Lithium-ion battery

Abstract

A lithium-ion battery, comprising a negative electrode and an electrolyte, wherein the electrolyte comprises an additive and a lithium salt, the additive comprises an additive A, the negative electrode comprises a negative electrode active material, and the negative electrode active material comprises a silicon-based negative electrode material and a carbon-based negative electrode material; and the average particle size Dv50M μm of the silicon-based negative electrode material and the average particle size Dv50N μm of the carbon-based negative electrode material satisfy 0.5≤M / N≤1.7. The lithium-ion battery can significantly improve the high-temperature stability of a negative electrode interface and alleviate the side reactions on the surface of the negative electrode, thereby improving the cyclic volume expansion of the silicon-based negative electrode material in the negative electrode, and further improving the long cycle performance, fast charging performance and energy density of the silicon-doped lithium-ion battery.

Description

A lithium-ion battery

[0001] This application claims priority to Chinese Patent Application No. 202410937493.5, filed on July 12, 2024, entitled "A Lithium-ion Battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This application relates to the field of lithium-ion battery technology, and more particularly to a lithium-ion battery. Background Technology

[0003] In recent years, with researchers' in-depth study of anode materials, silicon-based anode materials, which have a higher specific capacity than graphite anodes, have become one of the key research directions. However, silicon-based anode materials exhibit high volume expansion during battery cycling, which can exacerbate side reactions between the battery anode and the electrolyte, affecting the battery's long-cycle performance. Simultaneously, the poor conductivity of silicon-based anode materials leads to a high ion transport barrier at the particle interface, significantly deteriorating the battery's fast-charging performance. Furthermore, the uncontrollable expansion direction of silicon-based anode materials causes a rapid increase in battery expansion during cycling, resulting in a significant reduction in the energy density of lithium-ion batteries with silicon-based anode materials in practical applications. Summary of the Invention

[0004] Based on the above problems, this application provides a lithium-ion battery that can significantly improve the high-temperature stability of the negative electrode interface, alleviate the side reactions on the negative electrode surface, thereby improving the cycle volume expansion of the silicon-based negative electrode material in the negative electrode, and thus improving the long cycle performance, fast charging performance and energy density of the silicon-doped lithium-ion battery.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0006] A first aspect of this application provides a lithium-ion battery comprising a negative electrode and an electrolyte, the electrolyte comprising an additive and a lithium salt, the additive comprising additive A having the structural formula shown in formula (I).

[0007] In formula (I), R1, R2, R3, R4, R5, and R6 are each independently selected from hydrogen, deuterium, halogen, substituted or unsubstituted C. 1-8 Alkoxy, substituted or unsubstituted C 2-5 Alkenyl group, substituted or unsubstituted C 6-12 One of the aryloxy groups; wherein, when substitution occurs, the substituent used is a halogen;

[0008] The negative electrode includes a negative electrode active material, which includes silicon-based negative electrode material and carbon-based negative electrode material;

[0009] The average particle size Dv50 Mμm of the silicon-based anode material and the average particle size Dv50 Nμm of the carbon-based anode material satisfy 0.5≤M / N≤1.7.

[0010] Compared with the prior art, this application has at least the following advantages through the above technical solution:

[0011] (1) The additive A in the electrolyte of the lithium-ion battery provided in this application has excellent high-temperature stability. The additive A can generate a stable SEI film in the early stage of cycling, which significantly improves the interface stability of the silicon-doped anode, thereby alleviating the side reactions on the surface of the anode and suppressing the cycling volume expansion of the silicon-based anode material in the anode.

[0012] (2) The lithium-ion battery provided in this application can significantly improve the wettability of silicon-based anode material and electrolyte by adjusting the ratio between the average particle size of silicon-based anode material and carbon-based anode material, thereby helping to maintain the stability of SEI film in the later stage of cycling, further reducing the side effects caused by electrolyte decomposition, improving the cycle volume expansion of silicon-based anode material in the anode, and thus improving the long cycle performance of silicon-doped lithium-ion battery.

[0013] (3) The additive A in the electrolyte of the lithium-ion battery provided in this application, due to its low viscosity and high dielectric constant, combined with the appropriate average particle size ratio of silicon-based anode material and carbon-based anode material, can reduce the polarization phenomenon caused by local expansion and circuit breaking of the anode active material, thereby avoiding the particle crushing caused by excessive lithium intercalation of some anode active materials. At the same time, it can also improve the stability of the SEI film generated by additive A, further alleviate the occurrence of side reactions on the anode surface, and significantly improve the cycle performance of lithium-ion battery. Moreover, the additive A in the electrolyte, combined with the appropriate particle size of the anode active material, can also make the anode have a better electrolyte passage and better expansion and release space, thereby effectively improving the cycle volume expansion of silicon-doped anode, avoiding the compression of energy density of silicon-doped lithium-ion battery in practical application, thereby improving the energy density of lithium-ion battery.

[0014] (4) The lithium-ion battery of this application can also improve the stacking mode of silicon-based anode material particles and carbon-based anode material by adjusting the ratio between the average particle size of silicon-based anode material and carbon-based anode material, thereby alleviating the influence of silicon-based anode material particles on the conductivity of the anode, forming a more stable conductive network, and thus improving the fast charging performance of lithium-ion battery.

[0015] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein. Detailed Implementation

[0016] The specific embodiments of this application are described in detail below. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit this application.

[0017] Studies have found that conventional sulfonate additives in electrolytes mainly improve the high-temperature gas generation performance of batteries in practical applications. However, when sulfonate additives are used in anode systems with silicon-based anode materials (i.e., silicon-doped anodes), they preferentially form incompatible high-resistivity interface films on the surface of silicon-doped anodes. This results in the surface of porous carbon in the silicon-carbon structure of the silicon-based anode material being blocked, increasing the difficulty of lithium intercalation in the silicon-based anode material. Consequently, side reactions on the anode surface continue to occur, exacerbating the cycle volume expansion of the silicon-doped anode, thereby affecting the cycle performance of lithium-ion batteries.

[0018] In view of the problems existing in the prior art, the first aspect of this application provides a lithium-ion battery, which includes a negative electrode and an electrolyte, wherein the electrolyte includes an additive and a lithium salt, and the additive includes an additive A having the structural formula shown in formula (I).

[0019] In formula (I), R1, R2, R3, R4, R5, and R6 are each independently selected from hydrogen, deuterium, halogen, substituted or unsubstituted C. 1-8 Alkoxy, substituted or unsubstituted C 2-5 Alkenyl group, substituted or unsubstituted C 6-12 One of the aryloxy groups; wherein, when substitution occurs, the substituent used is a halogen;

[0020] The negative electrode includes a negative electrode active material, which includes silicon-based negative electrode material and carbon-based negative electrode material;

[0021] The average particle size Dv50 Mμm of the silicon-based anode material and the average particle size Dv50 Nμm of the carbon-based anode material satisfy 0.5≤M / N≤1.7.

[0022] The electrolyte of this application uses additive A with the structure shown in formula (Ⅰ) to replace traditional sulfonate additives, significantly reducing the attack of sulfonate additive decomposition products on silicon-based anode materials, avoiding the formation of a high-resistivity interface film on the surface of silicon-carbon anodes. Moreover, the high-temperature stability of additive A can improve the storage performance degradation caused by the removal of sulfonate additives, avoid the aggravation of gas production in lithium-ion batteries, and improve the high-temperature cycle stability of lithium-ion batteries. Furthermore, the unique framework structure of additive A in the electrolyte of the lithium-ion battery provided by this application, composed of alternating phosphorus and nitrogen atoms, gives it excellent chemical stability and can generate a stable SEI film in the early stage of cycling, which significantly improves the interface stability of silicon-doped anodes, thereby alleviating side reactions on the anode surface and suppressing the cycle volume expansion of silicon-based anode materials in the anode.

[0023] Furthermore, this application controls the average particle size Dv50 Mμm of the silicon-based anode material and the average particle size Dv50 Nμm of the carbon-based anode material to satisfy 0.5≤M / N≤1.7. For example, M / N can be 0.5, 0.6, 0.7, 0.8, 0.9, 1, 1.1, 1.2, 1.3, 1.4, 1.5, 1.6, or 1.7. When the ratio between the average particle size of silicon-based and carbon-based anode materials is too small, it leads to poor matching between the two types of particles, significantly degrading the conductivity of the silicon-doped anode. This can easily cause small-sized silicon-based anode particles to experience conductive network failures in large-sized carbon-based anode particles, resulting in a decrease in the actual amount of silicon-doped anode material participating in charging and discharging, leading to low capacity utilization of the lithium-ion battery. Furthermore, the battery's cycle performance degradation due to conductive network failure during cycling is exacerbated, affecting fast charging and cycle stability. Conversely, when the ratio between the average particle size of silicon-based and carbon-based anode materials is too large, the high cyclic expansion of silicon-based anode particles causes simultaneous displacement of both silicon-based and carbon-based anode particles. This reduces the effectiveness of the binder in the anode material and may even cause binder failure, making the active material layer in the anode sheet more porous. This exacerbates side reactions at the anode interface, and the accumulation of side reaction products after long cycles further degrades cycle stability and expansion. Therefore, it is necessary to control the ratio M / N between the average particle size of the silicon-based anode material and the carbon-based anode material within a suitable range. In a preferred embodiment, 1 ≤ M / N ≤ 1.5.

[0024] The Dv50 in this application refers to the particle size corresponding to a cumulative volume percentage of 50%, which can be obtained by testing with a laser particle size analyzer.

[0025] Furthermore, due to the unique structure of additive A in the electrolyte, it possesses low viscosity and high dielectric constant, exhibiting excellent wetting properties in silicon-doped anode materials. Therefore, by adding additive A to the silicon-doped anode, and combining it with a suitable average particle size ratio of silicon-based and carbon-based anode materials, the electrolyte can penetrate more fully into the interior of the silicon-based anode material, reserving buffer space for the volume expansion of the silicon-based anode material. This reduces the mechanical stress caused by volume changes, alleviates the battery expansion caused by the uncontrolled expansion of the silicon-based anode material, and prevents the energy density of silicon-doped lithium-ion batteries from being compressed in practical applications, thereby improving the energy density of lithium-ion batteries. It can also reduce the polarization phenomenon caused by local expansion and circuit breakage of the anode active material, thus preventing the particle crushing of some anode active materials due to excessive lithium intercalation. At the same time, it can also improve the stability of the SEI film formed by additive A, further mitigating the occurrence of side reactions on the anode surface and significantly improving the cycle performance of lithium-ion batteries.

[0026] In summary, the lithium-ion battery provided in this application replaces conventional sulfonate additives with additive A, which has excellent high-temperature stability and good wetting effect in silicon-doped anodes. In addition, by adjusting the average particle size ratio of silicon-based anode materials and carbon-based anode materials, the side reactions on the anode surface can be significantly alleviated, the stability of the anode active material during cycling can be improved, and the volume expansion of silicon-based anode materials can be reduced, thereby improving the cycle performance and energy density of the lithium-ion battery.

[0027] Furthermore, the lithium-ion battery of this application can improve the stacking mode of silicon-based anode material particles and carbon-based anode material by adjusting the ratio between the average particle size of silicon-based anode material and carbon-based anode material, thereby mitigating the influence of silicon-based anode material particles on the conductivity of the anode, forming a more stable conductive network, and thus improving the fast charging performance of the lithium-ion battery.

[0028] In this application, the volume expansion of the silicon-doped anode and the cycle performance of the lithium-ion battery can be further mitigated by adjusting the specific mass content of additive A in the electrolyte. In one specific embodiment, the mass content A wt% of additive A satisfies 0.2wt% ≤ A wt% ≤ 8wt%. For example, A wt% can be 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.5wt%, 2wt%, 2.5wt%, 3wt%, 3.5wt%, 4wt%, 4.5wt%, 5wt%, 5.5wt%, 6wt%, 6.5wt%, 7wt%, 7.5wt%, or 8wt%. Excessive additive A can lead to decreased stability of the generated SEI film, resulting in a rough and loose interface, thus weakening the protective effect of the interface film and failing to effectively mitigate side reactions on the negative electrode surface. Conversely, insufficient additive A will result in minimal benefit in improving cycle volume expansion, leading to continuous deterioration of battery cycle performance. Therefore, it is necessary to reasonably control the mass content of additive A. In a preferred embodiment, 0.5 wt% ≤ A wt% ≤ 3 wt%.

[0029] This application does not specify a particular method for testing the mass content of additive A, which can be obtained by conventional methods in the art. In one embodiment, it is obtained, for example, by gas chromatography (GC), gas chromatography-mass spectrometry (GCMS), or liquid chromatography (LC).

[0030] In this application, based on satisfying the above-mentioned average particle size ratio of silicon-based anode material and carbon-based anode material, further adjusting the average particle size Dv50 Mμm of silicon-based anode material and the average particle size Dv50 Nμm of carbon-based anode material can further expand the benefits of adjusting the particle size ratio of anode active materials.

[0031] In one specific embodiment, the average particle size Dv50 Mμm of the silicon-based anode material satisfies 4μm≤Mμm≤25μm. For example, Mμm can be 4μm, 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, or 25μm. When the average particle size Dv50 of the silicon-based anode material is less than 4 μm, the actual amount of silicon-doped anode material participating in charging and discharging decreases, affecting the battery's fast charging and cycle stability. When the average particle size Dv50 of the silicon-based anode material is greater than 25 μm, the expansion of excessively large silicon-based anode material particles can cause displacement of carbon-based anode material particles, leading to intensified side reactions at the anode interface. Simultaneously, the excessively large size of the silicon-based anode material also reduces the battery's volumetric energy density. Therefore, it is necessary to control the size of the silicon-based anode material within a suitable range. In a preferred embodiment, 4 μm ≤ M μm ≤ 15 μm.

[0032] In one specific embodiment, the average particle size Dv50 Nμm of the carbon-based anode material satisfies 5μm≤Nμm≤30μm. For example, Nμm can be 5μm, 6μm, 7μm, 8μm, 9μm, 10μm, 11μm, 12μm, 13μm, 14μm, 15μm, 16μm, 17μm, 18μm, 19μm, 20μm, 21μm, 22μm, 23μm, 24μm, 25μm, 26μm, 27μm, 28μm, 29μm, or 30μm. When the average particle size Dv50 of the carbon-based anode material is less than 5 μm, it indicates that the size of the carbon-based anode material is too small. Therefore, it may not be able to withstand the volume expansion of the silicon-based anode material during charge and discharge, causing damage to the material structure and leading to rapid capacity decay of the battery. When the average particle size Dv50 of the carbon-based anode material is greater than 30 μm, it is difficult to achieve high-density stacking of large-particle carbon-based anode materials, which reduces the volumetric energy density of the battery and thus affects the overall performance of the battery. Therefore, it is necessary to control the size of the carbon-based anode material within a suitable range. In a preferred embodiment, 10 μm ≤ N μm ≤ 25 μm.

[0033] In this application, the additive also includes additive D, which is a lithium borate additive. When the silicon-doped lithium-ion battery reaches the later stage of cycling, although the volume expansion of the silicon-based anode material in the anode will be improved to a certain extent, it will still cause some of the interface SEI film to be damaged due to the expansion of the silicon-based anode material, affecting the long-cycle performance of the silicon-doped anode lithium-ion battery. Therefore, in order to improve the above problems, the lithium-ion battery of this application further adds additive D to the electrolyte, which can enrich the inner layer of the SEI film at the broken part with boron, thereby inducing additive A to anchor and repair at the broken interface, accelerating the formation of a stable SEI film in the later stage of cycling, so that additive A, with the synergy of additive D, maintains the stability of the inner SEI film during cycling, thereby mitigating the impact of the anode surface side reaction in the later stage of cycling, and further improving the long-cycle performance of the lithium-ion battery.

[0034] In one specific embodiment, the lithium borate additive includes at least one of lithium difluorooxalate borate, lithium difluorobis(oxalate) borate, lithium tetrafluoroborate, and lithium bis(oxalate) borate.

[0035] In one specific embodiment, the mass content of additive D, D wt%, satisfies 0.1wt% ≤ D wt% ≤ 3wt%. For example, D wt% can be 0.1wt%, 0.2wt%, 0.3wt%, 0.4wt%, 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, 1wt%, 1.2wt%, 1.4wt%, 1.6wt%, 1.8wt%, 2wt%, 2.1wt%, 2.3wt%, 2.5wt%, 2.7wt%, 2.9wt%, or 3wt%. Excessive additive D increases the viscosity of the electrolyte, leading to a decrease in the electrolyte's spreading ability on the electrode surface, which reduces the wettability of the electrolyte in the silicon-doped anode. Insufficient additive D fails to repair the SEI film in the later stages of cycling, thus exacerbating side reactions on the anode surface and affecting the battery's cycle performance. Therefore, it is necessary to reasonably control the mass content of additive D. In a preferred embodiment, 0.2wt% ≤ D wt% ≤ 1wt%.

[0036] Furthermore, by further controlling the range of the sum of the mass contents of additive A and additive D in the electrolyte, the improvement of cycle stability by lithium borate additives can be further enhanced. In one specific embodiment, based on the total mass of the electrolyte, the mass content of additive A (Awt%) and the mass content of additive D (Dwt%) satisfy 1.5 ≤ A + D ≤ 4. For example, A + D can be 1.5, 1.6, 1.7, 1.8, 1.9, 2, 2.1, 2.2, 2.3, 2.4, 2.5, 2.6, 2.7, 2.8, 2.9, 3, 3.1, 3.2, 3.3, 3.4, 3.5, 3.6, 3.7, 3.8, 3.9, or 4. When A+D is excessive, it indicates that the content of additive A or additive D is excessive, or both additives are excessive. Excessive additives will increase the interfacial impedance of the negative electrode material and degrade the fast-charging performance of the lithium-ion battery. When A+D is insufficient, it indicates that the content of additive A or additive D is insufficient, or both additives are relatively low. Insufficient additives will cause the lithium-ion battery to experience a rapid decline in capacity retention during long-cycle periods due to insufficient protection and repair capabilities. In a preferred embodiment, 2 ≤ A+D ≤ 3.

[0037] In this application, the high porosity of the silicon-doped anode active material can further coordinate the volume expansion of the silicon-based anode material, providing greater lateral and longitudinal stress release space for the expanding anode active material layer. This buffers the severe deformation of the silicon-based anode material particles caused by the large expansion. Simultaneously, the higher stress release space of the silicon-doped anode can mitigate the risk of binder failure and reduce the risk of anode active material pulverization and detachment. However, excessively high porosity in the silicon-doped anode active material can limit the volumetric energy density of lithium-ion batteries, failing to meet the high energy density requirements. Therefore, it is necessary to control a reasonable porosity range for the silicon-doped anode active material to better mitigate the cyclic volume expansion of the silicon-based anode material in the anode, further improving the cycle performance of the lithium-ion battery. In one specific embodiment, the porosity P of the negative electrode active material is 5% to 60%; exemplaryly, the porosity P can be 5%, 10%, 15%, 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, or 60%. In a preferred embodiment, the porosity P of the negative electrode active material is 20% to 60%.

[0038] Furthermore, the porosity P of the negative electrode active material also affects the wetting effect of the electrolyte on the negative electrode active material. Higher porosity is more beneficial for electrolyte wetting, but it also increases the contact area between the negative electrode active material and the electrolyte, exacerbating side reactions on the negative electrode surface. Therefore, to better complement the wetting effect brought by the high porosity of the negative electrode active material, in one specific embodiment, the porosity P of the negative electrode active material satisfies the relationship 0.02 ≤ M / NP ≤ 0.2 with respect to the average particle size Dv50 Mμm of the silicon-based negative electrode material and the average particle size Dv50 Nμm of the carbon-based negative electrode material. Preferably, 0.1 ≤ M / NP ≤ 1.6. By adjusting the size and porosity of the negative electrode active material using the above relationship, the silicon-doped negative electrode can achieve better lithium-ion battery cycle life under the above electrolyte system, further improving the long-cycle performance of the battery. In a preferred embodiment, 0.5 ≤ M / NP ≤ 1.4.

[0039] In this application, the cyclic volume expansion of the silicon-based anode material can be suppressed by adjusting the silicon content (C wt%) in the anode active material. Furthermore, the silicon-based anode material in the anode active material leads to a decrease in conductivity, resulting in increased anode polarization and further deterioration of the battery's high-temperature performance. Therefore, adjusting the silicon content (C wt%) in the anode active material can also ensure the high-temperature performance of the silicon-doped anode and improve the battery's fast-charging performance. In one specific embodiment, 3wt% ≤ C wt% ≤ 70wt%. Exemplarily, the silicon content (C wt%) can be 3wt%, 4wt%, 5wt%, 6wt%, 7wt%, 8wt%, 9wt%, 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, 35wt%, 40wt%, 45wt%, 50wt%, 55wt%, 60wt%, 65wt%, or 70wt%. In a preferred embodiment, 25wt% ≤ C wt% ≤ 45wt%.

[0040] Furthermore, in this application, by matching the variation in silicon content to the content of additive A, it can be further ensured that the silicon-doped anode can still achieve relatively excellent high-temperature performance under different silicon content mixing conditions, thereby further improving the fast-charging performance of the battery and avoiding the anode polarization growth and high-temperature performance degradation caused by silicon-based anode materials. In a specific embodiment, the mass content A wt% of additive A based on the total mass of the electrolyte and the mass content C wt% of silicon based on the total mass of the anode active material satisfy 0.05 ≤ A / C ≤ 0.2. For example, A / C can be 0.05, 0.06, 0.07, 0.08, 0.09, 0.1, 0.11, 0.12, 0.13, 0.14, 0.15, 0.16, 0.17, 0.18, 0.19, or 0.2. In a preferred embodiment, 0.1 ≤ A / C ≤ 0.15.

[0041] In this application, the lithium salt includes lithium bis(trifluoromethanesulfonyl)imide and / or lithium hexafluorophosphate. Macromolecular lithium salts, such as lithium bis(trifluoromethanesulfonyl)imide (LiTFSi) and / or lithium hexafluorophosphate (LiPF6), can reduce the concentration polarization of lithium salts around silicon-based anode material particles in silicon-doped anodes, thereby reducing the difficulty of lithium intercalation in silicon-doped anodes and improving the cycle performance of silicon-doped anodes.

[0042] In one specific embodiment, 0.5 wt% ≤ X wt% ≤ 20 wt%. For example, the mass content X wt% of the lithium bis(trifluoromethanesulfonyl)imide can be 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 5 wt%, 7 wt%, 9 wt%, 13 wt%, 15 wt%, 17 wt%, 19 wt%, or 20 wt%. In a preferred embodiment, 3 wt% ≤ X wt% ≤ 15 wt%.

[0043] In one specific embodiment, 5 wt% ≤ Y wt% ≤ 25 wt%. For example, the mass content Y wt% of lithium hexafluorophosphate can be 5 wt%, 6 wt%, 7 wt%, 8 wt%, 9 wt%, 10 wt%, 12 wt%, 14 wt%, 16 wt%, 18 wt%, 20 wt%, 22 wt%, 24 wt%, or 25 wt%. In a preferred embodiment, 8 wt% ≤ Y wt% ≤ 16 wt%.

[0044] Moreover, LiTFSi and LiPF6 have good compatibility with both silicon-based and carbon-based anode materials. Due to their suitable macromolecular structures, matching LiTFSi and LiPF6 in a certain ratio can ensure that silicon-based anode material particles have low concentration polarization while further ensuring the stability of carbon-based anode material particles. Therefore, in a preferred embodiment, the lithium salt includes lithium bis(trifluoromethanesulfonylimide) and lithium hexafluorophosphate.

[0045] Furthermore, pure LiTFSi is highly corrosive, easily corroding aluminum foil and degrading lithium-ion battery performance. Additionally, excessively high LiTFSi content can significantly increase electrolyte viscosity and decrease conductivity, worsening fast-charging performance. Pure LiPF6, on the other hand, increases concentration polarization around silicon-based anode material particles. Therefore, to avoid these problems, in one specific embodiment, when the lithium salt simultaneously comprises lithium bis(trifluoromethanesulfonyl)imide and lithium hexafluorophosphate, the mass content X wt% of lithium bis(trifluoromethanesulfonyl)imide and the mass content Y wt% of lithium hexafluorophosphate, based on the total mass of the electrolyte, satisfy 0.25 ≤ X / Y ≤ 1.5. For example, X / Y can be 0.25, 0.3, 0.35, 0.4, 0.45, 0.5, 0.55, 0.6, 0.65, 0.7, 0.75, 0.8, 0.85, 0.9, 0.95, 1, 1.05, 1.1, 1.15, 1.2, 1.25, 1.3, 1.35, 1.4, 1.45, or 1.5. This application, by controlling the mass ratio of lithium salt LiTFSi to LiPF6 in the electrolyte, can improve the performance of the silicon-doped anode while maintaining the fast-charging performance of the battery, and avoid exacerbating the anode polarization phenomenon.

[0046] This application does not specify a particular method for testing the mass content of lithium salts; the content can be obtained using conventional methods in the art. In one embodiment, it is detected by ion chromatography.

[0047] In one specific embodiment, R1, R2, R3, and R4 are each independently selected from F, substituted or unsubstituted C. 1-8 Alkoxy, substituted or unsubstituted C 2-5 Alkenyl group, substituted or unsubstituted C 6- 12 One of the aryloxy groups; wherein, when substituted, the substituent used is F. By introducing a fluorine atom with relatively high electronegativity into the structure of additive A, its compatibility with the electrolyte can be enhanced, and the distribution of the electrolyte on the electrode surface can be optimized, exhibiting better wetting performance, thereby better improving the wetting effect of silicon-based anode materials and further improving the cycle performance of lithium-ion batteries.

[0048] In one specific embodiment, the additive A comprises at least one of the compounds shown as (A1) to (A5):

[0049] In this application, the lithium-ion battery further includes a separator, and the adhesion force between the separator and the negative electrode is ≥5 N / m. For example, the adhesion force between the separator and the negative electrode can be 5 N / m, 6 N / m, 7 N / m, 8 N / m, 9 N / m, 10 N / m, 11 N / m, 12 N / m, 13 N / m, 14 N / m, 15 N / m, or 16 N / m. This application can further improve the cycle life of silicon-doped lithium-ion batteries by controlling the adhesion force between the separator and the negative electrode. The main reason is that the expansion of silicon-based negative electrode material particles is relatively large during cycling, which leads to a decrease in the adhesion between the separator and the negative electrode, making local detachment easy. However, when the adhesion force between the separator adhesive layer and the negative electrode is controlled to be ≥5 N / m, it can ensure that the separator and the negative electrode material maintain good adhesion during long cycles, providing better ion transport channels, thereby improving the stability of the negative electrode interface and further improving the long-cycle performance of the lithium-ion battery. In a preferred embodiment, the adhesion force between the diaphragm and the negative electrode is 10 N / m to 16 N / m.

[0050] This application does not specify a particular method for testing the adhesion between the separator and the negative electrode; the adhesion can be obtained using conventional methods in the art. In one embodiment, a fully charged battery is dissected, and a 30mm*15mm long and 15mm wide separator and negative electrode sample is selected along the tab direction. The separator and negative electrode are placed at a 180-degree angle and tested on a universal tensile testing machine at a speed of 100mm / min and a test displacement of 50mm. The test result is recorded as the adhesion between the separator and the negative electrode.

[0051] In this application, the carbon-based anode material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, and soft carbon.

[0052] In this application, the silicon-based anode material includes at least one of nano-silicon, silicon-oxygen anode material, and silicon-carbon anode material.

[0053] In this application, the lithium salt further includes at least one of lithium difluorophosphate, lithium hexafluoroantimony oxide, lithium hexafluoroarsenate, lithium di(pentafluoroethylsulfonyl)imide, and lithium tri(trifluoromethylsulfonyl)methyl.

[0054] In this application, the lithium-ion battery further includes a positive electrode, which comprises a positive electrode active material selected from layered lithium composite oxides with the chemical formula Li. (1+x) Ni y Co z M (1-y- z)O2, where -0.1≤x≤1; 0≤y≤1, 0≤z≤1, and 0≤y+z≤1; where M is one or more of Mg, Zn, Ga, Ba, Al, Fe, Cr, Sn, V, Mn, Sc, Ti, Nb, Mo, and Zr.

[0055] According to the lithium-ion battery of this application, the electrolyte further includes an organic solvent, which includes one or more of carbonates and / or carboxylic acid esters.

[0056] In one specific embodiment, the carbonate includes one or more of the following solvents: ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate.

[0057] In one specific embodiment, the carboxylic acid ester includes one or more of the following solvents: propyl acetate, n-butyl acetate, isobutyl acetate, n-pentyl acetate, isopentyl acetate, ethyl propionate, n-propyl propionate, methyl butyrate, ethyl butyrate, and n-ethyl butyrate.

[0058] According to the lithium-ion battery of this application, the electrolyte further includes additives, which may include one or more of the following: vinylene carbonate, vinyl ethylene carbonate, fluoroethylene carbonate, vinyl sulfate, succinate, glutaronitrile, adiponitrile, heptaonitrile, octanoic acid, sebaconitrile, 1,3,6-hexanetrionitrile, glycerol trionitrile, 1,2-bis(2-cyanoethoxy)ethane, 1,3-propanesulfonic acid lactone, and propenyl-1,3-sulfonic acid lactone.

[0059] In this application, the method for preparing a lithium-ion battery is as follows: the positive electrode sheet, separator, and negative electrode sheet prepared above are stacked in sequence to ensure that the separator is between the positive and negative electrode sheets to play a role in isolation, and then the bare cell without electrolyte is obtained by winding; the bare cell is placed in an outer packaging foil, and the prepared electrolyte is injected into the dried bare cell; after vacuum sealing, standing, formation, shaping, sorting and other processes, the desired lithium-ion battery is obtained.

[0060] The present application will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present application and should not be construed as limiting the scope of protection of the present application. All technologies implemented based on the above content of the present application are covered within the scope of protection intended by the present application.

[0061] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0062] Example 1

[0063] The lithium-ion battery of this application is obtained through the following method, as detailed in Table 1:

[0064] (1) Preparation of positive electrode

[0065] Lithium cobalt oxide, polyvinylidene fluoride (PVDF), conductive carbon black SP (super P), and carbon nanotubes (CNTs) were mixed in a mass ratio of 97.2:1:1.3:0.5. N-methylpyrrolidone (NMP) was added, and the mixture was stirred under vacuum until it formed a uniform and fluid positive electrode slurry. The positive electrode slurry was then uniformly coated onto both surfaces of an aluminum foil. The coated aluminum foil was dried, and then rolled and slit to obtain the desired positive electrode sheet.

[0066] (2) Preparation of negative electrode

[0067] Carbon-based anode material (artificial graphite, average particle size Dv50 Nμm), silicon-based anode material (silicon-carbon anode material, average particle size Dv50 Nμm), sodium carboxymethyl cellulose (CMC-Na), styrene-butadiene rubber, conductive carbon black (SP), and single-walled carbon nanotubes (SWCNTs) were mixed in a mass ratio of 79.5:15:2.5:1.5:1:0.5 and deionized water was added. The anode active material was obtained under vacuum stirring. The silicon content of the anode active material was C wt%. The anode active material was uniformly coated on both surfaces of copper foil. The coated copper foil was dried at room temperature and then transferred to an 80℃ oven for 10 h. After cold pressing and slitting, the anode sheet was obtained. The porosity P of the anode active material in the anode sheet was measured.

[0068] (3) Preparation of electrolyte

[0069] In an argon-filled glove box (H2O < 0.1 ppm, O2 < 0.1 ppm), EC / PC / DEC / PP were mixed uniformly at a mass ratio of 10 / 15 / 20 / 55. Then, lithium bis(trifluoromethanesulfonyl)imide (14.38 wt%) and lithium hexafluorophosphate (15.46 wt%) as lithium salts (X / Y = 0.93) were quickly added. After dissolution, additive A (A1) and additive D (lithium difluorooxalate borate) (A wt%) and other additives were added, specifically: FEC 15 wt%, PS 2 wt%, 1,3,6-hexanetrionitrile 2 wt%, ADN 2 wt%, SN 1 wt%. The mixture was stirred until homogeneous. After passing the tests for moisture and free acid, the desired electrolyte was obtained.

[0070] (4) Battery manufacturing

[0071] The positive electrode sheet from step 1), the negative electrode sheet from step 2), and the separator (wherein the adhesive force between the separator and the negative electrode sheet prepared above is measured to be 14 N / m) are stacked in the order of positive electrode sheet, separator, and negative electrode sheet, and then wound to obtain a battery cell. The battery cell is placed in an outer packaging aluminum foil, and the electrolyte from step 3) is injected into the outer packaging. After vacuum sealing, settling, formation, shaping, and sorting processes, a lithium-ion battery is obtained. The charge / discharge range of the battery in this application is 3.0-4.5V.

[0072] Example 2 group

[0073] Example 2 was carried out in accordance with Example 1, except that the content of additive A (wt%) was changed, as detailed in Table 1.

[0074] Example 3 Group

[0075] Example 3 was carried out in accordance with Example 1, except that the average particle size Dv50 Mμm of the silicon-based anode material was changed compared with the average particle size Dv50 Nμm of the carbon-based anode material, as detailed in Table 1.

[0076] Example 4 group

[0077] Example 4 was carried out in accordance with Example 1, except that the content of additive D (D wt%) was changed, as detailed in Table 1.

[0078] Example 5 group

[0079] Example 5 was carried out in accordance with Example 1, except that the porosity P of the negative electrode active material was changed by controlling the specific operation process of the coating and cold pressing steps of the negative electrode sheet, as detailed in Table 1.

[0080] Example 6 group

[0081] Example 6 was performed in accordance with Example 1, the only difference being that the specific type or content of lithium salt was changed, specifically:

[0082] In Example 6-1, the lithium salt in the electrolyte is only lithium hexafluorophosphate, and lithium bis(trifluoromethanesulfonyl)imide is not added;

[0083] In Example 6-2, the lithium salt in the electrolyte is only lithium bis(trifluoromethanesulfonyl)imide, and lithium hexafluorophosphate is not added;

[0084] In Example 6-3, lithium hexafluorophosphate and lithium bis(trifluoromethanesulfonyl)imide were not added to the electrolyte; instead, lithium tetrafluoroborate was used as the lithium salt in the electrolyte.

[0085] In Examples 6-4, the lithium salts bis(trifluoromethanesulfonyl)imide added to the electrolyte were changed to 3 wt% based on the total mass content of the electrolyte, and the lithium hexafluorophosphate was changed to 12 wt% based on the total mass content of the electrolyte, with X / Y = 0.25;

[0086] In Examples 6-5, the lithium salts bis(trifluoromethanesulfonyl)imide lithium added to the electrolyte were changed to 0.5 wt% based on the total mass content of the electrolyte, and the lithium hexafluorophosphate was changed to 5 wt% based on the total mass content of the electrolyte, with X / Y = 0.1.

[0087] Example 7 group

[0088] Example 7 was performed in accordance with Example 1, the only difference being that the specific type of additive A was changed, specifically:

[0089] Example 7-1: Additive A was replaced with the compound shown in (A2);

[0090] Example 7-2: Additive A was replaced with the compound shown in (A3);

[0091] In Example 7-3, additive A was replaced with the compound shown in (A4);

[0092] In Examples 7-4, additive A was replaced with the compound shown in (A5).

[0093] Example 8 group

[0094] Example 8 was performed in accordance with Example 1, the only difference being that the specific type of additive D was changed, specifically:

[0095] Example 8-1: Additive D was replaced with lithium difluorobis(oxalato)borate.

[0096] In Example 8-2, additive D was replaced with lithium tetrafluoroborate;

[0097] In Example 8-3, additive D was replaced with lithium bis(oxalato)borate.

[0098] Example 9

[0099] Example 9 was carried out in accordance with Example 1, except that the specific composition of the adhesive layer in the diaphragm was changed so that the measured adhesion force between the diaphragm and the negative electrode sheet prepared in Example 1 was less than 5 N / m.

[0100] Comparative Example 1

[0101] Comparative Example 1 was carried out in accordance with Example 1, except that additive A was not added to the electrolyte, as detailed in Table 1.

[0102] Comparative Example 2

[0103] Comparative Example 2 was carried out in accordance with Example 1, except that additives A and D were not added to the electrolyte, as detailed in Table 1.

[0104] Comparative Example 3 Groups

[0105] The three comparative examples were carried out in accordance with Example 1, except that the ratio M / N of the average particle size Dv50 Mμm of the silicon-based anode material to the average particle size Dv50 Nμm of the carbon-based anode material was changed, as detailed in Table 1.

[0106] Table 1

[0107] Lithium-ion battery test case

[0108] The lithium-ion batteries obtained in the above embodiments and comparative examples were tested using the following methods, and the test results are recorded in Table 2:

[0109] The specific testing methods for performance parameters are as follows:

[0110] (1) Cyclic testing of lithium-ion batteries at 25℃

[0111] The lithium-ion battery was placed at 25°C and charged at a constant current of 1C to the upper limit voltage (4.5V), then charged at a constant voltage of 4.5V to 0.05C, and allowed to rest for 5 minutes; then discharged at a constant current of 0.5C to 3V, and allowed to rest for 5 minutes. This constitutes one charge-discharge cycle. The capacity retention rate (%) of the lithium-ion battery after 1000T cycles was recorded. The results are shown in Table 2.

[0112] (2) High-temperature cycling test of lithium-ion battery at 45℃

[0113] The lithium-ion battery was placed at 45°C and charged at a constant current of 1C to the upper limit voltage (4.5V), then charged at a constant voltage of 4.5V to 0.05C, and allowed to rest for 5 minutes; then discharged at a constant current of 0.5C to 3V, and allowed to rest for 5 minutes. This constitutes one charge-discharge cycle. The capacity retention rate (%) of the lithium-ion battery after 400T cycles was recorded. The results are shown in Table 2.

[0114] (3) Cyclic thickness expansion test of lithium-ion batteries at 25℃

[0115] At 25℃, the battery, after capacity testing, was charged to 4.48V at a constant current and constant voltage of 0.7C, with a cutoff current of 0.05C. Then, it was discharged to 3.0V at a constant current of 0.5C. This cycle was repeated 400 times. The thickness expansion rate at the 400th cycle was calculated using the following formula:

[0116] The thickness expansion rate (%) after 400 cycles = (battery thickness after 400 cycles / battery thickness after the first cycle - 1) × 100%, and the results are recorded in Table 2.

[0117] (4) Volumetric energy density test of lithium-ion batteries

[0118] The volumetric energy density (Wh / L) of a lithium-ion battery is calculated as follows: capacity at room temperature (Ah) × system plateau voltage (V) / core volume (L). The results are shown in Table 2.

[0119] (5) Rate charging test of lithium-ion batteries

[0120] The resulting batteries were placed in a constant temperature environment at 25℃. The following steps were performed: ① let stand for 10 minutes; ② discharge at 0.2C to 3.0V; ③ let stand for 10 minutes; ④ charge at a certain rate to 4.45V with a cutoff current of 0.02C; ⑤ let stand for 10 minutes; ⑥ discharge at 0.2C to 3.0V; ⑦ let stand for 10 minutes. Steps ④ to ⑦ were repeated until all rate charging tests were completed. The charging rate was 3C. The constant current charge ratio for different rates was then collected. The constant current charge ratio = constant current charging capacity ÷ charging capacity × 100%, as shown in Table 2.

[0121] Table 2

[0122] As can be seen from Tables 1 and 2, the lithium-ion batteries prepared in the embodiments of this application have excellent negative electrode stability compared with the lithium-ion batteries prepared in the comparative examples. They can effectively alleviate the side reactions on the negative electrode surface, thereby improving the cycle volume expansion of the silicon-based negative electrode material. After 400T cycles, they still have a low thickness expansion rate. Furthermore, the cycle performance and lifespan of the silicon-doped lithium-ion batteries are also improved, and the fast charging performance and energy density are excellent.

[0123] The preferred embodiments of this application have been described in detail above; however, this application is not limited thereto. Within the scope of the technical concept of this application, various simple modifications can be made to the technical solution of this application, including combining various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in this application and are all within the protection scope of this application.

Claims

1. A lithium-ion battery comprising a negative electrode and an electrolyte, wherein, The electrolyte includes additives and lithium salts, and the additives include additive A having the structural formula shown in formula (I). In formula (I), R1, R2, R3, R4, R5, and R6 are each independently selected from hydrogen, deuterium, halogen, substituted or unsubstituted C. 1-8 Alkoxy, substituted or unsubstituted C 2-5 Alkenyl group, substituted or unsubstituted C 6-12 One of the aryloxy groups; wherein, when substitution occurs, the substituent used is a halogen; The negative electrode includes a negative electrode active material, which includes silicon-based negative electrode material and carbon-based negative electrode material; The average particle size Dv50 Mμm of the silicon-based anode material and the average particle size Dv50 Nμm of the carbon-based anode material satisfy 0.5≤M / N≤1.

7.

2. The lithium-ion battery according to claim 1, wherein, The mass content of additive A is A wt%, satisfying 0.2wt% ≤ A wt% ≤ 8wt%; preferably, 0.5wt% ≤ A wt% ≤ 3wt%.

3. The lithium-ion battery according to claim 1 or 2, wherein, The average particle size Dv50 Mμm of the silicon-based anode material satisfies 4μm≤Mμm≤25μm; preferably, 4μm≤Mμm≤15μm.

4. The lithium-ion battery according to any one of claims 1-3, wherein, The average particle size Dv of the carbon-based anode material is 50 Nμm, satisfying 5μm≤Nμm≤30μm; preferably, 10μm≤Nμm≤25μm.

5. The lithium-ion battery according to any one of claims 1-4, wherein, The additive also includes additive D, which is a lithium borate additive. Preferably, the lithium borate additive includes at least one of lithium difluorooxalate borate, lithium difluorobis(oxalate) borate, lithium tetrafluoroborate, and lithium bis(oxalate) borate. Preferably, based on the total mass of the electrolyte, the mass content of additive D, Dwt%, satisfies 0.1wt% ≤ Dwt% ≤ 3wt%; more preferably, 0.2wt% ≤ Dwt% ≤ 1wt%.

6. The lithium-ion battery according to claim 5, wherein, Based on the total mass of the electrolyte, the mass content of additive A (A wt%) and the mass content of additive D (D wt%) satisfy 1.5 ≤ A + D ≤ 4.

7. The lithium-ion battery according to claim 1, wherein, The porosity P of the negative electrode active material is 5% to 60%; Preferably, the porosity P of the negative electrode active material satisfies the relationship 0.02≤M / NP≤1.17 between the average particle size Dv50 Mμm of the silicon-based negative electrode material and the average particle size Dv50 Nμm of the carbon-based negative electrode material. More preferably, 0.02≤M / NP≤0.

2.

8. The lithium-ion battery according to claim 1, wherein, Based on the total mass of the negative electrode active material, the mass content of silicon element C wt% satisfies 3wt% ≤ C wt% ≤ 70wt%. Preferably, the mass content A wt% of the additive A, based on the total mass of the electrolyte, and the mass content C wt% of silicon, based on the total mass of the negative electrode active material, satisfy 0.05 ≤ A / C ≤ 0.

2.

9. The lithium-ion battery according to claim 1, wherein, The lithium salt includes lithium bis(trifluoromethanesulfonylimide) and / or lithium hexafluorophosphate; Preferably, 0.5wt% ≤ X wt% ≤ 20wt%; more preferably, 5wt% ≤ Y wt% ≤ 25wt%; Preferably, when the lithium salt comprises lithium bis(trifluoromethanesulfonyl)imide and lithium hexafluorophosphate, the mass content X wt% of lithium bis(trifluoromethanesulfonyl)imide and the mass content Y wt% of lithium hexafluorophosphate satisfy 0.25 ≤ X / Y ≤ 1.5, based on the total mass of the electrolyte.

10. The lithium-ion battery according to claim 1, wherein, R1, R2, R3, and R4 are each independently selected from F, substituted or unsubstituted C. 1-8 Alkoxy, substituted or unsubstituted C 2-5 Alkenyl group, substituted or unsubstituted C 6-12 One of the aryloxy groups; wherein, when substitution is performed, the substituent used is F; Preferably, additive A comprises at least one of the compounds shown in (A1) to (A5):

11. The lithium-ion battery according to claim 1, wherein, The lithium-ion battery further includes a separator, and the adhesion force between the separator and the negative electrode is ≥5N / m; Preferably, the adhesion force between the diaphragm and the negative electrode is 10 N / m to 16 N / m.

12. The lithium-ion battery according to claim 1, wherein, The carbon-based anode material includes at least one of artificial graphite, natural graphite, mesophase carbon microspheres, hard carbon, and soft carbon. And / or, the silicon-based anode material includes at least one of nano-silicon, silicon-oxygen anode material, and silicon-carbon anode material; And / or, the lithium salt further includes at least one of lithium difluorophosphate, lithium hexafluoroantimonyate, lithium hexafluoroarsenate, lithium di(pentafluoroethylsulfonyl)imide, and lithium tri(trifluoromethylsulfonyl)methyl.

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