embodiment is 0.17%, the mass percentage of the positive electrode film-forming agent is 1.0%, the mass percentage of the negative electrode film-forming agent is 1.5%, the concentration of lithium hexafluorophosphate (LiPF6) is 0.65 mol / L, and the concentration of lithium difluorosulfonyl imide (LiFSI) is 0.35 mol / L.

[0054] Example 3

[0055] This embodiment is basically the same as Embodiment 1, except that the mass ratio (NL) of lithium nickel cobalt manganese oxide and lithium manganese iron phosphate in this embodiment is 0.14%, the mass percentage of the positive electrode film-forming agent is 0.75%, the mass percentage of the negative electrode film-forming agent is 1.65%, the concentration of lithium hexafluorophosphate (LiPF6) is 0.7 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.32 mol / L.

[0056] Example 4

[0057] This embodiment is basically the same as Embodiment 1, except that the mass ratio (NL) of lithium nickel cobalt manganese oxide and lithium manganese iron phosphate in this embodiment is 0.05%, the mass percentage of the positive electrode film-forming agent is 0.2%, the mass percentage of the negative electrode film-forming agent is 2%, the concentration of lithium hexafluorophosphate (LiPF6) is 0.85 mol / L, and the concentration of lithium difluorosulfonyl imide (LiFSI) is 0.25 mol / L.

[0058] Example 5

[0059] This embodiment is basically the same as Embodiment 1, except that the mass ratio (NL) of lithium nickel cobalt manganese oxide and lithium manganese iron phosphate in this embodiment is 0.43%, the mass percentage of the positive electrode film-forming agent is 2.5%, the mass percentage of the negative electrode film-forming agent is 0.8%, the concentration of lithium hexafluorophosphate (LiPF6) is 0.35 mol / L, and the concentration of lithium difluorosulfonyl imide (LiFSI) is 0.5 mol / L.

[0060] Example 6

[0061] This embodiment is basically the same as Embodiment 1, except that the mass ratio (NL) of lithium nickel cobalt manganese oxide and lithium manganese iron phosphate in this embodiment is 0.1%, the mass percentage of the positive electrode film-forming agent is 0.5%, the mass percentage of the negative electrode film-forming agent is 1.8%, the concentration of lithium hexafluorophosphate (LiPF6) is 0.75 mol / L, and the concentration of lithium difluorosulfonyl imide (LiFSI) is 0.3 mol / L.

[0062] Example 7

[0063] This embodiment is basically the same as Embodiment 1, except that the mass ratio (NL) of lithium nickel cobalt manganese oxide and lithium manganese iron phosphate in this embodiment is 0.3%, the mass percentage of the positive electrode film-forming agent is 2%, the mass percentage of the negative electrode film-forming agent is 1%, the concentration of lithium hexafluorophosphate (LiPF6) is 0.45 mol / L, and the concentration of lithium difluorosulfonyl imide (LiFSI) is 0.45 mol / L.

[0064] Example 8

[0065] This embodiment is basically the same as Embodiment 1, except that the mass ratio (NL) of lithium nickel cobalt manganese oxide and lithium manganese iron phosphate in this embodiment is 0.13%, the mass percentage of the positive electrode film-forming agent is 0.7%, the mass percentage of the negative electrode film-forming agent is 1.8%, the concentration of lithium hexafluorophosphate (LiPF6) is 0.73 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.3 mol / L.

[0066] Example 9

[0067] This embodiment is basically the same as Embodiment 1, except that the concentration of lithium hexafluorophosphate (LiPF6) in this embodiment is 0.7 mol / L and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.5 mol / L.

[0068] Example 10

[0069] This embodiment is basically the same as Embodiment 1, except that the concentration of lithium hexafluorophosphate (LiPF6) in this embodiment is 0.9 mol / L and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.05 mol / L.

[0070] Comparative Example 1

[0071] This comparative example is basically the same as Example 1, except that the mass percentage of the positive electrode film-forming agent in this comparative example is 0.3%.

[0072] Comparative Example 2

[0073] This comparative example is basically the same as Example 1, except that the mass percentage of the negative electrode film-forming agent in this comparative example is 0.4%.

[0074] Test example:

[0075] 25℃ Cyclic Test: The batteries of the examples and comparative examples were fully charged and discharged at 25℃. The test steps were as follows: rest for 30 minutes; constant current and constant voltage charging, with a current of 0.33C, a constant voltage of 4.25V, and a cutoff current of 0.05C (C is the battery design capacity), three cycles, and the capacity of the last cycle was recorded as the calibrated capacity Q. Rest for 1 hour; constant current and constant voltage charging, with a current of 1Q, a constant voltage of 4.25V, and a cutoff current of 0.05Q; rest for 1 hour; constant current discharge, with a current of 1Q, 1000 cycles, and the capacity retention rate was measured, as shown in Table 1.

[0076] Soft-pack needle penetration test: For the fully charged individual cells of the embodiment and comparative batteries, a high-temperature resistant steel needle with a diameter of 7mm and a needle tip cone angle of 48° was used to penetrate the battery from a direction perpendicular to the battery plates at a speed of 25mm / s. The penetration point was close to the geometric center of the punctured surface. The steel needle remained in the lithium battery and was observed for one hour. The judgment criterion was that the battery did not catch fire or explode. All the batteries mentioned above did not catch fire. Therefore, the maximum temperature of the large surface area after one hour was used to judge the risk of needle penetration. The method for testing the maximum temperature of the large surface area was to directly attach the needle-pierced temperature sensing line to the large surface casing and record the temperature, as shown in Table 1.

[0077] Table 1

[0078]

[0079] As shown in Table 1:

[0080] Compared to Examples 9 and 10, the batteries of Examples 1-8 exhibit higher capacity retention and lower surface temperature of the casing. This is because, in Examples 1-8, as the proportion of nickel-cobalt-manganese lithium oxide (NCM) mixed in lithium manganese iron phosphate increases, the mass percentage content of the positive electrode film-forming agent increases accordingly, while the mass percentage content of the negative electrode film-forming agent decreases, i.e., A...dd This increases the concentration of lithium hexafluorophosphate (LiPF6) and lithium difluorosulfonylimide salt, while correspondingly decreasing the total concentration of S. alt Consequently, the concentration of LiPF6 decreased, while the concentration of LiFSI increased, resulting in a smaller LiPF6 / LiFSI ratio. This improved the battery's cycle performance and safety. In Example 9, the high total concentration of lithium hexafluorophosphate (LiPF6) and lithium difluorosulfonylimide resulted in a smaller improvement in the battery's cycle performance and safety. In Example 10, the high LiPF6 / LiFSI ratio also resulted in a smaller improvement in the battery's cycle performance and safety.

[0081] Compared to Comparative Example 1, the battery in Example 1 exhibits higher capacity retention. This is because the mass percentage of the positive electrode film-forming agent in Comparative Example 1 is smaller, resulting in... A higher value indicates a poorer film-forming and protective effect of the positive electrode film-forming agent, which in turn deteriorates the battery cycle performance.

[0082] Compared to Comparative Example 2, the battery in Example 1 exhibits higher capacity retention. This is because the negative electrode film-forming agent in Comparative Example 1 has a lower mass percentage content, resulting in... A smaller value indicates a poorer film-forming and protective effect of the negative electrode film-forming agent, which in turn worsens the battery cycle performance.

Claims

1. A lithium-ion battery, comprising a positive electrode and an electrolyte, wherein the active material in the positive electrode comprises lithium phosphate positive electrode material and lithium nickel cobalt manganese oxide, and the electrolyte comprises a positive electrode film-forming agent, a negative electrode film-forming agent, and a lithium salt, wherein the lithium salt comprises lithium hexafluorophosphate and lithium difluorosulfonylimide, and the lithium-ion battery satisfies the following formula: 0.1≤ ≤0.59, where, NL is the mass ratio of the lithium nickel cobalt manganese oxide to the lithium phosphate cathode material, and S alt A is the sum of the molar concentrations of the lithium hexafluorophosphate and the lithium difluorosulfonylimide salt in the electrolyte, expressed in mol / L. dd The mass ratio of the positive electrode film-forming agent to the negative electrode film-forming agent.

2. The lithium-ion battery as described in claim 1, wherein, The molar ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the electrolyte decreases as NL increases.

3. The lithium-ion battery as described in claim 1, wherein, The NL and the A dd Satisfy: A dd =a·NL-0.588, where a is 7.1~13.8; and / or The NL and the S alt Satisfy: S alt =b·NL+1.124, where b is -0.750 to -0.

456.

4. The lithium-ion battery as described in claim 1, wherein, The A dd The range is 0.1 to 3.1; and / or The NL is 0.05~0.43; and / or The S alt The value ranges from 0.85 to 1.

1.

5. The lithium-ion battery as described in claim 1, wherein, The molar ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the electrolyte is 0.7 to 3.4; and / or The concentration of lithium hexafluorophosphate in the electrolyte is 0.35 mol / L to 0.85 mol / L; and / or The concentration of the lithium difluorosulfonylimide salt in the electrolyte is 0.25 mol / L to 0.50 mol / L.

6. The lithium-ion battery as described in claim 1, wherein: The positive electrode film-forming agent has a mass percentage content of 0.2% to 2.5% in the electrolyte; and / or The negative electrode film-forming agent has a mass percentage content of 0.8% to 2.0% in the electrolyte.

7. The lithium-ion battery as described in claim 1, wherein: The lithium phosphate cathode material includes one or more of lithium manganese iron phosphate and lithium iron phosphate; and / or The positive electrode film-forming agent comprises one or more of 1,3-propanesulfonate lactone, lithium difluorooxalate borate, lithium bis(oxalate)borate, tris(trimethylsilane)phosphite, methanedisulfonate methylene, tris(trimethylsilane)borate, and hexanetricarbonyl nitrile; and / or The negative electrode film-forming agent includes one or more of vinylene carbonate, fluoroethylene carbonate, lithium difluorophosphate, lithium tetrafluoroborate, and vinyl sulfate.

8. The lithium-ion battery as claimed in claim 1, wherein: The surface density of the positive electrode sheet is 200 g / m². 2 ~260g / m 2 ; and / or The compaction density of the positive electrode sheet is 2.0 g / cm³. 3 ~2.6g / cm 3 ; and / or The electrolyte injection coefficient of the lithium-ion battery is 3.0 g / Ah to 5.0 g / Ah.

9. The lithium-ion battery as described in claim 1, further comprising a negative electrode: the active material of the negative electrode comprises graphite; the areal density of the negative electrode is 80 g / m². 2 ~110g / m 2 ; and / or The compaction density of the negative electrode sheet is 1.55 g / cm³. 3 ~1.75g / cm 3 .

10. An electrical device comprising a lithium-ion battery as described in any one of claims 1 to 9.

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