A lithium-ion battery, a preparation method thereof, and an electrical device

Abstract

The present application discloses a lithium-ion battery, a preparation method thereof, and an electrical device, relating to the field of new energy technologies. By controlling that the mass content of the negative electrode film-forming additive in the second electrolyte / the mass content of the silicon material in the active material of the negative electrode is higher than the mass content of the negative electrode film-forming additive in the first electrolyte / the mass content of the silicon material in the active material of the negative electrode, and that the total mass percentage content of the lithium salt and the second additive in the second electrolyte is higher than the total mass percentage content of the lithium salt and the first additive in the first electrolyte, the negative electrode SEI film and the positive electrode CEI film are made thin and stable, and the impedance of lithium-ion diffusion between the positive and negative electrodes is reduced, thereby improving the high-temperature cycling performance of the lithium-ion battery, and at the same time, greatly shortening the battery optimization research cycle.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy, and particularly relates to a lithium-ion battery, a preparation method thereof, and an electrical device using the same. Background Art

[0002] High-nickel ternary materials (lithium nickel cobalt manganese (aluminum) oxide, where the molar amount of nickel element accounts for more than 0.8 of the total molar amount of nickel, cobalt, manganese (aluminum) three elements) have a relatively high specific capacity due to the high nickel content; silicon anodes have a relatively high theoretical specific capacity (4200 mAh / g). Currently, high-nickel ternary / silicon-carbon lithium-ion batteries have become one of the main development directions of lithium-ion batteries. However, high-nickel ternary / silicon-carbon lithium-ion batteries will have technical problems such as lithium plating and rapid capacity decay after cycling 800 - 1600 times at 45°C.

[0003] Usually, the above technical problems are solved by optimizing the structure of high-nickel ternary materials, the structure of silicon-carbon anodes, the electrolyte formula, etc. However, the optimization research cycle of these methods is relatively long. Therefore, it is necessary to develop a method with a relatively short optimization research cycle to solve the above technical problems. Summary of the Invention

[0004] Based on the defects existing in the prior art, the purpose of the present invention is to provide a lithium-ion battery, a preparation method thereof, and an electrical device using the same, aiming to improve the high-temperature cycle performance of the lithium-ion battery at 45°C, reduce lithium plating, improve the capacity retention rate, and at the same time shorten the battery optimization research cycle.

[0005] In a first aspect, the present invention provides a lithium-ion battery, including a positive electrode, a negative electrode, a separator, and an electrolyte. The active material of the negative electrode includes graphite;

[0006] The first electrolyte includes a lithium salt, a first additive, a negative electrode film-forming additive, and an organic solvent;

[0007] The second electrolyte includes a lithium salt, a second additive, a negative electrode film-forming additive, and an organic solvent;

[0008] The first additive and the second additive respectively include trimethylsilyl-based additives, lithium difluorophosphate, and lithium difluorooxalate borate, where the trimethylsilyl-based additives include at least one of tris(trimethylsilyl) borate and tris(trimethylsilyl) phosphate;

[0009] The mass content of the negative electrode film-forming additive in the second electrolyte / the mass content of the silicon material in the active material of the negative electrode is higher than the mass content of the negative electrode film-forming additive in the first electrolyte / the mass content of the silicon material in the active material of the negative electrode;

[0010] The total mass percentage content of the lithium salt and the second additive in the second electrolyte is higher than that of the lithium salt and the first additive in the first electrolyte.

[0011] Preferably, in the first electrolyte, the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.2 to 1.7, and the total mass percentage content of the lithium salt and the first additive is 14% to 18%; in the second electrolyte, the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.6 to 2.4, and the total mass percentage content of the lithium salt and the second additive is 16% to 20%.

[0012] Preferably, in the first electrolyte, the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.3 to 1.5, and the total mass percentage content of the lithium salt and the first additive is 15% to 17%; in the second electrolyte, the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.8 to 2.0, and the total mass percentage content of the lithium salt and the second additive is 17% to 19%.

[0013] Preferably, at least one of the conditions (1)-(4) is satisfied:

[0014] (1) The lithium salt content in the second electrolyte is not lower than that in the first electrolyte;

[0015] (2) The total content of the trimethylsilyl group additives in the second electrolyte is not lower than that in the first electrolyte;

[0016] (3) The lithium difluorophosphate content in the second electrolyte is not lower than that in the first electrolyte;

[0017] (4) The lithium difluorooxalate borate content in the second electrolyte is not lower than that in the first electrolyte.

[0018] Preferably, the organic solvents in the first electrolyte and the second electrolyte respectively include diethyl carbonate; in the first electrolyte, the total mass percentage content of the negative electrode film-forming additive and diethyl carbonate is 35% to 45%; in the second electrolyte, the total mass percentage content of the negative electrode film-forming additive and diethyl carbonate is 40% to 50%.

[0019] Preferably, in the first electrolyte, the total mass percentage content of the trimethylsilyl group additive is 0.3% to 3%, the mass percentage content of lithium difluorophosphate is 0.3% to 3%, and the mass percentage content of lithium difluorooxalate borate is 0.3% to 3%; in the second electrolyte, the total mass percentage content of the trimethylsilyl group additive is 0.3% to 5%, the mass percentage content of lithium difluorophosphate is 0.3% to 5%, and the mass percentage content of lithium difluorooxalate borate is 0.3% to 5%.

[0020] Preferably, the mass percentage content of the first electrolyte in the electrolyte is 45% to 85%, and the mass percentage content of the second electrolyte in the electrolyte is 15% to 55%.

[0021] Preferably, at least one of the conditions (a)-(c) is satisfied:

[0022] (a) The negative electrode film-forming additives in the first electrolyte and the second electrolyte include at least one of fluoroethylene carbonate, 1,3-propane sultone, 1,4-butane sultone, vinylene carbonate, and ethylene vinylene carbonate;

[0023] (b) The silicon material includes at least one of silicon monoxide, silicon alloy, and silicon composite material;

[0024] (c) The active material of the positive electrode includes at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide, wherein in the lithium nickel cobalt manganese oxide, the molar amount of nickel element / the total molar amount of nickel element, cobalt element, and manganese element ≥ 0.8; in the lithium nickel cobalt aluminum oxide, the molar amount of nickel element / the total molar amount of nickel element, cobalt element, and aluminum element ≥ 0.8.

[0025] In a second aspect, the present invention provides a method for preparing the lithium ion battery, including the following steps: performing a first liquid injection on a dry battery cell with the first electrolyte, infiltrating, forming, aging, then performing a second liquid injection with the second electrolyte, backfilling helium and inserting nails, welding a sealing sheet, and grading capacitance to obtain a lithium ion battery.

[0026] In a third aspect, the present invention further provides an electrical device, including the lithium ion battery or the lithium ion battery prepared by the preparation method.

[0027] Compared with the prior art, the beneficial effects of the present application are as follows: By controlling that the mass content of the negative electrode film-forming additive in the second electrolyte / the mass content of the silicon material in the active material of the negative electrode is higher than that in the first electrolyte, and the total mass percentage content of the lithium salt and the second additive in the second electrolyte is higher than that in the first electrolyte, a thin and stable SEI film is formed on the negative electrode, a thin and stable CEI film is formed on the positive electrode, and continuous repair of the positive electrode CEI film and the negative electrode SEI film is achieved, ensuring good structural stability of both, reducing the impedance of lithium ion diffusion between the positive and negative electrodes, thereby improving the high-temperature (such as 45 °C) cycle performance of the lithium ion battery, avoiding lithium deposition, enhancing the capacity retention rate after 800 - 1600 high-temperature cycles, and greatly shortening the battery optimization research cycle. Detailed Embodiments

[0028] To better illustrate the purpose, technical solutions, and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments and comparative examples. The purpose is to understand the content of the present invention in detail, rather than to limit the present invention. All other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the present invention. The experimental reagents and instruments involved in the implementation of the present invention are all common ordinary reagents and instruments unless otherwise specified.

[0029] (1) Lithium Ion Battery

[0030] According to the first aspect of the present application, a lithium ion battery is provided, including a positive electrode, a negative electrode, a separator, and an electrolyte. The active material of the negative electrode includes a silicon material, and the electrolyte includes a first electrolyte and a second electrolyte;

[0031] The first electrolyte includes a lithium salt, a first additive, a negative electrode film-forming additive, and an organic solvent;

[0032] The second electrolyte includes a lithium salt, a second additive, a negative electrode film-forming additive, and an organic solvent;

[0033] The first additive and the second additive each include a trimethylsilyl-based additive, lithium difluorophosphate (LiPO2F2), and lithium difluorooxalate borate (LiODFB), where the trimethylsilyl-based additive includes at least one of tris(trimethylsilyl) borate (TMSB) and tris(trimethylsilyl) phosphate (TMSP);

[0034] The mass content of the negative electrode film-forming additive in the second electrolyte / the mass content of the silicon material in the active material of the negative electrode is higher than that in the first electrolyte;

[0035] The total mass percentage content of the lithium salt and the second additive in the second electrolyte is higher than that of the lithium salt and the first additive in the first electrolyte.

[0036] In this application, a thin and stable SEI film is formed on the negative electrode using the first electrolyte, and a thin and stable CEI film is formed on the positive electrode; by controlling that the mass content of the negative electrode film-forming additive in the second electrolyte / the mass content of the silicon material in the active material of the negative electrode is higher than that of the negative electrode film-forming additive in the first electrolyte / the mass content of the silicon material in the active material of the negative electrode, and the total mass percentage content of the lithium salt and the second additive in the second electrolyte is higher than that of the lithium salt and the first additive in the first electrolyte, continuous repair of the positive electrode CEI film and the negative electrode SEI film is achieved, ensuring that both have good structural stability, reducing the impedance of lithium ion diffusion between the positive and negative electrodes, thereby improving the high-temperature (such as 45 °C) cycle performance of the lithium ion battery, avoiding lithium deposition, enhancing the capacity retention rate after 800 - 1600 high-temperature cycles, and at the same time greatly shortening the battery optimization research cycle.

[0037] In some embodiments of this application, in the first electrolyte, the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.2 - 1.7, and the total mass percentage content of the lithium salt and the first additive is 14% - 18%; in the second electrolyte, the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.6 - 2.4, and the total mass percentage content of the lithium salt and the second additive is 16% - 20%. By controlling the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode and the lithium salt and the corresponding additives in the first electrolyte and the second electrolyte within this range, the lithium ion battery has good high-temperature (such as 45 °C) cycle performance, less lithium deposition, and a high capacity retention rate.

[0038] Furthermore, in the first electrolyte, the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.3 - 1.5, and the total mass percentage content of the lithium salt and the first additive is 15% - 17%; in the second electrolyte, the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.8 - 2.0, and the total mass percentage content of the lithium salt and the second additive is 17% - 19%, so as to make the high-temperature (such as 45 °C) cycle performance of the lithium ion battery better, less lithium deposition, and a higher capacity retention rate at a lower cost.

[0039] In some embodiments of this application, the content of the lithium salt in the second electrolyte should not be lower than that in the first electrolyte. That is, the content of the lithium salt in the second electrolyte can be the same as or higher than that in the first electrolyte to further improve the high-temperature (such as 45 °C) cycle performance of the lithium ion battery and enhance the high-temperature cycle capacity retention rate.

[0040] In some embodiments of the present application, the total content of the trimethylsilyl group additives in the second electrolyte should be not less than that in the first electrolyte. That is, the total content of the trimethylsilyl group additives in the second electrolyte can be the same as or higher than that in the first electrolyte, so as to further improve the high-temperature (such as 45 °C) cycling performance of the lithium-ion battery and enhance the high-temperature cycling capacity retention rate. In addition, the trimethylsilyl group additives in the first electrolyte and the second electrolyte can be the same or different, but usually only partially different, and the amount of the trimethylsilyl group additives in the second electrolyte that is different from those in the first electrolyte is generally controlled within 20 wt% of the total amount of the trimethylsilyl group additives in the second electrolyte. For example, if the trimethylsilyl group additive in the first electrolyte is tris(trimethylsilyl) borate, and the trimethylsilyl group additives in the second electrolyte are a mixture of tris(trimethylsilyl) borate and tris(trimethylsilyl) phosphate, the amount of tris(trimethylsilyl) phosphate is controlled within 20 wt% of the total amount of the trimethylsilyl group additives in the second electrolyte; another example is that if the trimethylsilyl group additive in the first electrolyte is tris(trimethylsilyl) phosphate, and the trimethylsilyl group additives in the second electrolyte are a mixture of tris(trimethylsilyl) borate and tris(trimethylsilyl) phosphate, the amount of tris(trimethylsilyl) borate is controlled within 20 wt% of the total amount of the trimethylsilyl group additives in the second electrolyte.

[0041] In the present application, the content of lithium difluorophosphate in the second electrolyte should be not less than that in the first electrolyte. That is, the content of lithium difluorophosphate in the second electrolyte can be the same as or higher than that in the first electrolyte, so as to further improve the high-temperature (such as 45 °C) cycling performance of the lithium-ion battery and enhance the high-temperature cycling capacity retention rate.

[0042] In the present application, the content of lithium difluoro(oxalato)borate in the second electrolyte should be not less than that in the first electrolyte. That is, the content of lithium difluoro(oxalato)borate in the second electrolyte can be the same as or higher than that in the first electrolyte, so as to further improve the high-temperature (such as 45 °C) cycling performance of the lithium-ion battery and enhance the high-temperature cycling capacity retention rate.

[0043] In some embodiments of the present application, the organic solvents in the first electrolyte and the second electrolyte include diethyl carbonate (DEC); in the first electrolyte, the total mass percentage of the negative electrode film-forming additive and diethyl carbonate is 35% to 45%; in the second electrolyte, the total mass percentage of the negative electrode film-forming additive and diethyl carbonate is 40% to 50%. Diethyl carbonate has a low viscosity and can improve the lithium ion migration rate. By controlling the content of diethyl carbonate in the first electrolyte and the second electrolyte within the above range, the lithium ion battery can have better high-temperature performance, such as high-temperature cycling and high-temperature storage performance.

[0044] In the present application, tris(trimethylsilyl) borate and / or tris(trimethylsilyl) phosphate can simultaneously participate in the film formation of the positive and negative electrodes, forming a more stable SEI film on the negative electrode and inhibiting the dissolution of transition metal ions in the positive electrode; lithium difluorophosphate can participate in the film formation of the negative electrode, reducing the film formation impedance of the negative electrode, reducing polarization, and also inhibiting the side reaction between the positive electrode and the electrolyte solvent, reducing gas generation at the positive electrode; lithium difluorooxalate borate can participate in the film formation of the negative electrode, reducing the film formation impedance of the negative electrode, reducing polarization, and also inhibiting the side reaction between the positive electrode and the electrolyte solvent, reducing gas generation at the positive electrode.

[0045] In some embodiments of the present application, in the first electrolyte, the total mass percentage of the trimethylsilyl group additives is 0.3% to 3%, the mass percentage of lithium difluorophosphate is 0.3% to 3%, and the mass percentage of lithium difluorooxalate borate is 0.3% to 3%; in the second electrolyte, the total mass percentage of the trimethylsilyl group additives is 0.3% to 5%, the mass percentage of lithium difluorophosphate is 0.3% to 5%, and the mass percentage of lithium difluorooxalate borate is 0.3% to 5%.

[0046] In some embodiments of the present application, the mass percentage of the first electrolyte in the electrolyte is 45% to 85%, and the mass percentage of the second electrolyte in the electrolyte is 15% to 55%. The proportion of the first electrolyte and the second electrolyte in the electrolyte affects the high-temperature cycling performance of the lithium ion battery. When the proportion of the two is within the above range, the high-temperature (such as 45 °C) cycling performance of the lithium ion battery can be better.

[0047] In the present application, the negative electrode film-forming additives in the second electrolyte can be the same as or different from those in the first electrolyte. However, the difference is usually only partial, and the amount of the negative electrode film-forming additive in the second electrolyte that is different from that in the first electrolyte is usually controlled within 20 wt% of the total amount of the negative electrode film-forming additives in the second electrolyte.

[0048] In some embodiments of the present application, the negative electrode film-forming additives in the first electrolyte and the second electrolyte include at least one of fluoroethylene carbonate (FEC), 1,3-propane sultone (PS), 1,4-butane sultone (1,4-BS), vinylene carbonate (VC), and ethylene vinylene carbonate (VEC), but are not limited thereto. Further, the negative electrode film-forming additive in the first electrolyte and the second electrolyte is fluoroethylene carbonate. Compared with the negative electrode film-forming additives in the first electrolyte and the second electrolyte being other negative electrode film-forming additives, such as at least one of 1,3-propane sultone, 1,4-butane sultone, vinylene carbonate, or ethylene vinylene carbonate, etc., when the negative electrode film-forming additive in the first electrolyte and the second electrolyte is fluoroethylene carbonate, the high-temperature (such as 45 °C) cycling performance of the lithium-ion battery is good, the capacity retention rate is high, the cost is low, and the comprehensive performance is better.

[0049] In the present application, the lithium salt in the second electrolyte may be the same as or different from the lithium salt in the first electrolyte. However, the difference is usually only partial, and the amount of the lithium salt in the second electrolyte that is different from the lithium salt in the first electrolyte is generally controlled within 20 wt% of the total amount of the lithium salt in the second electrolyte.

[0050] In some embodiments of the present application, the mass percentage content of the lithium salt in the second electrolyte in the first electrolyte is 11-18%. Preferably, the mass percentage content of the lithium salt in the second electrolyte in the first electrolyte is 12-16%.

[0051] In some embodiments of the present application, the lithium salt in the first electrolyte and the second electrolyte includes lithium hexafluorophosphate. Compared with the lithium salt in the first electrolyte and the second electrolyte being other lithium salts, such as lithium difluoro(oxalato)borate, etc., lithium hexafluorophosphate has good electrochemical performance, low price, and better comprehensive performance.

[0052] In some embodiments of the present application, the silicon material in the active material of the negative electrode includes at least one of silicon monoxide, silicon alloy, silicon composite material, etc. Among them, the silicon alloy can be selected as Si / Ag, but is not limited thereto, and the silicon composite material can be selected as a silicon-carbon composite material, but is not limited thereto.

[0053] In some embodiments of the present application, the active material of the positive electrode includes at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide. Among them, in the lithium nickel cobalt manganese oxide, the molar amount of nickel element / the total molar amount of nickel element, cobalt element and manganese element ≥ 0.8; in the lithium nickel cobalt aluminum oxide, the molar amount of nickel element / the total molar amount of nickel element, cobalt element and aluminum element ≥ 0.8. When the active material of the positive electrode of the lithium ion battery includes the aforementioned high-nickel ternary material, it still has a high capacity retention rate after cycling 800 - 1600 times at 45°C. For example, the capacity retention rate is above 76% after cycling 800 times, above 70% after cycling 1200 times, and above 63% after cycling 1600 times.

[0054] (2) Preparation method of lithium ion battery

[0055] According to the second aspect of the present application, a preparation method of the above-mentioned lithium ion battery is provided, including the following steps: performing the first liquid injection on the dried dry battery cell with the first electrolyte, infiltrating, forming, aging, then performing the second liquid injection with the second electrolyte, backfilling helium into the nail, welding the sealing sheet, and grading to obtain the lithium ion battery.

[0056] (3) Electrical equipment

[0057] According to the third aspect of the present application, an electrical equipment is provided, including the above-mentioned lithium ion battery or the lithium ion battery prepared by the above-mentioned preparation method.

[0058] The present application will be further described below through specific examples.

[0059] Examples 1 - 16 and Comparative Examples 1 - 4

[0060] Examples 1 - 16 and Comparative Examples 1 - 4 respectively provide a lithium ion battery. These lithium ion batteries include a positive electrode, a negative electrode, a separator disposed between the positive electrode sheet and the negative electrode sheet, and an electrolyte. Among them,

[0061] The active material of the positive electrode is a high-nickel ternary material, specifically LiNi 0.88 Co 0.05 Mn 0.07 O2;

[0062] The active material of the negative electrode is 450 mAh / g silicon carbon, including graphite and silicon material. Among them, the silicon material is silicon suboxide, and the mass content of the silicon material in the active material of the negative electrode is 0.079;

[0063] The separators all include a PE-based film and a mixed coating of ceramic and PVDF (polyvinylidene fluoride) disposed on the base film;

[0064] The electrolyte includes a first electrolyte and a second electrolyte. The compositions of the first electrolyte and the second electrolyte in each embodiment are shown in Table 1. The preparation methods of the first electrolyte and the second electrolyte are as follows: Mix the raw material components evenly to obtain the corresponding electrolyte.

[0065] The preparation method of these lithium-ion batteries includes the following steps: Assemble the positive electrode, negative electrode, and separator into an electrode core and then dry it. Conduct the first liquid injection with the first electrolyte, perform high-temperature infiltration, formation, aging, then conduct the second liquid injection with the second electrolyte, return helium and insert nails, weld the sealing sheet, and perform grading to obtain the corresponding lithium-ion battery.

[0066] Except for the different electrolyte formulations, the lithium-ion batteries of Examples 1 to 16 and Comparative Examples 1 to 4 are the same in other aspects (including the preparation method). The specific formulations are shown in Table 1 and Table 2.

[0067] Table 1

[0068]

[0069]

[0070]

[0071] Table 2

[0072]

[0073]

[0074]

[0075] Example 17

[0076] This example provides a lithium-ion battery. Except that the addition amount of the first electrolyte (i.e., the mass percentage content of the first electrolyte in the electrolyte, the same below) is 45%, other aspects (including the preparation method) are the same as those in Example 8.

[0077] Example 18

[0078] This example provides a lithium-ion battery. Except that the addition amount of the first electrolyte (i.e., the mass percentage content of the first electrolyte in the electrolyte, the same below) is 85%, other aspects (including the preparation method) are the same as those in Example 8.

[0079] Effect Example

[0080] Perform a high-temperature cycle test on the lithium-ion batteries of each example and comparative example in a blue electrochemical test system at 45°C with a 1C / 1C cycle (2.5 - 4.25V @ 0.02C). The specific test data are shown in Table 3.

[0081] Table 3

[0082]

[0083]

[0084] As can be seen from Table 3, the lithium-ion batteries of each example have a high capacity retention rate after cycling 800 to 1600 times at 45°C.

[0085] Compared with Comparative Examples 1 and 2 where the first electrolyte and the second electrolyte are the same, Comparative Example 3 where the mass content of the negative electrode film-forming additive in the second electrolyte / the mass content of the silicon material in the active material of the negative electrode is lower than that in the first electrolyte, and Comparative Example 4 where the total mass percentage content of the lithium salt and the second additive in the second electrolyte is lower than that of the lithium salt and the first additive in the first electrolyte, Example 8 has a significantly higher capacity retention rate after cycling 800 to 1600 times at 45°C because the mass content of the negative electrode film-forming additive in the second electrolyte / the mass content of the silicon material in the active material of the negative electrode is higher than that in the first electrolyte and the total mass percentage content of the lithium salt and the second additive in the second electrolyte is higher than that of the lithium salt and the first additive in the first electrolyte.

[0086] Comparing Examples 1 to 5, it can be seen that in the first electrolyte, when the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.3 to 1.5, and the total mass percentage content of the lithium salt and the first additive is 15% to 17%; in the second electrolyte, when the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.8 to 2.0, and the total mass percentage content of the lithium salt and the second additive is 17% to 19% (such as Examples 2 to 4), compared with the case where the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode and the total mass percentage content of the lithium salt and the first additive in the first electrolyte are relatively low, and the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode and the total mass percentage content of the lithium salt and the second additive in the second electrolyte are relatively low (such as Example 1), the lithium-ion battery has a significantly higher capacity retention rate when cycling 800 to 1600 times at 45°C; compared with the case where the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode and the total mass percentage content of the lithium salt and the first additive in the first electrolyte are relatively high, and the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode and the total mass percentage content of the lithium salt and the second additive in the second electrolyte are relatively high (such as Example 5), when cycling 800 to 1600 times at 45°C, it has a similar capacity retention rate and lower cost. Considering the cost and high-temperature cycling performance comprehensively, it is preferred that the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.3 to 1.5, and the total mass percentage content of the lithium salt and the first additive is 15% to 17%; in the second electrolyte, the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.8 to 2.0, and the total mass percentage content of the lithium salt and the second additive is 17% to 19%.

[0087] Comparing Examples 8 to 10, it can be seen that compared with the case where the lithium salt content in the second electrolyte is lower than that in the first electrolyte, when the lithium salt content in the second electrolyte is not lower than that in the first electrolyte, the high-temperature cycling performance of the lithium-ion battery is better and the capacity retention rate is higher.

[0088] Comparing Example 8 and Examples 11 to 12, it can be seen that compared with the case where the total content of the trimethylsilyl group additives in the second electrolyte is lower than that in the first electrolyte, when the total content of the trimethylsilyl group additives in the second electrolyte is not lower than that in the first electrolyte and the total content is within a suitable range, the high-temperature cycling performance of the lithium-ion battery is better and the capacity retention rate is higher.

[0089] Comparing Example 8 with Examples 13-14, it can be seen that when the content of lithium difluorophosphate in the second electrolyte is not lower than that in the first electrolyte, as compared with the case where the content of lithium difluorophosphate in the second electrolyte is lower than that in the first electrolyte, the high-temperature cycling performance of the lithium-ion battery is better and the capacity retention rate is higher.

[0090] Comparing Example 8 with Examples 15-16, it can be seen that when the content of lithium difluoro(oxalato)borate in the second electrolyte is not lower than that in the first electrolyte, as compared with the case where the content of lithium difluoro(oxalato)borate in the second electrolyte is lower than that in the first electrolyte, the high-temperature cycling performance of the lithium-ion battery is better and the capacity retention rate is higher.

[0091] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention rather than to limit the protection scope of the present invention. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A lithium-ion battery, characterized in that, It includes a positive electrode, a negative electrode, a separator and an electrolyte. The active material of the negative electrode includes a silicon material, and the electrolyte includes a first electrolyte and a second electrolyte; The first electrolyte includes a lithium salt, a first additive, a negative electrode film-forming additive and an organic solvent; The second electrolyte includes a lithium salt, a second additive, a negative electrode film-forming additive and an organic solvent; The first additive and the second additive each include a trimethylsilyl-based additive, lithium difluorophosphate and lithium difluorooxalate borate, wherein the trimethylsilyl-based additive includes at least one of tris(trimethylsilyl) borate and tris(trimethylsilyl) phosphate; The mass content of the negative electrode film-forming additive in the second electrolyte / the mass content of the silicon material in the active material of the negative electrode is higher than the mass content of the negative electrode film-forming additive in the first electrolyte / the mass content of the silicon material in the active material of the negative electrode; The total mass percentage content of the lithium salt and the second additive in the second electrolyte is higher than the total mass percentage content of the lithium salt and the first additive in the first electrolyte; In the first electrolyte, the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.2 to 1.7, and the total mass percentage content of the lithium salt and the first additive is 14% to 18%; in the second electrolyte, the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.6 to 2.4, and the total mass percentage content of the lithium salt and the second additive is 16% to 20%; The organic solvents in the first electrolyte and the second electrolyte each include diethyl carbonate; in the first electrolyte, the total mass percentage content of the negative electrode film-forming additive and diethyl carbonate is 35% to 45%; in the second electrolyte, the total mass percentage content of the negative electrode film-forming additive and diethyl carbonate is 40% to 50%; In the first electrolyte, the total mass percentage content of the trimethylsilyl-based additive is 0.3 to 3%, the mass percentage content of lithium difluorophosphate is 0.3 to 3%, and the mass percentage content of lithium difluorooxalate borate is 0.3 to 3%; in the second electrolyte, the total mass percentage content of the trimethylsilyl-based additive is 0.3 to 5%, the mass percentage content of lithium difluorophosphate is 0.3 to 5%, and the mass percentage content of lithium difluorooxalate borate is 0.3 to 5%; The mass percentage content of the first electrolyte in the electrolyte is 45% to 85%, and the mass percentage content of the second electrolyte in the electrolyte is 15% to 55%.

2. The lithium-ion battery according to claim 1, characterized in that, In the first electrolyte, the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.3 to 1.5, and the total mass percentage content of the lithium salt and the first additive is 15% to 17%; in the second electrolyte, the mass content of the negative electrode film-forming additive / the mass content of the silicon material in the active material of the negative electrode is 1.8 to 2.0, and the total mass percentage content of the lithium salt and the second additive is 17% to 19%.

3. The lithium-ion battery according to any one of claims 1 to 2, characterized in that, Meet at least one of the conditions (1)-(4): (1) The lithium salt content in the second electrolyte is not lower than the lithium salt content in the first electrolyte; (2) The total content of the trimethylsilyl group additives in the second electrolyte is not less than that in the first electrolyte; (3) The content of lithium difluorophosphate in the second electrolyte is not less than that in the first electrolyte; (4) The content of lithium difluoro(oxalato)borate in the second electrolyte is not less than that in the first electrolyte.

4. The lithium-ion battery according to any one of claims 1 to 2, characterized in that, Meet at least one of the conditions (a)-(c): (a) The negative electrode film-forming additives in the first electrolyte and the second electrolyte include at least one of fluoroethylene carbonate, 1,3-propane sultone, 1,4-butane sultone, vinylene carbonate, and ethylene vinylene carbonate; (b) The silicon material includes at least one of silicon monoxide, silicon alloy, and silicon composite material; (c) The active material of the positive electrode includes at least one of lithium nickel cobalt manganese oxide and lithium nickel cobalt aluminum oxide, wherein, in the lithium nickel cobalt manganese oxide, the molar amount of nickel element / the total molar amount of nickel element, cobalt element, and manganese element ≥ 0.8; in the lithium nickel cobalt aluminum oxide, the molar amount of nickel element / the total molar amount of nickel element, cobalt element, and aluminum element ≥ 0.

8.

5. A method for preparing a lithium-ion battery according to any one of claims 1 to 4, characterized in that, It includes the following steps: performing the first liquid injection on the dry battery cell with the first electrolyte, infiltrating, forming, aging, then performing the second liquid injection with the second electrolyte, backfilling helium into the nail, welding the sealing sheet, and grading to obtain a lithium-ion battery.

6. An electrical equipment, characterized in that, It includes the lithium-ion battery according to any one of claims 1 to 4 or the lithium-ion battery prepared by the preparation method according to claim 5.

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