Lithium-ion battery and electric device

Abstract

The present invention provides a lithium-ion battery, comprising a case, and a battery cell and an electrolyte which are provided in the case. The electrolyte comprises a carbon-carbon unsaturated bond containing nitrile additive with a mass percentage of 0.02%-2.5%; the battery cell comprises a positive electrode sheet and a negative electrode sheet; the positive electrode sheet comprises a positive electrode active material layer; the positive electrode active material layer comprises a positive electrode active particle containing a nitrile group on the surface; the mass ratio of nitrogen atoms in the nitrile group is X% within an area between an outer surface and a first selected surface of the positive electrode active particle, wherein 0.1≤X; the negative electrode sheet comprises a negative electrode active material layer; the negative electrode active material layer comprises a negative electrode active particle; and the mass ratio of nitrogen atoms is Y% within an area between an outer surface and a second selected surface of the negative electrode active particle, wherein 0<Y≤3. Compared with the prior art, the lithium-ion battery provided by the present invention effectively mitigates the problem that existing batteries cannot take into account both the safety performance and the cycle performance at a high temperature, thereby widening the application range of the lithium-ion battery.

Description

Lithium-ion battery and power-consuming device Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery and an electrical device. Background Art

[0002] Since its advent, lithium-ion batteries have developed rapidly due to their advantages such as long cycle life, high energy density and no memory effect. Currently, improving their safety performance and cycle performance at high temperatures is a key research direction, but it is often difficult to take both into account using conventional methods.

[0003] In view of this, it is indeed necessary to provide a technical solution to the above problems.

[0004] Summary of the Invention

[0005] One of the objectives of the present invention is to provide a lithium-ion battery to address the shortcomings of the prior art, so as to improve the problem that the current lithium-ion battery cannot achieve both safety performance and cycle performance at high temperatures.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions:

[0007] A lithium-ion battery comprises a housing, a battery cell and an electrolyte disposed in the housing; wherein:

[0008] The electrolyte includes a nitrile additive containing a carbon-carbon unsaturated bond in an amount of 0.02% to 2.5% by weight;

[0009] The battery cell comprises:

[0010] A positive electrode sheet comprising a positive electrode active material layer, the positive electrode active material layer comprising positive electrode active particles having nitrile groups on their surfaces, the positive electrode active particles having an outer surface and a first selected surface extending from the outer surface toward the center of the positive electrode active particle, wherein a nitrogen atomic mass fraction of the nitrile groups in the region between the outer surface and the first selected surface is X%, and 0.1≤X;

[0011] A negative electrode sheet comprising a negative electrode active material layer, the negative electrode active material layer comprising negative electrode active particles, the negative electrode active particles having an outer surface and a second selected surface extending from the outer surface toward the center of the negative electrode active particle, wherein a nitrogen atomic mass fraction in a region between the outer surface and the second selected surface is Y%, 0<Y≤3;

[0012] The diaphragm is arranged between the positive electrode sheet and the negative electrode sheet.

[0013] Preferably, the distance between the outer surface of the positive electrode active particle and the first selected surface is ≥1 nm, and the distance between the outer surface of the negative electrode active particle and the second selected surface is ≥3 nm.

[0014] Preferably, the value of X is: 0.1≤X≤5; the value of Y is: 0.01≤Y≤2, and Y <X。

[0015] Preferably, the specific surface area of ​​the negative electrode active particles is Z m 2 / g, 0.5≤Z≤5, and Y / Z≤3.

[0016] Preferably, the electrolyte is divided into a first electrolyte and a second electrolyte; wherein, the first electrolyte does not contain a nitrile additive containing a carbon-carbon unsaturated bond and is injected before the first formation; the second electrolyte includes a nitrile additive containing a carbon-carbon unsaturated bond and is injected before the second formation.

[0017] Preferably, the mass ratio of the first electrolyte injection amount to the second electrolyte injection amount is (1-4):1.

[0018] Preferably, the mass content of the nitrile additive containing carbon-carbon unsaturated bonds in the second electrolyte is 0.1% to 5%.

[0019] Preferably, the charging voltage of the second formation is greater than the reduction voltage of the nitrile additive containing a carbon-carbon unsaturated bond.

[0020] Preferably, the nitrile additive containing a carbon-carbon unsaturated bond includes at least one of butenedinitrile, glutenedinitrile, and 2,4-hexadienenitrile.

[0021] A second object of the present invention is to provide an electrical device comprising the lithium-ion battery described above.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: the lithium ion battery provided by the present invention introduces a nitrile additive containing a carbon-carbon unsaturated bond into the electrolyte, and ensures that the mass proportion of the nitrogen atoms in the nitrile group in a specific thickness area on the surface of the positive electrode active particles reaches at least 0.1%, so that the nitrile group can be deeply complexed with the metal ions in the positive electrode to form a coordination bond, thereby stabilizing the positive electrode active material and improving the safety performance of the battery at high temperatures; at the same time, the mass proportion of the nitrogen atoms in the negative electrode active particles in the specific thickness area on their surface is controlled to be no more than 3%, thereby reducing the reaction amount of the nitrile additive on the negative electrode surface, avoiding the problem that an excessively high proportion leads to an increase in the surface impedance of the battery negative electrode and deterioration of the high-temperature cycle performance of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] FIG1 is a schematic diagram of the structure of the positive electrode active particles of the present invention.

[0024] FIG2 is a schematic diagram of the structure of the negative electrode active particles of the present invention. DETAILED DESCRIPTION

[0025] To make the technical solutions and advantages of the present invention more clear, the present invention and its beneficial effects will be further described in detail below in conjunction with specific implementation methods, but the implementation methods of the present invention are not limited thereto.

[0026] The first aspect of the present invention is to provide a lithium-ion battery, comprising a shell, a battery cell and an electrolyte arranged in the shell; wherein the electrolyte includes a nitrile additive containing a carbon-carbon unsaturated bond with a mass content of 0.02% to 2.5%; the battery cell includes a positive electrode sheet, a negative electrode sheet and a separator arranged between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet includes a positive electrode active material layer, the positive electrode active material layer includes positive electrode active particles containing nitrile groups on the surface, the positive electrode active particles have an outer surface and a first selected surface extending from the outer surface toward the center of the positive electrode active particles, the mass proportion of nitrogen atoms in the nitrile groups in the area between the outer surface and the first selected surface is X%, and 0.1≤X; the negative electrode sheet includes a negative electrode active material layer, the negative electrode active material layer includes negative electrode active particles, the negative electrode active particles have an outer surface and a second selected surface extending from the outer surface toward the center of the negative electrode active particles, the mass proportion of nitrogen atoms in the area between the outer surface and the second selected surface is Y%, and 0<Y≤3.

[0027] Those skilled in the art should understand that the mass proportion of the nitrile additive containing a carbon-carbon unsaturated bond refers to the mass percentage of the nitrile additive containing a carbon-carbon unsaturated bond in the electrolyte.

[0028] In some embodiments, the distance between the outer surface of the positive electrode active particle and the first selected surface is ≥1 nm, preferably 1 to 30 nm, for example, 1 nm, 5 nm, 10 nm, 20 nm, 30 nm, etc. The distance between the outer surface of the negative electrode active particle and the second selected surface is ≥3 nm, preferably 3 nm.

[0029] As shown in Figure 1, the area between the outer surface of the positive electrode active particle and the first selected surface is area A, the thickness of area A is ≥1nm, and the mass proportion of nitrogen atoms in area A is at least 0.1%, and the mass proportion of nitrogen atoms in area A refers to the mass percentage of nitrogen atoms in area A to positive electrode active particles in area A. Among them, the thicker the area A and the higher the mass proportion of nitrogen atoms, the higher the content of nitrile groups in the positive electrode active particles, and the better the protection effect for the positive electrode. In addition, the mass proportion of nitrogen atoms in the surface of the positive electrode active particles referred to in the present invention refers to a single positive electrode active particle, and the positive electrode active material layer includes a plurality of positive electrode active particles, and a plurality of positive electrode active particles constitute the positive electrode active material.

[0030] As shown in Figure 2, the area between the outer surface of the negative electrode active particle and the second selected surface is region B, and the mass proportion of nitrogen atoms in region B is not more than 3%. The mass proportion of nitrogen atoms in region B refers to the mass percentage of nitrogen atoms in region B to negative electrode active particles in region B. The negative electrode active particles provided by the present invention have a limited penetration of nitrogen atoms into their thickness range, which avoids the problem of excessive nitrile group content in the negative electrode causing a significant increase in negative electrode interface impedance and poor high-temperature cycle performance of the battery. In addition, the mass proportion of nitrogen atoms in the negative electrode active particles referred to in the present invention also refers to the fact that in a single negative electrode active particle, the negative electrode active material layer includes a plurality of negative electrode active particles, and the plurality of negative electrode active particles constitute the negative electrode active material.

[0031] In some embodiments, the value of X is: 0.1≤X≤5. The larger the value of X, the higher the nitrile group content in the positive electrode, which can better stabilize the positive electrode transition metal ions, effectively slow down their dissolution, and thus ensure the stability of the positive electrode material. Preferably, the value of X is: 1≤X≤3.

[0032] In some embodiments, the value of Y is: 0.01≤Y≤2. The smaller the value of Y, that is, the lower the nitrile group content in the negative electrode, the smaller the impact on the negative electrode surface impedance, effectively improving the problem of excessive nitrile group content in the negative electrode causing increased negative electrode surface impedance and deteriorating high-temperature cycle performance of the battery. Preferably, the value of Y is: 0.01≤Y≤1. In practical applications, of course, keeping the value of Y as small as possible is better, but the lower the nitrogen atom content in the negative electrode during production, the higher the production difficulty. Keeping it within the above range, the battery still has relatively good cycle performance at high temperatures.

[0033] At the same time, it is ensured that the value of X is greater than the value of Y. For the same content of nitrile additives containing carbon-carbon unsaturated bonds, more of it is used for the reaction at the positive electrode, and a smaller part inevitably undergoes side reactions at the negative electrode, thereby greatly reducing the proportion of nitrogen atoms on the negative electrode surface.

[0034] In some embodiments, the specific surface area of ​​the negative electrode active particles is Z m 2 / g, 0.5≤Z≤5, and Y / Z≤3. Specifically, Z can be 0.5 to 1m 2 / g, 1~1.5m 2 / g, 1.5~2m 2 / g, 2~2.5m 2 / g, 2.5~3m 2 / g, 3~3.5m 2 / g, 3.5~4m 2 / g, 4~4.5m 2 / g or 4.5~5m 2 / g.

[0035] The present invention simultaneously regulates the specific surface area of ​​the negative electrode active particles. By increasing the specific surface area within a certain range, more surface sites in the negative electrode that can transmit lithium ions are present, more nitrogen atoms that can be tolerated on the negative electrode surface are present, and the impact on the surface impedance of the battery negative electrode is smaller. In conjunction with actual production, within the above-mentioned value range of Y, Y can take a larger value, which can effectively reduce the difficulty of actual production and increase practicality.

[0036] In addition, the inventors have also found through several experiments that after selecting the value of Z, synchronously controlling Y / Z≤3, and cooperating with each other, can more effectively reduce the impact of nitrogen atoms on the surface impedance of the negative electrode, thereby ensuring the cycle performance of the battery at high temperatures. This is mainly because under the premise of a certain nitrogen atom content, that is, Y is constant, increasing the Z value, the nitrogen atom density at the same depth on the surface of the negative electrode active particles decreases, which is equivalent to a decrease in the N atom content, thereby further reducing the impact of nitrogen atoms on the surface impedance of the negative electrode, thereby ensuring the cycle performance of the battery at high temperatures. However, it should be noted that if the specific surface area Z of the negative electrode active particles is too large, it will increase the side reactions at high temperatures, which in turn reduces the safety performance of the battery at high temperatures. Therefore, controlling the specific surface area Z within the above range and regulating Y / Z≤3 is more conducive to ensuring the cycle performance and safety performance of the battery at high temperatures.

[0037] In some embodiments, the electrolyte is divided into a first electrolyte and a second electrolyte; wherein the first electrolyte does not contain a nitrile additive containing a carbon-carbon unsaturated bond and is injected before the first formation; the second electrolyte includes a nitrile additive containing a carbon-carbon unsaturated bond and is injected before the second formation.

[0038] When the electrolyte is divided into a first electrolyte and a second electrolyte and injected separately, the sum of the total amounts of the first electrolyte and the second electrolyte is the total amount of the electrolyte, and 0.02% to 2.5% refers to the mass proportion of the nitrile additive containing carbon-carbon unsaturated bonds in the total amount of the electrolyte.

[0039] Among them, the nitrile groups on the surface of the positive electrode active particles are the products of oxidation of the nitrile additives containing carbon-carbon unsaturated bonds in the second electrolyte on the positive electrode surface. The nitrile groups can deeply combine with the metal ions in the positive electrode to form coordination bonds, and the mass proportion of the nitrogen atoms therein at the same thickness on the positive electrode surface is not less than 0.1%. The higher the content of nitrile groups, the better the protection effect on the positive electrode, and the higher the safety performance of the battery at high temperature.

[0040] The nitrogen atoms on the surface of the negative electrode active particles are by-products of the reduction of nitrile additives containing carbon-carbon unsaturated bonds in the second electrolyte on the negative electrode surface. Their formation is due to the structural characteristics of the substance itself. However, because the present invention forms an SEI film on the negative electrode surface after the first injection, the by-products of the reduction of the negative electrode surface are greatly reduced under the protection of the SEI film after the second injection. The nitrogen atoms can be confined to a thickness of 3nm from the surface of the negative electrode active particles to the inside, and the mass proportion is reduced to 3% at the same depth. The lower the content, the smaller the impact on the impedance of the battery negative electrode surface and the smaller the impact on the high-temperature cycle performance of the battery.

[0041] Compared with directly adding the electrolyte containing nitrile additives by the one-time injection method, although the nitrile additives can be used as positive electrode protection additives to form coordination bonds with the positive electrode transition metal ions to stabilize the positive electrode; however, because the negative electrode does not form a SEI protective film, the nitrile additives will inevitably react on the negative electrode surface, causing the battery polarization to increase and the cycle capacity to decay faster.

[0042] In addition, the second electrolyte of the present invention uses an additive containing a carbon-carbon unsaturated bond as a nitrile additive instead of the conventionally used adiponitrile. The inventors have found that when the nitrile additive containing a carbon-carbon unsaturated bond is combined with the secondary injection, the amount of reduction on the negative electrode surface is reduced, which reduces the impact of the structural characteristics of the substance itself, and better balances the safety performance and cycle performance of the battery at high temperatures.

[0043] Specifically, the first electrolyte is a conventional electrolyte, including a lithium salt, an organic solvent and a conventional additive, wherein the lithium salt may be at least one of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate and bis(trifluoromethanesulfonyl imide), preferably lithium hexafluorophosphate; the organic solvent may be at least three of ethylene carbonate (EC), propylene carbonate (PC), methyl propionate (MP), ethyl methyl carbonate (DEC), propyl propionate (PP), ethyl propionate (EP), methyl acetate (MA) and ethyl acetate (EA), preferably ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (DEC), propyl propionate (PP) and ethyl propionate (EP) mixed in a mass ratio of 1:2:2:2:2; the conventional additive may be 2 wt% of 1,3-propane sultone and 5 wt% of fluoroethylene carbonate.

[0044] Compared with the first electrolyte, the second electrolyte contains an additive containing a carbon-carbon unsaturated bond as a nitrile additive. The solvent content is adjusted according to the mass content of the nitrile additive. Conventional additives can be added as additives to the second electrolyte or not.

[0045] In some embodiments, the mass ratio of the first electrolyte injection amount to the second electrolyte injection amount is (1-4):1. Specifically, the mass ratio of the two injection amounts can be 1:1, 1:2, 1:3, or 1:4. Maintaining a constant total amount of electrolyte injection and rationally allocating the two electrolyte injection amounts can, on the one hand, ensure the formation of a stable SEI film on the surface of the negative electrode; on the other hand, after adding the nitrile additive containing carbon-carbon unsaturated bonds, simultaneously ensure a higher content of nitrile groups in the positive electrode and a lower content in the negative electrode, thereby better balancing the safety performance and cycle performance of the battery at high temperatures.

[0046] In some embodiments, because the first electrolyte does not contain a nitrile additive containing a carbon-carbon unsaturated bond, the weight content of the nitrile additive containing a carbon-carbon unsaturated bond in the second electrolyte is 0.1% to 5%. For example, when the mass ratio of the first electrolyte to the second electrolyte is 1:1, and the weight proportion of the nitrile additive containing a carbon-carbon unsaturated bond in the total electrolyte is 1%, the weight proportion of the nitrile additive containing a carbon-carbon unsaturated bond in the second electrolyte is 2%.

[0047] Specifically, the weight content of the nitrile additive containing carbon-carbon unsaturated bonds in the second electrolyte can be 0.1% to 1%, 1% to 2%, 2% to 3%, 3% to 4%, or 4% to 5%. This content of nitrile additive, combined with the control of the specific surface area of ​​the negative electrode, can better limit the nitrogen atomic content in the positive and negative electrode active particles to the above-mentioned preferred range, thereby ensuring both battery safety and high-temperature cycling performance.

[0048] In some embodiments, the charging voltage of the second formation is greater than the reduction voltage of the nitrile additive containing a carbon-carbon unsaturated bond. The secondary formation charging voltage is relatively high, and a SEI film has already formed on the negative electrode. Furthermore, the secondary formation charging voltage exceeds the reduction voltage of the nitrile additive. Therefore, the nitrile additive does not reduce to form a film on the negative electrode surface. The positive electrode can more smoothly oxidize the nitrile additive, thereby forming a CEI protective film on the positive electrode surface. The resulting battery has better safety performance without deteriorating its cycling performance at high temperatures.

[0049] In some embodiments, the nitrile additive containing a carbon-carbon unsaturated bond includes at least one of butenedinitrile, glutenedinitrile, and 2,4-hexadienenitrile. Preferably, the nitrile additive containing a carbon-carbon unsaturated bond is butenedinitrile.

[0050] In some embodiments, the positive electrode sheet further comprises a positive electrode current collector, and the positive electrode active material layer coats at least one surface of the positive electrode current collector. The positive electrode active particles may include but are not limited to the chemical formula such as Li x Ni h Co y M z O 2-dN d (wherein 0.95≤x≤1.2, h>0, y≥0, z≥0, and h+y+z=1, 0≤d≤1, M is selected from a combination of one or more of Mn and Al, and N is selected from a combination of one or more of F, P, and S), the positive electrode active particles may also be, but are not limited to, LiCoO2, LiNiO2, LiVO2, LiCrO2, LiMn2O4, LiCoMnO4, Li2NiMn3O8, LiNi 0.5 Mn 1.5 The positive electrode active particles may be a combination of one or more of O4, LiCoPO4, LiMnPO4, LiFePO4, LiNiPO4, LiCoFSO4, CuS2, FeS2, MoS2, NiS, TiS2, etc. The positive electrode active particles may also be modified. Methods for modifying the positive electrode active particles should be known to those skilled in the art. For example, the positive electrode active particles may be modified by coating, doping, etc. The materials used for the modification may include, but are not limited to, a combination of one or more of Al, B, P, Zr, Si, Ti, Ge, Sn, Mg, Ce, W, etc. The positive electrode current collector may be any material suitable for use as a positive electrode current collector for lithium-ion batteries in the art. For example, the positive electrode current collector may include, but is not limited to, metal foil, and more specifically, may include, but is not limited to, aluminum foil.

[0051] In some embodiments, the negative electrode sheet further includes a negative electrode current collector, and a negative electrode active material layer is coated on at least one surface of the negative electrode current collector. The negative electrode active particles may be those commonly used in lithium-ion batteries, including but not limited to one or more of graphite, soft carbon, hard carbon, carbon fiber, mesocarbon microbeads, silicon-based materials, tin-based materials, lithium titanate, or other metals capable of forming alloys with lithium. The graphite may be selected from one or more of artificial graphite, natural graphite, and modified graphite; the silicon-based material may be selected from one or more of elemental silicon, silicon oxide compounds, silicon-carbon composites, and silicon alloys; and the tin-based material may be selected from one or more of elemental tin, tin oxide compounds, and tin alloys. The negative electrode current collector may be a metal foil or a foil containing a metal layer, specifically copper foil or a foil containing a copper layer.

[0052] The separator can be any material suitable for lithium-ion battery separators in the art, for example, it can be a combination of one or more materials including but not limited to polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester and natural fibers.

[0053] 2. Electrical devices

[0054] A second aspect of the present invention is to provide an electrical device comprising the lithium-ion battery described above.

[0055] The electrical device may be a vehicle, mobile phone, portable device, laptop computer, ship, spacecraft, electric toy, electric tool, etc. Vehicles may be fuel-powered vehicles, gas-powered vehicles, or new energy vehicles. New energy vehicles may be pure electric vehicles, hybrid vehicles, or extended-range vehicles. Spacecraft include aircraft, rockets, space shuttles, and spacecraft. Electric toys include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys. Electric tools include metal cutting power tools, grinding power tools, assembly power tools, and railway power tools, such as electric drills, electric grinders, electric wrenches, electric screwdrivers, electric hammers, impact drills, concrete vibrators, and electric planers.

[0056] The present invention and its beneficial effects will be described in further detail below with reference to specific embodiments, but the embodiments of the present invention are not limited thereto.

[0057] Example 1

[0058] Preparation of the first electrolyte: In an argon-filled glove box with a moisture content of <5 ppm and an oxygen content of <5 ppm, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (DEC), propyl propionate (PP), and ethyl propionate (EP) were mixed in a mass ratio of 1:2:2:2:2 to obtain an organic solvent. The organic solvent was mixed with lithium hexafluorophosphate so that the weight percentage of the lithium salt in the electrolyte was 13.70%, thereby obtaining a mixture of the organic solvent and lithium hexafluorophosphate. 2 wt% of 1,3-propane sultone and 5 wt% of fluoroethylene carbonate were then added and mixed uniformly to obtain the first electrolyte, designated as electrolyte A.

[0059] Example 2

[0060] Preparation of the second electrolyte: In an argon-filled glove box with a moisture content of <5 ppm and an oxygen content of <5 ppm, ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (DEC), propyl propionate (PP), and ethyl propionate (EP) were mixed in a mass ratio of 1:2:2:2:2 to obtain an organic solvent. The organic solvent was mixed with lithium hexafluorophosphate according to conventional techniques such that the lithium salt constituted 13.70% by weight of the electrolyte, thereby obtaining a mixture of the organic solvent and lithium hexafluorophosphate. 0.1 wt% of butenedinitrile was then added and mixed uniformly to obtain a second electrolyte, designated as Electrolyte B.

[0061] Example 3

[0062] The difference from Example 2 is the content of dibutyl cyanide added in this example, which is 2 wt %. The proportion of the organic solvent is adjusted accordingly so that the contents of other components remain unchanged. The obtained second electrolyte is recorded as electrolyte C.

[0063] The rest is the same as in Example 2 and will not be described again here.

[0064] Example 4

[0065] The difference from Example 2 is the content of dibutyl cyanide added in this example, which is 5 wt %. The proportion of the organic solvent is adjusted accordingly so that the contents of other components remain unchanged. The obtained second electrolyte is recorded as electrolyte D.

[0066] The rest is the same as in Example 2 and will not be described again here.

[0067] Example 5

[0068] The difference from Example 2 is the choice of nitrile additive containing carbon-carbon unsaturated bonds. In this example, the nitrile additive is 2,4-hexadienenitrile, and the content is 2 wt %. The proportion of the organic solvent is adjusted accordingly so that the content of other components remains unchanged. The obtained second electrolyte is recorded as electrolyte E.

[0069] The rest is the same as in Example 2 and will not be described again here.

[0070] Example 6

[0071] A battery cell comprising a positive electrode sheet, a negative electrode sheet and a separator, wherein the positive electrode active particles in the positive electrode sheet are NCM (8:1:1); the negative electrode active particles in the negative electrode sheet are graphite with a specific surface area of ​​0.5m 2 / g, the graphite is recorded as graphite A; the separator is a polyethylene separator coated with ceramic on one side, which is wound in the order of positive electrode sheet, separator, and negative electrode sheet. For details, please refer to the existing battery cell preparation method, which will not be repeated here.

[0072] Example 7

[0073] The difference from Example 6 is that the specific surface area of ​​graphite B used in this example is 1.5m 2 / g.

[0074] The rest is the same as in Example 6 and will not be described again here.

[0075] The first electrolyte obtained in Example 1, the second electrolyte obtained in Examples 2 to 5, and the battery cells obtained in Examples 6 to 7 were applied to the lithium-ion batteries of Examples 8 to 19 and Comparative Examples 1 to 5.

[0076] The preparation method of the lithium-ion battery comprises the following steps: encapsulating the obtained battery cell in an aluminum-plastic film, vacuum drying at 80° C., injecting the obtained first electrolyte after the water content reaches the standard, encapsulating, allowing to stand and undergoing a first formation process, injecting the second electrolyte, and undergoing formation, liquid extraction, volume separation, aging and other processes to prepare the lithium-ion battery.

[0077] Specifically, the compositions of Examples 8 to 19 and Comparative Examples 1 to 5 are shown in Table 1 below.

[0078] Table 1

[0079] After the obtained lithium-ion battery was disassembled and cleaned, XPS was used to test the mass proportion of nitrogen atoms in the positive electrode active particles at the same thickness on the surface and the mass proportion of nitrogen atoms in the negative electrode active particles at the same depth. BET was used to test the specific surface area of ​​graphite (negative electrode active particles). The results are shown in Table 2 below.

[0080] Table 2

[0081] In addition, performance tests were performed on the lithium-ion batteries obtained in Examples 8 to 19 and Comparative Examples 1 to 5.

[0082] Performance testing:

[0083] 1) Cycling Performance Test: Lithium-ion batteries were placed in a 45°C constant temperature chamber and allowed to stand for 30 minutes to reach a constant temperature. The constant temperature lithium-ion batteries were then charged at a constant current of 0.5C to a voltage of 4.48V, then charged at a constant voltage of 4.48V to a current of 0.05C, and then discharged at a constant current of 0.5C to a voltage of 3.0V. This constituted one charge-discharge cycle. This charging and discharging cycle was repeated, and the capacity retention of the lithium-ion batteries was calculated after 500 cycles.

[0084] 2) Safety Performance Test: Charge the lithium-ion battery at a constant current of 0.5C to 4.48V, then charge at a constant voltage to a current of 0.05C until fully charged. Place 3 batteries in an explosion-proof incubator, heat at a rate of 5°C / min to the target temperature, maintain for 30 minutes, and cool back to room temperature. Tests are considered to have passed if there is no fire or explosion.

[0085] The test results are shown in Table 3 below.

[0086] Table 3

[0087] Comparisons between Comparative Examples 1-2 and 3-5 show that the addition of nitrile additives resulted in nitrogen atoms in both the positive and negative electrodes, improving battery safety. However, the excess nitrogen in the negative electrode also reduced the battery's high-temperature cycling performance. Comparative Examples 8-19 show that the addition of nitrile additives containing carbon-carbon unsaturated bonds via secondary injection can improve the battery's cycling performance at high temperatures. Within the preferred addition range, the battery's safety performance is significantly improved while maintaining good high-temperature cycling performance.

[0088] In addition, it can be seen from the comparison of Examples 8 to 10 and Examples 12 to 14 that as the content of the nitrile additive containing carbon-carbon unsaturated bonds increases, the nitrogen atom content on the surface of the positive and negative electrodes increases, and the hot box test pass rate of the battery is improved. However, due to the influence of the nitrile in the negative electrode, the high-temperature cycle performance of the battery shows a downward trend. Preferably, when 1 wt% to 1.25 wt% is added, both can be better taken into account. In addition, the specific surface area of ​​the negative electrode is adjusted synchronously, and more nitrogen atoms can be accommodated in the negative electrode, but the battery still has good high-temperature cycle performance, such as the comparison of Examples 14 and 15, and the comparison of Examples 9 and 17. However, the specific surface area of ​​the negative electrode should be reasonably controlled to avoid the increase of high-temperature side reactions due to excessive specific surface area, thereby reducing the safety performance of the battery at high temperatures. Preferably, the nitrogen atom content and specific surface area on the surface of the negative electrode are limited to Y / Z≤3, which is more conducive to reducing the influence of the nitrile additive on the negative electrode, such as the test results of Examples 18 and 19.

[0089] In addition, a comparison of Examples 16 to 18 also shows that maintaining the mass ratio of the first electrolyte injection amount to the second electrolyte injection amount within the range of (1 to 4):1 can better balance the safety performance and cycle performance of the battery at high temperatures. This is mainly because when the first injection amount is sufficient, the SEI film formed on the negative electrode surface is more stable. After the second injection, the negative electrode is protected by the SEI film and the amount of reduction of the negative electrode is minimal, which reduces the impact of the nitrile additive on the negative electrode surface. At the same time, a CEI protective film can also be formed on the positive electrode surface.

[0090] In summary, the lithium-ion battery provided by the present invention effectively improves the problem that current lithium-ion batteries cannot achieve both safety performance and cycle performance at high temperatures, and broadens the application scope of lithium-ion batteries.

[0091] Based on the disclosure and teachings of the above description, those skilled in the art will be able to make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments. Any obvious improvements, substitutions, or modifications made by those skilled in the art based on the present invention fall within the scope of protection of the present invention. In addition, although certain specific terms are used in this description, these terms are only for convenience of description and do not constitute any limitation to the present invention.

Claims

1. A lithium-ion battery, characterized in that, It includes a casing, a battery cell and an electrolyte disposed within the casing; wherein, the electrolyte includes a nitrile additive containing a carbon-carbon unsaturated bond with a mass content ratio of 0.02% to 2.5%; the battery cell includes: a positive electrode sheet, including a positive electrode active material layer, the positive electrode active material layer includes positive electrode active particles with a nitrile group on the surface, the positive electrode active particles have an outer surface and a first selected surface extending from the outer surface towards the center of the positive electrode active particles, and the mass ratio of nitrogen atoms in the nitrile group within the region between the outer surface and the first selected surface is X%, 0.1 ≤ X; a negative electrode sheet, including a negative electrode active material layer, the negative electrode active material layer includes negative electrode active particles, the negative electrode active particles have an outer surface and a second selected surface extending from the outer surface towards the center of the negative electrode active particles, and the mass ratio of nitrogen atoms within the region between the outer surface and the second selected surface is Y%, 0 < Y ≤ 3; a separator, disposed between the positive electrode sheet and the negative electrode sheet.

2. The lithium ion battery according to claim 1, characterized in that, The distance between the outer surface and the first selected surface of the positive electrode active particles is ≥ 1 nm, and the distance between the outer surface and the second selected surface of the negative electrode active particles is ≥ 3 nm.

3. The lithium-ion battery according to claim 1 or 2, characterized in that, The value of X is: 0.1 ≤ X ≤ 5; the value of Y is: 0.01 ≤ Y ≤ 2, and Y < X.

4. The lithium-ion battery according to claim 1, characterized in that, The specific surface area of the negative electrode active particles is Z m 2 / g, 0.5 ≤ Z ≤ 5, and Y / Z ≤ 3.

5. The electrolyte according to claim 1, wherein The electrolyte is divided into a first electrolyte and a second electrolyte; wherein, the first electrolyte does not contain a nitrile additive with a carbon-carbon unsaturated bond and is injected before the first formation; the second electrolyte includes a nitrile additive with a carbon-carbon unsaturated bond and is injected before the second formation.

6. The lithium ion battery according to claim 5, wherein The mass ratio of the injection amount of the first electrolyte to the injection amount of the second electrolyte is (1 to 4):

1.

7. The lithium ion battery according to claim 5 or 6, characterized in that, The mass content of the nitrile additive with a carbon-carbon unsaturated bond in the second electrolyte is 0.1% to 5%.

8. The lithium ion battery according to claim 5, characterized in that, The charging voltage of the second formation is greater than the reduction voltage of the nitrile additive with a carbon-carbon unsaturated bond.

9. The lithium ion battery according to claim 1, wherein The nitrile additive with a carbon-carbon unsaturated bond includes at least one of butenedinitrile, pentenedinitrile, 2,4 - hexadienenitrile.

10. An electrical device, characterized in that, It includes a lithium-ion battery according to any one of claims 1 to 9.

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