Lithium-ion battery

Abstract

A lithium-ion battery having excellent high-temperature storage and high-temperature cycling performance. The lithium-ion battery comprises a positive electrode, a negative electrode, and a non-aqueous electrolyte solution. The negative electrode comprises a negative electrode material layer containing a silicon-based material. The non-aqueous electrolyte solution comprises a lithium salt, an organic solvent, and an additive, the organic solvent comprising fluoroethylene carbonate, and the additive comprising a silane compound containing at least one carbon-carbon double bond. The lithium-ion battery satisfies the following conditions: 5≤(S*R) / (F*T)≤35, 5≤f≤15, 1.4≤R≤1.68, 9≤S≤18, and 0.01≤T≤0.5. According to the lithium-ion battery, the mass percentage content of the organic solvent and the additive in the non-aqueous electrolyte solution are controlled, and the mass percentage content of elemental silicon in the negative electrode material layer is controlled and the compaction density of the negative electrode material layer is controlled to be within a certain range, such that the lithium-ion battery has excellent high-temperature storage performance and an excellent high-temperature cycle life, while also taking into account high energy density.

Description

A lithium-ion battery Technical Field

[0001] The present application relates to the technical field of lithium-ion batteries, and in particular to a lithium-ion battery with excellent high-temperature storage and high-temperature cycle performance. Background Art

[0002] Lithium-ion batteries, with their advantages of high operating voltage, wide operating temperature range, high output power, no memory effect, and long cycle life, have found widespread application in smartphones, portable appliances, medical electronics, aerospace, power tools, hybrid vehicles, and other fields. With the rapidly increasing demand for battery energy density in various fields, there is an urgent need to develop lithium-ion batteries with higher energy density.

[0003] Currently, the negative electrodes used in lithium-ion secondary batteries are primarily carbon-based materials, which offer advantages in terms of charge-discharge cycle life and cost. Silicon-based materials, however, have rapidly developed due to their higher theoretical capacity and ability to achieve high energy density. However, the expansion and contraction of the active materials in silicon-based negative electrodes during lithium ion absorption and desorption causes large volume changes, which continuously break down and reorganize the SEI film (solid electrolyte interphase). The active material particles cleave during repeated charge and discharge cycles, exposing new active surfaces. This new active surface easily decomposes the electrolyte solvent, thereby degrading the battery's cycling characteristics. Furthermore, under high temperature conditions, the volume change of the silicon-based negative electrode active material increases further, accelerating the failure of the lithium-ion secondary battery. In real life, lithium-ion secondary batteries used in power tools and hybrid electric vehicles are difficult to maintain at their optimal temperature for long periods of time. Lithium-ion secondary batteries are typically exposed to high temperatures during prolonged use, and the expansion and contraction of the silicon-based negative electrode active material further increases the volume change, damaging the SEI film on the negative electrode surface or interfering with its repair, thereby shortening the battery's service life.

[0004] Therefore, there is a need to develop secondary lithium-ion batteries that have excellent high-temperature storage and high-temperature cycling performance while achieving high energy density.

[0005] Application Contents

[0006] In order to solve the above technical problems, the present application provides a lithium-ion battery with excellent high-temperature storage and high-temperature cycle performance.

[0007] This application adopts the following technical solutions:

[0008] A lithium-ion battery comprising a positive electrode, a negative electrode and a non-aqueous electrolyte;

[0009] The negative electrode includes a negative electrode material layer containing a negative electrode active material, and the negative electrode active material includes a silicon-based material;

[0010] The non-aqueous electrolyte includes a lithium salt, an organic solvent, and an additive, wherein the organic solvent includes fluoroethylene carbonate, and the additive includes a silane compound shown in Structural Formula 1:

[0011] wherein R1, R2, R3 and R4 are each independently selected from substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C5 alkenyl and substituted or unsubstituted C2-C5 alkynyl, and at least one of R1-R4 is selected from substituted or unsubstituted C2-C5 alkenyl;

[0012] The lithium-ion battery meets the following conditions:

[0013] 5≤(S×R) / (F×T)≤35, and 9≤S≤18, 1.4≤R≤1.68, 5≤F≤15, 0.025≤T≤0.5;

[0014] Wherein, S is the mass percentage of silicon element in the negative electrode material layer, in wt%;

[0015] R is the compaction density of the negative electrode material layer, in g / cm 3 ;

[0016] F is the mass percentage of fluoroethylene carbonate in the non-aqueous electrolyte, in wt%;

[0017] T is the mass percentage of the silane compound represented by structural formula 1 in the non-aqueous electrolyte, in wt%.

[0018] The lithium-ion battery of the present application uses a silicon-based negative electrode material, which can effectively improve the battery energy density. The higher the silicon content in the negative electrode active material, the higher its theoretical energy density. However, since the volume of silicon-based negative electrode active materials changes greatly (100-300%) as lithium ions are inserted and removed during the charge and discharge process of the lithium-ion battery, it is easy to cause degradation problems such as disconnection of the electron conduction path in the electrode and particle micronization. The micronization of particles will cause the exposure of new surfaces with high activity. Their surfaces will react with the electrolyte and cause the surface of the active material to deteriorate. In addition, under high temperature conditions, the reaction between the electrolyte and the surface of the negative electrode active material becomes more intense, resulting in problems such as a decrease in the capacity of the active material and a shortened battery life. Therefore, it is necessary to control the silicon content. In addition, the higher the silicon content in the negative electrode active material, the greater the volume change caused by the insertion / extraction of lithium ions. Therefore, while controlling the silicon content, the battery performance is guaranteed by regulating the compaction density of the negative electrode material layer. Specifically, since the smaller the compaction density of the negative electrode material layer, the more developed the pore structure of the negative electrode material layer, the more conducive to the liquid phase conduction of the active particles. Even if the silicon content in the negative electrode active material increases, the negative electrode material layer can withstand the repeated expansion of the battery after multiple charge and discharge cycles. However, if the compaction density is too small, the negative electrode plate will peel off and powder will fall off, and the poor electronic conductivity during charging will cause lithium precipitation, which will affect the battery life and reduce the energy density of the battery. Therefore, the present application controls the silicon content in the negative electrode material layer while regulating the compaction density of the negative electrode material layer. By adjusting the compaction density of the negative electrode material layer, the compaction density of the negative electrode material layer can be reduced while the silicon content increases, so as to maintain the product (S×R) of the mass percentage S of the silicon element in the negative electrode material layer and the compaction density R of the negative electrode material layer in the negative electrode plate relatively stable. Specifically, the mass percentage content S of silicon in the negative electrode material layer is 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt%, 16wt%, 17wt%, 18wt% or any range thereof; preferably, the mass percentage content S of silicon in the negative electrode material layer is 10wt% to 16wt%. The compaction density R of the negative electrode material layer is 1.4g / cm 3 , 1.45g / cm 3 , 1.48g / cm 3 , 1.5g / cm 3 , 1.52g / cm 3 , 1.55g / cm 3 、1.58g / cm 3 , 1.6g / cm 3 , 1.63g / cm 3 , 1.65g / cm 3 , 1.68g / cm 3Or any range of the above values; preferably, the compaction density R of the negative electrode material layer is 1.5g / cm 3 ~1.65g / cm 3 .

[0019] Fluoroethylene carbonate (FEC) can form a solid electrolyte film with good elasticity on the surface of silicon-based negative electrodes, effectively connecting the silicon-based active material, inhibiting its volume change during the charge and discharge process, ensuring good contact between particles, significantly improving the capacity retention rate of lithium-ion batteries, and reducing the thickness expansion rate of the negative electrode sheet. During the cycle process, when the content of fluoroethylene carbonate is insufficient, the cycle life of the negative electrode containing silicon-based negative electrode active material will suddenly drop; however, too high a fluoroethylene carbonate content may lead to an aggravation of the battery gas production problem, which will also cause the battery cycle life to decline. In addition, excessive fluoroethylene carbonate will increase the charge exchange impedance of the interface, causing an increase in battery impedance and affecting the battery's electrochemical performance. Therefore, the amount of fluoroethylene carbonate added needs to be controlled according to the silicon content in the negative electrode material layer to effectively extend the cycle life of the negative electrode containing silicon-based negative electrode active material. Specifically, the mass percentage F of fluoroethylene carbonate in the non-aqueous electrolyte is 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt% or any range consisting of the above values; preferably, the mass percentage F of fluoroethylene carbonate in the non-aqueous electrolyte is 6wt% to 12wt%.

[0020] Silicon-based negative electrodes lack stability, and side reactions are more numerous and intense than in other systems. The silane compound shown in Structural Formula 1, due to its unsaturated carbon-carbon double bond, can absorb unstable free radicals in the electrolyte, reducing side reactions and gaining electrons on the negative electrode surface to form organic carbonates to protect the negative electrode. It also forms a film on the positive electrode, protecting the battery's high-temperature performance and suppressing gas generation during high-temperature storage. However, similar to fluoroethylene carbonate, excessive use of the silane compound shown in Structural Formula 1 can increase battery impedance and affect its electrochemical performance. Therefore, it is necessary to control the amount of the silane compound shown in Structural Formula 1 and fluoroethylene carbonate used. The content of fluoroethylene carbonate in the non-aqueous electrolyte (F) and the product of the mass percentage of the silane compound shown in Structural Formula 1 in the non-aqueous electrolyte (T) (F×T) should be adjusted based on the product of the silicon content S in the negative electrode material layer and the compacted density R of the negative electrode material layer (S×R) to balance their effects on high-temperature performance and the overall electrochemical performance of the battery. Specifically, the mass percentage T of the silane compound represented by the structural formula 1 in the non-aqueous electrolyte may be, but is not limited to, 0.025wt%, 0.03wt%, 0.05wt%, 0.07wt%, 0.09wt%, 0.1wt%, 0.12wt%, 0.15wt%, 0.16wt%, 0.18wt%, 0.2wt%, 0.24wt%, 0.25wt%, 0.27wt%, 0.3wt%, 0.35wt%, 0.38wt%, 0.4wt%, 0.42wt%, 0.45wt%, 0.48wt%, 0.5wt% or any range consisting of the above values; preferably, the mass percentage F of the silane compound represented by the structural formula 1 in the non-aqueous electrolyte is 0.05wt% to 0.3wt%.

[0021] Specifically, the value of (S×R) / (F×T) can be, but is not limited to, 5, 6, 7, 8, 9, 10, 12, 14, 15, 16, 18, 20, 21, 22, 24, 25, 27, 28, 30, 32, 33, or 35; preferably, the value of (S×R) / (F×T) is 6 to 30, which allows the lithium-ion battery to have high energy density while having excellent high-temperature storage performance and high-temperature cycle life.

[0022] In some embodiments, in the silane compound represented by structural formula 1, R1, R2, R3 and R4 are each independently selected from substituted or unsubstituted C2 to C5 alkenyl and substituted or unsubstituted C2 to C5 alkynyl; more preferably, R1, R2, R3 and R4 are each independently selected from substituted or unsubstituted C2 to C5 alkenyl.

[0023] In some preferred embodiments, the silane compound represented by Structural Formula 1 includes at least one of tetravinylsilane, trivinylethylsilane, divinyldiethylsilane, trivinylethoxysilane, vinyltriethylsilane, trivinylethynylsilane, tetrapropylenesilane, trivinylpropylsilane, tripropylenepropylsilane, dipropylenedipropylsilane, and divinyldipropylsilane. More preferably, the silane compound represented by Structural Formula 1 is tetravinylsilane.

[0024] In some embodiments, the silicon-based material includes at least one of a silicon material, a silicon oxide material, a silicon carbon material, and a silicon alloy material.

[0025] In some preferred embodiments, the silicon material is a nano-silicon material.

[0026] In some preferred embodiments, the silicon oxide material is SiO x Materials, where 0≤x<2.

[0027] In some preferred embodiments, the silicon-carbon material is a silicon-based material containing silicon and carbon material, and / or containing SiO y and silicon-based materials of carbon materials, wherein 0≤y<2.

[0028] In some preferred embodiments, the silicon alloy material is a Mg2Si alloy material and / or a Fe2Si alloy material.

[0029] Silicon-based materials have high specific capacity, but their lithium insertion mechanism is prone to volume expansion, which can lead to cracking and failure of the electrode material. Carbon-based materials are more stable than silicon-based materials. In some preferred embodiments, the silicon-based material is selected from silicon-carbon materials. The silicon and carbon in the silicon-carbon material form a complementary relationship. The high specific capacity of the silicon-based material combined with the cyclic stability of the carbon-based material can effectively solve the problem of material expansion failure while taking into account good cyclic performance. More preferably, the silicon-carbon material is a silicon-based material containing silicon monoxide and graphite.

[0030] In some embodiments, the organic solvent further comprises at least one of cyclic carbonates, linear carbonates, carboxylates, and ether compounds other than fluoroethylene carbonate.

[0031] In some preferred embodiments, the cyclic carbonate includes at least one of ethylene carbonate, propylene carbonate, vinylene carbonate and butylene carbonate.

[0032] In some preferred embodiments, the linear carbonate includes at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate.

[0033] In some preferred embodiments, the carboxylic acid ester includes at least one of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate, and ethyl trimethylacetate.

[0034] In some preferred embodiments, the ether compound includes at least one of ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

[0035] In some embodiments, the non-aqueous electrolyte further includes an auxiliary additive, and the auxiliary additive includes at least one of a cyclic sulfate compound, a sultone compound, a cyclic carbonate compound, a phosphate compound, a borate compound, and a nitrile compound.

[0036] In some preferred embodiments, the cyclic sulfate ester compound includes at least one of 4-methylethylene sulfate and propylene sulfate.

[0037] In some preferred embodiments, the sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone, and propenyl-1,3-sultone.

[0038] In some preferred embodiments, the cyclic carbonate compound includes at least one of vinylene carbonate, vinyl ethylene carbonate, methylene carbonate, fluoroethylene carbonate (FEC), trifluoromethyl ethylene carbonate, bisfluoroethylene carbonate and the compound represented by the following structural formula 2:

[0039] In the structural formula 2 shown, R 21 、R 22 、R 23 、R 24 、R 25 、R 26 Each is independently selected from a hydrogen atom, a halogen atom, and a C1-C5 group;

[0040] In some preferred embodiments, the compound represented by structural formula 2 includes at least one of the following compounds 2-1 to 2-6:

[0041] In some preferred embodiments, the phosphate compound includes at least one of tris(trimethylsilyl)phosphate (TMSP), tris(triethylsilyl)phosphate and the compound represented by the following structural formula 3:

[0042] In the structural formula 3, R 31 、R 32 、R33 Each independently selected from C1-C5 saturated hydrocarbon group, unsaturated hydrocarbon group, halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 、R 32 、R 33 At least one of the groups is an unsaturated hydrocarbon group; more preferably, the compound represented by structural formula 3 includes at least one of tripropargyl phosphate, dipropargyl methyl phosphate, dipropargyl ethyl phosphate, dipropargyl propyl phosphate, dipropargyl trifluoromethyl phosphate, dipropargyl-2,2,2-trifluoroethyl phosphate, dipropargyl-3,3,3-trifluoropropyl phosphate, dipropargyl hexafluoroisopropyl phosphate, triallyl phosphate, diallyl methyl phosphate, diallyl ethyl phosphate, diallyl propyl phosphate, diallyl trifluoromethyl phosphate, diallyl-2,2,2-trifluoroethyl phosphate, diallyl-3,3,3-trifluoropropyl phosphate, and diallyl hexafluoroisopropyl phosphate.

[0043] In some preferred embodiments, the borate compound includes at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate.

[0044] In some preferred embodiments, the nitrile compound includes at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrionitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebaconitrile.

[0045] In some embodiments, based on the total mass of the non-aqueous electrolyte as 100%, the content of the auxiliary additive is 0.01wt% to 10wt%. Preferably, the content is 0.1wt% to 5wt%; more preferably, the content is 0.1wt% to 2wt%. Specifically, the content of any one of the optional substances in the auxiliary additives can be 0.01%, 0.05%, 0.08%, 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.2%, 2.5%, 2.8%, 3%, 3.2%, 3.5%, 3.8%, 4%, 4.5%, or 5%.

[0046] In some embodiments, the lithium salt includes LiPF6, LiPO2F2, LiBF4, LiBOB, LiSbF6, LiAsF6, LiCF3SO3, LiDFOB, LiDFOP, LiN(SO2CF3)2, LiC(SO2CF3)3, LiN(SO2C2F5)2, LiN(SO2F)2, LiCl, LiBr, LiI, LiClO4, LiB 10 Cl 10, at least one of LiAlCl4, lithium chloroborane, lithium lower aliphatic carboxylate having less than 4 carbon atoms, lithium tetraphenylborate, and lithium imide.

[0047] In a specific embodiment, the total molar content of the lithium salt is 0.1 mol / L to 4 mol / L. In a preferred embodiment, the total molar content of the lithium salt is 0.5 mol / L - 2.5 mol / L. Specifically, the total molar content of the lithium salt can be 0.5 mol / L, 0.55 mol / L, 0.6 mol / L, 0.65 mol / L, 0.7 mol / L, 0.8 mol / L, 0.85 mol / L, 0.9 mol / L, 0.95 mol / L, 1.0 mol / L, 1.1 mol / L, 1.15 mol / L, 1.2 mol / L, 1.3 mol / L, 1.4 mol / L, 1.45 mol / L, 1.5 mol / L, 1.6 mol / L, 1.7 mol / L, 1.8 mol / L, 1.9 mol / L, 2.0 mol / L, 2.1 mol / L, 2.2 mol / L, 2.3 mol / L, 2.4 mol / L or 2.5 mol / L.

[0048] In some embodiments, the positive electrode material layer includes a positive electrode material layer containing a positive electrode active material, a positive electrode binder, and a positive electrode conductive agent. The positive electrode active material includes Li 1+x Ni a Co b M’ 1-a-b O 2-y A y , where -0.1 ≤ x ≤ 0.2, 0 < a < 1, 0 ≤ b < 1, 0 < a + b < 1, 0 ≤ y < 0.2, M’ includes one or more of Mn, Al, Sr, Mg, Ti, Ca, Zr, Zn, Si, Fe, Ce, Nb, Ga, Cu, Sn, Cr, W or V; specifically, the positive electrode active material includes LiNi 0.5 Co 0.2 Mn 0.3 O2, LiNi 0.5 Co 0.2 Mn 0.2 Al 0.1 O2, LiNi 0.6 Co 0.1 Mn 0.3 O2, LiNi 0.6 Co 0.2 Mn 0.2 O2, LiNi 0.65 Mn 0.35 O2, LiNi 0.75 Mn0.25 O2、LiNi 0.7 Co 0.1 Mn 0.2 O2、LiNi 0.8 Co 0.05 Mn 0.15 O2、LiNi 0.8 Co 0.1 Mn 0.1 O2、LiNi 0.9 Co 0.05 Mn 0.05 O2、LiNi 0.8 Co 0.15 Al 0.05 One or more of O2.

[0049] The positive electrode binder includes polyvinylidene fluoride, a copolymer of vinylidene fluoride, polytetrafluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene, a copolymer of tetrafluoroethylene-hexafluoropropylene, a copolymer of tetrafluoroethylene-perfluoroalkyl vinyl ether, a copolymer of ethylene-tetrafluoroethylene, a copolymer of vinylidene fluoride-tetrafluoroethylene, a copolymer of vinylidene fluoride-trifluoroethylene, a copolymer of vinylidene fluoride-trichloroethylene, a copolymer of vinylidene fluoride-fluoroethylene, a copolymer of vinylidene fluoride-hexafluoropropylene-tetrafluoroethylene, thermoplastic polyimide, a thermoplastic resin such as polyethylene and polypropylene; an acrylic resin; and one or more of styrene butadiene rubber.

[0050] The positive electrode conductive agent includes one or more of conductive carbon black, conductive carbon balls, conductive graphite, conductive carbon fibers, carbon nanotubes, graphene, or reduced graphene oxide.

[0051] In some embodiments, the negative electrode further comprises a negative electrode current collector, and the negative electrode material layer is disposed on the surface of the negative electrode current collector. The material of the negative electrode current collector can be the same as that of the positive electrode current collector, which will not be described in detail here.

[0052] In some embodiments, the negative electrode material layer further includes a negative electrode binder and a negative electrode conductive agent. The negative electrode active material, the negative electrode binder, and the negative electrode conductive agent are blended together to form the negative electrode material layer. The negative electrode binder and the negative electrode conductive agent may be the same as the positive electrode binder and the positive electrode conductive agent, respectively, and are not further described here.

[0053] In some embodiments, the lithium-ion battery further includes a separator, and the separator is located between the positive electrode and the negative electrode.

[0054] The separator can be a conventional existing separator, such as a ceramic separator, a polymer separator, a non-woven fabric, an inorganic-organic composite separator, etc., including but not limited to single-layer PP (polypropylene), single-layer PE (polyethylene), double-layer PP / PE, double-layer PP / PP, and three-layer PP / PE / PP separators.

[0055] For the lithium-ion battery of the present application, a silicon-based negative electrode active material is selected, fluorinated ethylene carbonate is used as an organic solvent, and a silane compound having at least one carbon-carbon double bond shown in Structural Formula 1 is used as an additive. By controlling the mass percentage of fluorinated ethylene carbonate and the silane compound shown in Structural Formula 1 in the non-aqueous electrolyte, the capacity retention rate of the battery is increased and gas generation during high-temperature storage is inhibited; at the same time, the mass percentage of silicon element in the negative electrode material layer and the compaction density of the negative electrode material layer are controlled within a certain range, which can not only ensure the insertion / extraction of lithium ions in the negative electrode, but also control the compaction density of the negative electrode to ensure the battery life; when the lithium-ion battery satisfies the following conditions: 5 ≤ (S × R) / (F × T) ≤ 35, and 5 < F ≤ 15, 1.4 ≤ R ≤ 1.68, 9 ≤ S ≤ 18, 0.01 ≤ T ≤ 0.5, the lithium-ion battery can have excellent high-temperature storage performance and high-temperature cycle life while taking into account high energy density. Detailed implementation manners

[0056] The technical solutions in the embodiments of the present application will be clearly and completely described below in conjunction with the embodiments in the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. All other embodiments obtained by those of ordinary skill in the art based on the embodiments in the present application without creative efforts shall fall within the protection scope of the present application.

[0057] Embodiment 1

[0058] The preparation method of the lithium-ion battery in this embodiment includes the following steps:

[0059] 1) Preparation of the electrolyte:

[0060] Ethylene carbonate (EC), diethyl carbonate (DEC), and ethyl methyl carbonate (EMC) are mixed in a volume ratio of EC:DEC:EMC = 20:30:50, then lithium hexafluorophosphate (LiPF₆) is added to a molar concentration of 1.0 mol / L, and then fluorinated ethylene carbonate (FEC) and tetravinylsilane are added. Based on the total weight of the electrolyte being 100%, the mass percentages of fluorinated ethylene carbonate (FEC) and tetravinylsilane in the electrolyte are shown in Table ①.

[0061] 2) Preparation of the positive electrode:

[0062] Mix the positive electrode active material LiNi in a mass ratio of0.8 Co 0.1 Mn 0.1 O2, conductive carbon black Super-P, and a binder called polyvinylidene fluoride (PVDF) are then dispersed in N-methyl-2-pyrrolidone (NMP) to create a positive electrode slurry. The slurry is evenly coated on both sides of aluminum foil, dried, rolled, and vacuum-dried. Aluminum lead wires are then ultrasonically welded to create the positive electrode plate, which is between 120 and 150 μm thick.

[0063] 3) Preparation of negative electrode:

[0064] A silicon-carbon material (a mixture of silicon oxide and graphite, with a silicon content of 7% by weight), conductive carbon black Super-P, binders styrene-butadiene rubber (SBR), and carboxymethyl cellulose (CMC) were mixed in a mass ratio of 94:1.5:3.0:1.5 and dispersed in deionized water to produce a negative electrode slurry. The slurry was coated on both sides of a copper foil, dried, rolled, and vacuum-dried, and nickel lead wires were ultrasonically welded to produce a negative electrode plate. The plate thickness ranged from 120 to 150 μm. The compaction density of the negative electrode material layer is shown in Table 1.

[0065] 4) Battery assembly:

[0066] A separator is placed between the positive plate and the negative plate, and then the sandwich structure consisting of the positive plate, negative plate and separator is wound. The wound body is flattened and placed in an aluminum-plastic shell. After welding the tabs, the aluminum-plastic shell is sealed to obtain a battery cell ready for liquid injection.

[0067] In a glove box with a dew point controlled below -40°C, the prepared electrolyte was injected into the battery cell, and the cell was sealed after being left to rest for 1 hour. After sealing, the battery was aged at 45°C for 48 hours.

[0068] Then, the first charge was performed at 45°C hot pressing according to the following steps: 0.05C constant current charging for 3 hours, upper limit voltage 4.0V, pressure 3kg / cc; 0.1C constant current charging for 2 hours, upper limit voltage 4.0V, pressure 5kg / cc; 0.2C constant current charging for 2 hours, upper limit voltage 4.0V, pressure 5kg / cc; 45°C shelving for 48 hours, and then further charged at a constant current of 0.2C to 4.2V, and discharged at a constant current of 0.2C to 2.75V.

[0069] Examples 2-25 and Comparative Examples 1-14

[0070] This Example and Comparative Example are used to compare and illustrate the lithium-ion battery disclosed in this application. They include most of the operating steps in the above-mentioned Example 1. The differences are as follows: based on the total weight of the non-aqueous electrolyte being 100%, the mass percentages of fluoroethylene carbonate and the silane compound represented by Structural Formula 1 in the non-aqueous electrolyte, the composition of the negative electrode active material, the silicon content in the negative electrode material layer, and the compaction density of the negative electrode material layer are as shown in Table 1.

[0071] Table 1

[0072] The lithium-ion batteries prepared in the examples and comparative examples were subjected to performance tests as follows:

[0073] 1. High temperature storage performance test

[0074] At 25°C, the formed battery was charged to 4.2V using a constant current and constant voltage of 0.5C, with a cutoff current of 0.05C. It was then discharged to 2.75V using a constant current of 1C, and the initial discharge capacity was recorded. It was then charged to 4.2V using a constant current and constant voltage of 0.5C, with a cutoff current of 0.05C. The battery was then fully charged and stored at 45°C for 60 days, and then discharged to 2.75V using a constant current of 1C. The battery's retention capacity was measured, and the capacity retention rate after 60 days of high-temperature storage was calculated. The calculation formula is as follows:

[0075] Battery capacity retention rate (%) = retention capacity / initial discharge capacity×100%.

[0076] 2. High temperature cycle performance test

[0077] At 45°C, the formed battery is charged to 4.2V with a constant current and constant voltage of 1C, then discharged to 2.75V with a constant current of 1C. After 800 charge / discharge cycles, the capacity retention rate at the 800th cycle is calculated. The calculation formula is as follows:

[0078] 800th cycle capacity retention rate (%)=(800th cycle discharge capacity / 1st cycle discharge capacity)×100%.

[0079] (1) The test results of Examples 1-14 and Comparative Examples 1-14 are shown in Table 2.

[0080] Table 2

[0081] It can be seen from the test results of Examples 1-14 that the lithium-ion battery of the present application uses a silicon-based negative electrode active material, uses fluoroethylene carbonate as an organic solvent, and uses a silane compound containing at least one carbon-carbon double bond as an additive. By controlling the mass percentage of fluoroethylene carbonate and the silane compound shown in Structural Formula 1 in the non-aqueous electrolyte, the capacity retention rate of the battery is improved and gas generation during high-temperature storage is suppressed; at the same time, the mass percentage of silicon element in the negative electrode material layer and the compaction density of the negative electrode material layer are controlled within a certain range, It can ensure the insertion / ejection of lithium ions in the negative electrode and control the compaction density of the negative electrode to ensure the battery life; when the mass percentage S of the silicon element in the negative electrode material layer of the lithium ion battery, the mass percentage F of the fluoroethylene carbonate in the non-aqueous electrolyte, the mass percentage T of the silane compound represented by the structural formula 1 in the non-aqueous electrolyte, and the compaction density R of the negative electrode material layer meet the following conditions: 5≤(S×R) / (F×T)≤35, and 9≤S≤18, 1.4≤R≤1.68, 5≤F≤15, 0.025≤T≤0.5

[0082] (2) The test results of Example 1 and Examples 15-19 are shown in Table 3.

[0083] Table 3

[0084] It can be seen from the test results of Example 1 and Examples 15-19 that in the battery system of the present application, when different types of silane compounds represented by structural formula 1 containing at least one carbon-carbon double bond are used as additives, when the mass percentage S of the silicon element in the negative electrode material layer, the mass percentage F of fluoroethylene carbonate in the non-aqueous electrolyte, the mass percentage T of the silane compound represented by structural formula 1 in the non-aqueous electrolyte, and the compaction density R of the negative electrode material layer meet the corresponding conditions, the high-temperature storage and high-temperature cycle performance of the lithium-ion battery can be improved, indicating that the battery system of the present application is universal for different compounds represented by structural formula 1.

[0085] (3) The test results of Example 1 and Examples 20-22 are shown in Table 4.

[0086] Table 4

[0087] It can be seen from the test results of Example 1 and Examples 20-22 that in the battery system of the present application, different silicon-based negative electrode materials are used. When the mass percentage S of the silicon element in the negative electrode material layer, the mass percentage F of fluoroethylene carbonate in the non-aqueous electrolyte, the mass percentage T of the silane compound shown in structural formula 1 in the non-aqueous electrolyte, and the compaction density R of the negative electrode material layer meet the corresponding conditions, the high-temperature storage and high-temperature cycle performance of the lithium-ion battery can be improved, indicating that the battery system of the present application is universal for different silicon-based negative electrode materials.

[0088] (4) The test results of Example 1 and Examples 23-25 ​​are shown in Table 5.

[0089] Table 5

[0090] It can be seen from the test results of Example 1 and Examples 23-25 ​​that in the battery system provided in the present application, the additional addition of additives such as lithium difluorophosphate (LiPO2F2), vinyl sulfate (DTD), and vinylene carbonate (VC) can further improve the high-temperature storage and high-temperature cycle performance of lithium-ion batteries, indicating that there is a complementary effect between the compound shown in Structural Formula 1 and other additives.

[0091] The present application is further described above with the help of specific embodiments, but it should be understood that the specific description here should not be construed as limiting the essence and scope of the present application. Various modifications made to the above embodiments by ordinary technicians in this field after reading this specification are all within the scope of protection of this application.

Claims

1. A lithium ion battery, characterized in that: including a positive electrode, a negative electrode and a non-aqueous electrolyte; The negative electrode comprises a negative electrode material layer comprising a negative electrode active material, wherein the negative electrode active material comprises a silicon-based material; The non-aqueous electrolyte includes a lithium salt, an organic solvent and an additive, wherein the organic solvent includes fluoroethylene carbonate, and the additive includes a silane compound shown in structural formula 1: wherein R1, R2, R3 and R4 are each independently selected from substituted or unsubstituted C1-C5 alkyl, substituted or unsubstituted C2-C5 alkenyl and substituted or unsubstituted C2-C5 alkynyl, and at least one of R1-R4 is selected from substituted or unsubstituted C2-C5 alkenyl; The lithium-ion battery meets the following conditions: 5≤(S×R) / (F×T)≤35, and 9≤S≤18, 1.4≤R≤1.68, 5≤F≤15, 0.025≤T≤0.5; Wherein, S is the mass percentage of silicon element in the negative electrode material layer, in wt%; R is the compaction density of the negative electrode material layer, in g / cm 3 ; F is the mass percentage of fluoroethylene carbonate in the non-aqueous electrolyte, in wt%; T is the mass percentage of the silane compound represented by structural formula 1 in the non-aqueous electrolyte, in wt%.

2. The lithium-ion battery according to claim 1, characterized in that The lithium ion battery satisfies the following condition: 6≤(S×R) / (F×T)≤30.

3. The lithium-ion battery according to claim 1, characterized in that The mass percentage S of silicon element in the negative electrode material layer is 10wt% to 16wt%.

4. The lithium-ion battery according to claim 1, characterized in that: The mass percentage F of fluoroethylene carbonate in the non-aqueous electrolyte is 6wt% to 12wt%.

5. The lithium-ion battery according to claim 1, characterized in that: The mass percentage T of the silane compound represented by the structural formula 1 in the non-aqueous electrolyte is 0.05 wt % to 0.3 wt %.

6. The lithium-ion battery according to claim 1, characterized in that The compaction density R of the negative electrode material layer is 1.5 g / cm 3 ~1.65g / cm 3 .

7. The lithium-ion battery according to claim 1, characterized in that: The silane compound shown in the structural formula 1 includes at least one of tetravinylsilane, trivinylethylsilane, divinyldiethylsilane, trivinylethoxysilane, vinyltriethylsilane, trivinylethynylsilane, tetrapropylenesilane, trivinylpropylsilane, tripropylenepropylsilane, dipropylenedipropylsilane and divinyldipropylsilane.

8. The lithium-ion battery according to claim 1, characterized in that The silicon-based material includes at least one of a silicon material, a silicon oxide material, a silicon-carbon material and a silicon alloy material.

9. The lithium-ion battery according to claim 8, characterized in that: The silicon material is a nano silicon material; and / or, The silicon oxide material is SiO x Materials, where 0≤x<2; and / or The silicon-carbon material is a silicon-based material containing silicon and carbon materials, and / or containing SiO y and a silicon-based material of a carbon material, wherein 0≤y<2; and / or, The silicon alloy material is a Mg2Si alloy material and / or a Fe2Si alloy material.

10. The lithium ion battery according to claim 1, characterized in that: The organic solvent further comprises at least one of cyclic carbonate, linear carbonate, carboxylic acid ester and ether compound except fluoroethylene carbonate.

11. The lithium ion battery according to claim 10, characterized in that: The cyclic carbonate comprises at least one of propylene carbonate, ethylene carbonate, vinylene carbonate and butylene carbonate; and / or, The linear carbonate comprises at least one of dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate and methyl propyl carbonate; and / or, The carboxylic acid ester comprises at least one of methyl acetate, ethyl acetate, methyl propionate, ethyl propionate, methyl butyrate, methyl isobutyrate, methyl trimethylacetate and ethyl trimethylacetate; and / or, The ether compound includes at least one of ethylene glycol dimethyl ether, 1,3-dioxolane and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether.

12. The lithium ion battery according to claim 1, characterized in that: The non-aqueous electrolyte also includes auxiliary additives, and the auxiliary additives include at least one of cyclic sulfate compounds, sultone compounds, cyclic carbonate compounds, phosphate compounds, borate compounds and nitrile compounds.

13. The lithium ion battery according to claim 12, characterized in that: Based on the total mass of the non-aqueous electrolyte being 100%, the content of the auxiliary additive is 0.01wt% to 10wt%.

14. The lithium ion battery according to claim 12, characterized in that: The cyclic sulfate ester compound includes at least one of vinyl sulfate, 4-methylvinyl sulfate, and propylene sulfate; and / or, The sultone compound includes at least one of 1,3-propane sultone, 1,4-butane sultone and propenyl-1,3-sultone; and / or, The cyclic carbonate compound includes at least one of vinylene carbonate, ethylene carbonate, methylene carbonate, fluoroethylene carbonate, trifluoromethylethylene carbonate, bisfluoroethylene carbonate and the compound shown in the following structural formula 2: In the structural formula 2 shown, R 21 , R 22 , R 23 , R 24 , R 25 , R 26 Each is independently selected from a hydrogen atom, a halogen atom, a C1-C5 group; and / or, The phosphate compound includes at least one of tris(trimethylsilyl)phosphate, tris(triethylsilyl)phosphate and the compound shown in the following structural formula 3: In the structural formula 3, R 31 , R 32 , R 33 Each independently selected from a C1-C5 saturated hydrocarbon group, an unsaturated hydrocarbon group, a halogenated hydrocarbon group, -Si(C m H 2m+1 )3, m is a natural number from 1 to 3, and R 31 , R 32 , R 33 At least one of them is an unsaturated hydrocarbon group; and / or, The borate compound includes at least one of tris(trimethylsilyl)borate and tris(triethylsilyl)borate; and / or, The nitrile compound includes at least one of succinonitrile, glutaronitrile, ethylene glycol bis(propionitrile) ether, hexanetrinitrile, adiponitrile, pimelonitrile, suberonitrile, azelaic acid dinitrile and sebaconitrile.

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