Battery and terminal equipment

Abstract

The invention provides a battery and terminal equipment, the battery comprises a positive electrode, a negative electrode and an electrolyte, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material; the negative electrode comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, and the negative electrode active material layer comprises a negative electrode active material; the electrolyte comprises electrolyte salt, an organic solvent and a film-forming additive, the film-forming additive comprises fluorocarbonate and sulfonate, the mass content of fluorocarbonate in the electrolyte is a, and the mass content of sulfonate in the electrolyte is b; the negative electrode active material comprises a silicon-carbon compound; the mass ratio of the silicon-carbon compound in the negative electrode active material is c; the battery meets the following relation: a * b / c is more than 0.00465 and less than 0.064. According to the battery and the terminal equipment, the cycle performance of the battery can be improved under the condition that the energy density is not changed.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of organic compound synthesis, in particular to a battery and a terminal device. BACKGROUND

[0002] Lithium ion batteries are widely used in 3C consumer electronics such as mobile phones and notebook computers due to their high specific energy, small self-discharge, no memory effect and long cycle life, and are widely used in new energy vehicles and energy storage. The energy density of the current power lithium ion battery cannot meet the increasing demand of the application end for battery energy density. As a potential next-generation lithium ion battery anode material option with greater specific capacity, silicon anode materials have problems such as low initial efficiency, volume expansion and repeated interface layer thickening during cycling, which need to be overcome. Among the many options for silicon anode materials, silicon-based materials based on amorphous porous carbon deposition stand out due to their low expansion and good interface performance.

[0003] At the same time, due to the low initial efficiency of silicon-based materials, pre-lithiation treatment can also exacerbate these problems in silicon anodes. The interaction between film-forming additives is not yet clear, making it difficult to optimize the composition of electrolyte additives.

[0004] Therefore, how to improve the cycle performance of the battery without changing the energy density is a problem to be solved at present. SUMMARY

[0005] The present application provides a battery and a terminal device, which can improve the energy density of the battery and improve the cycle performance of the battery.

[0006] In a first aspect, the present application provides a battery, comprising a positive electrode, a negative electrode and an electrolyte, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material; the negative electrode comprising a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material;

[0007] The electrolyte comprises an electrolyte salt, an organic solvent and a film-forming additive, the film-forming additive comprising a fluorinated carbonate and a sulfonate, wherein the mass content of the fluorinated carbonate in the electrolyte is a, and the mass content of the sulfonate in the electrolyte is b;

[0008] The negative electrode active material comprises a silicon-carbon composite; the mass fraction of the silicon-carbon composite in the negative electrode active material is c;

[0009] The battery satisfies the following relationship: 0.00465 < a*b / c < 0.064.

[0010] In some embodiments, the silicon-carbon composite includes a carbon matrix having pores and nano-silicon at least partially located in the pores of the carbon matrix.

[0011] The porosity of the carbon matrix is 10% to 90%, the most probable pore diameter of the carbon matrix is greater than 1.05 nm, and the mass ratio of the nano-silicon in the negative electrode active material is 10% to 90%.

[0012] In some embodiments, the mass ratio of the silicon-carbon composite in the negative electrode active material is c, and 0.1≤c≤1.

[0013] In some embodiments, the porosity of the carbon matrix is 30% to 70%, the most probable pore diameter of the carbon matrix is 1.5 nm to 5 nm, and the mass ratio of the nano-silicon in the negative electrode active material is 30% to 80%; the mass ratio of the negative electrode active material in the negative electrode active material is c, and 0.3≤c≤0.7.

[0014] In some embodiments, the mass content of the fluorinated carbonate in the electrolyte is a, and when 0.1≤c≤0.4, 0.12

[0015] In some embodiments, the fluorinated carbonate includes fluorinated ethylene carbonate (FEC), difluorinated ethylene carbonate (DFEC).

[0016] In some embodiments, the mass content of the sulfonate in the electrolyte is b, and 0.02≤b≤0.04; the sulfonate includes at least one of 1,3-propanesultone, prop-1-ene-1,3-sulfone, vinyl sulfite, 1,4-butanesultone, 1,3,2-dioxathiane-2,2-dioxide, and pentaerythritol bis cyclic sulfate.

[0017] In some embodiments, the electrolyte further includes a lithium-containing additive, and the lithium-containing additive includes at least one of lithium bis(oxalato)borate, lithium difluoroborate, lithium difluoro(oxalato)borate, lithium difluorophosphate, and lithium difluorobis(oxalato)phosphate.

[0018] In some embodiments, the organic solvent includes at least two of propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), methyl butyl carbonate (BMC), ethyl acetate (EA), propyl propionate (PP), and ethyl difluoroacetate (DFEA).

[0019] In some embodiments, the positive electrode active material includes at least one of lithium cobaltate or lithium nickel cobalt manganese oxide.

[0020] In a second aspect, the application provides a terminal device comprising the battery of the first aspect.

[0021] Compared with the prior art, the electrolyte contains a film-forming additive, the film-forming additive includes fluorinated carbonate and sulfonate, and the film-forming additive continuously decomposes as the electrochemical reaction proceeds, and has a significant influence on the cycle life and the high-temperature stability and safety performance of the battery. Among them, the fluorinated carbonate in the electrolyte forms a mixture of a polyethylene glycol polymer and lithium fluoride, participates in the formation of an interface solid electrolyte film (abbreviated as SEI film), so that the SEI film on the surface of the negative active material can have better electrical conductivity and mechanical strength. The sulfonate additive decomposes to form an organic sulfonate, the organic sulfonate has better thermal stability and lower solubility at high temperature, and the decomposition product of the sulfonate also participates in the formation of the SEI film. The sulfonate can effectively complement the fluorinated carbonate, so that the solid electrolyte film on the surface of the negative active material particles is more stable, thereby improving the cycle stability of the negative active material at high temperature and high pressure. According to the mass ratio of the silicon-carbon composite in the negative active material as c, the application optimizes the mass content b of the film-forming additive in the electrolyte and c, so that 0.00465 < a * b / c < 0.064. In this way, the fluorinated carbonate and the sulfonate can continuously decompose and participate in the formation of the SEI film on the surface of the negative active material during the cycle charging and discharging process, can stabilize the reaction interface of the negative active material, reduce the rupture of the surface SEI film caused by the expansion and contraction of the negative active material, improve the quality of the SEI film on the surface of the negative active material, reduce the occurrence of side reactions, and improve the cycle performance of the battery without changing the energy density. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The application provides a structural schematic diagram of the battery.

[0023] Figure 2a And Figure 2b The application provides an electron microscope image of the silicon-carbon composite at different magnifications.

[0024] Figure 3 The application provides a normal-temperature cycle performance comparison diagram of Example 1, Example 4 and Comparative Example 1 at 25 DEG C.

[0025] Figure 4 The application provides a normal-temperature cycle performance comparison diagram of Example 13 and Comparative Example 3 at 25 DEG C.

[0026] Figure 5 The application provides a high-temperature cycle performance comparison diagram of Example 13 and Comparative Example 5 at 45 DEG C. DETAILED DESCRIPTION

[0027] The technical solutions provided by the present invention are further described below in conjunction with specific examples and comparative examples, but the present application is not limited to the following examples.

[0028] In order to better understand the technical solution of the present application, the embodiments of the present application are described in detail below.

[0029] It should be clear that the embodiments described are only part of the embodiments of this application, not all of the embodiments. Based on the embodiments in this application, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of this application.

[0030] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be understood to indicate or imply relative importance or to implicitly indicate the quantity of the technical features indicated. Thus, a feature specified as "first" or "second" may explicitly or implicitly include one or more of the features.

[0031] Lithium-ion battery is a common secondary battery. Figure 1 As shown, a lithium-ion battery consists of a positive electrode, a negative electrode, an electrolyte, and a separator. The positive and negative electrode active materials are the primary components of a lithium-ion battery's energy storage function, determining the battery's energy density, cycling performance, and safety. The electrolyte is the carrier for lithium ions to transfer between the positive and negative electrodes. The ionically conductive but electronically insulating separator ensures lithium ion migration while separating the positive and negative electrodes to prevent short circuits. The electrolyte is the medium for lithium ion transfer between the positive and negative electrodes and plays a crucial role in the battery's electrochemical performance and safety. During the initial charge of a lithium-ion battery, a solid electrolyte interphase (SEI) film forms on the surface of the negative electrode active material. The formation of the SEI film has a significant impact on the performance of the lithium-ion battery. On the one hand, the SEI film maintains its stability in the electrolyte, preventing solvent molecules from entering the negative electrode active material, thereby improving the cycling performance of the lithium-ion battery. On the other hand, the formation of the SEI film consumes lithium ions, increasing the irreversible capacity during the initial charge and discharge period and reducing the initial efficiency of the lithium-ion battery.

[0032] At present, as the negative active material, the silicon-carbon composite generally needs to be pre-lithiated due to its relatively low first coulomb efficiency, and the pre-lithiation is mainly divided into physical pre-lithiation and electrochemical pre-lithiation. The physical pre-lithiation is to make lithium metal and the silicon negative electrode contact through a mechanical method, and under the action of external force, lithium-silicon alloy is generated to supplement the active lithium ions consumed irreversibly in the first cycle. The electrochemical pre-lithiation is to add materials that can release excess active lithium in the positive electrode to make up for the active lithium ions consumed irreversibly in the first cycle. Although these methods can effectively improve the initial efficiency, cycle life and cycle performance of the battery, pre-lithiation means that there is an excess of negative active material in the negative electrode, and these active materials and components in the electrolyte can cause side reactions, which makes the solid electrolyte interface (SEI) film of the active material and the electrolyte contact thickens rapidly, further affecting the cycle performance.

[0033] The application provides a battery, which comprises a positive electrode, a negative electrode and an electrolyte, the positive electrode comprises a positive electrode current collector and a positive electrode active material layer arranged on the positive electrode current collector, and the positive electrode active material layer comprises a positive electrode active material; the negative electrode comprises a negative electrode current collector and a negative electrode active material layer arranged on the negative electrode current collector, and the negative electrode active material layer comprises a negative electrode active material;

[0034] The electrolyte comprises an electrolyte salt, an organic solvent and a film-forming additive, the film-forming additive comprises a fluorinated carbonate and a sulfonate, wherein the mass content of the fluorinated carbonate in the electrolyte is a, and the mass content of the sulfonate in the electrolyte is b;

[0035] The negative electrode active material comprises a silicon-carbon composite, and the mass proportion of the silicon-carbon composite in the negative electrode active material is c;

[0036] The battery satisfies the following relationship: 0.00465 < a*b / c < 0.064.

[0037] Compared with the prior art, the electrolyte contains a film-forming additive, the film-forming additive includes a fluorinated carbonate and a sulfonate, the film-forming additive continuously decomposes as the electrochemical reaction proceeds, and has a significant influence on the cycle life and the high-temperature stability and safety performance of the battery. Among them, the fluorinated carbonate in the electrolyte forms a mixture of a polyethylene glycol polymer and lithium fluoride, participates in the formation of an interface solid electrolyte film (abbreviated as SEI film), so that the SEI film on the surface of the negative electrode active material can have good electrical conductivity and mechanical strength. The sulfonate additive decomposes to form an organic sulfonate, the organic sulfonate has better thermal stability and lower solubility at high temperature, and the decomposition product of the sulfonate also participates in the formation of the SEI film. The sulfonate can effectively complement the fluorinated carbonate, so that the solid electrolyte film on the surface of the negative electrode active material particles is more stable, thereby improving the cycle stability of the negative electrode active material at high temperature and high pressure. According to the mass ratio of the silicon-carbon composite in the negative electrode active material as c, the mass content b of the film-forming additive in the electrolyte and c are optimized in the application, so that 0.00465 < a * b / c < 0.064. In this way, the fluorinated carbonate and the sulfonate can continuously decompose and participate in the formation of the SEI film on the surface of the negative electrode active material during the cycle charging and discharging process, can stabilize the reaction interface of the negative electrode active material, reduce the rupture of the surface SEI film caused by the expansion and contraction of the negative electrode active material, improve the quality of the SEI film on the surface of the negative electrode active material, reduce the occurrence of side reactions, improve the specific capacity of the negative electrode active material while effectively improving the cycle performance of the negative electrode active material, and further improve the electrochemical performance and cycle performance of the battery.

[0038] In some embodiments, the positive electrode includes a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, and the positive electrode active material layer includes a positive electrode active material. The specific type of the positive electrode active material is not limited and can be selected as needed. The positive electrode active material includes at least one of lithium nickel cobalt manganese ternary material (abbreviated as NCM), lithium manganate (LiMn2O4) or lithium cobaltate (LiCoO2). Preferably, the positive electrode active material is lithium cobaltate. The positive electrode current collector can be an aluminum foil or a nickel foil, etc., which is not limited here.

[0039] In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, and the negative electrode active material layer includes a negative electrode active material, and the negative electrode active material includes a silicon-carbon composite.

[0040] In some embodiments, the mass ratio of the silicon-carbon composite in the negative active material is c, 0.1≤c≤1. Specifically, c can be 0.1, 0.2, 0.3, 0.4, 0.5, 0.55, 0.6, 0.7, 0.8, 0.9 or 1, and of course can be other values within the above range, which are not limited herein. For example, when the mass ratio of the silicon-carbon composite in the negative active material is 1, all of the negative active material is the silicon-carbon composite; when the mass ratio of the silicon-carbon composite in the negative active material is 0.5, the negative active material can be a mixture of the silicon-carbon composite and graphite with a mass ratio of 1:1. In the present application, by controlling the mass ratio of the negative active material in the negative active material, the specific capacity of the negative active material can be optimized, and the high capacity and high cycle performance of the negative active material can be balanced.

[0041] In the alternative technical solution of the present application, the silicon-carbon composite includes a carbon matrix having pores and nano-silicon at least partially located in the pores of the carbon matrix. The carbon matrix may, for example, be a composite of one or more of hard carbon, soft carbon, graphene, carbon nanotube, etc. The grain size of the nano-silicon is 0.1 nm to 5 nm, and specifically can be 0.1 nm, 0.5 nm, 1 nm, 1.5 nm, 2.0 nm, 2.5 nm, 3.0 nm, 3.5 nm, 4.0 nm, 4.5 nm or 5 nm, and of course can be other values within the above range, which are not limited herein. By controlling the grain size of the nano-silicon, the expansion of the silicon-carbon composite can be reduced, and the cycle stability of the battery can be improved.

[0042] As an alternative technical solution of the present application, the carbon matrix can be placed in a gas-phase silicon source for gas-phase silicon deposition, so that the nano-silicon particles can fill the pores of the carbon matrix, and the above-mentioned silicon-carbon composite is obtained. In some other embodiments, the carbon matrix having pores and the nano-silicon particles can also be mixed in liquid phase or solid phase, so that the silicon particles can enter the pores of the carbon matrix. From the preparation process and cost consideration, preferably, a silicon deposition process is adopted using a gas-phase silicon source.

[0043] The gas-phase deposition process allows the gas-phase silicon source to enter the pores of the carbon matrix, and the nano-silicon formed by deposition is located in the pores of the carbon matrix, and a small part of the nano-silicon is deposited on the surface of the carbon matrix. In some embodiments, in order to reduce the side reaction of the nano-silicon exposed on the surface of the carbon matrix with the electrolyte, a coating layer (such as a carbon coating layer) is further formed on the surface of the silicon-carbon composite, thereby reducing the side reaction of the nano-silicon with the electrolyte, improving the cycle performance of the silicon-carbon composite, and improving the cycle stability of the battery. For example, the carbon matrix can be prepared by carbonization and pore formation of a carbon source such as coconut shell, rice husk, phenolic resin, epoxy resin, starch, cellulose, lignin, etc.

[0044] In some embodiments, the carbon matrix has a porosity of 10% to 90%, and a most probable pore diameter greater than 1.05 nm.

[0045] Specifically, the porosity of the carbon matrix can be 10%, 20%, 30%, 40%, 50%, 55%, 60%, 70%, 80%, or 90%, etc., and can be other values within the above range, which are not limited herein. The abundant porosity can provide sufficient accommodation space for the silicon particles. Considering the structural strength and stability of the carbon matrix, the porosity of the carbon matrix is 30% to 70%.

[0046] The most probable pore diameter of the carbon matrix is greater than 1.05 nm, and can be 1.1 nm, 1.3 nm, 1.5 nm, 1.6 nm, 1.7 nm, 1.8 nm, 1.9 nm, 2.0 nm, 2.1 nm, 2.3 nm, 2.5 nm, 3.0 nm, 3.5 nm, 3.8 nm, 4.0 nm, 4.2 nm, 4.4 nm, 4.5 nm, 4.8 nm, or 5.0 nm, etc., and can be other values within the above range, which are not limited herein. The most probable pore diameter of the carbon matrix can represent the pore size range of the pore channel of the carbon matrix, and the appropriate pore size can adjust the grain size of the silicon particles deposited into the pore channel, thereby improving the problem of excessive local expansion stress caused by the overlarge silicon particle in some areas. Preferably, the most probable pore diameter of the carbon matrix is 1.5 nm to 5 nm.

[0047] In some embodiments, the pores in the carbon matrix are mainly micropores, that is, pores with a pore diameter less than 2 nm. The pores with a suitable pore diameter can control the particle size of the nanosilicon formed by vapor deposition, and reduce the problem of excessive local expansion stress caused by silicon segregation. The pores in the silicon-carbon composite are mainly mesopores, which can provide sufficient expansion buffer space for the nanosilicon, and reduce the problem of cracking and pulverization of the composite particles caused by the expansion of the nanosilicon.

[0048] Understandably, the silicon particles are accommodated in the pore channel of the carbon matrix, and the existence of the pore channel structure can not only provide suitable expansion space for the silicon particles to relieve the expansion stress of the negative active material, but also facilitate the full infiltration of the electrolyte into the negative active material, enrich the diffusion path of lithium ions, and improve the electrochemical performance of the negative active material.

[0049] In some embodiments, the mass ratio of the nanosilicon in the negative active material is 10% to 90%. Specifically, the mass ratio of the nanosilicon can be 10%, 20%, 30%, 40%, 50%, 55%, 60%, 70%, 80%, or 90%, etc., and can be other values within the above range, which are not limited herein. Preferably, the mass ratio of the nanosilicon in the negative active material is 30% to 80%; more preferably, the mass ratio of the nanosilicon in the negative active material is 35% to 50%.

[0050] In some embodiments, the porosity of the carbon matrix is 30% to 70%, the most probable pore diameter of the carbon matrix is 1.5 nm to 5 nm, the mass ratio of the nanosilicon in the negative electrode active material is 30% to 80%, and the mass ratio of the negative electrode active material in the negative electrode active substance is c, 0.30≤c≤0.70. Through a large number of tests, it is found that when the porosity of the carbon matrix, the mass ratio of the nanosilicon, and the mass ratio of the negative electrode active material in the negative electrode active substance are within the above ranges, and the added amount of the film-forming additive satisfies 0.00465

[0051] In some embodiments, the specific surface area of the negative electrode active material is 0.5 m 2 / g to 5 m 2 / g. Specifically, the specific surface area of the first negative electrode material can be 0.5 m 2 / g, 1 m 2 / g, 1.5 m 2 / g, 2 m 2 / g, 2.5 m 2 / g, 3 m 2 / g, 3.5 m 2 / g, 4 m 2 / g, 4.5 m 2 / g, or 5 m 2 / g, and of course other values within the above range are also possible, which are not limited herein. When the specific surface area of the negative electrode active material is too large, the active sites of the negative electrode active material increase, which is beneficial to the formation of a dense negative electrode protective film, but the consumption of lithium ions increases, the active lithium ions in the electrolyte decrease, the lithium ion conductivity decreases, and the first coulombic efficiency of the battery decreases. When the specific surface area of the negative electrode active material is too small, it is not conducive to the formation of the negative electrode protective film, and the contact between the negative electrode active material particles increases.

[0052] In some embodiments, the negative electrode active substance layer on the negative electrode current collector can be a single-sided coating or a double-sided coating. The single-sided coating is that the active substance layer can be coated on any one side of the current collector, and the double-sided coating is that the active substance layer is coated on both sides of the current collector.

[0053] In some embodiments, the negative electrode current collector can be selected from copper foil, nickel foil, stainless steel foil, titanium foil, foamed nickel, foamed copper, polymer substrate coated with conductive metal, and combinations thereof. In some embodiments, the negative electrode current collector is copper foil, and the thickness of the copper foil is 4 μm to 10 μm, specifically 5 μm, 6 μm, 7 μm, 8 μm, 9 μm, or 10 μm, and the like. Preferably, the thickness of the copper foil is 4 μm to 6 μm.

[0054] As an optional technical solution of the present application, the negative electrode further comprises a binder selected from at least one of polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon, etc.

[0055] It should be noted that the negative electrode can be manufactured by any method known in the art. In some embodiments, the negative electrode can be formed by adding a binder and a solvent to the negative electrode active material, and adding a thickening agent, a conductive material, a filler, etc. as needed to form a slurry, coating the slurry on a current collector, drying, and then pressing. When the negative electrode includes an alloy material, a method such as evaporation, sputtering, plating, etc. can be used to form the negative electrode active material layer.

[0056] In some embodiments, the positive electrode can further include a binder to improve the binding between the positive electrode active material particles and also to improve the binding between the positive electrode active material and the positive electrode current collector. Optionally, the binder includes at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polyethylene oxide-containing polymer, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylated styrene butadiene rubber, epoxy resin, or nylon.

[0057] The positive electrode can further include a positive electrode conductive material to impart electrical conductivity to the electrode. The positive electrode conductive material can include any conductive material, so long as it does not cause chemical changes. Non-limiting examples of positive electrode conductive materials include carbon-based materials (e.g., natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fibers, etc.), metal-based materials (e.g., metal powders, metal fibers, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0058] In some embodiments, the battery includes an electrolyte, the electrolyte includes an electrolyte salt, an organic solvent, and a film-forming additive, the film-forming additive includes a fluorinated carbonate and a sulfonate, wherein the mass content of the fluorinated carbonate in the electrolyte is a%, the mass content of the sulfonate in the electrolyte is b%, and the battery satisfies the following relationship: 0.00465 < a*b / c < 0.064.

[0059] Specifically, a*b / c can be specifically 0.004651, 0.00466, 0.00468, 0.0047, 0.00475, 0.00478, 0.0048, 0.0049, 0.0051, 0.0054, 0.0055, 0.0057, 0.0059, 0.0060, 0.0061, 0.0062, 0.0063, or 0.00639, etc., and of course can also be other values within the above range, which are not limited herein. When a*b / c is too large, it indicates that the film-forming additive is excessive, and the excessive fluorocarbonate will affect the high-temperature cycle performance, and the excessive sulfonate will cause the decrease of the room-temperature cycle capacity retention. When a*b / c is too small, it indicates that the fluorocarbonate and / or the sulfonate is insufficient, which often shows the early rapid capacity decrease and causes the decrease of the cycle life.

[0060] Understandably, with the increase of the mass ratio of the negative electrode active material, the mass ratio of the silicon-carbon composite in the negative electrode active material increases, and by adjusting the mass content of the fluorocarbonate in the electrolyte, more fluorocarbonate can form the solid electrolyte membrane on the surface of the negative electrode active material, which is beneficial to improve the electrochemical performance of the negative electrode active material.

[0061] In some embodiments, the electrolyte salt in the electrolyte is selected from lithium hexafluorophosphate LiPF6. The concentration of the lithium salt in the electrolyte is 0.3 mol / L to 2 mol / L.

[0062] In some embodiments, the organic solvent in the electrolyte includes but is not limited to a carbonate compound, an ester-based compound, an ether-based compound, a ketone-based compound, an alcohol-based compound, an aprotic solvent, or a combination thereof.

[0063] Optionally, the carbonate compound includes a chain carbonate compound, a cyclic carbonate compound, etc.

[0064] The chain carbonate compound includes at least one of diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), methyl butyl carbonate (BMC), ethyl propyl carbonate (EPC), and methyl ethyl carbonate (EMC). The cyclic carbonate compound can be at least one of ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), and vinyl ethylene carbonate (VEC). The ester-based compound includes at least one of methyl acetate, ethyl acetate (EA), ethyl difluoroacetate (DFEA), n-propyl acetate, t-butyl acetate, methyl propionate, ethyl propionate, propyl propionate (PP), γ-butyrolactone, decanolactone, valerolactone, methylvaleronolactone, caprolactone, and methyl formate.

[0065] Ether-based compounds include at least one of dibutyl ether, tetraethylene glycol dimethyl ether, diethylene glycol dimethyl ether, 1,2-dimethoxyethane, 1,2-diethoxyethane, ethoxymethoxyethane, 2-methyltetrahydrofuran, and tetrahydrofuran.

[0066] Examples of ketone-based compounds include, but are not limited to, cyclohexanone. Examples of alcohol-based compounds include, but are not limited to, ethanol and isopropanol. Aprotic solvents include at least one of dimethyl sulfoxide, 1,2-dioxolane, sulfolane, methylsulfolane, 1,3-dimethyl-2-imidazolidinone, N-methyl-2-pyrrolidinone, formamide, dimethylformamide, acetonitrile, nitromethane, trimethyl phosphate, triethyl phosphate, trioctyl phosphate, and phosphates. In some embodiments, the solvent is ethyl propionate.

[0067] In some embodiments, the film-forming additive includes fluoro-carbonate, sulfonate, which can improve the film-forming stability of the battery at the negative electrode, reduce the interface side reaction caused by pre-lithiation, inhibit the impedance growth, and improve the cycle performance of the lithium ion battery at high voltage.

[0068] It should be noted that the decomposition product of the sulfonate additive is an organic sulfonate, which has a lower solubility at high temperature and is more stable than the organic components produced by the decomposition of fluoro-carbonate, and can effectively complement the fluoro-carbonate. However, the sulfonate itself has a silicon affinity, which may cause a decrease in cycle performance at room temperature, and the decomposition product has a large impedance, which causes the cell impedance to increase, which is not conducive to the performance of the battery. Moreover, there is a competitive film-forming between fluoro-carbonate and sulfonate, and any deviation from the equilibrium constant of either substance will result in an excess of the other additive, which is not conducive to the performance of the battery. Therefore, 0.00465 < a * b / c < 0.064 is controlled, which can balance the addition amount of the two substances and the balance between the negative active material, which can ensure that the film-forming additive can continuously decompose to cope with the periodic expansion of the negative active material, stabilize the solid-state reaction interface of the negative active material, relieve the rupture and pulverization of the negative active material particles caused by the periodic expansion, and improve the cycle stability of the negative active material.

[0069] In some embodiments, the fluoro-carbonate includes, but is not limited to, fluoro-ethylene carbonate (abbreviated as FEC) or bis-fluoro-ethylene carbonate (abbreviated as DFEC), etc.

[0070] In some embodiments, the mass percentage of the silicon-carbon composite in the negative active material is c, and the mass content of the fluorinated carbonate in the electrolyte is a. When 0.1≤c≤0.4, 0.12

[0071] In some embodiments, when 0.4

[0072] In some embodiments, the sulfonate includes, but is not limited to, 1,3-propanesulfonic acid lactone (abbreviated as PS), prop-1-ene-1,3-sulfone, vinyl sulfonic acid (abbreviated as DTD), 1,4-butanesulfonic acid lactone, 1,3,2-dioxathiane-2,2-dioxide, pentaerythritol bis-cyclic sulfates, or a mixture of one or more thereof.

[0073] Specifically, the mass content of the sulfonate in the electrolyte is b, 0.02≤b≤0.04, b can be 0.02, 0.025, 0.03, 0.031, 0.032, 0.033, 0.034, 0.035, 0.036, 0.037, 0.038, 0.039, or 0.04, etc., and of course can be other values within the above range, which are not limited herein. Preferably, the mass content of the sulfonate in the electrolyte is b, 0.03≤b≤0.04.

[0074] In some embodiments, the electrolyte further includes a lithium-containing additive, and the lithium-containing additive includes at least one of lithium bis(oxalato)borate LiB(C2O4)2 (abbreviated as LiBOB), lithium difluoroborate, lithium difluoro(oxalato)borate LiBF2(C2O4) (abbreviated as LiDFOB), lithium difluorophosphate, and lithium difluorobis(oxalato)phosphate.

[0075] Specifically, the mass content of the lithium-containing additive in the electrolyte is d, 0 < d < 0.02, which can be 0.001, 0.002, 0.005, 0.01, 0.015, 0.018, 0.02, etc., and of course can also be other values within the above range, which is not limited herein. The main role of the lithium-containing additive is to provide active lithium ions in addition to the electrolyte salt, and can provide an organic anion to form a good negative electrode protection film SEI with the negative electrode.

[0076] In some embodiments, the separator film is selected from a composite of one or more of a polyethylene film, a polypropylene film, a polyvinylidene fluoride film, and of course, an inorganic or organic coating can be coated on the surface of the separator film substrate to enhance the hardness of the battery cell or improve the adhesion of the separator film and the negative electrode interface according to actual needs.

[0077] In specific embodiments, the above-mentioned battery can be a primary battery, a secondary battery, a solid-state battery or a lithium-ion battery, which is not limited herein.

[0078] In some embodiments, the preparation of the battery comprises the following steps:

[0079] The above-prepared negative electrode sheet is subjected to processes such as rolling, slitting, die cutting and assembly, and is combined with a suitable positive electrode sheet to prepare a lithium-ion battery. The battery manufacturing process can be stacking or winding. The battery specification can be a cylindrical battery cell, a soft package battery cell, a square battery cell or other types of lithium-ion batteries.

[0080] The required environment and equipment: planetary high-speed stirring dispersion equipment, extrusion coating equipment, transfer coating equipment, vacuum heating equipment, lithium-ion battery production and manufacturing equipment, dust-free room, etc., which is not limited herein.

[0081] In a second aspect, the present application also provides a terminal device, the battery of the present application has good cycle performance and safety performance, therefore, the above-mentioned battery is applied in the terminal device, so that the terminal device has good safety performance, and the service life of the terminal device can be also prolonged.

[0082] The terminal device in the present application can specifically be a mobile phone, a computer, a tablet computer, a smart bracelet, a smart watch, etc., which is not limited herein.

[0083] The above is only a preferred embodiment of the present application, and is not used to limit the present application, any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0084] In a second aspect, the present application also provides a terminal device, the battery of the present application has good cycle performance and safety performance, therefore, the above-mentioned battery is applied in the terminal device, so that the terminal device has good safety performance, and the service life of the terminal device can be also prolonged.

[0085] The present application will be further described below with reference to the following examples. It should be understood that these examples are only used to illustrate the present application and are not intended to limit the scope of the present application.

[0086] (1) Positive electrode preparation

[0087] The positive electrode active material lithium cobalt oxide (LiCoO2), the conductive agent (acetylene black), and the binder polyvinylidene fluoride (abbreviated as PVDF) are dissolved in N-methylpyrrolidone (abbreviated as NMP) solvent in a weight ratio of about 97.6:1.2:1.2 and are fully stirred and mixed to obtain a positive electrode slurry; the positive electrode slurry is then coated on the positive electrode current collector aluminum foil; the aluminum foil is dried, cold pressed, cut, slit, and dried to obtain a positive electrode sheet.

[0088] (2) Negative electrode preparation

[0089] The negative electrode active material, binder styrene butadiene rubber (SBR), and thickener sodium carboxymethyl cellulose (CMC) are dispersed in deionized water solvent at a weight ratio of 97.7:1.2:1.1, stirred and mixed thoroughly, and then coated on the negative electrode current collector copper foil pre-coated with a conductive coating. The copper foil is dried and cold pressed to obtain a negative electrode sheet. Figure 2a and Figure 2b As shown, the negative electrode active material includes a silicon-carbon composite, the mass content of silicon element in the silicon-carbon composite is 45%, the porosity of the silicon-carbon composite is 70%, and the most probable pore diameter is 4 nm.

[0090] (3) Preparation of isolation membrane

[0091] A polyethylene (PE) film with a thickness of about 5-9 μm was used as the separator.

[0092] (4) Preparation of electrolyte

[0093] The electrolyte was prepared according to the different ratios of fluorocarbonate and sulfonate specified in Table 1 and Table 2 (Comparative Examples and Examples). The concentration of lithium hexafluorophosphate was 1 mol / L, and the remaining solvent components were dimethyl carbonate (DMC) and ethyl methyl carbonate (EMC). In addition, 1% by mass of LiDFOB, 2% of succinonitrile, 2% of 1,3,6-hexanetrinitrile and 1% of ethylene glycol bis(propionitrile) ether were added.

[0094] (5) Preparation of lithium-ion batteries

[0095] In the drying room, the soft-pack battery, with lithium cobalt oxide as the positive electrode and graphite and silicon-carbon composite as the negative electrode, is manufactured according to the process flow of the laminated soft-pack battery. The battery is injected once and then subjected to processes such as standing, fixture formation, and capacity separation. The performance of the obtained soft-pack battery is tested with a cycle rate of 2C and the test temperature set according to Tables 1 and 2.

[0096] Test of performance

[0097] (1) Lithium-ion battery 45°C cycle performance test:

[0098] The prepared lithium-ion battery was placed in a 45°C constant temperature box and allowed to stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. The lithium-ion battery was then charged at a constant current of 0.5C to a voltage of 4.25V, then charged at a constant voltage of 4.25V to a current of 0.05C, and then discharged at a constant current of 0.5C to a voltage of 3.0V. This is one charge and discharge cycle. Taking the capacity of the first discharge as the benchmark of 100%, the charge and discharge cycle test was repeated until the discharge capacity decayed to 80% of the benchmark, the charge and discharge test was stopped, and the number of cycles that had been cycled was recorded.

[0099] (2) Lithium-ion battery cycle performance test at 25°C:

[0100] The prepared lithium-ion battery was placed in a 25°C constant temperature box and allowed to stand for 30 minutes to allow the lithium-ion battery to reach a constant temperature. The lithium-ion battery was then charged at a constant current of 0.5C to a voltage of 4.25V, then charged at a constant voltage of 4.25V to a current of 0.05C, and then discharged at a constant current of 0.5C to a voltage of 3.0V. This is one charge and discharge cycle. Taking the capacity of the first discharge as the benchmark of 100%, the charge and discharge cycle test was repeated until the discharge capacity decayed to 80% of the benchmark, the charge and discharge test was stopped, and the number of cycles that had been cycled was recorded.

[0101] Examples 1 to 19 and Comparative Examples 1 to 6 were prepared according to the above preparation method, wherein the ratio of the amount of the negative electrode material to the fluorocarbonate and sulfonate added to the electrolyte and its effect on the cycle capacity retention rate of the lithium-ion battery are shown in Table 1.

[0102] Table 1. Room temperature cycling performance data of lithium-ion batteries at 25°C

[0103]

[0104]

[0105] According to the data in Table 1, the present application controls the mass proportion of the silicon-carbon composite in the negative electrode active material and optimizes the mass content of the film-forming additive in the electrolyte, so that the fluorocarbonate and sulfonate can continuously decompose and participate in the formation of the SEI film on the surface of the negative electrode active material during the cyclic charge and discharge process, stabilize the reaction interface of the negative electrode active material, reduce the rupture of the surface SEI film caused by the expansion and contraction of the negative electrode active material, improve the quality of the SEI film on the surface of the negative electrode active material, reduce the occurrence of side reactions, and the battery has good cycle stability and electrochemical performance at room temperature and high temperature.

[0106] According to the test data of embodiments 1-4 and embodiments 5-8, the mass content of fluorinated carbonate in the film-forming additive of the electrolyte gradually decreases, and the cycle life of the battery also shows a downward trend. It can be seen that fluorinated carbonate can participate in the formation of the SEI film on the surface of the negative active material, thereby improving the cycle stability of the battery. When the mass content of fluorinated carbonate in the electrolyte reaches 0.32, the cycle performance of the battery decreases instead. It can be seen that when 0.4 < c ≤ 1, the range of 0.155 < a ≤ 0.31 is controlled, the cycle performance of the battery is better.

[0107] According to the test data of embodiment 9 and embodiment 2, the mass content of the silicon-carbon composite in embodiment 9 decreases to 0.8, the expansion effect of the silicon-carbon composite decreases, and the cycle performance of the battery increases compared to embodiment 2. According to the test data of embodiments 10-13, as the mass content of the silicon-carbon composite in the negative active material decreases, the cycle performance of the battery also gradually improves compared to embodiment 4. This is because the reduction of the expansion effect of the silicon-carbon composite improves the cycle performance stability of the battery.

[0108] According to the test data of embodiments 14 and 15 and embodiment 12, when 0.1 ≤ c ≤ 0.4, the range of 0.12 < a ≤ 0.155 is controlled, the cycle performance of the battery is better.

[0109] According to the test data of embodiments 16-19, different types of fluorinated carbonates and sulfonates can effectively improve the cycle performance of the battery. Compared to comparative example 6, which does not add any film-forming additive, the cycle performance of the battery decreases rapidly. It can be seen that fluorinated carbonates and sulfonates can stabilize the reaction interface between the negative active material and the electrolyte during the cycle charging and discharging process.

[0110] Figure 3 The normal temperature cycle performance comparison chart of embodiments 1, 4 and comparative example 1 at 25°C is shown in FIG. 1. When the negative active material is 100% silicon-carbon composite, 0.00465 < a * b / c < 0.064, 0.155 < a ≤ 0.31, the cycle life of embodiments 1 and 4 is significantly higher than that of comparative example 1. Figure 3

[0111] Figure 4 The normal temperature cycle performance comparison chart of embodiments 13 and comparative example 3 at 25°C is shown in FIG. 3. When the negative active material is a silicon-carbon composite and graphite with a mass ratio of 1:9, when 0.00465 < a * b / c < 0.064, the cycle life of embodiment 13 is significantly higher than that of comparative example 3. Figure 4

[0112] ​​According to the above preparation method, Examples 1 to 6, 13, and Comparative Examples 1 to 5 were prepared and subjected to cycle performance tests at room temperature and high temperature. The effects of the cycle capacity retention rate of the lithium-ion battery are shown in Table 2.

[0113] Table 2 Cycling performance data of lithium-ion batteries of Examples 1 to 6, 13 and Comparative Examples 1 to 5 at room temperature and high temperature

[0114]

[0115] Combined with the data in Table 2, it can be seen that fluorinated carbonates and sulfonates were added in Examples 1 to 6, and the added amounts were kept within a suitable range with respect to the silicon content in the negative electrode active material. The cycling performance of the lithium-ion batteries at both 25°C and 45°C was maintained at a high level.

[0116] The amount of fluorinated carbonate added to the electrolyte of the lithium ion battery provided in Comparative Example 1 is insufficient. Compared with Example 3, the cycle performance of the lithium ion battery at 25° C. is significantly reduced.

[0117] The amount of sulfonic acid ester added to the electrolyte of the lithium ion battery provided in Comparative Example 4 is insufficient. Compared with Example 1, the cycle performance of the lithium ion battery at 45° C. is significantly reduced.

[0118] Figure 5 This is a comparison chart of the high temperature cycle performance of Example 13 of the present application and Comparative Example 5 at 45°C. Figure 5 As shown, when the negative electrode active material is 100% silicon-carbon composite, when the mass content of the sulfonic acid ester in Example 13 is greater than 0.03, since the high-temperature decomposition performance of the sulfonic acid ester is more excellent, it can synergize with the fluorocarbonate, so that the battery can still have good cycle stability under high-temperature cycling. Therefore, the high-temperature 45°C cycle life of Example 13 is still higher than the high-temperature cycle life of Comparative Example 5.

[0119] Although the present application is disclosed as above with preferred embodiments, it is not intended to limit the claims. Any person skilled in the art may make several possible changes and modifications without departing from the concept of the present application. Therefore, the scope of protection of the present application shall be based on the scope defined by the claims of the present application.

Claims

1. A battery comprising a positive electrode, a negative electrode, and an electrolyte, the positive electrode comprising a positive electrode current collector and a positive electrode active material layer disposed on the positive electrode current collector, the positive electrode active material layer comprising a positive electrode active material; the negative electrode comprising a negative electrode current collector and a negative electrode active material layer disposed on the negative electrode current collector, the negative electrode active material layer comprising a negative electrode active material; characterized in that, the electrolyte comprises an electrolyte salt, an organic solvent, and a film-forming additive, the film-forming additive comprising a fluorinated carbonate and a sulfonate, wherein the mass content of the fluorinated carbonate in the electrolyte is a, and the mass content of the sulfonate in the electrolyte is b; the negative electrode active material comprises a silicon-carbon composite; the mass fraction of the silicon-carbon composite in the negative electrode active material is c; the battery satisfies the following relationship: 0.00465 < a * b / c < 0.

064.

2. The battery of claim 1, wherein, the silicon-carbon composite comprises a carbon matrix having pores and nanosilicon at least partially located in the pores of the carbon matrix; the porosity of the carbon matrix is 10% to 90%, the most probable pore diameter of the carbon matrix is greater than 1.05 nm, and the mass fraction of the nanosilicon in the negative electrode active material is 10% to 90%.

3. The battery of claim 2, wherein, the mass fraction of the negative electrode active material in the negative electrode active material is c, and 0.1 ≤ c ≤ 1.

4. The battery of claim 2, wherein, the porosity of the carbon matrix is 30% to 70%, the most probable pore diameter of the carbon matrix is 1.5 nm to 5 nm, and the mass fraction of the nanosilicon in the negative electrode active material is 30% to 80%; the mass fraction of the negative electrode active material in the negative electrode active material is c, and 0.3 ≤ c ≤ 0.

7.

5. The battery of claim 1, wherein, the mass content of the fluorinated carbonate in the electrolyte is a, when 0.1 ≤ c ≤ 0.4, 0.12 < a ≤ 0.155; and when 0.4 < c ≤ 1, 0.155 < a ≤ 0.

31.

6. The battery of claim 5, wherein, the fluorinated carbonate comprises fluoroethylene carbonate (FEC) and difluoroethylene carbonate (DFEC).

7. The battery of claim 1, wherein, the mass content of the sulfonate in the electrolyte is b, and 0.02 ≤ b ≤ 0.04, the sulfonate comprising at least one of 1,3-propane sultone, prop-1-ene-1,3-sulfone, vinyl sulfate, 1,4-butane sultone, 1,3,2-dioxathiane-2,2-dioxide, and pentaerythritol bis cyclic sulfate.

8. The battery of claim 1, wherein, the electrolyte further comprises a lithium-containing additive, the lithium-containing additive comprising at least one of lithium bis(oxalato)borate, lithium difluoroborate, lithium difluoro(oxalato)borate, lithium difluorophosphate, and lithium difluorobis(oxalato)phosphate.

9. The battery according to any one of claims 1 to 8, characterized in that the positive electrode satisfies at least one of (1) and (2): (1) the organic solvent comprises at least two of propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), dipropyl carbonate (DPC), methyl ethyl carbonate (EMC), methyl propyl carbonate (MPC), methyl butyl carbonate (BMC), ethyl acetate (EA), propyl propionate (PP), and ethyl difluoroacetate (DFEA); (2) the positive electrode active material comprises at least one of lithium cobaltate or lithium nickel cobalt manganese oxide.

10. A terminal device, comprising: a battery comprising any one of claims 1 to 9.

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