Lithium ion battery and electric device

Abstract

The invention provides a lithium ion battery, which comprises a positive electrode, a silicon-based negative electrode and an electrolyte, the silicon-based negative electrode comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material contains a manganese element; the electrolyte comprises a first additive, a second additive and a third additive, the first additive comprises methyl ethyl carbonate, the second additive comprises a monomer compound containing vinyl, and the third additive comprises an acrylate compound containing polyfunctional groups; the lithium ion battery satisfies the following formula: (A + B + C) * 100 / X is greater than or equal to 0.44, A% is 5%-40%, B% is 0.5%-5%, and C% is 0.5%-5%; according to the lithium ion battery provided by the invention, a plurality of additives have a synergistic effect, so that the problem of silicon-based negative electrode degradation caused by manganese dissolution is effectively solved, and the electrical properties of the lithium ion battery are synergistically improved in a wide temperature range of high and low temperatures; when a plurality of additives are controlled to meet the relational expression (A + B + C) * 100 / X > = 0.44, the synergistic effect can be better exerted, and the high-temperature stability, high-temperature storage and low-temperature discharge performance of the lithium ion battery are synergistically improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery and a power utilization device. BACKGROUND

[0002] As the most mainstream electrochemical energy storage device in the contemporary, lithium ion batteries have become the core power source in the field of consumer electronics and electric vehicles due to their outstanding energy density characteristics, extremely low static loss and excellent cycle stability. The realization of its electrochemical performance requires the organic cooperation of four core components: positive electrode material bearing redox reaction, negative electrode matrix storing lithium ions, electrolyte system providing ion migration channel, and porous separator ensuring electronic insulation. Under high temperature working conditions, manganese ions in silicon-based negative electrodes will undergo disproportionation reaction Catalytic chain oxidation of carbonate-based electrolyte not only accelerates the gas generation side reaction, but also induces the deposition of inorganic compounds containing Mn-O bonds. After the migration of dissolved manganese ions to the silicon negative electrode, the high valence state (Mn 3+ / Mn 4+ ) of the manganese ions will cause local oxidation of the silicon lattice, resulting in blockage of the lithium ion diffusion channel; at the same time, the reduced metal manganese nanoparticles will be embedded in the silicon matrix, forming an electrochemically inert region. The synergistic effect of this multi-valence manganese will significantly worsen the volume effect of silicon material, on the one hand, the MnOx deposit weakens the mechanical toughness of the electrode, and on the other hand, the manganese-induced local charge imbalance will exacerbate the stress gradient distribution during lithiation, ultimately leading to the radial expansion of electrode cracks and the detachment of the current collector. Compared with cobalt, the multi-electron redox characteristics of manganese cause the rapid capacity decay of silicon-based negative electrodes during high-temperature cycling. SUMMARY

[0003] In view of the problem of the deterioration of the storage and cycle performance of the battery caused by the migration of manganese elements in the silicon-based negative electrode battery under high temperature environment in the prior art, a lithium ion battery and a power utilization device are provided.

[0004] The technical solution adopted by the present application to solve the above technical problems is as follows: On the one hand, the present application provides a lithium ion battery, comprising a positive electrode, a silicon-based negative electrode and an electrolyte, the silicon-based negative electrode comprising a negative electrode active material layer, the negative electrode active material layer comprising a negative electrode active material, the negative electrode active material containing manganese elements; The electrolyte comprises a first additive, a second additive and a third additive, the first additive comprising methyl ethyl carbonate, the second additive comprising a monomer compound containing a vinyl group, and the third additive comprising a multi-functional acrylate compound; The lithium ion battery satisfies the following conditions: Formula 1: (A+B+C) *100 / X≥0.44, and A% is 5%-40%, B% is 0.5%-5%, and C% is 0.5%-5%; A% is the mass percentage content of the first additive in the electrolyte; B% is the mass percentage content of the second additive in the electrolyte; C% is the mass percentage content of the third additive in the electrolyte; X is the content of manganese element in the negative electrode active material, in ppm.

[0005] Optionally, the lithium ion battery satisfies the following conditions: Formula 2: 0.6≤(A+B+C) *100 / X≤120.

[0006] Optionally, the first additive, the second additive, and the third additive satisfy the following conditions: Formula 3: 0.667≤A / (B+C)≤24.375.

[0007] Optionally, the first additive, the second additive, and the third additive satisfy the following conditions: Formula 4: 1.667≤A / (B+C)≤20.

[0008] Optionally, the second additive and the third additive satisfy the following conditions: Formula 5: 0.16≤B / C≤6.25.

[0009] Optionally, the content X of the manganese element in the negative electrode active material is 10-2000 ppm.

[0010] Optionally, the second additive includes one or more of the following compounds: .

[0011] Optionally, the third additive includes one or more of the following compounds: .

[0012] Optionally, the positive electrode includes a positive electrode active material, and the positive electrode active material includes one or more of transition metal lithium oxides, lithium iron phosphate, lithium manganese oxide, lithium manganese iron phosphate, and lithium vanadium phosphate; The chemical formula of the transition metal lithium oxide is Li 1+x Ni y Co z M (1-y-z)O2, wherein -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; wherein M is selected from one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, Zr.

[0013] In another aspect, the present application provides a lithium ion battery comprising the lithium ion battery.

[0014] The present application has the following beneficial effects: In the lithium ion battery provided by the present application, the first additive ethyl methyl carbonate (EMC) forms an inorganic-organic hybrid SEI film rich in Li2CO3 at the negative electrode interface by the lower molecular symmetry of its linear carbonate structure (-O-CO-O-), which significantly improves the low-temperature ion mobility due to the low crystallinity of the film, thereby improving the discharge capacity retention rate, and its moderate chemical stability can alleviate the interface side reactions during high-temperature cycling. However, the alkoxy lithium produced by the decomposition of EMC can catalyze the reconstruction of the positive electrode interface film, leading to continuous consumption of electrolyte during high-temperature storage and causing irreversible loss of capacity; the second additive contains a double-bond monomer, which forms a loosely crosslinked polymer network at the electrode interface through its carbon-carbon double bond (C=C) polymerization, and the compound contains Si or F or N elements, which can participate in interface film formation to form SiN, LiN, and LiF substances, thereby improving the stability of the battery interface. This semi-rigid structure can effectively inhibit the penetration of electrolyte at high temperatures while retaining part of the ion channels, thereby improving the high-temperature cycling and storage performance, but the incompletely crosslinked molecular chains introduce additional interface impedance, leading to a decrease in low-temperature discharge capacity; the third additive multifunctional acrylate builds a three-dimensional network SEI film with high crosslinking density through free radical polymerization, and its rich ester groups (-COOR) can anchor electrolyte decomposition products, thereby prolonging the high-temperature cycle life and reducing the storage gas production, but the dense crosslinked structure increases the lithium ion migration activation energy, causing a sharp drop in the low-temperature discharge efficiency of the lithium ion battery.

[0015] In the silicon-based negative electrode battery system, the three additives described above simultaneously act on the silicon-based negative electrode, the first additive EMC builds an ion conductive base layer to improve the low-temperature performance, the double-bond monomer of the second additive forms a buffer intermediate layer to balance the impedance, and the third additive acrylate compound containing multiple double bonds builds a surface protection network to enhance the high-temperature stability. When the three additives synergistically inhibit the dissolution of manganese elements in the silicon-based negative electrode, the first additive decomposition product fixes the free manganese through the Mn-O coordination bond, the double-bond monomer polymerization network of the second additive forms a steric hindrance barrier, and the carboxyl group of the acrylate in the third additive forms a stable five-membered chelate ring with Mn 2+ to form a stable five-membered chelate ring; Further, the application can better play a synergistic effect and effectively solve the electrolyte oxidation and silicon-based negative electrode deterioration caused by manganese dissolution by controlling the mass percentage contents of the first additive A, the second additive B, the third additive C and the mass of the manganese element X in the negative active material, meeting the relationship (A+B+C)*100 / X≥0.44 and A% being 5%-40%, B% being 0.5%-5%, and C% being 0.5-5%, so that the lithium ion battery can realize the synergistic improvement of electrical performance in a wide temperature range of high and low temperatures. DETAILED DESCRIPTION

[0016] In order to make the technical problems, technical solutions and beneficial effects solved by the application clearer and more apparent, the application will be further described in detail below in combination with embodiments. It should be understood that the specific embodiments described herein are only used to explain the application and not to limit the application.

[0017] The application provides a lithium ion battery, comprising a positive electrode, a silicon-based negative electrode and an electrolyte, the silicon-based negative electrode comprising a negative active material layer, the negative active material layer comprising a negative active material, the negative active material containing a manganese element; The electrolyte comprises a first additive, a second additive and a third additive, the first additive comprising methyl ethyl carbonate, the second additive comprising a monomer compound containing a vinyl group, and the third additive comprising a multi-functional acrylate compound; The lithium ion battery meets the following conditions: Formula 1: (A+B+C)*100 / X≥0.44, and A% being 5%-40%, B% being 0.5%-5%, and C% being 0.5%-5%; A% is the mass percentage content of the first additive in the electrolyte; B% is the mass percentage content of the second additive in the electrolyte; C% is the mass percentage content of the third additive in the electrolyte; X is the content of the manganese element in the negative active material, in ppm.

[0018] Specifically, in the lithium ion battery provided by the application, the first additive ethyl methyl carbonate (EMC) forms a Li2CO3-rich inorganic-organic hybrid SEI film at the negative electrode interface by the lower molecular symmetry of its linear carbonate structure (-O-CO-O-), the low crystallinity of the film significantly improves the low-temperature ion mobility, and the discharge capacity retention rate is improved, and the moderate chemical stability of the film can alleviate the interface side reaction during high-temperature cycling. However, the alkoxy lithium produced by the decomposition of EMC can catalyze the reconstruction of the positive electrode interface film, causing the continuous consumption of electrolyte during high-temperature storage, and causing irreversible loss of capacity; the second additive contains a double bond monomer, which forms a loosely crosslinked polymer network at the electrode interface through the polymerization reaction of its carbon-carbon double bond (C=C), and the compound contains Si or F or N elements, which can participate in interface film formation to form SiN, LiN and LiF substances, thereby improving the stability of the battery interface. This semi-rigid structure can effectively inhibit the penetration of electrolyte at high temperature, while retaining part of the ion channel, thereby improving the high-temperature cycling and storage performance, but the incompletely crosslinked molecular chain will introduce additional interface impedance, resulting in a decrease in low-temperature discharge capacity; the third additive multifunctional acrylate builds a three-dimensional network SEI film with high crosslinking density through free radical polymerization, and the rich ester groups (-COOR) can anchor the electrolyte decomposition products, thereby prolonging the high-temperature cycle life and reducing the storage gas production, but the dense crosslinked structure increases the lithium ion migration activation energy, which causes the low-temperature discharge efficiency of the lithium ion battery to drop sharply.

[0019] In the silicon-based negative electrode battery system, the three additives act on the silicon-based negative electrode at the same time, the first additive EMC builds an ion conductive base layer to improve the low-temperature performance, the double bond monomer of the second additive forms a buffer intermediate layer to balance the impedance, and the third additive acrylate compound containing multiple double bonds builds a surface protection network to enhance the high-temperature stability, and when the three additives synergistically inhibit the dissolution of manganese elements in the silicon-based negative electrode, the decomposition products of the first additive fix the free manganese through Mn-O coordination bond, the double bond monomer of the second additive forms a steric hindrance barrier through the polymerization network, and the carboxyl group of the acrylate in the third additive forms a stable five-membered chelate ring with Mn 2+ forms a stable five-membered chelate ring; Further, when the mass percentage content of the first additive A, the second additive B and the third additive C and the mass of the manganese element X in the negative electrode active material satisfy the relationship (A+B+C)*100 / X≥0.44 and A% is 5%-40%, B% is 0.5%-5%, and C% is 0.5-5%, the synergistic effect can be better played, the electrolyte oxidation and the degradation of the silicon-based negative electrode caused by manganese dissolution can be effectively solved, and the lithium ion battery can realize the synergistic improvement of the electrical performance in a wide temperature range of high and low temperatures.

[0020] Further, methyl ethyl carbonate (EMC) as the first additive preferentially forms a Li2CO3-rich inorganic-organic hybrid SEI film at the negative electrode interface due to the molecular asymmetry of its linear carbonate structure (-O-CO-O-). The low-temperature properties of this film are derived from the low-crystallinity structure promoting lithium ion migration, which improves the low-temperature discharge capacity retention. Meanwhile, its moderate thermal stability can inhibit the interface side reactions during high-temperature cycling. When the mass percentage of EMC is less than 5%, the insufficient reduction of the -O-CO-O- group leads to insufficient Li2CO3 crystal nucleus density, and the SEI film presents a porous structure that cannot effectively block the penetration of electrolyte. At high temperatures, manganese ions accelerate the dissolution and catalyze the decomposition of electrolyte. Meanwhile, the amount of alkoxy lithium generated is too small to neutralize the acidic byproducts at the positive electrode interface, exacerbating the continuous consumption of electrolyte caused by the reconstruction of the CEI film. When the mass percentage of EMC exceeds 40%, the excess EMC decomposition produces alkoxy lithium, which triggers excessive reconstruction of the positive electrode interface and forms a dense LiF / Li2O mixed layer that hinders charge transfer, increasing the room temperature impedance. Meanwhile, the accumulation of low-boiling-point carbonate byproducts leads to interface swelling. Experiments show that when the mass percentage of the first additive is in the range of 5%-40%, the low-temperature conductivity and high-temperature stability can be balanced.

[0021] The mass percentage A% of the first additive in the electrolyte can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, or 40%, i.e., the content of the first additive can be in the range of 5-40%.

[0022] The second additive (a monomer compound containing a vinyl group) forms a semi-rigid polymer network at the electrode interface through in-situ polymerization of the C=C bond, and its Si / F / N elements participate in the construction of a composite interface layer rich in SiN, LiN, and LiF, significantly improving the high-temperature stability of the battery. When the mass percentage of the additive is less than 0.5%, the insufficient polymerization reaction leads to insufficient interface coverage, and the low reaction density of the C=C double bond cannot form a continuous protective layer, exacerbating electrolyte penetration and high-temperature side reactions. Meanwhile, the insufficient release of Si / F / N elements makes it difficult to generate sufficient high-stability compounds such as LiF, and the interface anchoring ability decreases significantly. When the mass percentage exceeds 5%, the excess polymer forms a dense insulating layer that hinders lithium ion transport, leading to low-temperature capacity decay. The aggregation of unreacted monomers also causes interface swelling, generating microcracks during cycling and accelerating performance degradation. Experiments show that controlling the mass percentage of the second additive in the range of 0.5%-5% can effectively balance the high-temperature protection and low-temperature impedance, forming a gradient interface structure with a "flexible-rigid" transition, thereby optimizing and regulating the performance of lithium ion batteries.

[0023] The mass percentage content B% of the second additive in the electrolyte can be 0.5%, 0.8%, 1.0%, 1.3%, 1.5%, 1.7%, 2.0%, 2.4%, 2.8%, 3.0%, 3.5%, 4.0%, 4.5% or 5%, that is, B% can be in the range of 0.5%-5%.

[0024] The third additive (containing a multi-functional acrylate compound) builds a high cross-linking density three-dimensional network SEI film at the electrode interface through free radical polymerization, and the rich ester groups (-COOR) can effectively anchor the electrolyte decomposition products, significantly improve the high-temperature cycle stability and reduce the storage gas production. The mass percentage content of the additive in the range of 0.5%-5% can form an interface structure with both chemical stability and moderate ion conductivity. When the mass percentage content is less than 0.5%, the free radical polymerization reaction is insufficient, resulting in insufficient cross-linking network density, and the coverage rate of ester group functional groups is below the critical value, which cannot effectively fix the electrolyte decomposition products. The interface side reaction is intensified at high temperature, which makes the capacity attenuation rate, and the sparse network structure is difficult to inhibit the dissolution of manganese ions, which accelerates the phase change of the material; while the mass percentage content exceeds 5%, the three-dimensional network of excessive cross-linking makes the porosity of the SEI film decrease, and the lithium ion migration activation energy increases, resulting in a sharp drop in discharge efficiency at-20°C; the dense polymer layer also causes stress concentration, and micro-cracks are generated during the cycle, which become electrolyte infiltration channels, thereby accelerating the interface deterioration. Experiments show that optimizing the additive amount can balance the "anchoring ability-ion transmission" problem and form a gradient cross-linked buffer interface layer.

[0025] In summary, the content of the third additive can be balanced in the range of 0.5%-5% to maintain the best performance, and the mass percentage content C% of the third additive in the electrolyte can be 0.5%, 0.8%, 1.0%, 1.3%, 1.5%, 1.7%, 2.0%, 2.4%, 2.8%, 3.0%, 3.5%, 4.0%, 4.5% or 5%, that is, C% can be in the range of 0.5%-5%.

[0026] In some embodiments, the lithium ion battery satisfies the following conditions: Formula 2: 0.6≤(A+B+C)*100 / X≤120.

[0027] Specifically, when the first additive, the second additive and the third additive simultaneously satisfy the relationship formula 2, the first additive, the second additive and the third additive have a better synergistic effect, thereby better improving the high-temperature cycle and high-temperature storage performance and low-temperature discharge performance of the lithium ion battery; In some embodiments, the first additive, the second additive and the third additive satisfy the following conditions: Formula 3: 0.667≤A / (B+C)≤24.375.

[0028] Specifically, the first additive, the second additive and the third additive synergize to form a gradient SEI film structure under high-temperature working conditions, effectively inhibiting the multiple failure mechanisms triggered by manganese ions, the core of which is that the total content of the first additive (methyl ethyl carbonate, EMC) and the second additive and the third additive satisfies the relationship 0.667≤A / (B+C)≤24.375, to ensure the balance of low-temperature performance and high-heat storage stability. When A / (B+C)<0.667, the content of the first additive EMC is insufficient, which makes the thickness of the Li2CO3-rich base layer formed by EMC too thin, resulting in insufficient Mn-O coordination site density, accelerated free manganese ion catalyzed disproportionation reaction and electrolyte chain oxidation, and a surge in gas byproduct reaction, while the buffer intermediate layer collapses due to lack of support, unable to block the embedding of manganese particles into the silicon matrix, resulting in deterioration of the low-temperature performance of the lithium ion battery; when A / (B+C)>24.375, the content of EMC is excessive, and the alkoxy lithium produced by the decomposition of excessive EMC catalyzes the excessive reconstruction of the positive electrode interface film, triggering continuous consumption of electrolyte and irreversible capacity loss, insufficient polymerization degree of the buffer layer monomer, stress cracks on the surface protection network due to the absence of the intermediate layer, and an increase in the electrode crack propagation rate due to the failure of the synergistic effect, affecting the high-temperature storage performance, causing accelerated electrolyte oxidation and decomposition, and intensified transition metal dissolution, resulting in shortened high-temperature cycle life and a surge in storage gas production. In summary, 0.667≤A / (B+C)≤24.375 can maintain the best performance balance.

[0029] In some embodiments, the first additive, the second additive and the third additive satisfy the following conditions: Formula 4: 1.667≤A / (B+C)≤20.

[0030] Specifically, when the first additive, the second additive and the third additive simultaneously satisfy the relationship 1.667≤A / (B+C)≤20, the three additives synergize to better improve the high-temperature cycle and high-temperature storage performance, and low-temperature discharge performance of the lithium ion battery.

[0031] In some embodiments, the second additive and the third additive satisfy the following conditions: Formula 5: 0.16≤B / C≤6.25.

[0032] Specifically, in the silicon-based negative electrode battery system, when the ratio of the second additive (monomer compound containing vinyl group) to the third additive is limited in the range of 0.16-6.25, the two synergistically build a buffer interlayer and a surface protection network, that is, the mild polymerization of the second additive monomer compound containing vinyl group forms a semi-rigid barrier, effectively blocking the migration path of manganese ions, and the high crosslinking density of the third additive containing multifunctional acrylate compounds provides mechanical stability, which together inhibits electrolyte decomposition and silicon volume expansion; through specific examples, if the ratio of the second additive and the third additive is unbalanced (does not satisfy relationship 5), it will cause the performance to deteriorate, specifically, when B / C < 0.16, the third additive is excessive, the crosslinking is too dense, the interface impedance is significantly increased, the lithium ion migration channel is blocked, which causes the low-temperature discharge efficiency to drop sharply, and the rigid structure aggravates the cycle stress cracking, and when B / C > 6.25, the second additive is excessive, the crosslinking density is insufficient, the buffer layer steric barrier is weak, and it cannot anchor metal ions or inhibit high-temperature electrolyte penetration, the gas production during storage increases, and the manganese dissolution in high-temperature cycling is intensified, accelerating the capacity decay.

[0033] In summary, B / C in the range of 0.16-6.25 can maintain the best performance balance, B / C can be 0.16, 1, 2, 3, 4, 5, 6, 6.25, that is, B / C in the range of 0.16-6.25 is all possible.

[0034] In some embodiments, the content X of the manganese element in the negative electrode active material is 10-2000 ppm.

[0035] Specifically, when X is in this range, in combination with the content of the first additive, the second additive, and the third additive satisfying the relationship (A+B+C) / X≥0.003, the total amount of the three additives and the content of the manganese element can be ensured to be in a suitable ratio, if the content of the manganese element exceeds 2000 ppm, the excess manganese impurities form a local metal enrichment area in the silicon-based negative electrode, causing the lithium ion deintercalation path to be disordered (kinetic distribution is uneven), aggravating the lattice distortion stress of the silicon particles, and the multi-valence redox characteristics (Mn 2+ / Mn 3+ / Mn 4+ ) generated at the manganese-silicon heterojunction will catalyze the electrolyte chain oxidation through disproportionation, generating a deposition layer containing Mn-O bonds and unstable MnF2 / Li2O composite phases, and the solid solution of manganese atoms in the silicon lattice not only blocks the lithium ion diffusion channel, but also has high valence (Mn 3+ / Mn 4+) will also cause the local oxidation of silicon lattice, resulting in the surge of charge transfer impedance. In addition, the multi-electron redox properties of manganese further reduce the thermal runaway initiation temperature, at which even if the three additives are used together, the interface modification effect will be offset by the continuous catalytic activity of manganese, ultimately leading to irreversible degradation of high-temperature cycle performance; when the content of manganese element in the negative active material is 10-2000ppm, the synergistic mechanism can better enhance the effect of improving high-temperature cycle stability and storage performance.

[0036] Further, the content of manganese element in the negative active material of the application can be detected by the following method: Take 5mg of negative active material, add 3mL of concentrated sulfuric acid and 3mL of concentrated nitric acid in turn, heat to 180℃ until the solution is clear and transparent, after cooling, add water to 50mL, send sample for detection, and use ICP (Inductive Coupled Plasma Emission Spectrometer) to test the content of manganese element.

[0037] In some embodiments, the second additive includes one or more of the following compounds: .

[0038] Specifically, when the second additive is selected from one or more of the above-mentioned compounds, it can synergize with the first additive and the third additive to improve the high-temperature cycle and high-temperature storage performance and low-temperature discharge performance of the battery.

[0039] In some embodiments, the third additive includes one or more of the following compounds: .

[0040] Specifically, the third additive described in the application can be selected from any one or more of the above-mentioned compounds a-i, and when the third additive is preferably the above-mentioned compounds, it is more conducive to synergize with the first additive and the second additive to improve the performance of the lithium ion battery.

[0041] In some embodiments, the positive electrode includes a positive active material, and the positive active material includes one or more of transition metal lithium oxide, lithium iron phosphate, lithium manganate, lithium manganese iron phosphate, and lithium vanadium phosphate. The chemical formula of the transition metal lithium oxide is Li 1+x Ni y Co z M (1-y-z) O2, wherein -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1. M is selected from one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, Zr.

[0042] Specifically, the positive active material can be selected from one or more of the above.

[0043] The negative active material is artificial graphite and silicon-carbon composite material.

[0044] In the present application, the negative current collector is not particularly limited as long as the purpose of the present application can be achieved, and can be, for example, a copper foil, a copper alloy foil, a nickel foil, a stainless steel foil, a titanium foil, a nickel foam, a copper foam, or a composite current collector.

[0045] In some preferred embodiments, the negative current collector comprises a copper foil.

[0046] In some embodiments, the negative electrode further comprises a negative active material layer disposed on at least one side surface of the current collector, the negative active material layer further comprising a negative conductive agent, a negative binder, a thickening agent, and a solvent.

[0047] The negative conductive agent comprises at least one of natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, graphene, and other carbon materials. The negative binder comprises butyl rubber latex and the like, and the thickening agent comprises CMC and the like. The solvent comprises deionized water.

[0048] In some embodiments, the positive electrode comprises a positive current collector and a positive active material layer disposed on at least one surface of the positive current collector, the positive active material layer comprising a positive active material.

[0049] In the present application, the type of the positive current collector is not particularly limited, and can be any known material suitable for use as a positive current collector. In one embodiment, the positive current collector comprises metal materials such as aluminum, stainless steel, nickel plating, titanium, tantalum, and carbon materials such as carbon cloth and carbon paper. In one embodiment, the positive current collector is a metal material.

[0050] In some embodiments, the positive active material layer further comprises a positive conductive agent, a positive binder, and a solvent.

[0051] In some embodiments, the type of the positive conductive agent mentioned in the present application is not limited, and any known conductive agent can be used.

[0052] In some embodiments, the positive conductive agent mentioned in the present application comprises at least one of natural graphite, artificial graphite, acetylene black, needle coke, carbon nanotubes, graphene, and other carbon materials.

[0053] In one embodiment, the kind of the cathode binder is not limited, and any known cathode binder can be used.

[0054] In some embodiments, the cathode binder includes at least one of polyethylene, polypropylene, polyethylene terephthalate, polymethyl methacrylate, polyimide, aromatic polyamide, cellulose, and nitrocellulose.

[0055] In the lithium ion battery mentioned in the present application, a separator is usually provided between the cathode and the anode to prevent short circuit. The material and shape of the separator are not particularly limited, as long as the effects of the present application are not significantly impaired.

[0056] In some embodiments, the separator includes a porous sheet-like or non-woven fabric-like substance having excellent liquid retention, and the material of the separator includes, but is not limited to, polyolefin, aromatic polyamide, polytetrafluoroethylene, polyether sulfone, and the like.

[0057] In some embodiments, the lithium ion battery can include an outer package that can be used to package the above-mentioned electrode assembly and electrolyte.

[0058] In some embodiments, the outer package of the lithium ion battery can be a hard shell, such as a hard plastic shell, an aluminum shell, a steel shell, and the like. The outer package of the lithium ion battery can also be a soft package, such as a bag-type soft package. The material of the soft package can be plastic, and as the plastic, polypropylene, polybutylene terephthalate, and polybutylene succinate, and the like can be listed.

[0059] The shape of the lithium ion battery according to the present application is not particularly limited, and it can be cylindrical, square, or any other arbitrary shape.

[0060] Another embodiment of the present application provides an electric device including the lithium ion battery mentioned above.

[0061] Specifically, the electric device mentioned above can include a mobile device (such as a mobile phone, a notebook computer, and the like), an electric vehicle (such as a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart, an electric truck, and the like), an electric train, a ship and a satellite, an energy storage system, and the like, but is not limited thereto.

[0062] The present application is further illustrated by the following examples.

[0063] Table 1 Example 1 This example is used to illustrate the lithium ion battery disclosed in the present application, including the following operating steps: Preparation of the positive electrode The positive electrode active material lithium cobaltate, the positive electrode conductive agent acetylene black (Super P) and the polyvinylidene fluoride (PVDF) binder are mixed uniformly in a mass ratio of 97:1.5:1.5, and uniformly dispersed with 1-methyl-2-pyrrolidone (NMP) to prepare a uniform positive electrode slurry. After the mixed slurry is coated on both sides of the aluminum foil current collector, it is baked, rolled, and cut into pieces to obtain the positive electrode. Preparation of the silicon-based negative electrode The negative electrode active material artificial graphite, silicon carbon, the negative electrode conductive agent acetylene black (Super P), the thickening agent CMC and the negative electrode binder SBR are mixed uniformly in a mass ratio of 84:10:2:1.2:2.8, and uniformly dispersed with deionized water to prepare a uniform negative electrode slurry. After the mixed slurry is coated on both sides of the copper foil current collector, it is baked, rolled, and cut into pieces to obtain the silicon-based negative electrode. The specific value of the content of manganese element in the added negative electrode active material is shown in Table 1.

[0064] Preparation of the electrolyte a. The vinyl carbonate (EC), propyl propionate (EP) and diethyl carbonate (DEC) are mixed and stirred in a mass ratio of 30:40:30 to form a mixed solvent, which is dehydrated with molecular sieves and used by adding 1M LiPF6 and uniformly mixing; b. The initiator azobisisobutyronitrile 0.1% (content in the colorless transparent liquid) and the additive (the type and amount of the additive are shown in Table 1) are added to the colorless transparent liquid obtained in step a to obtain the electrolyte.

[0065] Preparation of the lithium ion battery The prepared positive electrode sheet, the separator and the negative electrode sheet are stacked in order with the separator between the positive and negative electrode sheets, and then wound and tab welded to obtain a bare cell. The bare cell is placed in an aluminum plastic film, injected, packaged, etc. to obtain the lithium ion battery.

[0066] Examples 2-43 are used to illustrate the lithium ion battery disclosed in the present application, including most of the operations in Example 1, the difference being that: The first additive type, the first additive mass percentage A / %, the second additive type, the second additive mass percentage B / %, the third additive type, the third additive mass percentage C / %, the content X / ppm of manganese element in the negative electrode active material, the value of B / C, the value of A / (B+C), and the value of (A+B+C) / X in Examples 2-43 are all referred to Table 1.

[0067] Comparative Example 1-23 Comparative Example 1-23 is used to illustrate the lithium ion battery disclosed in the present application, including most of the operations in Example 1, the difference is that: The first additive type, the first additive mass percentage A / %, the second additive type, the second additive mass percentage B / %, the third additive type, the third additive mass percentage C / %, the content X / ppm of nickel element in the negative electrode active material, the value of B / C, the value of A / (B+C), and the value of (A+B+C) / X in Comparative Example 1-23 are all referred to Table 1.

[0068] Performance test The above-prepared Examples 1-43 and Comparative Example 1-23 are subjected to the following performance tests: 60℃ storage performance test The lithium ion batteries prepared in the above examples and comparative examples are charged at 25℃ to the cut-off voltage at 1C rate, the cut-off current is 0.025C, and the thickness H1 of the lithium ion battery is tested after standing for 5min. Then the lithium ion battery is stored at 60℃ for 60 days, and the thickness H2 of the lithium ion battery is tested after the end of the storage.

[0069] Thickness expansion rate = [(H2-H1) / H1]x100%.

[0070] 45℃ cycle performance test The lithium ion batteries prepared in the above examples and comparative examples are subjected to charge-discharge cycling at 45℃ in the range of charge-discharge cut-off voltage at 1C / 1C rate, the discharge capacity of the first week is counted as C1, and the discharge capacity of the Nth cycle is counted as C2. The cycle capacity retention rate R2 of the Nth week is obtained by dividing the capacity of the Nth week by the capacity of the first week, and the cycle number of the lithium ion battery when the cycle capacity retention rate R2 is 70% is recorded.

[0071] -20℃ low-temperature discharge test The lithium ion batteries prepared in each of the above examples and comparative examples were subjected to charge-discharge cycling at 25°C within the charge-discharge cut-off voltage range at a rate of 0.2C / 0.2C for 3 weeks, and the discharge capacity in the 3rd week was tested as C3; then the lithium ion batteries were subjected to charge-discharge cycling at -20°C within the charge-discharge cut-off voltage range at a rate of 0.2C / 0.2C for 3 weeks, and the discharge capacity in the 3rd week was tested as C4; and the low-temperature charge capacity retention rate R3 = C4 / C3 at -20°C was obtained.

[0072] The test results obtained were filled in Table 2.

[0073] Table 2 As can be seen from the test results in Table 2, the test results of Examples 1-43 are overall better than those of Comparative Examples 1-23, because Examples 1-43 meet the limited conditions of the types, contents and manganese element ratios of the additives, and the three additives synergistically form a gradient SEI film, which performs better in the tests of -20°C low-temperature discharge capacity retention rate, 45°C cycle number and 60°C storage thickness expansion rate. In Examples 1-6, the mass percentage content A of the first additive was gradually increased from 5% to 40%, and as can be seen from the test results of Examples 1-6, as the content of A increased, the -20°C low-temperature discharge capacity retention rate showed a gradually increasing trend (from 62.1% to 72.1%), which indicated that the increase of the content of the first additive had a positive effect on improving the low-temperature discharge performance of the battery, and the number of cycles at 45°C to a capacity retention rate of 70% also gradually increased, indicating that the increase of the content of A within the limited range of the application was helpful to improve the stability of the battery under high-temperature cycling. In Comparative Example 9, the mass percentage content of the first additive was 60%, which exceeded the limited range of the application, and as can be seen from the test results, although the low-temperature retention rate was high, the cycle performance and expansion rate were poor, which from the side verified that when the content of the first additive exceeded the limited range of the application, it was easy to cause excessive reconstruction of the positive electrode interface, which was also not conducive to improving the overall electrical performance of the lithium ion battery. In Examples 7-11, the content of the second additive was gradually increased from 0.5% to 5%, and as can be seen from the test results of Examples 7-11, as the content of B increased, the expansion rate was effectively inhibited, but the -20°C low-temperature discharge capacity retention rate decreased, which was presumably due to the increase of the content of the second additive B, the semi-rigid network formed by polymerization enhanced the high-temperature barrier property, and the storage expansion rate decreased, but when the content of the second additive B was high, the molecular chains that were not completely crosslinked introduced interface impedance, and the low-temperature performance decreased. In Comparative Example 10, the content of the second additive is 0.1%, the retention rate at -20°C is 65.5%, and the cycle at 45°C is 580 times. The test effect is relatively poor, and the reason is that when the content of the second additive is too low (<0.5%), the polymer layer is discontinuous and cannot effectively block the migration of manganese ions, and the high-temperature cycle life is shortened; In Examples 12-16, the content of the third additive is between 0.5% and 5%. In the test data of Examples 12-16, the cycle at 45°C increases from 735 to 820 times, and the retention rate at -20°C decreases from 65.3% to 57.3%. The reason is that the content of the third additive (multi-functional acrylate compound) increases, the cross-linking density increases, the ability to anchor electrolyte decomposition products increases, and the cycle life is prolonged. However, when the addition amount is too high, the three-dimensional network porosity decreases, the lithium ion migration energy barrier increases, and the low-temperature performance deteriorates; In Comparative Example 12, the content of the third additive is 0.1%, the cycle at 45°C is 554 times, and the expansion rate at 60°C is only 64.2%. Since the content of the third additive is less than 0.5%, the cross-linked network is sparse and cannot fix manganese ions and decomposition products, and the gas generation side reaction is intensified; In Examples 17-22, the content X of detected manganese element is between 10-2000ppm. According to the specific test data, the retention rate at -20°C of Examples 17-22 decreases from 69.5% to 53.4%, and the cycle at 45°C decreases from 750 to 690. The reason is that the increase of the content of manganese element leads to the increase of manganese ion dissolution, catalyzing the chain oxidation of electrolyte and generating Mn-O deposition layer to block the lithium ion channel; In Comparative Example 14, the content of the detected manganese element is 3000ppm, the retention rate at -20°C is only 30.0%, and the cycle at 45°C is 359 times. The reason is that the content of manganese element exceeds the upper limit of 2000ppm in the limited range of the application, manganese forms a metal-rich region in the silicon-based negative electrode, causing lattice distortion and local oxidation, and the interface impedance increases sharply; In the test data of Examples 23-24, the cycle at 45°C is 671 and 666 times respectively, and the retention rate at -20°C is 57.4% and 64.5% respectively. When B / C is at the critical value, the buffer layer of the second additive and the protective network of the third additive are in a balanced state. However, if the second additive is too low (Example 23), the low-temperature impedance is high, and if the second additive is too high (Example 24), the high-temperature barrier property is weak; In Examples 25-26, Example 25 satisfies (A / (B+C)=0.667), which has a -20℃ retention rate of 43.5%, and the deficiency of the first additive leads to a thin Li2CO3 base layer, a small number of Mn-O coordination sites, and intensified manganese dissolution; Example 26 satisfies (A / (B+C)=24.375), which has a 60℃ expansion rate of 48.9%, and the first additive is over-added compared with Example 25, thereby triggering excessive reconstruction of the positive electrode interface and electrolyte consumption and gas production; According to Examples 28-43 and Example 2, when the second additive / third additive is another compound defined in the application, the same improvement effect as in other examples can be achieved; in Comparative Examples 1-4, three additives defined in the application are simultaneously added, and due to the absence of additives, the -20℃ capacity retention rate is as low as 34.4%-40.8%, the 60℃ expansion rate is 51.0%-73.7%, and the cycle number is only 507-569 cycles, thereby indicating that the synergistic effect of the additives is indispensable; Similarly, in Comparative Examples 5-7, the synergistic effect of the three additives is not performed, the high-temperature storage expansion rate suddenly increases, and the cycle stability deteriorates; In Comparative Examples 8-13, the additives are not within the scope defined in the application, such as A=1% when the low-temperature retention rate is only 35.5%, B=8% when the low-temperature performance decreases to 30.3%, and C=8% when the cycle number is only 557 cycles; In Comparative Examples 14-17, the manganese content is more than 2000ppm or the additive type defined in the application is not used, and the -20℃ retention rate is as low as 30.0%; In Comparative Examples 18-23, the B / C ratio and the A / (B+C) ratio are imbalanced, and the extreme content combination (such as A being 60% or X being 3000ppm) leads to the collapse of the interface film structure and the deterioration of the low-temperature performance to 25.1%-32.3%, and the shortest cycle number is only 335 cycles.

[0074] Through the specific analysis of the above examples and comparative examples, it is concluded that the lithium ion battery provided by the application has a synergistic effect of multiple additives, effectively solves the deterioration of the silicon-based negative electrode caused by manganese dissolution, and enables the lithium ion battery to achieve a synergistic improvement in electrical performance in a wide temperature range of high and low temperatures.

[0075] The above only describes the preferred embodiments of the application and should not be used to limit the application, and any modifications, equivalent replacements, and improvements made within the spirit and principles of the application should be included in the protection scope of the application.

Claims

1. A lithium-ion battery, characterized by, The lithium ion battery comprises a positive electrode, a silicon-based negative electrode, and an electrolyte, the silicon-based negative electrode comprises a negative electrode active material layer, the negative electrode active material layer comprises a negative electrode active material, and the negative electrode active material contains manganese elements; The electrolyte comprises a first additive, a second additive, and a third additive, the first additive comprises methyl ethyl carbonate, the second additive comprises a monomer compound containing a vinyl group, and the third additive comprises a multi-functional acrylate compound; The lithium ion battery satisfies the following conditions: Formula 1: (A+B+C)*100 / X≥0.44, and A% is 5%-40%, B% is 0.5%-5%, and C% is 0.5%-5%. A% is the mass percentage content of the first additive in the electrolyte; B% is the mass percentage content of the second additive in the electrolyte; C% is the mass percentage content of the third additive in the electrolyte; X is the content of manganese elements in the negative electrode active material, and the unit is ppm.

2. The lithium-ion battery of claim 1, wherein, The lithium ion battery satisfies the following conditions: Formula 2: 0.6≤(A+B+C)*100 / X≤120.

3. The lithium-ion battery of claim 1, wherein, The first additive, the second additive, and the third additive satisfy the following conditions: Formula 3: 0.667≤A / (B+C)≤24.

375.

4. The lithium-ion battery of claim 1, wherein, The first additive, the second additive, and the third additive satisfy the following conditions: Formula 4: 1.667≤A / (B+C)≤20.

5. The lithium-ion battery of claim 1, wherein, The second additive and the third additive satisfy the following conditions: Formula 5: 0.16≤B / C≤6.

25.

6. The lithium-ion battery of claim 1, wherein, The content X of the manganese elements in the negative electrode active material is 10-2000 ppm.

7. The lithium-ion battery of claim 1, wherein, The second additive comprises one or more of the following compounds: 。 8. The lithium-ion battery of claim 1, wherein, The third additive comprises one or more of the following compounds: 。 9. The lithium-ion battery of claim 1, wherein, The positive electrode comprises a positive electrode active material, and the positive electrode active material comprises one or more of transition metal lithium oxides, lithium iron phosphate, lithium manganate, lithium manganese iron phosphate, and lithium vanadium phosphate. The transition metal lithium oxide has a chemical formula of Li 1+x Ni y Co z M (1-y-z) O2, wherein -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1. M is selected from one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

10. An electrical device, characterized by The lithium ion battery comprises the lithium ion battery according to any one of claims 1-9.

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