Lithium ion battery and electric device

Abstract

The application provides a lithium ion battery and an electric device, the lithium ion battery comprising a positive electrode sheet and an electrolyte, an active substance in the positive electrode sheet comprising a phosphate lithium positive electrode material and a lithium nickel cobalt manganese oxide, the electrolyte comprising a positive electrode film former, a negative electrode film former and a lithium salt, the lithium salt comprising lithium hexafluorophosphate and a lithium bisfluorosulfonylimide salt, the lithium ion battery satisfying the following formula: wherein NL is a mass ratio of the lithium nickel cobalt manganese oxide and the phosphate lithium positive electrode material, S alt is a value of a molar concentration of the lithium hexafluorophosphate and the lithium bisfluorosulfonylimide salt in the electrolyte in mol / L, and A dd is a mass ratio of the positive electrode film former and the negative electrode film former. The application can adjust the ratio of the positive electrode film former and the negative electrode film former and the ratio of the high-heat-resistance lithium salt according to the mixing ratio of the ternary material doped in the lithium manganese iron phosphate or the lithium iron phosphate, so that the cycle performance of the battery is improved.

Description

Technical Field

[0001] This application relates to the field of battery technology, and in particular to a lithium-ion battery and an electrical device thereof. Background Technology

[0002] 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 or lithium iron phosphate will become an important future development direction. The advantages of this material are mainly reflected in its higher energy density compared to pure lithium manganese iron phosphate, and its higher safety and lower cost compared to pure ternary materials. While increasing the blending ratio of ternary materials improves the rate performance and energy density of the battery, it also negatively impacts the battery's cycle performance. Summary of the Invention

[0003] The embodiments of the present invention provide a lithium-ion battery and electrical device, which can improve the technical problem of poor cycle performance of lithium manganese iron phosphate or lithium iron phosphate doped ternary materials in related technologies.

[0004] In a first aspect, embodiments of the present invention provide 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 salt, and the lithium-ion battery satisfies the following formula:

[0005] Wherein, NL is the mass ratio of the nickel-cobalt-manganese lithium 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.

[0006] In one embodiment, the molar ratio of the lithium hexafluorophosphate to the lithium difluorosulfonylimide salt in the electrolyte decreases as the NL increases.

[0007] In one embodiment, the NL and the A dd Satisfy: A dd = a·NL-0.588, where a is 7.1 to 13.8; and / or

[0008] The NL and the S alt Satisfy: S alt = b·NL+1.124, where b is -0.750 to -0.456.

[0009] In one embodiment, the Add The range is 0.1 to 3.1; and / or

[0010] The NL is 0.05 to 0.43; and / or

[0011] The S alt The value ranges from 0.85 to 1.1.

[0012] In one embodiment, the molar concentration ratio of the lithium hexafluorophosphate to the lithium difluorosulfonylimide salt in the electrolyte is 0.7 to 3.4; and / or

[0013] The concentration of lithium hexafluorophosphate in the electrolyte is 0.35 mol / L to 0.85 mol / L; and / or

[0014] The concentration of the lithium difluorosulfonylimide salt in the electrolyte is 0.25 mol / L to 0.50 mol / L.

[0015] In one embodiment, the positive electrode film-forming agent has a mass percentage content of 0.2% to 2.5% in the electrolyte; and / or

[0016] The negative electrode film-forming agent has a mass percentage content of 0.8% to 2.0% in the electrolyte.

[0017] In one embodiment, the lithium phosphate cathode material includes one or more of lithium manganese iron phosphate and lithium iron phosphate; and / or

[0018] 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

[0019] The negative electrode film-forming agent includes one or more of vinylene carbonate, fluoroethylene carbonate, lithium difluorophosphate, lithium tetrafluoroborate, and vinyl sulfate.

[0020] In one embodiment, the areal density of the positive electrode sheet on one side is 200 g / m². 2 ~260g / m 2 ; and / or

[0021] The compaction density of the positive electrode sheet is 2.0 g / cm³. 3 ~2.6g / cm 3 ; and / or

[0022] The electrolyte injection coefficient of the lithium-ion battery is 3.0 g / Ah to 5.0 g / Ah.

[0023] In one embodiment, the lithium-ion battery further includes a negative electrode sheet, the active material of which includes graphite;

[0024] The negative electrode sheet has a single-sided surface density of 80 g / m². 2 ~110g / m 2 ; and / or

[0025] The compaction density of the negative electrode sheet is 1.55 g / cm³. 3 ~1.75g / cm 3 .

[0026] Secondly, embodiments of the present invention provide an electrical device including the aforementioned lithium-ion battery.

[0027] The beneficial effects of the embodiments of the present invention are as follows:

[0028] In embodiments of the present invention, 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 difluorosulfonyl imide 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 when doping ternary materials into lithium manganese iron phosphate or lithium iron phosphate, thereby improving the cycle performance of the battery. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. 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. Furthermore, it should be understood that the specific embodiments described herein are only for illustration and explanation of the present invention and are not intended to limit the present invention. In the present invention, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in actual use or operation; while "inner" and "outer" refer to the outline of the device.

[0030] As the proportion of ternary materials in lithium manganese iron phosphate 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.

[0031] The technical solution of this application is as follows:

[0032] In a first aspect, embodiments of this application provide 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 (NCM). 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 (LiPF6) and lithium bis(fluorosulfonyl)imide (LiFSI). The lithium-ion battery satisfies the following formula:

[0033] Wherein, 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.

[0034] 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 of lithium salt is more likely to cause thermal runaway than low concentration of lithium salt.

[0035] The concentrations of lithium hexafluorophosphate and lithium difluorosulfonylimide in the electrolyte refer to the sum of their concentrations in the electrolyte before formation during 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 during battery filling. 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.

[0036] In some embodiments, the lithium-ion battery satisfies: 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.

[0037] In some embodiments, the lithium phosphate cathode material includes one or more of lithium manganese iron phosphate and lithium iron phosphate.

[0038] In some embodiments, the NL is 0.05 to 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 or lithium iron phosphate can have different effects. Too much NCM will affect the battery's safety performance, while too little NCM will only result in a small increase in energy density and rate performance.

[0039] In some embodiments, the 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.

[0040] In some embodiments, the NL and the A dd Satisfy: A dd = a·NL-0.588, where a is 7.1 to 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 higher the content of lithium nickel cobalt manganese oxide (NCM) in the positive electrode, and the lower the content of lithium manganese iron phosphate or lithium iron phosphate, the corresponding A... dd The larger the concentration of lithium nickel cobalt manganese oxide (NCM), the more positive electrode film-forming agent is added to the electrolyte, and the less negative electrode film-forming agent is added. This allows the amount of positive electrode film-forming agent added to increase with the increase of NCM content, while the amount of negative electrode film-forming agent added to decrease with the decrease of lithium manganese iron phosphate 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 or lithium iron phosphate decreases, but the amount of negative electrode film-forming agent does not decrease, the negative electrode film-forming agent will be excessive, resulting in a thicker negative electrode film and increased impedance.

[0041] 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.

[0042] In some embodiments, the 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... ddIf 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.

[0043] In some embodiments, the A dd The value can range from 0.3 to 2.0, for example, it can be 0.3, 0.5, 0.7, 1.0, 1.2, 1.5, 1.7, 2.0, etc.

[0044] In some embodiments, the positive electrode film-forming agent has a mass percentage content of 0.2% to 2.5% in the electrolyte, for example, 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.

[0045] In some embodiments, the positive electrode film-forming agent has a mass percentage content of 0.5% to 2.0% in the electrolyte, for example, 0.5%, 0.7%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2.0%, etc. This provides sufficient protection for the positive electrode.

[0046] In some embodiments, the negative electrode film-forming agent has a mass percentage content of 0.8% to 2.0% in the electrolyte, for example, 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.

[0047] In some embodiments, the negative electrode film-forming agent has a mass percentage content of 1.0% to 1.8% in the electrolyte, for example, it can be 1.0%, 1.1%, 1.2%, 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, 1.8%, etc.

[0048] 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 the positive electrode material in high-potential regions, maintaining the stability of the positive electrode material, and improving battery capacity and cycle performance.

[0049] 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 ethylene 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.

[0050] In some embodiments, the NL and the 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 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.

[0051] 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.

[0052] In some embodiments, the S alt The concentration ranges from 0.85 to 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.

[0053] In some embodiments, the S alt The value ranges from 0.90 to 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.

[0054] In some embodiments, the molar ratio of lithium hexafluorophosphate to lithium difluorosulfonylimide in the electrolyte decreases as the 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 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.

[0055] In some embodiments, the molar ratio of the lithium hexafluorophosphate to the lithium difluorosulfonylimide salt 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.

[0056] 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.

[0057] 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 form an HF layer, thereby improving the stability of the battery.

[0058] 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.

[0059] In some embodiments, the concentration of the lithium bis(fluorosulfonyl)imide salt 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.

[0060] In some embodiments, the concentration of the lithium bis(fluorosulfonyl)imide salt 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.

[0061] 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 2 This allows the battery to have a higher energy density, but excessive areal density can affect lithium-ion transport, increase battery impedance, and deteriorate battery cycle performance.

[0062] 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.

[0063] 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 / cm3 2.2g / cm 3 2.3g / cm 3 2.4g / cm 3 2.5g / cm 3 2.6g / cm 3 This allows the battery to have a higher energy density, but excessive compaction can crush the particles and destroy the effectiveness of the active materials.

[0064] 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.

[0065] 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 leads to increased side reactions and also increases battery cost; too little electrolyte leads to insufficient electrode wetting, increased interfacial impedance, and deterioration of battery cycle performance.

[0066] 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.

[0067] In some embodiments, the lithium-ion battery further includes a negative electrode sheet, the active material of which comprises graphite. This can improve battery performance. Graphite is low in cost and possesses high specific energy, good chemical stability, and a long cycle life.

[0068] 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 2This allows the battery to have a higher energy density, but excessive areal density can affect lithium-ion transport, increase battery impedance, and deteriorate battery cycle performance.

[0069] 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 allows the battery to have a higher energy density, but excessive compaction can crush the particles and destroy the effectiveness of the active materials.

[0070] This application also provides an electrical device including the lithium-ion battery described above.

[0071] Example 1

[0072] 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 manganese iron phosphate to lithium nickel cobalt manganese oxide is 0.25%; the positive electrode film-forming agent is methylene disulfonate (MMDS), and its mass percentage in the electrolyte before formation is 1.5%; the negative electrode film-forming agent is vinylene carbonate (VC), and its 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.

[0073] Example 2

[0074] This embodiment is basically the same as Embodiment 1, except that the mass ratio (NL) of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is 0.17%, the mass percentage of positive electrode film-forming agent is 1.0%, the mass percentage of negative electrode film-forming agent is 1.5%, the concentration of lithium hexafluorophosphate (LiPF6) is 0.65 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.35 mol / L.

[0075] Example 3

[0076] This embodiment is basically the same as Embodiment 1, except that the mass ratio (NL) of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide 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.

[0077] Example 4

[0078] This embodiment is basically the same as Embodiment 1, except that the mass ratio (NL) of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is 0.05%, the mass percentage of positive electrode film-forming agent is 0.2%, the mass percentage of 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.

[0079] Example 5

[0080] This embodiment is basically the same as Embodiment 1, except that the mass ratio (NL) of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is 0.43%, the mass percentage of positive electrode film-forming agent is 2.5%, the mass percentage of 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.

[0081] Example 6

[0082] This embodiment is basically the same as Embodiment 1, except that the mass ratio (NL) of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is 0.1%, the mass percentage of positive electrode film-forming agent is 0.5%, the mass percentage of negative electrode film-forming agent is 1.8%, the concentration of lithium hexafluorophosphate (LiPF6) is 0.75 mol / L, and the concentration of lithium bis(fluorosulfonyl)imide (LiFSI) is 0.3 mol / L.

[0083] Example 7

[0084] This embodiment is basically the same as Embodiment 1, except that the mass ratio (NL) of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide 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 bis(fluorosulfonyl)imide (LiFSI) is 0.45 mol / L.

[0085] Example 8

[0086] This embodiment is basically the same as Embodiment 1, except that the mass ratio (NL) of lithium manganese iron phosphate and lithium nickel cobalt manganese oxide is 0.13%, the mass percentage of positive electrode film-forming agent is 0.7%, the mass percentage of 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.

[0087] Example 9

[0088] 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.

[0089] Example 10

[0090] 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.

[0091] Comparative Example 1

[0092] 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%.

[0093] Comparative Example 2

[0094] 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%.

[0095] Test example:

[0096] 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.

[0097] 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.

[0098] Table 1

[0099]

[0100] As shown in Table 1:

[0101] 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, which 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 battery cycle performance and safety. In Example 10, the high LiPF6 / LiFSI ratio also resulted in a smaller improvement in battery cycle performance and safety.

[0102] Compared to Comparative Example 1, the battery in Example 1 exhibits a higher capacity retention rate. 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.

[0103] Compared to Comparative Example 2, the battery in Example 1 exhibits a higher capacity retention rate. 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 deteriorates the battery cycle performance.

[0104] The embodiments of the present invention have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of the present invention. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of the present invention. Therefore, the content of this specification should not be construed as a limitation of the present invention.

Claims

1. A lithium-ion battery, characterized by: The lithium ion battery comprises a positive electrode tab and an electrolyte, the active material in the positive electrode tab comprises a phosphate lithium positive electrode material and a lithium nickel cobalt manganese oxide, the electrolyte comprises a positive electrode film former, a negative electrode film former and a lithium salt, the lithium salt comprises lithium hexafluorophosphate and a lithium bisfluorosulfonylimide salt, and the lithium ion battery satisfies the following formula: 0.1≤ ≤0.59, wherein NL is the mass ratio of the lithium nickel cobalt manganese oxide and the lithium phosphate cathode material, S alt is the value of the molar concentration of the lithium hexafluorophosphate and the lithium bisfluorosulfonylimide salt in the electrolyte in mol / L and A dd is the mass ratio of the cathode film former and the anode film former; The NL and the A dd satisfies: A dd =a·NL-0.588, where a is 7.1~13.8; The NL and the S alt Satisfies: S alt = b·NL+ 1.124, wherein b is -0.750 ~ -0.456; The A dd is 0.1 to 3.1; The NL is 0.05-0.

43. The S alt is 0.85-1.1; The positive electrode film former comprises one or more of 1,3-propane sultone, lithium difluoro(oxalato)borate, lithium bis(oxalato)borate, tris(trimethylsilyl)phosphite, methanedisulfonate methylene, tris(trimethylsilyl)borate and hexanetrimethylnitrile. The negative electrode film former comprises one or more of vinyl carbonate, fluoroethylene carbonate, lithium difluorophosphate, lithium tetrafluoroborate and vinyl sulfate.

2. The lithium-ion battery of claim 1, wherein: The ratio of the molar concentration of the lithium hexafluorophosphate to the lithium bisfluorosulfonylimide salt in the electrolyte decreases with the increase of the NL.

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

4. The lithium-ion battery of claim 1, wherein: The mass percentage content of the positive electrode film former in the electrolyte is 0.2%-2.5%; and / or The mass percentage content of the negative electrode film former in the electrolyte is 0.8%-2.0%.

5. The lithium-ion battery of claim 1, wherein: The phosphate lithium positive electrode material comprises one or more of lithium manganese iron phosphate and lithium iron phosphate.

6. The lithium-ion battery of claim 1, wherein: The single surface area density of the positive electrode plate is 200 g / m 2 260 g / m 2 ; and / or The compacted density of the positive electrode plate is 2.0 g / cm 3 2.6 g / cm 3 ; and / or The injection coefficient of the lithium ion battery is 3.0 g / Ah-5.0 g / Ah.

7. The lithium-ion battery of claim 1, wherein, The lithium ion battery further includes a negative electrode tab: an active material of the negative electrode tab includes graphite; a single-sided area density of the negative electrode tab is 80 g / m 2 110 g / m 2 ; and / or The compacted density of the negative electrode sheet is 1.55 g / cm 3 1.75 g / cm 3 .

8. An electrical device, characterized by: The lithium ion battery comprises the lithium ion battery according to any one of claims 1-7.

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