A battery having excellent rate performance and high-temperature storage performance

Abstract

The application provides a battery with excellent rate performance and high-temperature storage performance. The battery comprises a positive electrode, a negative electrode, a separator and an electrolyte; the electrolyte comprises an organic solvent and an electrolyte salt; the organic solvent comprises solvent X, ethylene carbonate (EC) and fluoroethylene carbonate (FEC), the solvent X comprises a halogenated or non-halogenated saturated alkane containing more than 6 carbon atoms or a halogenated or non-halogenated unsaturated alkane containing more than 6 carbon atoms; the battery satisfies the following relationship: B+C>=A / 5; A>=35*(D-1.6); this can effectively improve the rate performance of the battery, avoid the occurrence of side reactions at the positive and negative electrode interface, inhibit the occurrence of lithium precipitation problems of the negative electrode, and improve the storage performance of the battery at high temperature. Further, a groove structure is arranged on the surface of the negative electrode active material layer of the negative electrode, which can effectively improve the kinetic performance of the battery and completely avoid the occurrence of lithium precipitation problems of the negative electrode.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of batteries, and particularly relates to a battery with excellent rate performance and high-temperature storage performance. BACKGROUND

[0002] Lithium ion batteries, as an important means of modern energy storage, have been widely used in portable electronic devices, electric vehicles and large-scale energy storage systems. With the increasing demand for fast-charging performance of high-energy-density lithium ion batteries, the demand for fast-charging electrolyte has also increased. However, in the development of fast-charging electrolyte, it is a technical problem to simultaneously meet the requirements of high-temperature performance of lithium ion batteries.

[0003] Traditional fast-charging electrolyte mainly relies on traditional organic solvents, including short-chain carboxylic acid esters and carbonic acid esters. These solvents have low boiling points and are prone to decomposition or other chemical reactions in high-temperature environments, resulting in a significant decrease in the high-temperature performance of the battery. In addition, the charging and discharging speed of the battery in a high-temperature environment will be accelerated, which makes the interfacial stability of the electrolyte even more important. Therefore, it is an urgent need to develop an electrolyte that can work stably in a high-temperature environment and has good fast-charging performance. SUMMARY

[0004] In order to improve the problem that the battery of the prior art cannot simultaneously consider the rate performance and high-temperature storage performance, the present application provides a battery with excellent rate performance and high-temperature storage performance. It is found that the battery of the prior art cannot simultaneously consider the rate performance and high-temperature storage performance mainly because the organic solvent used in the electrolyte of the battery is a short-chain carboxylic acid ester and / or a short-chain carbonic acid ester. These organic solvents have the characteristics of low boiling point and poor high-temperature and high-pressure stability, which leads to the instability of the interfacial film formed on the surface of the positive and negative electrodes in the battery, and the interfacial film is prone to decomposition, thereby significantly deteriorating the rate performance and high-temperature storage performance of the battery. By selecting an electrolyte containing a specific composition and matching a high-pressure density negative electrode, the stability of the interfacial film on the surface of the positive and negative electrodes in the battery can be significantly improved, the occurrence of lithium precipitation on the negative electrode can be inhibited, and the rate performance and high-temperature storage performance of the battery can be simultaneously considered.

[0005] The purpose of the present application is achieved by the following technical solution:

[0006] A battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte; the electrolyte comprises an organic solvent and an electrolyte salt; the organic solvent comprises a solvent X, ethylene carbonate (EC) and fluoroethylene carbonate (FEC), the solvent X comprises a halogenated or non-halogenated saturated alkane containing more than 6 carbon atoms or a halogenated or non-halogenated unsaturated alkane containing more than 6 carbon atoms;

[0007] The battery satisfies the following relationship:

[0008] B+C≥A / 5;

[0009] A≥35×(D-1.6);

[0010] wherein A is the percentage of the mass of the solvent X in the total mass of the electrolyte; B is the percentage of the mass of the vinyl carbonate in the total mass of the electrolyte; C is the percentage of the mass of the fluoro-vinyl carbonate in the total mass of the electrolyte; and D is the compacted density of the negative electrode, in mg / cm 3 .

[0011] According to the embodiments of the present application, when the organic solvent comprises solvent X, vinyl carbonate (EC) and fluoro-vinyl carbonate (FEC), and the battery satisfies B+C≥A / 5 and A≥35×(D-1.6), the rate performance of the battery can be effectively improved, the occurrence of side reactions at the interface between the positive and negative electrodes can be avoided, the occurrence of lithium precipitation at the negative electrode can be inhibited, and the high-temperature storage performance of the battery can be improved.

[0012] Specifically, the vinyl carbonate (EC) and the fluoro-vinyl carbonate (FEC) have excellent negative electrode film-forming effects, EC can form an organic interface film with a large elasticity, FEC can form an inorganic interface film with a large strength, and the combination of the two in the electrolyte and the use of the negative electrode with a specific compacted density can ensure that the electrolyte has better film-forming stability. The solvent X has the properties of high boiling point and low viscosity, the boiling point of the solvent X is higher than that of conventional low-viscosity solvents such as ethyl propionate (EP) and dimethyl carbonate (DMC), and the viscosity of the solvent X is equivalent to or lower than that of conventional low-viscosity solvents. Therefore, the solvent X can not only significantly improve the conductivity and rate performance of the electrolyte, but also improve the high-temperature stability of the electrolyte. The compacted density of the negative electrode is large, and the porosity is low, which makes the proportion of the electrolyte contained in the negative electrode smaller, which has higher requirements for the kinetic performance and film-forming stability of the electrolyte. The combined use of the negative electrode sheet with a specific compacted density, the solvent X, the vinyl carbonate (EC) and the fluoro-vinyl carbonate (FEC), and the satisfaction of B+C≥A / 5 and A≥35×(D-1.6) by the battery can produce a significant synergistic effect, and the electrolyte can have the characteristics of high conductivity, fast charging interface stability and high-temperature storage stability. Therefore, the rate performance of the battery can be effectively improved, the occurrence of side reactions at the interface between the positive and negative electrodes can be avoided, the storage performance of the battery at high temperature can be improved, and the improvement of lithium precipitation at the negative electrode can be achieved.

[0013] When the battery satisfies B+C<A / 5 or A<35×(D-1.6), the rate performance of the battery cannot be effectively improved, the side reaction at the interface of the positive and negative electrodes cannot be avoided, the problem of lithium precipitation at the negative electrode cannot be inhibited, and the storage performance of the battery at high temperature is poor. This is mainly because when the battery satisfies B+C<A / 5, the film-forming stability of the electrolyte is poor, and the lithium salt cannot be fully dissociated, resulting in poor cycle stability of the battery, and the problem of lithium precipitation at the negative electrode is prone to occur. When the battery satisfies A<35×(D-1.6), the electrolyte dynamics is small, the rate performance of the battery cannot be improved, and the problem of lithium precipitation at the negative electrode is prone to occur.

[0014] According to the embodiments of the present application, the mass percentage A of the solvent X in the total mass of the electrolyte satisfies 60%≥A≥5%, for example, 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%. Research has found that when the mass percentage A of the solvent X in the total mass of the electrolyte satisfies 60%≥A≥5%, the rate performance of the battery can be effectively improved, the side reaction at the interface of the positive and negative electrodes can be avoided, the problem of lithium precipitation at the negative electrode can be inhibited, and the storage performance of the battery at high temperature can be improved. When the mass percentage A of the solvent X in the total mass of the electrolyte is greater than 60%, since the solvent X cannot promote the dissociation of the electrolyte salt, and has no interface protection effect itself, it will have a deteriorating effect on the rate performance and cycle performance of the battery; and in order to match the high content of the solvent X, more ethylene carbonate and fluoroethylene carbonate need to be used, but since ethylene carbonate and fluoroethylene carbonate are prone to oxidative decomposition at high temperature, forming harmful components such as gas and acid, which will inevitably cause the storage performance of the battery at high temperature to deteriorate. When the mass percentage A of the solvent X in the total mass of the electrolyte is less than 5%, since the amount added is too small, it cannot effectively match the high compaction density of the negative electrode, and cannot provide effective dynamic performance guarantee for it, and the rate performance of the battery obtained is significantly deteriorated.

[0015] According to an embodiment of the present application, the percentage B of the mass of the ethylene carbonate in the total mass of the electrolyte satisfies 30% ≥ B ≥ 2%, for example, 2%, 3%, 4%, 5%, 8%, 10%, 12%, 15%, 16%, 18%, 20%, 22%, 25%, 26%, 28% or 30%. Research shows that when the percentage B of the mass of the ethylene carbonate in the total mass of the electrolyte satisfies 30% ≥ B ≥ 2%, the rate performance of the battery can be effectively improved, the side reaction at the interface between the positive and negative electrodes can be avoided, the problem of lithium precipitation at the negative electrode can be inhibited, and the storage performance of the battery at high temperature can be improved. When the percentage B of the mass of the ethylene carbonate in the total mass of the electrolyte is greater than 30%, the ethylene carbonate itself is prone to oxidative decomposition at high temperature to form harmful components such as gas and acid, thereby causing the storage performance of the battery at high temperature to deteriorate and the oven temperature performance of the battery to be seriously deteriorated. When the percentage B of the mass of the ethylene carbonate in the total mass of the electrolyte is less than 2%, the amount of addition is too small to fully promote the dissociation of the electrolyte salt, and it is impossible to form sufficient interface protection on the surfaces of the positive and negative electrodes, which will seriously deteriorate the rate performance and cycle performance of the battery.

[0016] According to an embodiment of the present application, the percentage C of the mass of the fluoroethylene carbonate in the total mass of the electrolyte satisfies 20% ≥ C ≥ 1%, for example, 1%, 2%, 3%, 4%, 5%, 8%, 10%, 12%, 15%, 16%, 18% or 20%. Research shows that when the percentage C of the mass of the fluoroethylene carbonate in the total mass of the electrolyte satisfies 20% ≥ C ≥ 1%, the rate performance of the battery can be effectively improved, the side reaction at the interface between the positive and negative electrodes can be avoided, the problem of lithium precipitation at the negative electrode can be inhibited, and the storage performance of the battery at high temperature and high pressure can be improved. When the percentage C of the mass of the fluoroethylene carbonate in the total mass of the electrolyte is greater than 20%, the fluoroethylene carbonate itself is prone to oxidative decomposition at high temperature to form harmful components such as gas and acid, thereby causing the storage performance at high temperature to deteriorate and the oven temperature performance of the battery to be seriously deteriorated. When the percentage C of the mass of the fluoroethylene carbonate in the total mass of the electrolyte is less than 1%, the amount of addition is too small to fully promote the dissociation of the electrolyte salt, and it is impossible to form sufficient interface protection on the surfaces of the positive and negative electrodes, which will seriously deteriorate the rate performance and cycle performance of the battery.

[0017] According to an embodiment of the present application, the solvent X includes a halogenated or non-halogenated saturated alkane containing 6-18 carbon atoms or a halogenated or non-halogenated unsaturated alkane containing 6-18 carbon atoms; preferably, the solvent X includes a halogenated or non-halogenated saturated alkane containing 6-13 carbon atoms or a halogenated or non-halogenated unsaturated alkane containing 6-13 carbon atoms and 1-6 unsaturated bonds.

[0018] Exemplarily, the solvent X comprises at least one of n-hexane, cyclohexane, n-heptane, cycloheptane, n-octane, n-nonane, n-decane, undecane, dodecane, tridecane, 1-fluorohexane, 1-fluoroheptane, 2-methylpentane, 3-methylpentane, 2,3-dimethylbutane, 2-methylhexane, 3-methylhexane and 2,4-dimethylpentane.

[0019] According to the embodiments of the present application, the solvent X can be obtained by commercial channels or prepared by methods known in the art.

[0020] According to the embodiments of the present application, the electrolyte further comprises an additive, and the additive comprises a nitrile additive and / or a sulfur-containing additive.

[0021] According to the embodiments of the present application, the nitrile additive comprises at least one of 1,3,6-hexanetricarbonitrile (HTCN), adiponitrile (AND), succinonitrile (SN), ethylene glycol bis(propionitrile) ether (DENE), phosphoric acid tripropionitrile (PCN) and pentaerythritol tetranitrile, etc. The nitrile additive can coordinate with the positive electrode to improve the stability of the positive electrode interfacial film and improve the electrical performance of the battery at high voltage. As preferred, the mass of the nitrile additive accounts for 2-8wt% of the total mass of the electrolyte, for example, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt% or 8wt%.

[0022] According to the embodiments of the present application, the sulfur-containing additive comprises one or more of 1,3-propane sultone (PS) and vinyl sulfate (DTD). The sulfur-containing additive can form a structure of lithium alkyl sulfonate with high thermal stability on the surface of the negative electrode, thereby improving the stability of the battery in high-temperature cycling and storage. As preferred, the mass of the sulfur-containing additive accounts for 2-8wt% of the total mass of the electrolyte, for example, 2wt%, 3wt%, 4wt%, 5wt%, 6wt%, 7wt% or 8wt%.

[0023] According to the embodiments of the present application, the electrolyte salt is selected from at least one of electrolyte lithium salt, electrolyte sodium salt, electrolyte potassium salt, electrolyte aluminum salt, electrolyte zinc salt, electrolyte magnesium salt, etc.

[0024] According to the embodiments of the present application, the electrolyte lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium difluorophosphate (LiPO2F2), lithium difluoro oxalate borate (LiDFOB), lithium bisfluorosulfonylimide (LiTFSI), lithium bis-trifluoromethylsulfonylimide, lithium difluorobisoxalate phosphate, lithium tetrafluoroborate, lithium bisoxalate borate, lithium hexafluoroantimonate, lithium hexafluoroarsenate, lithium bis(trifluoromethylsulfonyl)imide, lithium bis(pentafluoroethylsulfonyl)imide, lithium tris(trifluoromethylsulfonyl)methide or lithium bis(trifluoromethylsulfonyl)imide.

[0025] According to an embodiment of the present application, the mass of the electrolyte salt is 11-18wt% of the total mass of the electrolyte, for example 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt% or 18wt%.

[0026] According to an embodiment of the present application, the organic solvent further comprises at least one of propylene carbonate (PC), dimethyl carbonate, diethyl carbonate (DEC), methyl ethyl carbonate, propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, propyl propionate (PP), ethyl propionate (EP), methyl butyrate, ethyl n-butyrate.

[0027] According to an embodiment of the present application, the compaction density D of the negative electrode satisfies 2mg / cm 3 ≥D, for example 2mg / cm 3 ≥D≥1.6mg / cm 3 , for example 1.6mg / cm 3 , 1.7mg / cm 3 , 1.8mg / cm 3 , 1.9mg / cm 3 or 2mg / cm 3 . Research has found that when the compaction density D of the negative electrode satisfies 2mg / cm 3 ≥D, it can produce a significant synergistic effect after being used in combination with the solvent X, ethylene carbonate (EC) and fluoroethylene carbonate (FEC) in the electrolyte, can effectively improve the rate performance of the battery, avoid side reactions at the positive and negative electrode interface, improve the storage performance of the battery at high temperature, and at the same time can realize the improvement of lithium precipitation of the negative electrode, and also obtain a battery with high energy density. When the compaction density D of the negative electrode is >2mg / cm 3 , the compaction density of the negative electrode is large and the porosity is low, which makes the proportion of electrolyte contained in the negative electrode less, and the dynamics performance and film forming stability of the electrolyte have higher requirements, which requires more solvent X to make the electrolyte have better dynamics performance, but since the solvent X cannot promote the dissociation of the electrolyte salt and has no interface protection effect itself, more solvent X will have a deteriorating effect on the rate performance and cycle performance of the battery; at the same time, in order to match the high content of solvent X, more ethylene carbonate and fluoroethylene carbonate need to be used, since ethylene carbonate and fluoroethylene carbonate themselves are easy to oxidize and decompose at high temperature, forming harmful components such as gas and acid, which will inevitably cause the battery to have poor high-temperature storage performance and oven temperature performance.

[0028] According to an embodiment of the present application, the negative electrode comprises a negative electrode active material, and the negative electrode active material comprises graphite, and the graphite has a layer structure orientation ratio (OI value) of 8-40, for example, 8, 10, 12, 15, 20, 25, 30, 35 or 40. It has been found that when the graphite has a layer structure orientation ratio (OI value) of 8-40, the ductility of the obtained negative electrode is better, and the negative electrode does not have a powder dropping phenomenon. Moreover, the expansion performance of the obtained negative electrode is moderate, and the phenomenon of excessively high expansion performance of the battery due to a too high OI value can be avoided.

[0029] According to an embodiment of the present application, the negative electrode comprises a negative electrode active material layer and a negative electrode current collector, and the negative electrode active material layer is arranged on at least one side surface of the negative electrode current collector.

[0030] According to an embodiment of the present application, the negative electrode active material layer has a groove structure on the surface.

[0031] According to an embodiment of the present application, the groove is arranged along the length direction of the negative electrode active material layer, for example.

[0032] According to an embodiment of the present application, the groove structure is obtained by etching the surface of the negative electrode active material layer by a laser or other technology.

[0033] According to an embodiment of the present application, the distance between adjacent grooves is 0.5-1.5 mm, for example, 0.5 mm, 0.6 mm, 0.8 mm, 1 mm, 1.2 mm or 1.5 mm.

[0034] According to an embodiment of the present application, the width of the groove is 50-200 μm, for example, 50 μm, 60 μm, 80 μm, 100 μm, 120 μm, 150 μm, 180 μm or 200 μm.

[0035] According to an embodiment of the present application, the depth of the groove is 5-20 μm, for example, 5 μm, 6 μm, 8 μm, 10 μm, 12 μm, 15 μm, 18 μm or 20 μm.

[0036] According to an embodiment of the present application, the negative electrode does not have a groove structure at the head and tail of 2 mm.

[0037] It has been found that when the negative electrode active material layer on the surface of the negative electrode has a groove structure, the kinetic performance of the battery can be effectively improved, and the problem of lithium precipitation of the negative electrode can be completely avoided.

[0038] According to an embodiment of the present application, the battery is a lithium ion battery, for example.

[0039] According to an embodiment of the present application, the negative electrode active material further comprises a silicon-based negative electrode material and / or other carbon-based negative electrode material.

[0040] According to an embodiment of the present application, the silicon-based negative electrode material comprises at least one of nano-silicon (Si), silicon-oxygen negative electrode material (SiOx (0 < x < 2)) and silicon-carbon negative electrode material.

[0041] According to an embodiment of the present application, the other carbon-based negative electrode material comprises at least one of meso-carbon microbead, hard carbon, soft carbon.

[0042] According to an embodiment of the present application, the negative electrode active material layer further comprises a conductive agent and a binder.

[0043] According to an embodiment of the present application, the mass percentage of each component in the negative electrode active material layer is: 80-99.8wt% of negative electrode active material, 0.1-10wt% of conductive agent, 0.1-10wt% of binder.

[0044] Preferably, the mass percentage of each component in the negative electrode active material layer is: 90-99.6wt% of negative electrode active material, 0.2-5wt% of conductive agent, 0.2-5wt% of binder.

[0045] According to an embodiment of the present application, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer coated on one side or both sides of the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material, a conductive agent and a binder.

[0046] According to an embodiment of the present application, the mass percentage of each component in the positive electrode active material layer is: 80-99.8wt% of positive electrode active material, 0.1-10wt% of conductive agent, 0.1-10wt% of binder.

[0047] Preferably, the mass percentage of each component in the positive electrode active material layer is: 90-99.6wt% of positive electrode active material, 0.2-5wt% of conductive agent, 0.2-5wt% of binder.

[0048] According to an embodiment of the present application, the conductive agent is selected from at least one of conductive carbon black, acetylene black, ketjen black, conductive graphite, conductive carbon fiber, carbon nanotube, metal powder, carbon fiber.

[0049] According to an embodiment of the present application, the binder is selected from at least one of sodium carboxymethyl cellulose, styrene butadiene latex, polytetrafluoroethylene, polyethylene oxide.

[0050] According to an embodiment of the present application, the positive electrode active material is selected from one or more of transition metal lithium oxide, lithium iron phosphate, lithium manganate; the chemical formula of the transition metal lithium oxide is Li 1+x Ni y Coz M (1-y-z) O2, wherein -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; wherein M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, Zr.

[0051] Advantages of the present application:

[0052] The present application provides a battery with excellent rate performance and high-temperature storage performance. The battery comprises a positive electrode, a negative electrode, a separator and an electrolyte; the electrolyte comprises an organic solvent and an electrolyte salt; the organic solvent comprises solvent X, ethylene carbonate (EC) and fluoroethylene carbonate (FEC), the solvent X comprises halogenated or non-halogenated saturated alkanes containing more than 6 carbon atoms or halogenated or non-halogenated unsaturated alkanes containing more than 6 carbon atoms; the battery satisfies the following relationships: B+C≥A / 5; A≥35×(D-1.6); this can effectively improve the rate performance of the battery, avoid side reactions at the positive and negative electrode interface, inhibit the occurrence of lithium precipitation problems at the negative electrode, and at the same time improve the storage performance of the battery at high temperature. Further, the negative electrode active material layer surface of the negative electrode is provided with a groove structure, which can effectively improve the kinetic performance of the battery and completely avoid the occurrence of lithium precipitation problems at the negative electrode. BRIEF DESCRIPTION OF DRAWINGS

[0053] Figure 1 Structure diagram of the negative electrode sheet according to a preferred embodiment of the present application. DETAILED DESCRIPTION

[0054] The present application will be further described in detail below with reference to specific examples. It should be understood that the following examples are only illustrative and explanatory of the present application, and should not be interpreted as limiting the scope of protection of the present application. Any technology realized based on the above description of the present application is covered within the scope of protection intended by the present application.

[0055] The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0056] 1) Preparation of the positive electrode sheet

[0057] The positive active material lithium cobaltate (LiCoO2), polyvinylidene fluoride (PVDF), SP (super P) and carbon nanotubes (CNTs) are mixed in a mass ratio of 96:2:1.5:0.5, N-methyl pyrrolidone (NMP) is added, and stirring is performed under the action of a vacuum stirrer until the mixed system becomes a positive active paste with uniform fluidity; the positive active paste is uniformly coated on both surfaces of an aluminum foil; the coated aluminum foil is dried, then rolled, and cut to obtain the required positive electrode sheet.

[0058] 2) Preparation of negative electrode sheet

[0059] The negative active material artificial graphite (OI value of 20), sodium carboxymethyl cellulose (CMC-Na), butadiene rubber, conductive carbon black (SP) and single-walled carbon nanotubes (SWCNTs) are mixed in a mass ratio of 94.5:2.5:1.5:1:0.5, deionized water is added, and a negative active paste is obtained under the action of a vacuum stirrer; the negative active paste is uniformly coated on both surfaces of a copper foil; the coated copper foil is dried at room temperature, then transferred to a 80℃ oven for drying for 10h, and then cold-pressed and cut to obtain a negative electrode sheet. Etching is performed on the surface of the negative active material layer by laser technology, wherein the grooves are arranged along the length direction of the negative active material layer, the distance between adjacent grooves is 0.8mm; the width of the groove is 100μm; the depth of the groove is 10μm, and the head and tail of the negative electrode sheet are not provided with groove structures.

[0060] 3) Preparation of electrolyte

[0061] In an argon-filled glove box (H2O<0.1ppm, O2<0.1ppm), the solvent X (n-octane) / EC / FEC / DEC is mixed uniformly in a mass ratio of A:B:C:(82-A-B-C). Then 12wt% of fully dried lithium hexafluorophosphate (LiPF6) based on the total mass of the electrolyte is quickly added, followed by 2wt% of HTCN, 1wt% of ADN and 3wt% of PS based on the total mass of the electrolyte. After stirring uniformly, the obtained electrolyte is qualified by water content and free acid detection.

[0062] 4) Preparation of lithium ion battery

[0063] The positive electrode sheet of step 1), the negative electrode sheet of step 2) and the separator are stacked in the order of positive electrode sheet, separator and negative electrode sheet, and then wound to obtain a battery cell; the battery cell is placed in an outer packaging aluminum foil, the electrolyte of step 3) is injected into the outer packaging, and then vacuum packaging, standing, formation, shaping, sorting and other processes are performed to obtain a lithium ion battery. The battery of the present application has a charge-discharge range of 3.0-4.5V.

[0064] The lithium ion batteries obtained in the examples and comparative examples were subjected to performance tests, and the test results are shown in Table 2.

[0065] 1) 60℃ storage performance test

[0066] The prepared lithium ion battery was charged at 25℃ to the cut-off voltage at a rate of 1C, the cut-off current was 0.025C, and the lithium ion battery was rested for 5 min. The thickness of the lithium ion battery was tested (as the thickness before storage). The fully charged cell / battery was left to stand open-circuit at (60±2)℃ for 35 days, and after 35 days of storage, it was left to stand open-circuit at room temperature for 2h. The thickness after storage was measured, and the thickness expansion rate of the lithium ion battery was calculated:

[0067] Thickness expansion rate = [(thickness after storage - thickness before storage) / thickness before storage] x 100%.

[0068] 2) 25℃ cycle performance test

[0069] The prepared lithium ion battery was subjected to charge-discharge cycling at 25℃ at a rate of 3C within the charge-discharge cut-off voltage range. The discharge capacity of the first week was counted as x1 mAh, and the discharge capacity of the Nth cycle was counted as y1 mAh. The cycle capacity retention rate R2 of the Nth week was obtained by dividing the capacity of the Nth week by the capacity of the first week, and the cycle number of the battery when the cycle capacity retention rate R2 was 80% was recorded.

[0070] 3) Furnace temperature performance test

[0071] The prepared lithium ion battery was subjected to a furnace temperature performance test. Five fully charged batteries were stored at 130℃ for 1h, and the number of batteries that did not catch fire or explode was observed.

[0072] 4) Negative electrode lithium precipitation test

[0073] The prepared lithium ion battery was charged at 1C, and after reaching the rated voltage, it was cut off at a constant voltage of 0.05C. The battery was disassembled in a dry room, and the negative electrode was exposed. The surface of the negative electrode was observed for signs of lithium metal deposition. A normally fully charged negative electrode has a golden yellow uniform surface, and the presence of lithium metal deposition will have a silver white trace.

[0074] Table 1 Composition of electrolyte and compaction density of negative electrode sheet of examples and comparative examples

[0075]

[0076] Example 21

[0077] The other operations were the same as in Example 2, except that the negative electrode sheet was not subjected to laser treatment, and no groove structure was provided on the negative electrode active material layer on the surface of the negative electrode.

[0078] Example 22

[0079] Other operations are the same as in Example 2, except that the negative active material is selected to be artificial graphite with an OI value of 40.

[0080] Example 23

[0081] Other operations are the same as in Example 2, except that the negative active material is selected to be artificial graphite with an OI value of 50.

[0082] Example 24

[0083] Other operations are the same as in Example 2, except that the negative active material is artificial graphite and silicon-carbon negative material in a mass ratio of 95:5.

[0084] Example 25

[0085] Other operations are the same as in Example 2, except that the negative active material is artificial graphite and silicon-oxygen negative material in a mass ratio of 95:5.

[0086] Example 26

[0087] Other operations are the same as in Example 2, except that the solvent X is n-hexane.

[0088] Table 2 Performance test results of batteries of Examples and Comparative Examples

[0089]

[0090]

[0091] From the above performance test results, it can be seen that by jointly using the negative electrode sheet with a specific compaction density, the solvent X, ethylene carbonate (EC) and fluoroethylene carbonate (FEC), and by making the battery satisfy B+C≥A / 5 and A≥35×(D-1.6), a significant synergistic effect can be produced, the electrolyte can have the characteristics of high electrical conductivity, fast charging interface stability and high temperature storage stability. Therefore, the rate performance of the battery can be effectively improved, the side reaction at the positive and negative electrode interface can be avoided, the storage performance of the battery at high temperature can be improved, and the improvement of lithium precipitation at the negative electrode can be realized. When the battery satisfies B+C<A / 5 or A<35×(D-1.6), the rate performance of the battery cannot be effectively improved, the side reaction at the positive and negative electrode interface cannot be avoided, the problem of lithium precipitation at the negative electrode cannot be inhibited, and the storage performance of the battery at high temperature is poor.

[0092] The above describes embodiments of the present application. However, the present application is not limited to the above embodiments. Any modification, equivalent replacement, improvement, etc. made within the spirit and principles of the present application shall be included in the protection scope of the present application.

Claims

1. A battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte solution; the electrolyte solution comprises an organic solvent and an electrolyte salt; the organic solvent comprises solvent X, ethylene carbonate (EC) and fluoroethylene carbonate (FEC), the solvent X comprises a halogenated or non-halogenated saturated alkane containing more than 6 carbon atoms or a halogenated or non-halogenated unsaturated alkane containing more than 6 carbon atoms; the battery satisfies the following relationship: B+C≥A / 5; A≥35×(D-1.6); the negative electrode comprises a negative electrode active material layer and a negative electrode current collector, the negative electrode active material layer is arranged on at least one side surface of the negative electrode current collector; the negative electrode active material layer surface has a groove structure; the distance between adjacent grooves is 0.5mm-1.5mm; the width of the groove is 50-200μm; the depth of the groove is 5-20μm. The solvent X comprises a halogenated or non-halogenated saturated alkane containing 6-18 carbon atoms or a halogenated or non-halogenated unsaturated alkane containing 6-18 carbon atoms. The solvent X comprises a halogenated or non-halogenated saturated alkane containing 6-13 carbon atoms or a halogenated or non-halogenated unsaturated alkane containing 6-13 carbon atoms and 1-6 unsaturated bonds. The solvent X comprises at least one of n-hexane, cyclohexane, n-heptane, cycloheptane, n-octane, n-nonane, n-decane, undecane, dodecane, tridecane, 1-fluorohexane, 1-fluoroheptane, 2-methylpentane, 3-methylpentane, 2,3-dimethylbutane, 2-methylhexane, 3-methylhexane and 2,4-dimethylpentane. wherein, A is the percentage of the mass of the solvent X in the total mass of the electrolyte; B is the percentage of the mass of the ethylene carbonate in the total mass of the electrolyte; C is the percentage of the mass of the fluoroethylene carbonate in the total mass of the electrolyte; D is the compacted density of the negative electrode, in mg / cm 3 ; The percentage A of the mass of the solvent X in the total mass of the electrolyte satisfies 60% ≥ A ≥ 5%; the percentage B of the mass of the ethylene carbonate in the total mass of the electrolyte satisfies 30% ≥ B ≥ 2%; the percentage C of the mass of the fluoroethylene carbonate in the total mass of the electrolyte satisfies 20% ≥ C ≥ 1%; and the compaction density D of the negative electrode satisfies 2 mg / cm 3 ≥ D ≥ 1.6 mg / cm 3 . The electrolyte solution further comprises an additive, the additive comprises a nitrile-based additive and / or a sulfur-containing additive.

2. The battery of claim 1, wherein, The nitrile-based additive comprises at least one of 1,3,6-hexanetricarbonitrile (HTCN), adiponitrile (AND), succinonitrile (SN), ethylene glycol bis(propionitrile) ether (DENE), phosphoric acid tripropionitrile (PCN) and pentaerythritol cyanophosphate; the sulfur-containing additive comprises one or more of 1,3-propanesultone (PS) and ethylene sulfate (DTD).

3. The battery of claim 2, wherein, The negative electrode comprises a negative electrode active material, the negative electrode active material comprises graphite, and the graphite has a layer structure orientation ratio of 8-40.

4. The battery of claim 3, wherein, The negative electrode active material further comprises a silicon-based negative electrode material and / or a carbon-based negative electrode material; the silicon-based negative electrode material comprises at least one of nano-silicon, silicon-oxygen negative electrode material and silicon-carbon negative electrode material; the carbon-based negative electrode material comprises at least one of mesocarbon microbead, hard carbon and soft carbon.

5. The battery of claim 1, wherein, ​ 6. The battery of claim 5, wherein, ​ 7. The battery of claim 1, wherein, ​ 8. The battery of claim 7, wherein, ​

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