Lithium-ion battery and electric device

Abstract

The present invention provides a lithium-ion battery and an electric device. The lithium-ion battery comprises a case, and a battery cell and an electrolyte, which are arranged in the case, wherein the battery cell comprises a positive electrode sheet, a negative electrode sheet, and a separator disposed between the positive electrode sheet and the negative electrode sheet to separate same; the positive electrode sheet comprises a positive electrode active layer, the positive electrode active layer comprising a positive electrode active material having Dv90 of 9.5±1.5 μm; and the electrolyte comprises an electrolyte additive, the electrolyte additive comprising a trinitrile compound and a tetranitrile compound. Compared with the prior art, the lithium-ion battery provided by the present invention, in which the specially designed positive electrode active material and electrolyte additive are used in combination, has high-rate discharge performance, low-temperature discharge performance and high-temperature performance.

Description

Lithium-ion battery and power-consuming device Technical Field

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

[0002] Lithium-ion batteries are mainly composed of a positive electrode, a negative electrode, a separator, an electrolyte and an outer packaging. With the development of technology, not only are there high requirements for the high-temperature performance of lithium-ion batteries, but people also have increasingly higher requirements for high-rate discharge and low-temperature discharge. In particular, in high-rate discharge scenarios such as e-cigarettes, power tools, and drones, or ultra-high-rate discharge scenarios such as start-stop power supplies and model aircraft, there are also high requirements for the high-rate discharge and low-temperature discharge performance of lithium-ion batteries.

[0003] Currently, the commonly used technical approach is to improve the high-rate discharge and low-temperature discharge performance of lithium-ion batteries by combining conventional cathode materials with high-kinetic, low-impedance electrolytes. However, this is mainly limited by the selection of cathode materials and electrolytes, and the improvement effect is very weak, far from meeting the high-rate discharge and low-temperature discharge requirements of special lithium-ion batteries. Some solutions also use specially designed cathode materials to make lithium-ion batteries, but the matching between the materials is still limited, and the improvement of the high-rate discharge and low-temperature discharge performance of lithium-ion batteries cannot meet the requirements. On the contrary, it will affect other performance such as high temperature, and reduce battery safety.

[0004] In view of this, it is indeed necessary to provide a technical solution to the above problems.

[0005] Summary of the Invention

[0006] One of the purposes of the present invention is to provide a lithium-ion battery to address the shortcomings of the existing technology, so as to improve the problem that the current positive electrode material and electrolyte have a low matching degree and cannot take into account the high-rate discharge performance, low-temperature discharge performance and high-temperature performance of the lithium-ion battery.

[0007] In order to achieve the above object, the present invention adopts the following technical solutions:

[0008] A lithium-ion battery, comprising a housing, a battery cell and an electrolyte disposed within the housing; wherein:

[0009] The battery cell includes a positive electrode sheet, a negative electrode sheet, and a separator between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet includes a positive electrode active layer, and the positive electrode active layer includes a positive electrode active material with a Dv90 of 9.5±1.5 μm;

[0010] The electrolyte includes an electrolyte additive, and the electrolyte additive includes a trinitrile compound and a tetranitrile compound.

[0011] Preferably, the weight of the positive electrode active material is a, and the sum of the weights of the trinitrile compound and the tetranitrile compound is b, satisfying the following relationship: 0.6%≤b / a≤1.1%.

[0012] Preferably, the total mass proportion of the trinitrile compound and the tetranitrile compound in the electrolyte is 0.5% to 3.5%.

[0013] Preferably, the trinitrile compound is at least one of 1,3,6-hexanetrinitrile, 1,2,3-propanetricarbonitrile, glyceroltrinitrile, 1,3,5-benzenetrinitrile, 1,3,5-cyclohexanetrinitrile, and 2,4,6-trifluorobenzene-1,3,5-trinitrile.

[0014] Preferably, the mass proportion of the trinitrile compound in the electrolyte is 0.01%-3.00%.

[0015] Preferably, the tetranitrile compound is at least one of the following structural formulas I to III:

[0016] Among them, R1, R 2、 R3 and R4 are independently selected from alkyl groups having 1 to 4 carbon atoms.

[0017] Preferably, structural formula I is at least one of the following structural formulas;

[0018] Preferably, the mass proportion of the tetranitrile compound in the electrolyte is 0.01%-2.00%.

[0019] Preferably, the electrolyte further comprises a lithium salt and an organic solvent; the lithium salt is at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium oxalate phosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate and lithium bisfluorosulfonyl imide; the mass proportion of the lithium salt in the electrolyte is 0.01% to 20%; the organic solvent is at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl propionate, ethyl acetate, ethyl butyrate, γ-butyrolactone, dimethoxymethane, diethoxymethane and propyl butyrate; the mass proportion of the organic solvent in the electrolyte is 50% to 90%; the electrolyte additive further comprises at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, methylene disulfonate, propylene sultone, citraconic anhydride and lithium difluorooxalatoborate.

[0020] A second object of the present invention is to provide an electrical device comprising any of the lithium-ion batteries described above.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows: the lithium ion battery provided by the present invention, in combination with specially designed positive electrode active materials and electrolyte additives, can take into account the high rate discharge performance, low temperature discharge performance and high temperature performance of the lithium ion battery. Among them, the positive electrode active material with small particles has good rate performance and low temperature performance, but at the same time it has the characteristics of large specific surface area and high reaction activity, extremely poor stability at high temperature, serious performance deterioration at high temperature, and cannot meet the use requirements of the lithium ion battery. On this basis, the present invention matches the electrolyte additive containing trinitrile compounds and tetranitrile compounds, and the ability of the trinitrile compounds and tetranitrile compounds to act together and complex with the positive electrode is greatly enhanced, effectively improving the serious problem of transition metal dissolution at high temperature in small particle positive electrode active materials, stabilizing the structure of the positive electrode active material, thereby effectively improving the high rate discharge performance, low temperature discharge performance and high temperature performance of the current lithium ion battery, and meeting people's requirements for high rate discharge and low temperature discharge of lithium ion batteries. DETAILED DESCRIPTION

[0022] To make the technical solutions and advantages of the present invention more clear, the present invention and its beneficial effects will be described in further detail below, but the embodiments of the present invention are not limited thereto.

[0023] The term "Dv90" means that the volume content of particles smaller than or equal to this particle size accounts for 90% of the total particle volume.

[0024] Currently, the particle size Dv90 of commonly used cathode active materials generally ranges from 15 to 40 μm, resulting in a mixture of large and small particles. This leads to differences in compaction density and electronic conductivity between materials of different particle sizes, resulting in significant variations in the electrochemical performance of the resulting lithium-ion batteries. Using a mixture of large and small particles allows small particles to fill the gaps between larger particles, making it easier to achieve a relatively high compaction density. Within the material's allowable compaction range, a higher electrode density increases the battery capacity. However, as market demands for lithium-ion batteries continue to rise, commonly used cathode active materials are no longer able to meet the requirements for high-rate discharge performance and low-temperature discharge performance. Even if these cathode active materials are matched with suitable electrolytes and anode materials, the improvement in high-rate discharge and low-temperature performance is limited. However, if small particles of cathode active materials are used as the primary component, such as those with a Dv90 less than 11 μm, the lithium ion transport path within the cathode particles is shortened, resulting in better rate and low-temperature performance. However, due to the large interaction force between small particles, it is difficult for the particles to flow and rearrange, and the positive electrode active materials formed are mostly characterized by high porosity, large specific surface area, and low compaction density, making them extremely unstable at high temperatures and posing a major safety hazard. Therefore, positive electrode active materials with small particle size are basically not used at present.

[0025] Based on this, the first aspect of the present invention aims to provide a lithium-ion battery, comprising a shell and a battery cell and an electrolyte arranged in the shell; wherein: the battery cell comprises a positive electrode sheet, a negative electrode sheet, and a separator separated between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet comprises a positive electrode active layer, and the positive electrode active layer comprises a positive electrode active material with a Dv90 of 9.5±1.5μm; the electrolyte comprises an electrolyte additive, and the electrolyte additive comprises a trinitrile compound and a tetranitrile compound.

[0026] The present invention is specially designed to use small particles as the main positive electrode active material, and use an electrolyte containing trinitrile compounds and tetranitrile compounds to solve the contradiction between high temperature and rate and low temperature of small-particle positive electrodes. The electrolyte can effectively improve the shortcomings of poor high-temperature performance caused by small-particle materials, while maintaining the battery's good high-rate discharge performance and low-temperature discharge performance.

[0027] In some embodiments, the weight of the positive electrode active material is a, and the sum of the weights of the trinitrile compound and the tetranitrile compound is b, satisfying the following relationship: 0.6% ≤ b / a ≤ 1.1%. The present inventors have discovered that, under the premise of satisfying the above relationship, the small-particle positive electrode active material has a higher degree of compatibility with the trinitrile compound and the tetranitrile compound, and the trinitrile compound and the tetranitrile compound are present in relatively sufficient amounts to jointly improve the high-temperature stability of the small-particle material, thereby achieving the purpose of improving high-rate discharge and low-temperature discharge performance while ensuring high-temperature performance.

[0028] Specifically, the following relationships may be satisfied: 0.6%≤b / a<0.7%, 0.7%≤b / a<0.8%, 0.8%≤b / a<0.9%, 0.9%≤b / a<1.0%, 1.0%≤b / a≤1.1%.

[0029] The value of a varies depending on the specific size and capacity of the battery. The content of b is regulated based on the value of a while satisfying the above range.

[0030] In some embodiments, the trinitrile compound is at least one of 1,3,6-hexanetrinitrile, 1,2,3-propanetricarbonitrile, glyceroltrinitrile, 1,3,5-benzenetrinitrile, 1,3,5-cyclohexanetrinitrile, and 2,4,6-trifluorobenzene-1,3,5-trinitrile.

[0031] In some embodiments, the mass percentage of the trinitrile compound in the electrolyte is 0.01%-3.00%. Specifically, it can be 0.01%-0.1%, 0.1%-1%, 1%-1.5%, 1.5%-2%, 2%-2.5%, or 2.5%-3%. Setting the mass percentage of the trinitrile compound within the above range improves its compatibility with the tetranitrile compound and the positive electrode active material, and overall improves the high-rate, low-temperature, and high-temperature performance of the lithium-ion battery. However, if the mass percentage of the trinitrile compound in the electrolyte exceeds 3.00%, the kinetic performance of the electrolyte deteriorates sharply, and both high-rate performance and low-temperature performance are reduced.

[0032] In some embodiments, the tetranitrile compound is at least one of the following structural formulas I to III:

[0033] Among them, R1, R 2、 R3 and R4 are independently selected from alkyl groups having 1 to 4 carbon atoms.

[0034] Specifically, structural formula I is at least one of the following structural formulas;

[0035] In some embodiments, the mass proportion of the tetranitrile compound in the electrolyte is 0.01%-2.00%. Specifically, it can be 0.01%-0.1%, 0.1%-1%, 1%-1.5%, or 1.5%-2%. Similarly, when the content of the trinitrile compound is set within the above range, the content of the tetranitrile compound is further adjusted to be within 0.01%-2.00%. Its content is more compatible with the trinitrile compound and the positive electrode active material, and the overall high-rate, low-temperature, and high-temperature performance of the lithium-ion battery is better. If the mass proportion of the tetranitrile compound in the electrolyte exceeds 2.00%, the kinetic performance of the electrolyte will deteriorate sharply, and both high-rate performance and low-temperature performance will decrease.

[0036] Preferably, the combined mass proportion of the trinitrile compound and the tetranitrile compound in the electrolyte is 0.5% to 3.5%. The inventors have discovered that controlling the combined mass proportions of the two within this range prevents the inability to effectively prevent the dissolution of the positive electrode transition metal due to a low total amount of the two nitrile compounds, while also preventing the deterioration of high-rate performance and low-temperature performance due to excessive amounts of the two nitrile compounds. More preferably, when the combined mass proportion of the trinitrile compound and the tetranitrile compound in the electrolyte is 3%, the high-temperature thickness expansion ratio of the lithium-ion battery is ≤10%, effectively improving the battery's high-temperature performance while also maintaining good high-rate performance and low-temperature performance.

[0037] Compared to existing dinitrile compounds, the trinitrile compound or tetranitrile compound provided by the present invention contains more nitrile groups and has a stronger ability to complex with the positive electrode transition metal. In addition, the present invention combines the tetranitrile compound and the trinitrile compound of the above structure. Compared with the use of a single trinitrile compound or a single tetranitrile compound, the synergistic effect of the two compounds on the complexing of the positive electrode transition metal is stronger, more effectively preventing the dissolution of the positive electrode transition metal, stabilizing the positive electrode structure, and more effectively improving the high-temperature performance of the small-particle positive electrode material system.

[0038] The tetranitrile and trinitrile compounds described in the present invention are well-suited for use with small-particle positive electrode active materials, improving their high-temperature performance while also maintaining good high-rate and low-temperature performance. If used with conventional positive electrode active materials, such as materials with a Dv90 greater than 25 μm, the nitrile compounds can complex with positive electrode transition metal ions to improve high-temperature performance, but they cannot improve rate and low-temperature performance, and instead can lead to a significant deterioration in high-rate performance. Furthermore, if small-particle positive electrode active materials are used in conjunction with other electrolyte additives with high-temperature-improving effects, while the high-temperature stability of the small-particle positive electrode active materials can be improved to a certain extent, the high-rate and low-temperature performance of the battery cannot be maintained, and thus widespread application is still unacceptable.

[0039] In addition, the preferred tetranitrile compound of formula I of the present invention also has a certain flame retardant effect. It can effectively absorb the released active radicals during the initial combustion, further reducing the high-temperature safety hazards caused by small-particle positive electrode active materials, and ensuring the safe use of the battery of this system.

[0040] In some embodiments, the electrolyte further includes a lithium salt; the lithium salt is at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalatophosphate, lithium tetrafluorooxalatophosphate, lithium oxalatephosphate, lithium bisoxalatoborate, lithium difluorooxalatoborate, lithium tetrafluoroborate and lithium bisfluorosulfonyl imide.

[0041] In some embodiments, the lithium salt accounts for 0.01% to 20% by weight in the electrolyte, and may specifically be 0.01% to 0.1%, 0.1% to 1%, 1% to 2%, 2% to 4%, 4% to 6%, 6% to 8%, 8% to 10%, 10% to 12%, 12% to 14%, 14% to 16%, 16% to 18%, or 18% to 20%.

[0042] In some embodiments, the electrolyte further includes an organic solvent, and the organic solvent is at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl propionate, ethyl acetate, ethyl butyrate, γ-butyrolactone, dimethoxymethane, diethoxymethane, and propyl butyrate.

[0043] In some embodiments, the mass proportion of the organic solvent in the electrolyte is 50% to 98%, specifically 50% to 55%, 55% to 60%, 60% to 65%, 65% to 70%, 70% to 75%, 75% to 80%, 80% to 85%, 85% to 90%, 90% to 95%, or 95% to 98%.

[0044] In some embodiments, the electrolyte additive further includes at least one of fluoroethylene carbonate (FEC), vinylene carbonate, 1,3-propane sultone (PS), diethylene sulfate (DTD), methylene disulfonate, propene sultone, citraconic anhydride, and lithium difluorooxalatoborate (LiODFB). These additives are commonly used and can form an SEI film on the negative electrode. Their combined addition as electrolyte additives can further enhance the electrochemical performance of the battery.

[0045] In some embodiments, the mass proportion of conventional additives in the electrolyte is 0.01% to 15%, specifically 0.01% to 1%, 1% to 3%, 3% to 6%, 6% to 10%, or 10% to 15%.

[0046] In some embodiments, the positive electrode sheet also includes a positive electrode current collector for supporting the positive electrode active layer. The positive electrode current collector can be various materials in the art that are suitable for use as a positive electrode current collector for lithium-ion batteries. For example, the positive electrode current collector can include but is not limited to metal foil, and more specifically can include but is not limited to aluminum foil.

[0047] In some embodiments, the negative electrode plate includes a negative electrode current collector and a negative electrode active material layer coated on at least one surface of the negative electrode current collector. The negative electrode active material layer may include, but is 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 is typically a structure or component that collects current. The negative electrode current collector may be any material suitable for use as a negative electrode current collector in lithium-ion batteries. For example, the negative electrode current collector may include, but is not limited to, metal foil, and more specifically, may include, but is not limited to, copper foil.

[0048] In some embodiments, the separator can be any of various materials suitable for lithium-ion battery separators in the art, for example, 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.

[0049] In some embodiments, the housing may be an aluminum-plastic film.

[0050] A second aspect of the present invention is to provide an electrical device comprising any of the lithium-ion batteries described above.

[0051] The electrical device can be a vehicle, a mobile phone, a portable device, a laptop computer, a ship, a spacecraft, an electric toy, an electric tool, and the like. The vehicle can be a fuel vehicle, a gas vehicle, or a new energy vehicle. The new energy vehicle can be a pure electric vehicle, a hybrid vehicle, or an extended-range vehicle. The spacecraft includes airplanes, 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. Preferably, the lithium-ion battery of the present invention is preferably used in electrical devices that require high-rate discharge performance and low-temperature discharge performance.

[0052] 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.

[0053] Example 1

[0054] A lithium-ion battery comprises a housing, a battery cell disposed within the housing, and an electrolyte; wherein: the battery cell comprises a positive electrode sheet, a negative electrode sheet, and a separator separated between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet comprises a positive electrode active layer, wherein the positive electrode active layer comprises a positive electrode active material having a Dv90 of 9.5±1.5μm; and the electrolyte comprises an electrolyte additive, wherein the electrolyte additive comprises a trinitrile compound and a tetranitrile compound.

[0055] The trinitrile compound is 1,3,6-hexanetrinitrile (HTCN); and the tetranitrile compound is 1,2,3,4-tetrakis-(2-cyanoethoxy)butane, that is, a tetranitrile compound with an A4 structure.

[0056] The preparation method of the lithium ion battery is as follows:

[0057] 1) Preparation of the positive electrode sheet: 48.55 kg of 97.1 wt% lithium cobalt oxide (LCO small particles, Dv90: 9.5 μm), 0.35 kg of 0.7 wt% conductive carbon (SP), 0.35 kg of 0.7 wt% carbon nanotubes (CNT), and 0.75 kg of 1.5 wt% polyvinylidene fluoride (PVDF) were evenly dispersed in N-methylpyrrolidone (NMP) solvent using a double planetary mixer, and evenly coated on a 9 μm aluminum foil using an extrusion coater. After drying, rolling, and slitting, the positive electrode sheet was obtained.

[0058] 2) Preparation of the negative electrode sheet: 29.31 kg of 97.7 wt% graphite (GR), 0.33 kg of 1.2 wt% polystyrene butadiene copolymer (SBR), and 0.36 kg of 1.1 wt% sodium carboxymethyl cellulose (CMC) were evenly dispersed in deionized water using a double planetary mixer and evenly coated on a 5 μm copper foil using an extrusion coater. After drying, rolling, and slitting, the negative electrode sheet was obtained.

[0059] 3) Preparation of electrolyte: In an argon-filled glove box, ethylene carbonate (EC), propylene carbonate (PC), diethyl carbonate (DEC), ethyl propionate (EP), and propyl propionate (PP) were added to a PP bottle in a ratio of 20:20:20:10:30 and stirred evenly. After sealing, the mixture was fully cooled in a refrigerator below 10°C. Lithium hexafluorophosphate (LiPF6) was added in batches to the fully cooled mixed solvent, a total of 1.1 mol was added, and stirred until completely dissolved to obtain a basic electrolyte. 0.5 wt% of the A4 structure tetranitrile compound, 0.5% wt HTCN, 4 wt% PS, 8 wt% FEC, 0.5 wt% LiODFB, and 0.5 wt% DTD were added and shaken until all additives were fully dissolved to obtain the electrolyte of Example 1. The final total amount of the electrolyte was 100 g.

[0060] 4) The obtained positive electrode sheet, negative electrode sheet, and separator are welded to the tabs on a winding machine, glued, wound, cut, and hot-pressed to obtain a bare cell. An aluminum-plastic film of appropriate size is punched out, and the bare cell is encapsulated in the punched aluminum-plastic film. The encapsulated cell is injected with the electrolyte of Example 1 above and pre-sealed. After standing at high temperature and room temperature for a certain period of time, it is hot-pressed and formed. After formation, the air bag is removed, the cell is re-sealed, and the capacity is divided to obtain the lithium-ion battery of this embodiment, wherein the lithium-ion battery satisfies the following relationship: 0.6% ≤ b / a ≤ 1.1%, where a is the weight of the positive electrode active material and b is the sum of the weights of the trinitrile compound and the tetranitrile compound. In the lithium-ion battery, the weight of the positive electrode active material is 19.42g, and the weight of the electrolyte is 5.25g.

[0061] By adjusting the content of the trinitrile compound and the tetranitrile compound in the electrolyte according to the above composition and selecting lithium cobalt oxide of different particle sizes, Examples 2-18 and Comparative Examples 1-6 were obtained. The specific compositions are shown in Table 1 below. The adjustment of the content of the trinitrile compound and the tetranitrile compound was accommodated by adjusting the PC content in the organic solvent. The weight proportions of other organic solvents, lithium salts, and other additives were the same as in Example 1 and are not further described here.

[0062] Table 1

[0063] The lithium ion batteries obtained in Examples 1 to 18 and Comparative Examples 1 to 6 were tested for rate performance, low temperature performance, and high temperature performance.

[0064] Performance testing:

[0065] 1) Rate test (25°C constant temperature environment): (1) Charge at 0.5C constant current and constant voltage to 4.45V, with a cut-off rate of 0.02C; (2) Wait for 10 minutes; (3) Discharge at 0.2C to 3.0V; (4) Wait for 10 minutes; (5) Repeat steps (1) and (2) to discharge at 3C. Calculate the 3C discharge capacity ÷ 0.2C discharge capacity.

[0066] 2) Low-temperature discharge performance test: (1) At a constant temperature of 25°C, charge the battery at a constant current and constant voltage of 0.5C to 4.45V, with a cut-off rate of 0.02C; (2) Leave the battery for 10 minutes; (3) Discharge the battery at a constant current and constant voltage of 0.2C to 3.0V; (4) Leave the battery for 10 minutes; (5) Charge the battery at a constant current and constant voltage of 0.5C to 4.45V, with a cut-off rate of 0.02C; (6) Leave the battery at a constant temperature of -20°C for 120 minutes; and discharge the battery at a constant current and constant voltage of 0.2C to 3.0V. Calculate the -20°C discharge capacity ÷ the 25°C discharge capacity.

[0067] 3) High-temperature storage performance test: (1) At 25°C, charge the battery to 4.45V at 0.5C constant current and constant voltage, with a cut-off rate of 0.02C. (2) Allow the battery to rest for 10 minutes. (3) Discharge the battery to 3.0V at 0.2C. (4) Allow the battery to rest for 10 minutes. (5) Charge the battery to 4.45V at 0.5C constant current and constant voltage, with a cut-off rate of 0.02C, and test the battery thickness. (6) Place the battery in an 85°C air drying oven for 24 hours and test the battery thickness. Calculate (24h storage thickness - initial thickness) ÷ initial thickness.

[0068] The test results are shown in Table 2 below.

[0069] Table 2

[0070] Those skilled in the art should understand that in the design of battery cell performance, safety performance is the primary consideration and has priority over other electrical properties. The "85℃24h%" in the above table represents the high-temperature storage thickness expansion rate. The larger the value, the more gas the battery cell produces at high temperatures and the worse the safety performance. Conversely, the smaller the value, the less gas the battery cell produces at high temperatures and the better the safety performance. According to industry requirements, the safety performance of the battery cell can be guaranteed when "85℃24h%" does not exceed 10%. On the premise that safety performance is guaranteed, when 3C discharge %>58% and -20℃ discharge %>30%, the electrical performance of the battery cell is better and can better meet the use requirements.

[0071] From the comparison of the results of Examples 1 to 18 and Comparative Examples 1 to 4, it can be seen that the trinitrile compounds and tetranitrile compounds provided by the present invention can effectively improve the high-temperature storage performance of the battery; and from the comparison of Examples 1 to 18 and Comparative Examples 5 to 6, it can be seen that the trinitrile compounds and tetranitrile compounds provided by the present invention are more suitable for matching small-particle positive electrode active materials. The obtained lithium-ion battery not only improves the high-temperature performance of the small-particle positive electrode active material system, but also maintains high rate performance and low-temperature discharge performance.

[0072] In addition, it can be seen from the comparison of Examples 1 to 13 that as the content of the trinitrile compound or the content of the tetranitrile compound increases, the better the improvement effect on the high temperature storage performance of the battery, but at the same time, too much nitrile content will also affect the high rate performance and low temperature discharge performance of the battery, which violates the original intention of the design of the lithium ion battery of the present invention. At the preferred added content of the trinitrile compound and the tetranitrile compound, the content of the positive electrode active material is matched, and under the premise of satisfying the above relationship, the battery has better high rate discharge performance, low temperature discharge performance and high temperature performance, such as Examples 8, 12 and Examples 14 to 17.

[0073] In summary, the lithium-ion battery of the present invention, in combination with a specially designed positive electrode active material and electrolyte additive, effectively takes into account the high-rate discharge performance, low-temperature discharge performance, and high-temperature performance of the lithium-ion battery, provided that the contents of the two satisfy the above relationship.

[0074] 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 comprises a housing, a battery cell and an electrolyte arranged in the housing; wherein: The battery cell comprises a positive electrode sheet, a negative electrode sheet, and a separator spaced between the positive electrode sheet and the negative electrode sheet; the positive electrode sheet comprises a positive electrode active layer, and the positive electrode active layer comprises a positive electrode active material with a Dv90 of 9.5±1.5 μm; The electrolyte includes an electrolyte additive, and the electrolyte additive includes a trinitrile compound and a tetranitrile compound.

2. The lithium-ion battery according to claim 1, characterized in that The weight of the positive electrode active material is a, and the sum of the weights of the trinitrile compound and the tetranitrile compound is b, satisfying the following relationship: 0.6%≤b / a≤1.1%.

3. The lithium-ion battery according to claim 2, characterized in that: The total mass proportion of the trinitrile compound and the tetranitrile compound in the electrolyte is 0.5% to 3.5%.

4. The lithium ion battery according to any one of claims 1 to 3, characterized in that: The trinitrile compound is at least one of 1,3,6-hexanetrinitrile, 1,2,3-propanetricarbonitrile, glyceroltrinitrile, 1,3,5-benzenetrinitrile, 1,3,5-cyclohexanetrinitrile and 2,4,6-trifluorobenzene-1,3,5-trinitrile.

5. The lithium-ion battery according to claim 4, characterized in that: The mass proportion of the trinitrile compound in the electrolyte is 0.01%-3.00%.

6. The lithium ion battery according to any one of claims 1 to 3, characterized in that: The tetranitrile compound is at least one of the following structural formulas I to III, Here, R1, R2, R3, and R4 are independently selected from alkyl groups having 1 to 4 carbon atoms.

7. The lithium-ion battery according to claim 6, characterized in that: Structural formula I is at least one of the following structural formulas; 8. The lithium-ion battery according to claim 6, characterized in that: The mass proportion of the tetranitrile compound in the electrolyte is 0.01%-2.00%.

9. The lithium-ion battery according to claim 1, characterized in that: The electrolyte also includes a lithium salt and an organic solvent; the lithium salt is at least one of lithium hexafluorophosphate, lithium difluorophosphate, lithium difluorobisoxalate phosphate, lithium tetrafluorooxalate phosphate, lithium oxalate phosphate, lithium bisoxalate borate, lithium difluorooxalate borate, lithium tetrafluoroborate and lithium bisfluorosulfonyl imide; the mass proportion of the lithium salt in the electrolyte is 0.01% to 20%; the organic solvent is at least one of ethylene carbonate, propylene carbonate, diethyl carbonate, ethyl methyl carbonate, ethyl propionate, propyl propionate, ethyl acetate, ethyl butyrate, γ-butyrolactone, dimethoxymethane, diethoxymethane, and propyl butyrate; the mass proportion of the organic solvent in the electrolyte is 50% to 90%; the electrolyte additive also includes at least one of fluoroethylene carbonate, vinylene carbonate, 1,3-propane sultone, vinyl sulfate, methylene disulfonate, propylene sultone, citraconic anhydride, and lithium difluorooxalate borate.

10. An electrical device, characterized in that: A lithium ion battery comprising any one of claims 1 to 9.

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