Electrolyte suitable for silicon-based negative electrode material, lithium ion battery containing electrolyte and electronic device

Abstract

The invention provides an electrolyte suitable for a silicon-based negative electrode material, a lithium ion battery containing the electrolyte and an electronic device. The electrolyte suitable for the silicon-based negative electrode material comprises an electrolyte additive, a metal salt and a non-aqueous solvent, wherein the electrolyte additive comprises a basic additive and a functional additive; the functional additive comprises a combination of at least two of an oxide material, a thiocarbonate compound or a cyanoacrylate compound, so that the electrochemical performance and the safety performance of the lithium ion battery under high-temperature and low-temperature conditions are effectively improved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of battery materials, and particularly relates to an electrolyte suitable for a silicon-based negative electrode material, a lithium ion battery containing the same, and an electronic device. BACKGROUND

[0002] With the increasing application of lithium ion batteries in electric vehicles, energy storage systems, aerospace and polar exploration, the requirements for their operating temperature range are also increasing. In order to meet the needs of different application scenarios, developing high-energy lithium ion batteries with wide temperature range is one of the important research directions in the current new energy field. This battery system aims to solve the performance degradation problem of traditional lithium ion batteries under extreme temperature conditions, thereby improving the reliability and safety of lithium ion batteries.

[0003] Silicon-based materials are considered as ideal negative electrode materials for high-energy lithium ion batteries due to their high theoretical specific capacity (3580 mAh / g at room temperature and up to 4200 mAh / g at high temperature). However, there are still some problems in the application of existing silicon-based lithium ion batteries in high-temperature and low-temperature environments, as shown below:

[0004] (1) In a high-temperature environment, the decomposition and consumption of electrolyte will significantly increase when silicon-based negative electrode materials alloy with lithium ions. Due to the volume expansion of silicon particles, new active areas are continuously exposed on their surface, which will continuously generate new SEI films after contacting with electrolyte. This process not only consumes a large amount of electrolyte, but also leads to the loss of active lithium ions, thereby reducing the coulombic efficiency and capacity retention rate of the battery. In addition, high temperature will accelerate the decomposition and failure of the binder, further weakening its adhesion to the silicon particles, leading to the instability of the electrode structure. The above factors make most of the negative active materials easily peel off from the current collector during the cycling process, resulting in excessive volume expansion of the lithium ion battery during high-temperature cycling and rapid degradation of the cycle life.

[0005] (2) Silicon is a typical semiconductor material, with an electrical conductivity of only 1×10 -3 S / cm at room temperature, which makes the electron transport efficiency low. At the same time, under low-temperature conditions, the viscosity of the electrolyte increases, affecting the diffusion speed of lithium ions in the electrolyte. With the continuous extraction and intercalation of lithium ions, the volume change of silicon particles destroys the electrode structure, further exacerbating the sluggishness of charge transport. The dual effects of increased electrolyte viscosity and silicon particle volume expansion make the lithium ion battery based on silicon-based negative electrode materials have poor conductivity under low-temperature conditions.

[0006] (3) Silicon particles will undergo significant volume expansion and contraction during charging and discharging, leading to continuous rupture and regeneration of the SEI film on the negative electrode surface, exposing new surfaces, which will react with the electrolyte again to regenerate the SEI film, which not only consumes a large amount of electrolyte and active lithium ions, but also increases the thickness of the SEI film (rich in insulating components such as LiF and Li2CO3), thereby reducing the first coulombic efficiency of the lithium ion battery and increasing the interface side reactions.

[0007] Therefore, how to further expand the application temperature range of the lithium ion battery while ensuring that the lithium ion battery has high capacity is a technical problem that those skilled in the art need to solve. SUMMARY

[0008] In view of the technical problems of the prior art that the silicon-based negative electrode material has large volume expansion during high-temperature cycling, poor low-temperature conductivity, and more interface side reactions, the purpose of the present application is to provide an electrolyte suitable for a silicon-based negative electrode material, a lithium ion battery comprising the same, and an electronic device, which effectively improve the electrochemical performance and safety performance of the lithium ion battery under high-temperature and low-temperature conditions.

[0009] To achieve the purpose of the present application, the following technical solutions are adopted:

[0010] In a first aspect, the present application provides an electrolyte suitable for a silicon-based negative electrode material, the electrolyte suitable for a silicon-based negative electrode material comprising an electrolyte additive, a metal salt and a non-aqueous solvent, the electrolyte additive comprising a base additive and a functional additive.

[0011] The functional additive comprises a combination of at least two of an oxide material, a thiocarbonic acid ester compound or a cyanoacrylate compound.

[0012] The electrolyte additive formed by compounding the base additive and the functional additive can not only form a uniform, stable and dense SEI film on the surface of the silicon-based negative electrode material, improving the interface performance of the electrode / electrolyte, but also improve the ionic conductivity and chemical stability of the electrolyte. The electrolyte comprising the above electrolyte additive can effectively improve the high-temperature and low-temperature cycling performance and high-temperature safety of the lithium ion battery based on the silicon-based negative electrode material, which is specifically manifested as follows:

[0013] (1) The oxide material used in the present application not only can adsorb a small amount of water in the electrolyte, but also can neutralize free hydrogen fluoride, thereby prolonging the cycle life of the lithium ion battery. At the same time, it can modify the SEI film on the surface of the silicon-based negative electrode material, thereby enhancing the mechanical strength of the film, so as to inhibit the volume expansion of the silicon-based negative electrode material.

[0014] (2) The sulfide carbonate compound adopted in the present application can absorb oxygen free radicals generated by the structure change of the positive electrode material at high temperature, avoid further oxidation and decomposition of the electrolyte, and form a SEI film with high stability and high conductivity on the surface of the positive and negative electrodes, thereby reducing the interface impedance and improving the cycle performance of the lithium ion battery under high and low temperature conditions.

[0015] (3) The cyano acrylate compound adopted in the present application can undergo a polymerization reaction to generate a solid polymer, and the compound can participate in the formation of positive and negative electrode films during the polymerization reaction, thereby forming a solid electrolyte interface film containing the solid polymer on the surface of the positive and negative electrode materials, which can reduce the direct contact between the positive and negative electrode materials and the electrolyte, reduce the interface impedance, inhibit the dissolution and precipitation of transition metals and the release of lattice oxygen, and reduce the generation of side reactions inside the lithium ion battery.

[0016] Preferably, the oxide material comprises a nano metal oxide.

[0017] Preferably, the nano metal oxide comprises a nano aluminum oxide.

[0018] Preferably, the sulfide carbonate compound comprises trithioethylene carbonate (CAS number: 930-35-8).

[0019] Preferably, the cyano acrylate compound comprises any one or a combination of at least two of methyl cyano acrylate, ethyl cyano acrylate or secondary octyl alpha-cyano acrylate.

[0020] Preferably, the functional additive comprises a combination of the oxide material, the sulfide carbonate compound and the cyano acrylate compound.

[0021] Preferably, the mass percentage of the functional additive is 0.55%-11%, preferably 3%-8%, for example, it can be 0.55%, 0.8%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9% or 11%, etc., not limited to the listed values, and other values not listed in the range are also applicable.

[0022] Preferably, the mass percentage of the oxide material is 0.05%-2%, preferably 0.1%-1.5%, for example, it can be 0.05%, 0.08%, 0.1%, 0.2%, 0.5%, 0.8%, 1%, 1.5%, 1.8% or 2%, etc., not limited to the listed values, and other values not listed in the range are also applicable.

[0023] In the present application, by regulating the mass percentage of the oxide material to a suitable range, the stability of the electrolyte can be better improved.

[0024] Preferably, the mass percentage of the sulfocarbonic compound is 0.5%-5%, preferably 1%-3%, for example, it can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3% or 5%, etc., not limited to the listed values, other values not listed in the range are also applicable.

[0025] In the present application, by regulating the mass percentage of the sulfocarbonic compound to a suitable range, the high and low temperature cycle performance of the lithium ion battery can be better improved.

[0026] Preferably, the mass percentage of the cyanopropenoate compound is 0.5%-4%, preferably 1%-3%, for example, it can be 0.5%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3%, 3.5% or 4%, etc., not limited to the listed values, other values not listed in the range are also applicable.

[0027] In the present application, by regulating the mass percentage of the cyanopropenoate compound to a suitable range, the film forming quality of the positive and negative electrodes can be better improved, and the internal side reaction of the battery is inhibited.

[0028] Preferably, the basic additive includes a carbonic compound and / or a nitrile compound.

[0029] Preferably, the mass percentage of the basic additive is 0.1%-8%, for example, it can be 0.1%, 0.3%, 0.6%, 1%, 2%, 3%, 4%, 5%, 6%, 7% or 8%, etc., not limited to the listed values, other values not listed in the range are also applicable.

[0030] Preferably, the carbonic compound includes fluoroethylene carbonate (FEC) and / or vinylene carbonate (VC). The vinylene carbonate can generate a SEI film containing polyalkyl lithium carbonate on the surface of the silicon-based negative electrode material, the fluoroethylene carbonate can be reduced to generate a fluorine-containing polymer on the silicon-based negative electrode material, thereby improving the stability of the SEI film, and the film forming quality is good, not only helps to inhibit the reduction and decomposition of the electrolyte, but also can buffer the volume expansion of the silicon particles.

[0031] Preferably, the mass percentage of the carbonate compound is 0.5%-5%, preferably 1%-3%, such as 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3% or 5%, etc., not limited to the listed values, and other values not listed in the range are also applicable.

[0032] In the present application, by regulating the mass percentage of the carbonate compound to an appropriate range, the film forming quality of the silicon-based negative electrode material can be better improved, and the occurrence of side reactions can be reduced.

[0033] Preferably, the nitrile compound includes butanedinitrile (SN) and / or 1,3,6-hexanetricarbonitrile (HTCN). Butanedinitrile has a high oxidation potential and can chelate with cobalt ions in the positive electrode material, thereby inhibiting high-temperature gas production and improving the high-temperature cycle performance of the lithium ion battery. 1,3,6-hexanetricarbonitrile can bind to the surface of the silicon-based negative electrode material through the cyano group, reducing the exposed active sites, further reducing the side reactions between the electrolyte and the negative electrode under high-temperature conditions, and inhibiting gas production.

[0034] Preferably, the mass percentage of the nitrile compound is 0.1%-3%, preferably 0.5%-2%, such as 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2% or 3%, etc., not limited to the listed values, and other values not listed in the range are also applicable, based on 100% of the total mass of the electrolyte suitable for the silicon-based negative electrode material.

[0035] In the present application, by regulating the mass percentage of the nitrile compound to an appropriate range, the high-temperature performance of the lithium ion battery based on the silicon-based negative electrode material can be better improved.

[0036] Preferably, the metal salt includes a lithium salt.

[0037] Preferably, the mass percentage of the metal salt is 7%-30%, such as 7%, 10%, 12%, 15%, 18%, 20%, 22%, 25% or 30%, etc., not limited to the listed values, and other values not listed in the range are also applicable, based on 100% of the total mass of the electrolyte suitable for the silicon-based negative electrode material.

[0038] Preferably, the lithium salt includes a combination of lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB).

[0039] Preferably, the mass ratio of the lithium hexafluorophosphate and the lithium difluoro(oxalato)borate is (5-20):(2-10), such as 5:2, 8:3, 10:4, 12:5, 15:6, 16:7, 17:8, 18:9 or 20:10, etc., not limited to the listed values, and other values not listed within the range are also applicable.

[0040] In the present application, by regulating the mass ratio of the lithium hexafluorophosphate and the lithium difluoro(oxalato)borate to an appropriate range, a double salt system can be constructed in the electrolyte, thereby comprehensively improving the ionic conductivity and high-temperature performance of the electrolyte. Among them, the lithium hexafluorophosphate can provide a higher ionic conductivity, which is conducive to the transmission of lithium ions through the electrolyte; the lithium difluoro(oxalato)borate can be preferentially reduced on the surface of the negative electrode during charging and discharging and form a dense SEI film containing boron and / or fluorine elements, further inhibit the hydrolysis reaction of lithium hexafluorophosphate, and reduce the content of HF, thereby improving the high-temperature stability of the electrolyte.

[0041] Preferably, the non-aqueous solvent comprises a combination of a carbonate-based solvent and a carboxylate-based solvent.

[0042] Preferably, the mass percentage content of the non-aqueous solvent is 50%-75%, such as 50%, 55%, 60%, 65%, 70% or 75%, etc., based on the total mass of the electrolyte suitable for the silicon-based negative electrode material, not limited to the listed values, and other values not listed within the range are also applicable.

[0043] Preferably, the carbonate-based solvent comprises ethylene carbonate (EC) and propylene carbonate (PC).

[0044] Preferably, the carboxylate-based solvent comprises propyl propionate (PP).

[0045] Preferably, the non-aqueous solvent comprises a combination of ethylene carbonate, propylene carbonate and propyl propionate.

[0046] Preferably, the mass ratio of the ethylene carbonate, propyl propionate and propylene carbonate is (15-30):(40-60):(10-45), such as 15:40:10, 18:42:15, 20:45:20, 22:48:25, 25:50:30, 28:55:35 or 30:60:45, etc., not limited to the listed values, and other values not listed within the range are also applicable.

[0047] In the present application, by regulating the mass ratio of ethylene carbonate, propyl propionate and propylene carbonate to a suitable range, not only good compatibility between it and the silicon-based negative electrode material is obtained, but also good film forming ability is obtained. Among them, ethylene carbonate and propylene carbonate have high dielectric constant, which can promote the dissociation of lithium ions, improve the conductivity and ion migration speed of the electrolyte, thereby improving the low temperature performance of the electrolyte; and the melting point of propyl propionate is low and the boiling point is high, which improves the high temperature performance of the electrolyte.

[0048] In a second aspect, the present application provides a lithium ion battery, which comprises a negative electrode sheet, a positive electrode sheet, an electrolyte and a separator, and the electrolyte comprises the electrolyte suitable for silicon-based negative electrode material as described in the first aspect.

[0049] Preferably, the negative electrode sheet comprises a negative electrode current collector, a porous conductive layer and a negative electrode active material layer, the porous conductive layer is arranged on the surface of at least one side of the negative electrode current collector, and the negative electrode active material layer is arranged on the surface of the porous conductive layer away from the negative electrode current collector.

[0050] Preferably, the material of the porous conductive layer comprises a first conductive agent, a first binder and nano-oxide particles.

[0051] Preferably, the mass percentage content of the first conductive agent is 15%-30%, for example, it can be 15%, 18%, 20%, 22%, 25%, 28% or 30%, etc., not only limited to the listed values, other values not listed in this range are also applicable.

[0052] Preferably, the first conductive agent comprises a combination of carbon nanotubes, graphene and conductive carbon black.

[0053] Preferably, the mass ratio of the carbon nanotubes, graphene and conductive carbon black is (5-10):(5-10):(5-10), for example, it can be 5:5:5, 6:7:6, 7:8:7, 8:8:9, 9:8:7 or 10:9:10, etc., not only limited to the listed values, other values not listed in this range are also applicable.

[0054] Preferably, the nano-oxide particles comprise nano-aluminum oxide particles.

[0055] Preferably, the mass percentage content of the nano-oxide particles is 0.5%-5%, for example, it can be 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, 3% or 5%, etc., not only limited to the listed values, other values not listed in this range are also applicable.

[0056] Preferably, the mass percentage of the first binder is 3-5%, such as 3%, 3.5%, 4%, 4.5%, or 5%, etc., not limited to the listed values, and other values not listed within the range are also applicable.

[0057] Preferably, the thickness of the porous conductive layer is 10-20 μm, such as 10 μm, 12 μm, 15 μm, 18 μm, or 20 μm, etc., not limited to the listed values, and other values not listed within the range are also applicable.

[0058] Preferably, the material of the negative electrode active material layer comprises a negative electrode active material, a second conductive agent, a second binder, and a first solid electrolyte material.

[0059] Preferably, the first solid electrolyte material comprises a first oxide solid electrolyte material.

[0060] Preferably, the first oxide solid electrolyte material comprises a LATP material.

[0061] Preferably, the mass percentage of the first solid electrolyte material is 0.1-3%, such as 0.1%, 0.5%, 0.8%, 1%, 1.2%, 1.5%, 1.8%, 2%, 2.5%, or 3%, etc., not limited to the listed values, and other values not listed within the range are also applicable, based on the total mass of the solid components in the slurry of the negative electrode active material layer being 100%.

[0062] Preferably, the mass percentage of the negative electrode active material is 88-95%, such as 88%, 89%, 90%, 91%, 92%, 93%, 94%, or 95%, etc., not limited to the listed values, and other values not listed within the range are also applicable, based on the total mass of the solid components in the slurry of the negative electrode active material layer being 100%.

[0063] Preferably, the mass percentage of the second conductive agent is 1-6%, such as 1%, 2%, 3%, 4%, 5%, or 6%, etc., not limited to the listed values, and other values not listed within the range are also applicable, based on the total mass of the solid components in the slurry of the negative electrode active material layer being 100%.

[0064] Preferably, the mass percentage of the second binder is 3-7%, such as 3%, 4%, 5%, 6%, or 7%, etc., not limited to the listed values, and other values not listed within the range are also applicable, based on the total mass of the solid components in the slurry of the negative electrode active material layer being 100%.

[0065] Preferably, the thickness of the negative active material layer is 70-90 μm, for example, 70 μm, 75 μm, 80 μm, 85 μm or 90 μm, etc., not limited to the listed values, other values not listed in the range are also applicable.

[0066] Preferably, the separator comprises a substrate and a coating disposed on at least one side of the substrate, the coating comprising a second solid-state electrolyte material.

[0067] Preferably, the second solid-state electrolyte material comprises a second oxide solid-state electrolyte material.

[0068] Preferably, the second oxide solid-state electrolyte material comprises a LATP material.

[0069] Preferably, the coating is disposed on a side facing the positive electrode sheet.

[0070] In a third aspect, the present application provides an electronic device comprising the lithium ion battery of the second aspect.

[0071] The numerical ranges recited herein also include any and all point values and sub-ranges contained therein, limited by the terms of the disclosure and by the preamble to the claims. In the interest of clarity, not all combinations of values are listed. The more specific examples herein specified are indicative, by way of example only, of the more general values to which they refer.

[0072] Compared with the prior art, the present application has the following beneficial effects:

[0073] The present application provides an electrolyte suitable for silicon-based negative electrode material, by using the electrolyte additive formed by compounding the base additive and the functional additive, which can not only form a uniform, stable and dense SEI film on the surface of the silicon-based negative electrode material, improve the interface performance of the electrode / electrolyte, but also improve the ionic conductivity and chemical stability of the electrolyte, and the electrolyte containing the above electrolyte additive can effectively improve the high and low temperature cycle performance and high temperature safety of the lithium ion battery based on the silicon-based negative electrode material, and the specific performance is as follows:

[0074] (1) The oxide material used in the present application can not only adsorb a small amount of water in the electrolyte, but also neutralize free hydrogen fluoride, thereby prolonging the cycle life of the lithium ion battery. At the same time, it can modify the SEI film on the surface of the silicon-based negative electrode material, thereby enhancing the mechanical strength of the film, so as to inhibit the volume expansion of the silicon-based negative electrode material.

[0075] (2) The sulfide ester group in the sulfide carbonate compound can absorb oxygen free radicals generated by the structural change of the positive electrode material at high temperature, avoiding further oxidation and decomposition of the electrolyte, and at the same time, can form a SEI film with high stability and high conductivity on the surface of the positive and negative electrodes, thereby reducing the interface impedance and improving the cycle performance of the lithium ion battery under high and low temperature conditions.

[0076] (3) The cyano acrylate compound can undergo a polymerization reaction to generate a solid polymer, and at the same time, the compound can participate in the formation of positive and negative electrode films during the polymerization reaction, thereby forming a solid electrolyte interface film containing a solid polymer on the surface of the positive and negative electrode materials, which can reduce the direct contact between the positive and negative electrode materials and the electrolyte, reduce the interface impedance, inhibit the dissolution and release of transition metal and lattice oxygen, and reduce the generation of internal side reactions of the lithium ion battery. DETAILED DESCRIPTION

[0077] The technical solutions of the present application will be further described below through specific embodiments. Those skilled in the art should understand that the embodiments are only to help understand the present application and should not be regarded as specific limitations of the present application.

[0078] Embodiment 1

[0079] The present embodiment provides an electrolyte suitable for silicon-carbon negative electrode material, which comprises lithium salt, electrolyte additive and non-aqueous solvent. The mass percentage of lithium salt is 18%, the mass percentage of electrolyte additive is 8.3%, and the rest is non-aqueous solvent, based on the total mass of the electrolyte being 100%.

[0080] In the electrolyte, the lithium salt is a combination of lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB), and the mass ratio of LiPF6 and LiDFOB is 12:6; the electrolyte additive comprises basic additive and functional additive. Among them, the basic additive comprises fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinonitrile (SN) and 1,3,6-hexanetricarbonitrile (HTCN); the functional additive comprises nano-alumina, trisulfide carbonate vinylene and methyl cyano acrylate. Based on the total mass of the electrolyte being 100%, the mass percentage of FEC in the basic additive is 1%, the mass percentage of VC is 1%, the mass percentage of SN is 0.5%, and the mass percentage of HTCN is 1%; the mass percentage of nano-alumina in the functional additive is 0.8%, the mass percentage of trisulfide carbonate vinylene is 2%, and the mass percentage of methyl cyano acrylate is 2%.

[0081] The non-aqueous solvent comprises ethylene carbonate (EC), propyl propionate (PP) and propylene carbonate (PC) in a mass ratio of 22:50:28.

[0082] The embodiment also provides a preparation method of the electrolyte suitable for the silicon-carbon negative electrode material.

[0083] In an argon-filled glove box with H2O < 10 ppm and O2 < 1 ppm, EC, PC and PP are mixed according to the formula to obtain a non-aqueous solvent; after standing for 0.5 h, lithium salt is added, a magnetic stirrer is used for constant-temperature stirring at 35 ℃ for 12 h until the lithium salt is completely dissolved, electrolyte additives are added again after standing for 0.5 h, and stirring is continued at 25 ℃ for 7 h to ensure uniform dispersion of the electrolyte additives, and finally, 0.22 μm filter membrane is used for filtration to obtain the electrolyte suitable for the silicon-carbon negative electrode material.

[0084] Embodiment 2

[0085] The embodiment provides an electrolyte suitable for a silicon-carbon negative electrode material, which comprises lithium salt, electrolyte additives and a non-aqueous solvent. The mass percentage of the lithium salt is 20%, the mass percentage of the electrolyte additives is 8.55%, and the rest is the non-aqueous solvent, based on 100% of the total mass of the electrolyte.

[0086] In the electrolyte, the lithium salt is a combination of lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB), and the mass ratio of LiPF6 to LiDFOB is 5:2; the electrolyte additives comprise basic additives and functional additives. The basic additives comprise fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinonitrile (SN) and 1,3,6-hexanetricarbonitrile (HTCN); the functional additives comprise nano-aluminum oxide, trithioethylene carbonate and methyl cyano acrylate. The mass percentage of FEC is 0.5%, the mass percentage of VC is 0.5%, the mass percentage of SN is 1.5%, and the mass percentage of HTCN is 1.5% in the basic additives, based on 100% of the total mass of the electrolyte; the mass percentage of nano-aluminum oxide is 0.05%, the mass percentage of trithioethylene carbonate is 0.5%, and the mass percentage of methyl cyano acrylate is 4% in the functional additives.

[0087] The non-aqueous solvent comprises ethylene carbonate (EC), propyl propionate (PP) and propylene carbonate (PC) in a mass ratio of 22:50:28.

[0088] The embodiment also provides a preparation method of the electrolyte suitable for the silicon-carbon negative electrode material.

[0089] In an argon-filled glove box, the EC, PC and PP are mixed according to the formula to obtain a non-aqueous solvent; after standing for 0.5 h, the lithium salt is added, and a magnetic stirrer is used for constant temperature stirring at 35℃ for 12 h until the lithium salt is completely dissolved; after standing for 0.5 h, the electrolyte additive is added again, and stirring is continued at 25℃ for 7 h to ensure uniform dispersion of the electrolyte additive; finally, filtration is performed using a 0.22 μm filter membrane to obtain the electrolyte suitable for the silicon-carbon negative electrode material.

[0090] Example 3

[0091] The present embodiment provides an electrolyte suitable for a silicon-carbon negative electrode material, which comprises a lithium salt, an electrolyte additive and a non-aqueous solvent. The mass percentage of the lithium salt is 25%, the mass percentage of the electrolyte additive is 13%, and the balance is the non-aqueous solvent, based on the total mass of the electrolyte being 100%.

[0092] In the electrolyte, the lithium salt is a combination of lithium hexafluorophosphate (LiPF6) and lithium difluoro(oxalato)borate (LiDFOB), and the mass ratio of LiPF6 to LiDFOB is 20:10; the electrolyte additive comprises a basic additive and a functional additive. The basic additive comprises fluoroethylene carbonate (FEC), vinylene carbonate (VC), succinonitrile (SN) and 1,3,6-hexanetricarbonitrile (HTCN); the functional additive comprises nano-alumina, trithioethylene carbonate and methyl cyano acrylate. The mass percentage of FEC in the basic additive is 3%, the mass percentage of VC is 2%, the mass percentage of SN is 0.25%, and the mass percentage of HTCN is 0.25%, based on the total mass of the electrolyte being 100%; the mass percentage of nano-alumina in the functional additive is 2%, the mass percentage of trithioethylene carbonate is 5%, and the mass percentage of methyl cyano acrylate is 0.5%.

[0093] The non-aqueous solvent comprises vinyl carbonate (EC), propyl propionate (PP) and propylene carbonate (PC) in a mass ratio of 30:40:30.

[0094] The present embodiment also provides a preparation method of the above-mentioned electrolyte suitable for a silicon-carbon negative electrode material, which comprises the following steps:

[0095] In a glove box filled with argon, H2O < 10 ppm, O2 < 1 ppm, EC, PC and PP are mixed according to the formula to obtain a non-aqueous solvent; after standing for 0.5 h, lithium salt is added, a magnetic stirrer is used for constant temperature stirring at 35℃ for 12 h until the lithium salt is completely dissolved, electrolyte additives are added after standing for 0.5 h, and stirring is continued at 25℃ for 7 h to ensure uniform dispersion of the electrolyte additives, and finally 0.22 μm filter membrane is used for filtration to obtain the electrolyte suitable for silicon-carbon negative electrode material.

[0096] Example 4

[0097] The difference between this embodiment and Example 1 is that in the functional additive, the mass percentage of nano-aluminum oxide is 0.01%, the mass percentage of trithioethylene carbonate is 2.79%, and the mass percentage of methyl cyano acrylate is 2%, and the others are the same as Example 1.

[0098] Example 5

[0099] The difference between this embodiment and Example 1 is that in the functional additive, the mass percentage of nano-aluminum oxide is 5%, the mass percentage of trithioethylene carbonate is 2%, and the mass percentage of methyl cyano acrylate is 2%, and the total mass of each component in the electrolyte is adjusted to satisfy 100%, and the others are the same as Example 1.

[0100] Example 6

[0101] The difference between this embodiment and Example 1 is that in the functional additive, the mass percentage of nano-aluminum oxide is 0.8%, the mass percentage of trithioethylene carbonate is 0.1%, and the mass percentage of methyl cyano acrylate is 3.9%, and the others are the same as Example 1.

[0102] Example 7

[0103] The difference between this embodiment and Example 1 is that in the functional additive, the mass percentage of nano-aluminum oxide is 0.8%, the mass percentage of trithioethylene carbonate is 8%, and the mass percentage of methyl cyano acrylate is 2%, and the total mass of each component in the electrolyte is adjusted to satisfy 100%, and the others are the same as Example 1.

[0104] Example 8

[0105] The difference between this embodiment and Example 1 is that in the functional additive, the mass percentage of nano-aluminum oxide is 0.8%, the mass percentage of trithioethylene carbonate is 3.9%, and the mass percentage of methyl cyano acrylate is 0.1%, and the others are the same as Example 1.

[0106] Example 9

[0107] The difference between this example and Example 1 is that the mass percentage of nano-alumina in the functional additive is 0.8%, the mass percentage of trithioethylene carbonate is 2%, and the mass percentage of methyl cyano acrylate is 8%, and the content of organic solvent is adjusted so that the sum of the total mass of each component in the electrolyte satisfies 100%, and the others are the same as Example 1.

[0108] Comparative Example 1

[0109] The difference between this comparative example and Example 1 is that no functional additive is added, only basic additive is added, and the content of organic solvent is adjusted so that the sum of the total mass of each component in the electrolyte satisfies 100%, and the others are the same as Example 1.

[0110] Comparative Example 2

[0111] The difference between this comparative example and Example 1 is that no nano-alumina additive is added, and the content of organic solvent is adjusted so that the sum of the total mass of each component in the electrolyte satisfies 100%, and the others are the same as Example 1.

[0112] Comparative Example 3

[0113] The difference between this comparative example and Example 1 is that no trithioethylene carbonate additive is added, and the content of organic solvent is adjusted so that the sum of the total mass of each component in the electrolyte satisfies 100%, and the others are the same as Example 1.

[0114] Comparative Example 4

[0115] The difference between this comparative example and Example 1 is that no methyl cyano acrylate additive is added, and the content of organic solvent is adjusted so that the sum of the total mass of each component in the electrolyte satisfies 100%, and the others are the same as Example 1.

[0116] Application Examples 1-9 and Comparative Application Examples 1-4

[0117] The electrolytes provided by Examples 1-9 and Comparative Examples 1-4 are used to prepare lithium ion batteries, as shown below:

[0118] Preparation of negative electrode sheet:

[0119] The artificial graphite, CVD silicon-carbon powder and conductive agent Super P were added to a double planetary mixer for mixing, and stirred at a revolution rate of 20 rpm and a dispersion rate of 600 rpm for 45 min to obtain a uniformly mixed negative electrode active material powder. Then, sodium carboxymethyl cellulose solution, polyacrylic acid binder, LATP solution, VGCF solution and single-walled carbon nanotubes were added to the negative electrode active material powder, and then water was added to control the solid content of the overall slurry to 42%. The vacuum and circulating water were turned on, and the slurry was stirred at a revolution rate of 25 rpm and a dispersion rate of 2500 rpm for 200 min. After the stirring was completed, the viscosity was measured and controlled to be 5500 mPa·s to obtain a negative electrode active material layer slurry. In the negative electrode active material layer slurry, the mass percentage of the artificial graphite was 89.95%, the mass percentage of the CVD silicon-carbon powder was 5%, the mass percentage of the conductive agent Super P was 0.5%, the mass percentage of the sodium carboxymethyl cellulose was 1%, the mass percentage of the polyacrylic acid binder was 2%, the mass percentage of the LATP was 1%, the mass percentage of the VGCF was 0.5%, and the mass percentage of the single-walled carbon nanotubes was 0.05%, based on the total mass of the solid components in the slurry.

[0120] The conductive agent (carbon nanotubes, graphene and conductive carbon black, mass ratio 7:8:7) composed of carbon nanotubes (CNT), graphene and conductive carbon black was mixed with Al2O3 nanoparticles by a double planetary mixer, and then stirred at a revolution rate of 22 rpm and a dispersion rate of 1100 rpm for 45 min. After the stirring was completed, the pot wall and stirring paddle were scraped, and then the binder polyacrylic acid (PAA) and water were added. The vacuum and circulating water were turned on, and the slurry was stirred at a revolution rate of 28 rpm and a dispersion rate of 2500 rpm for 400 min. After the stirring was completed, the viscosity was tested and controlled to be 3500 mPa·s to obtain a porous conductive layer slurry. In the porous conductive layer slurry, the mass percentage of the conductive agent was 22%, the mass percentage of the Al2O3 nanoparticles was 2.5%, the mass percentage of the binder polyacrylic acid PAA was 4%, and the mass percentage of water was 71.5%, based on the total mass of the slurry.

[0121] The above porous conductive layer slurry was coated by a transfer coater at a surface density of 2.0 mg / cm 2 , the drying temperature of the oven was set to 90°C, the air frequency of the oven was set to 25 hz, and the coating thickness of the porous conductive layer was set to 15 μm after the oven drying. After the coating was completed, only one roll pressing was performed, and the roll pressing pressure was set to 7 Mpa. The above negative electrode active material layer slurry was coated by a transfer coater at a surface density of 6 mg / cm 2The negative electrode slurry was coated on the surface of the negative electrode substrate with a surface density of 1.5 mg / cm2, the oven drying temperature was set to 80°C, the air frequency of the oven was set to 25 hz, and the thickness of the coating after oven drying was controlled to 80 pm. After coating, secondary rolling was performed, with an interval of 2 h, to obtain the negative electrode sheet.

[0122] Preparation of the positive electrode sheet:

[0123] The LiCoO2 positive electrode material, conductive carbon black, carbon nanotubes (CNT), and polyvinylidene fluoride binder were mixed in a mass ratio of 98.4:0.4:0.4:0.8, and then N-methylpyrrolidone solvent was added to prepare a positive electrode slurry. The positive electrode slurry was blade-coated on an aluminum foil, and after subsequent drying and rolling treatment, a positive electrode sheet was obtained.

[0124] Preparation of the separator:

[0125] The LATP solution was blade-coated on one side of a polypropylene-based film, and after drying, a coating layer was formed to obtain a separator.

[0126] Preparation of the lithium ion battery:

[0127] The above-mentioned negative electrode sheet, positive electrode sheet, separator, and electrolyte provided by the examples and comparative examples were prepared into a lithium ion battery through winding, packaging, liquid injection, formation, capacity distribution, aging, and sorting, wherein the coating layer of the separator faced the positive electrode sheet.

[0128] Comparative application example 5

[0129] The difference between this comparative application example and application example 1 is that no porous conductive layer is provided in the negative electrode sheet, and the others are the same as in example 1.

[0130] Test conditions

[0131] The lithium ion batteries provided by the above-mentioned application examples and comparative application examples were tested for performance, as shown below:

[0132] (1) High-temperature cycle performance: At 60°C, the thickness before cycling of the lithium ion battery after formation was tested, then it was charged to 4.48 V (cut-off current was 0.01C) at 0.5C constant current and constant voltage, and then discharged to 3.0 V at 0.5C constant current, the thickness after cycling was tested, and the capacity retention rate after 100 cycles of charging / discharging was calculated, with the formula as follows:

[0133] Capacity retention rate (%) after 100 cycles = (discharge capacity after the 100th cycle / discharge capacity after the 1st cycle) x 100%.

[0134] Thickness expansion rate (%) after 100 cycles = (thickness after the 100th cycle - thickness before the 1st cycle) / thickness before the 1st cycle x 100%.

[0135] (2) Low-temperature cycle performance: under the conditions of -20℃ and -10℃ respectively, the lithium ion battery after formation was respectively charged to 4.48V (the cut-off current was 0.02C) by 0.2C constant current and constant voltage, and then discharged to 3.0V by 0.2C constant current, and then the capacity retention rate of 100 cycles of charge / discharge was calculated respectively, and the calculation formula was as follows:

[0136] Cycle capacity retention rate (%) = (100th cycle discharge capacity / 1st cycle discharge capacity) x 100%.

[0137] The test results are shown in Table 1.

[0138] Table 1

[0139]

[0140] As can be seen from Table 1, compared with Comparative Application Examples 1-4, the lithium ion batteries in Application Examples 1-3 provided by the application have good wide-temperature performance and high-temperature safety.

[0141] It can be known from Comparative Example 1, Examples 4-5 that adding an appropriate amount of nano-aluminum oxide in the electrolyte can modify the SEI film on the surface of the silicon-carbon negative electrode material, so as to enhance the mechanical strength of the film, thereby inhibiting the volume expansion of the silicon-carbon negative electrode material. When the content of nano-aluminum oxide is low, the modification effect is insufficient; when the content of nano-aluminum oxide is high, the nano-particles are easy to agglomerate, which destroys the uniformity of the electrolyte, and on the contrary, reduces the interface stability of the electrode / electrolyte.

[0142] It can be known from Comparative Example 1, Examples 6-7 that adding an appropriate amount of trithioethylene carbonate in the electrolyte can participate in the formation of the SEI film, so as to build a stable and flexible interface film layer, and further reduce the continuous decomposition of the electrolyte. When the content of trithioethylene carbonate is low, the stability of the film layer is insufficient; when the content of trithioethylene carbonate is high, the ester compound is excessively decomposed to produce by-products, which block the electrode pores and exacerbate the volume expansion of the silicon-carbon negative electrode material.

[0143] It can be known from Comparative Example 1, Examples 8-9 that adding an appropriate amount of methyl cyano acrylate in the electrolyte can improve the interface compatibility between the electrolyte and the silicon-carbon negative electrode material, reduce the interface impedance to improve the low-temperature discharge capacity. When the content of methyl cyano acrylate is low, the interface modification effect is insufficient; when the content of methyl cyano acrylate is high, the viscosity of the electrolyte is increased, the electrode conductive network is destroyed, and then the cycle performance, high and low temperature performance of the lithium ion battery are deteriorated.

[0144] It can be seen from comparative example 1 and comparative application example 5 that the porous conductive layer can buffer the volume expansion of the silicon-carbon negative electrode material and optimize the conductive network, and not setting the porous conductive layer will cause the cycle retention rate of the lithium ion battery to decrease significantly, the volume expansion of the silicon-carbon negative electrode material to be intensified, and the low-temperature discharge performance of the lithium ion battery to be further deteriorated.

[0145] The applicant declares that the above description is only a specific embodiment of the present application, but the protection scope of the present application is not limited thereto, and it should be understood by those skilled in the art that any changes or replacements within the technical scope disclosed by the present application can be easily thought of by those skilled in the art, and all fall within the protection scope and disclosure scope of the present application.

Claims

1. An electrolyte suitable for silicon-based anode materials, characterized in that, The electrolyte suitable for silicon-based anode materials includes electrolyte additives, metal salts, and non-aqueous solvents. The electrolyte additives include basic additives and functional additives. The functional additives include a combination of at least two of oxide materials, thiocarbonate compounds, or cyanoacrylate compounds.

2. The electrolyte suitable for silicon-based anode materials according to claim 1, characterized in that, The oxide material includes nano-metal oxides; Preferably, the nano-metal oxide includes nano-alumina; Preferably, the thiocarbonate compound includes trithioethylene carbonate; Preferably, the cyanoacrylate compound includes any one or a combination of at least two of methyl cyanoacrylate, ethyl cyanoacrylate, or 2-octyl α-cyanoacrylate; Preferably, the functional additive comprises a combination of oxide materials, thiocarbonate compounds, and cyanoacrylate compounds.

3. The electrolyte suitable for silicon-based anode materials according to claim 1 or 2, characterized in that, Based on the total mass of the electrolyte suitable for silicon-based anode materials as 100%, the mass percentage content of the functional additive is 0.55%-11%, preferably 3%-8%; Preferably, based on the total mass of the electrolyte suitable for silicon-based anode materials as 100%, the mass percentage content of the oxide material is 0.05%-2%, more preferably 0.1%-1.5%; Preferably, based on the total mass of the electrolyte suitable for silicon-based anode materials as 100%, the mass percentage of the thiocarbonate compound is 0.5%-5%, preferably 1%-3%; Preferably, based on the total mass of the electrolyte suitable for silicon-based anode materials as 100%, the mass percentage of the cyanoacrylate compound is 0.5%-4%, preferably 1%-3%.

4. The electrolyte suitable for silicon-based anode materials according to any one of claims 1-3, characterized in that, The basic additives include carbonate compounds and / or nitrile compounds; Preferably, based on the total mass of the electrolyte suitable for silicon-based anode materials as 100%, the mass percentage of the basic additive is 0.1%-8%. Preferably, the carbonate compound includes fluoroethylene carbonate and / or vinylene carbonate; Preferably, based on the total mass of the electrolyte suitable for silicon-based anode materials as 100%, the mass percentage content of the carbonate compound is 0.5%-5%, preferably 1%-3%; Preferably, the nitrile compound includes succinic anionylene and / or 1,3,6-hexanetrionitrile; Preferably, based on the total mass of the electrolyte suitable for silicon-based anode materials as 100%, the mass percentage of the nitrile compound is 0.1%-3%, more preferably 0.5%-2%.

5. The electrolyte suitable for silicon-based anode materials according to any one of claims 1-4, characterized in that, The metal salt includes lithium salt; Preferably, based on the total mass of the electrolyte suitable for silicon-based anode materials as 100%, the mass percentage content of the metal salt is 7%-30%; Preferably, the lithium salt comprises a combination of lithium hexafluorophosphate and lithium difluorooxalate borate; Preferably, the mass ratio of lithium hexafluorophosphate to lithium difluorooxalate borate is (5-20):(2-10); Preferably, the non-aqueous solvent comprises a combination of carbonate solvents and carboxylic acid ester solvents; Preferably, based on the total mass of the electrolyte suitable for silicon-based anode materials as 100%, the mass percentage of the non-aqueous solvent is 50%-75%. Preferably, the carbonate solvent includes ethylene carbonate and propylene carbonate; Preferably, the carboxylic acid ester solvent includes propyl propionate; Preferably, the non-aqueous solvent comprises a combination of ethylene carbonate, propylene carbonate, and propyl propionate; Preferably, the mass ratio of ethylene carbonate, propyl propionate and propylene carbonate is (15-30):(40-60):(10-45).

6. A lithium-ion battery, characterized in that, The lithium-ion battery includes a negative electrode, a positive electrode, an electrolyte, and a separator, wherein the electrolyte includes an electrolyte suitable for silicon-based negative electrode materials as described in any one of claims 1-5.

7. The lithium-ion battery according to claim 6, characterized in that, The negative electrode sheet includes a negative electrode current collector, a porous conductive layer, and a negative electrode active material layer. The porous conductive layer is disposed on at least one side of the surface of the negative electrode current collector, and the negative electrode active material layer is disposed on the surface of the porous conductive layer away from the negative electrode current collector. Preferably, the porous conductive layer is made of a first conductive agent, a first binder, and nano-oxide particles; Preferably, based on the total mass of the slurry of the porous conductive layer being 100%, the mass percentage of the first conductive agent is 15%-30%. Preferably, the first conductive agent comprises a combination of carbon nanotubes, graphene, and conductive carbon black; Preferably, the mass ratio of the carbon nanotubes, graphene, and conductive carbon black is (5-10):(5-10):(5-10); Preferably, the nano-oxide particles include nano-alumina particles; Preferably, based on the total mass of the porous conductive layer slurry (100%), the mass percentage of the nano-oxide particles is 0.5%-5%. Preferably, the thickness of the porous conductive layer is 10μm-20μm.

8. The lithium-ion battery according to claim 6 or 7, characterized in that, The material of the negative electrode active material layer includes a negative electrode active material, a second conductive agent, a second binder, and a first solid electrolyte material; Preferably, the first solid electrolyte material comprises a first oxide solid electrolyte material; Preferably, the first oxide solid electrolyte material includes LATP material; Preferably, based on the total mass of solid components in the slurry of the negative electrode active material layer being 100%, the mass percentage of the first solid electrolyte material is 0.1%-3%. Preferably, the thickness of the negative electrode active material layer is 70μm-90μm.

9. The lithium-ion battery according to any one of claims 6-8, characterized in that, The diaphragm includes a substrate and a coating disposed on at least one side of the substrate, the coating comprising a second solid electrolyte material; Preferably, the second solid electrolyte material comprises a second oxide solid electrolyte material; Preferably, the second oxide solid electrolyte material includes LATP material; Preferably, the coating is disposed on the side facing the positive electrode.

10. An electronic device, characterized in that, The electronic device includes a lithium-ion battery as described in any one of claims 6-9.

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