Lithium ion battery electrolyte for silicon-based negative electrode, preparation method of lithium ion battery electrolyte and lithium ion battery

Abstract

The invention discloses a lithium ion battery electrolyte for a silicon-based negative electrode, a preparation method of the lithium ion battery electrolyte and a lithium ion battery, and relates to the technical field of lithium ion batteries. The lithium ion battery electrolyte comprises the following components in percentage by mass: 6.25-25% of lithium salt, 0.01-4% of an additive A, 1-8% of an additive B and the balance of an organic solvent. The invention also provides a preparation method of the lithium ion battery electrolyte and a lithium ion battery comprising the electrolyte. The lithium ion battery electrolyte provided by the invention effectively inhibits volume expansion and electrolyte side reaction of a silicon-based negative electrode in a circulation process, and effectively solves the problems of high-rate circulation, high-temperature storage and the like of a commercial silicon-based negative electrode lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a lithium ion battery electrolyte for a silicon-based negative electrode, a preparation method thereof, and a lithium ion battery. Background Art

[0002] With the growth of portable electronic products and electric vehicle markets, the demand for high energy density lithium-ion batteries is increasing. At present, the theoretical specific capacity of silicon anode (4200mAh / g) is about ten times that of commercial graphite anode (372mAh / g), and its working voltage (0.4V) is suitable, making it a very promising anode material. In addition, silicon is abundant in the earth's crust, inexpensive and environmentally friendly.

[0003] Due to the huge volume effect of silicon-based negative electrode materials in the process of lithium insertion and removal, repeated volume expansion and contraction during the continuous charge and discharge cycle will cause the silicon particles to shatter and lead to electrical isolation. The inner layer of the SEI film formed by traditional electrolyte additives is an inorganic layer that is more brittle. It is difficult to form a stable SEI film on the surface of the silicon-based negative electrode to adapt to the huge volume expansion of the silicon-based negative electrode. The silicon particles will cause the solid electrolyte membrane interface (SEI) layer to rupture and continuously form the subsequent impedance increase during the repeated lithium insertion and removal process. At the same time, the destruction of the electrode structure will produce a new interface to form a new SEI film, resulting in the active Li + The loss of content will cause the battery performance to deteriorate. Summary of the invention

[0004] In order to solve the above technical problems, the purpose of the present invention is to provide a lithium-ion battery electrolyte for silicon-based negative electrodes, a preparation method thereof, and a lithium-ion battery. The lithium-ion battery electrolyte effectively inhibits the volume expansion of the silicon-based negative electrode and the side reactions of the electrolyte during the cycle, and effectively solves the problems of high-rate cycling and high-temperature storage of commercial silicon-based negative electrode lithium-ion batteries.

[0005] The technical solution of the present invention to solve the above technical problems is as follows: a lithium ion battery electrolyte for a silicon-based negative electrode is provided, comprising the following components in mass percentage: 6.25-25% lithium salt, 0.01-4% additive A, 1-8% additive B, and the balance being an organic solvent.

[0006] Further, the additive A is at least one of the following structural formulas:

[0007]

[0008] Furthermore, the additive B is at least one of tris(trimethylsilane)phosphate, tris(trimethylsilane)borate, tris(trimethylsilane)phosphite, vinyl sulfate and 1,3-propane sultone.

[0009] Furthermore, the lithium salt is a lithium salt system consisting of lithium hexafluorophosphate and lithium difluorooxalatoborate.

[0010] Furthermore, the lithium salt system accounts for 0.5-2 mol / L of the total concentration of the lithium ion battery electrolyte, and the molar percentage of lithium difluorooxalatoborate in the lithium salt system is 40-80%.

[0011] Furthermore, the organic solvent consists of a cyclic carbonate solvent and a linear carbonate solvent; the cyclic carbonate solvent and the linear carbonate solvent account for 10-60% and 40-90% of the total mass of the organic solvent respectively.

[0012] Furthermore, the cyclic carbonate solvent is at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate and difluoroethylene carbonate; the linear carbonate solvent is at least one of ethyl methyl carbonate, dimethyl carbonate, di(2,2,2-trifluoroethyl) carbonate and diethyl carbonate.

[0013] The present invention also provides a method for preparing the above-mentioned lithium ion battery electrolyte for silicon-based negative electrode, comprising the following steps:

[0014] Under the protection of inert gas, lithium salt is added to an organic solvent and fully dissolved, and then additive A and additive B are added and fully dissolved to obtain a lithium ion battery electrolyte for a silicon-based negative electrode.

[0015] The present invention also provides application of the lithium ion battery electrolyte for silicon-based negative electrode in lithium ion batteries.

[0016] A lithium ion battery comprises the lithium ion battery electrolyte for silicon-based negative electrode.

[0017] The present invention has the following beneficial effects:

[0018] 1. The molecular structure of the additive A of the present invention has an amide group with a high DN value, which has a strong Li + The ability to coordinate with Li + The solvated structure is formed and then preferentially decomposed on the negative electrode surface to form Li-rich x N inorganic layer SEI film. Li x N has excellent ionic conductivity, which is beneficial to Li +It diffuses rapidly in the SEI film, reduces the interfacial impedance of the battery, and improves battery performance. At the same time, the lactam cyclic structure contained in additive A forms a dense polymer SEI film containing amide segments on the surface of the silicon-based negative electrode through ring-opening polymerization. This polymer SEI film has good flexibility and stability, and can effectively homogenize the huge volume expansion / contraction of the Si negative electrode during the lithium insertion and extraction process. In addition, the molecular structure of additive A contains -N2H or -NH basic groups, which can have a strong complexation with PF5 / HF / H2O, can effectively inhibit the generation of PF5 / HF / H2O in the electrolyte, has the ability to stabilize LiPF6, and reduces the corrosion of silicon electrode materials.

[0019] 2. At the same time, additive B can form a low-impedance SEM film at the negative electrode and inhibit the battery from producing gas during high temperature. The lithium salt of the present invention is composed of lithium hexafluorophosphate and lithium difluorooxalate borate. The lithium salt system electrolyte has high conductivity and lithium difluorooxalate borate can form a LIF-rich SEI film on the negative electrode surface, reduce the negative electrode impedance, improve the reaction inertness and high-rate cycle of the silicon-based negative electrode in the battery, and more effectively inhibit the side reaction of the silicon surface during the cycle process, thereby improving the cycle life of the lithium ion battery and having good high-temperature storage performance.

[0020] 3. The present invention forms a SEI film rich in a high ion conductive LixN inorganic layer and an elastic and stable polymer SEI film through an amide group with a high DN value, an amide ring structure and an additive A containing a basic group in the molecular structure, which can remove water and inhibit acid at the same time. By adding additive B to form a low-impedance SEI film, the volume expansion of the silicon-based negative electrode and the side reaction of the electrolyte during the cycle are effectively suppressed, thereby improving the high-rate cycle and high-temperature storage performance of the battery. DETAILED DESCRIPTION

[0021] The principles and features of the present invention are described below, and the examples are only used to explain the present invention and are not used to limit the scope of the present invention. If no specific conditions are specified in the embodiments, they are carried out according to normal conditions or conditions recommended by the manufacturer. If the manufacturer of the reagents or instruments is not specified, they are all conventional products that can be purchased commercially.

[0022] Example 1

[0023] A lithium ion battery electrolyte for a silicon-based negative electrode, comprising the following components: an additive A is The addition amount is 0.05wt%; additive B is tri(trimethylsilyl) phosphate, and the addition amount is 1wt%; the molar concentration of lithium salt in the electrolyte is 1.1mol / L, specifically a lithium salt system composed of lithium hexafluorophosphate and lithium difluorooxalatoborate, and the molar percentage of lithium difluorooxalatoborate in the lithium salt system is 45%; the balance is an organic solvent, which is a mixture of ethylene carbonate: difluoroethylene carbonate: dimethyl carbonate in a ratio of 1:1:8.

[0024] The method for preparing the lithium-ion battery electrolyte for the silicon-based negative electrode comprises the following steps:

[0025] Under the protection of argon gas, lithium salt is added to an organic solvent and fully dissolved, and then additives A and additive B are added and fully dissolved to obtain a lithium ion battery electrolyte for a silicon-based negative electrode.

[0026] Example 2

[0027] A lithium ion battery electrolyte for a silicon-based negative electrode, comprising the following components: an additive A is The addition amount is 0.1wt%; additive B is tri(trimethylsilyl) phosphate, and the addition amount is 1wt%; the molar concentration of lithium salt in the electrolyte is 1.2mol / L, specifically a lithium salt system composed of lithium hexafluorophosphate and lithium difluorooxalatoborate, and the molar percentage of lithium difluorooxalatoborate in the lithium salt system is 50%; the balance is an organic solvent, which is a mixture of ethylene carbonate: difluoroethylene carbonate: dimethyl carbonate in a ratio of 1:1:8.

[0028] The method for preparing the lithium-ion battery electrolyte for the silicon-based negative electrode comprises the following steps:

[0029] Under the protection of argon gas, lithium salt is added to an organic solvent and fully dissolved, and then additives A and additive B are added and fully dissolved to obtain a lithium ion battery electrolyte for a silicon-based negative electrode.

[0030] Example 3

[0031] A lithium ion battery electrolyte for a silicon-based negative electrode, comprising the following components: an additive A is The addition amount is 0.5wt%; additive B is tri(trimethylsilyl)phosphite, and the addition amount is 1.5wt%; the molar concentration of lithium salt in the electrolyte is 1.5mol / L, specifically a lithium salt system composed of lithium hexafluorophosphate and lithium difluorooxalatoborate, and the molar percentage of lithium difluorooxalatoborate in the lithium salt system is 50%; the balance is an organic solvent, which is a mixture of ethylene carbonate: difluoroethylene carbonate: dimethyl carbonate in a ratio of 1:1:8.

[0032] The method for preparing the lithium-ion battery electrolyte for the silicon-based negative electrode comprises the following steps:

[0033] Under the protection of argon gas, lithium salt is added to an organic solvent and fully dissolved, and then additives A and additive B are added and fully dissolved to obtain a lithium ion battery electrolyte for a silicon-based negative electrode.

[0034] Example 4

[0035] A lithium ion battery electrolyte for a silicon-based negative electrode, comprising the following components: an additive A is The addition amount is 0.8wt%; additive B is tri(trimethylsilyl)borate, and the addition amount is 2wt%; the molar concentration of lithium salt in the electrolyte is 1.5mol / L, specifically a lithium salt system composed of lithium hexafluorophosphate and lithium difluorooxalatoborate, and the molar percentage of lithium difluorooxalatoborate in the lithium salt system is 70%; the balance is an organic solvent, which is a mixture of ethylene carbonate: difluoroethylene carbonate: dimethyl carbonate in a ratio of 1:1:8.

[0036] The method for preparing the lithium-ion battery electrolyte for the silicon-based negative electrode comprises the following steps:

[0037] Under the protection of argon gas, lithium salt is added to an organic solvent and fully dissolved, and then additives A and additive B are added and fully dissolved to obtain a lithium ion battery electrolyte for a silicon-based negative electrode.

[0038] Example 5

[0039] A lithium ion battery electrolyte for a silicon-based negative electrode, comprising the following components: an additive A is The addition amount is 2wt%; additive B is vinyl sulfate, and the addition amount is 5wt%; the molar concentration of lithium salt in the electrolyte is 1.8mol / L, specifically a lithium salt system composed of lithium hexafluorophosphate and lithium difluorooxalatoborate, and the molar percentage of lithium difluorooxalatoborate in the lithium salt system is 80%; the balance is an organic solvent, which is a mixture of vinyl carbonate: difluoroethylene carbonate: dimethyl carbonate in a ratio of 1:1:8.

[0040] The method for preparing the lithium-ion battery electrolyte for the silicon-based negative electrode comprises the following steps:

[0041] Under the protection of argon gas, lithium salt is added to an organic solvent and fully dissolved, and then additives A and additive B are added and fully dissolved to obtain a lithium ion battery electrolyte for a silicon-based negative electrode.

[0042] Example 6

[0043] A lithium ion battery electrolyte for a silicon-based negative electrode, comprising the following components: an additive A is The addition amounts are 6wt% and 2wt% respectively; additive B is tri(trimethylsilyl)phosphite and 1,3-propane sultone, and the addition amounts are 2wt% and 3wt% respectively; the molar concentration of lithium salt in the electrolyte is 0.6mol / L, specifically a lithium salt system composed of lithium hexafluorophosphate and lithium difluorooxalatoborate, and the molar percentage of lithium difluorooxalatoborate in the lithium salt system is 40%; the balance is an organic solvent, which is a mixture of ethylene carbonate: difluoroethylene carbonate: dimethyl carbonate in a ratio of 1:1:8.

[0044] The method for preparing the lithium-ion battery electrolyte for the silicon-based negative electrode comprises the following steps:

[0045] Under the protection of argon gas, lithium salt is added to an organic solvent and fully dissolved, and then additives A and additive B are added and fully dissolved to obtain a lithium ion battery electrolyte for a silicon-based negative electrode.

[0046] Example 7

[0047] A lithium ion battery electrolyte for a silicon-based negative electrode, comprising the following components: an additive A is The addition amounts are 4wt% and 4wt% respectively; additive B is vinyl sulfate and 1,3-propane sultone, and the addition amounts are 1wt% and 3wt% respectively; the molar concentration of lithium salt in the electrolyte is 0.8mol / L, specifically a lithium salt system composed of lithium hexafluorophosphate and lithium difluorooxalatoborate, and the molar percentage of lithium difluorooxalatoborate in the lithium salt system is 60%; the balance is an organic solvent, which is a mixture of ethylene carbonate: difluoroethylene carbonate: dimethyl carbonate in a ratio of 1:1:8.

[0048] The method for preparing the lithium-ion battery electrolyte for the silicon-based negative electrode comprises the following steps:

[0049] Under the protection of argon gas, lithium salt is added to an organic solvent and fully dissolved, and then additives A and additive B are added and fully dissolved to obtain a lithium ion battery electrolyte for a silicon-based negative electrode.

[0050] Example 8

[0051] A lithium ion battery electrolyte for a silicon-based negative electrode, comprising the following components: an additive A is The addition amount is 3wt%; additive B is tri(trimethylsilyl) phosphate and tri(trimethylsilyl) borate, and the addition amounts are 3wt% and 3wt% respectively; the molar concentration of lithium salt in the electrolyte is 2mol / L, specifically a lithium salt system composed of lithium hexafluorophosphate and lithium difluorooxalatoborate, and the molar percentage of lithium difluorooxalatoborate in the lithium salt system is 60%; the balance is an organic solvent, which is a mixture of ethylene carbonate: difluoroethylene carbonate: dimethyl carbonate in a ratio of 1:1:8.

[0052] The method for preparing the lithium-ion battery electrolyte for the silicon-based negative electrode comprises the following steps:

[0053] Under the protection of argon gas, lithium salt is added to an organic solvent and fully dissolved, and then additives A and additive B are added and fully dissolved to obtain a lithium ion battery electrolyte for a silicon-based negative electrode.

[0054] Comparative Example 1

[0055] A lithium ion battery electrolyte, see the embodiment part in patent CN116936929A for details, and the specific steps are as follows: in a glove box filled with argon, ethylene carbonate, propylene carbonate, diethyl carbonate and ethyl methyl carbonate are mixed in a mass ratio of EC:PC:DEC:EMC=15:15:20:50, and then 13.5wt% of lithium hexafluorophosphate, 3wt% of LiFSi, 1wt% of LiPO2F2 are slowly added to the mixed solution, and then 2.0% of (CH3Si)2-N-CH2-CH=CH2, 2wt% of VC, 0.5wt% of PS, 15wt% of FEC, 1wt% of TMSP and 1wt% of DTD based on the total weight of the electrolyte are added, and the lithium ion battery electrolyte is obtained after stirring evenly.

[0056] Comparative Example 2

[0057] A lithium ion battery electrolyte, see the embodiment section in patent CN107004899A for details, and the specific steps are as follows: prepare a mixture of vinylene carbonate / ethyl methyl carbonate with a volume ratio of 12:88. Dissolve 2 wt% of N, N'-bis(trimethylsilylmethyl)-N, N'-trimethylenemethylphosphonic acid diamide (cyPPA) and 1M LiPF6 in the mixture, and stir evenly to obtain a lithium ion battery electrolyte.

[0058] Comparative Example 3

[0059] The difference between Comparative Example 3 and Example 1 is that the molar concentration of lithium salt in the electrolyte is 1.5 mol / L, the molar percentage of lithium difluorooxalatoborate in the lithium salt system is 70%; Additive A is The added amount is 0.05wt%; additive B is not contained.

[0060] Comparative Example 4

[0061] The difference between Comparative Example 4 and Example 1 is that the molar concentration of lithium salt in the electrolyte is 1.5 mol / L, the molar percentage of lithium difluorooxalatoborate in the lithium salt system is 60%; additive A is not contained; additive B is tris(trimethylsilyl)borate, and the addition amount is 3wt%.

[0062] The electrolytes obtained in Examples 1-8 and Comparative Examples 1-4 were used to assemble batteries. The positive electrode was NMC811, the negative electrode was SiC, and the lithium-ion battery with a nominal capacity of 2.5 Ah was tested. The battery injection volume was 5.5 g, and 5.5 g of electrolyte was injected into each battery.

[0063] Then the battery performance test was carried out, and the high-rate cycle performance and high-temperature storage performance were tested respectively. The battery cells after fractionation were tested for the following electrical properties:

[0064] 1. Room temperature 30A high rate cycle performance test: At 25℃, charge to 4.2V with 1C constant current and constant voltage, the current is less than 0.08A, leave it for 10min, then discharge to 2.5V with 30A constant current, follow this step for 500 cycles, record the first cycle 1C discharge capacity C1 and the 500th cycle discharge capacity C2 step by step, the room temperature capacity retention rate calculation = C2 / C1*100%.

[0065] 2. High temperature storage at 60℃ for 30d: At 25℃, first charge and discharge once at 1C, then record the battery discharge capacity C3, then charge to 4.2V at 1C constant current and constant voltage, with a current less than 0.08A, and store in a blast drying oven at a temperature of 60±2℃ for 30 days, then take out the battery cell, discharge to 2.5V at 1C constant current, leave for 5min, charge to 4.2V at 1C constant current and constant voltage, with a cut-off current of 0.08A, leave for 5min, discharge to 2.5V at 1C constant current, and record the two discharge capacities C4 and C5; capacity retention rate calculation = C4 / C3*100%, capacity recovery rate calculation = C5 / C3*100%.

[0066] The above results are shown in Table 1.

[0067] Table 1 Battery performance test results of Examples 1-8 and Comparative Examples 1-4

[0068]

[0069]

[0070] As shown in Table 1, the present invention has higher performance than Comparative Examples 1 to 4 in terms of 1C charge-30A discharge cycle performance at room temperature and 60°C 30d storage at high temperature. It can be seen that the lithium ion battery electrolyte for silicon-based negative electrode of the present invention can significantly improve the room temperature high rate cycle performance of silicon-based negative electrode lithium ion battery, and has good high temperature storage performance.

[0071] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium ion battery electrolyte for a silicon-based negative electrode, characterized in that: The invention comprises the following components in percentage by weight: 6.25-25% of lithium salt, 0.01-4% of additive A, 1-8% of additive B, and the balance is organic solvent.

2. The lithium-ion battery electrolyte for silicon-based negative electrode according to claim 1, characterized in that: The additive A is at least one of the following structural formulas:

3. The lithium-ion battery electrolyte for silicon-based negative electrode according to claim 1, characterized in that: The additive B is at least one of tris(trimethylsilane)phosphate, tris(trimethylsilane)borate, tris(trimethylsilane)phosphite, vinyl sulfate and 1,3-propane sultone.

4. The lithium-ion battery electrolyte for silicon-based negative electrode according to claim 1, characterized in that: The lithium salt is a lithium salt system consisting of lithium hexafluorophosphate and lithium difluorooxalatoborate.

5. The lithium-ion battery electrolyte for silicon-based negative electrode according to claim 4, characterized in that: The lithium salt system accounts for 0.5-2 mol / L of the total concentration of the lithium ion battery electrolyte, and the molar percentage of lithium difluorooxalatoborate in the lithium salt system is 40-80%.

6. The lithium-ion battery electrolyte for silicon-based negative electrode according to claim 1, characterized in that: The organic solvent consists of a cyclic carbonate solvent and a linear carbonate solvent; the cyclic carbonate solvent and the linear carbonate solvent account for 10-60% and 40-90% of the total mass of the organic solvent respectively.

7. The lithium-ion battery electrolyte for silicon-based negative electrode according to claim 6, characterized in that: The cyclic carbonate solvent is at least one of ethylene carbonate, propylene carbonate, fluoroethylene carbonate and difluoroethylene carbonate; the linear carbonate solvent is at least one of ethyl methyl carbonate, dimethyl carbonate, bis(2,2,2-trifluoroethyl) carbonate and diethyl carbonate.

8. The method for preparing a lithium-ion battery electrolyte for a silicon-based negative electrode according to any one of claims 1 to 7, characterized in that: The following steps are involved: Under the protection of inert gas, lithium salt is added to an organic solvent and fully dissolved, and then additive A and additive B are added and fully dissolved to obtain a lithium ion battery electrolyte for a silicon-based negative electrode.

9. Use of the lithium ion battery electrolyte for silicon-based negative electrode according to any one of claims 1 to 7 in lithium ion batteries.

10. A lithium ion battery, characterized in that: A lithium-ion battery electrolyte for a silicon-based negative electrode comprising any one of claims 1 to 7.

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