Non-aqueous lithium ion battery electrolyte and preparation method and application thereof

Abstract

The invention belongs to the technical field of lithium ion batteries, and discloses a non-aqueous lithium ion battery electrolyte as well as a preparation method and application thereof. The non-aqueous lithium ion battery electrolyte comprises the following components: a lithium salt, an organic solvent and an additive, wherein the additive comprises a component A, a component B and a component C; the component A is any one of tris (trimethylsilane) phosphate, tris (trimethylsilyl) phosphite or tris (trimethylsilane) borate; the component B is a compound as shown in a formula (I); and the component C is a combination of vinylene carbonate and fluoroethylene carbonate. The electrolyte prepared by the preparation method is stable in storage, and can be subjected to oxidation-reduction decomposition before a solvent, so that compact and thin low-impedance solid electrolyte layers are formed on a positive electrode and a negative electrode, the electrolyte decomposition is effectively inhibited, and the consumption of active lithium is reduced.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a non-aqueous lithium ion battery electrolyte and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries are currently the most advanced electrochemical energy storage technology due to their good balance between performance and cost characteristics. The working principle of lithium-ion batteries is that lithium ions migrate from the electrolyte to the electrodes for embedding and de-embedding, while electrons maintain charge balance through the wires, thereby achieving multiple charge and discharge cycles. The operation of lithium-ion batteries depends on Li + Continuous internal migration. This process includes four main steps: (1) Migration of solvated lithium in the electrolyte. (2) Solvation / desolvation process of lithium ions. (3) Migration of lithium ions in the anode-electrolyte or cathode-electrolyte interphase. (4) Lithium ion embedding into the electrode. Effectively constructing a solid electrolyte layer with high ionic conductivity, high electronic shielding, interface stability and low active lithium consumption is the key to improving battery performance and service life. Based on this, the rational selection of additives is crucial.

[0003] Sulfur-containing electrolyte additives usually have a high reduction potential and a low oxidation potential. They can decompose before the solvent to form a stable inorganic solid electrolyte layer, which plays a very important role in improving the stability of the positive and negative electrode interfaces, inhibiting high-temperature gas production, stabilizing the electrolyte under high pressure, and reducing the interface impedance. For example, patent CN105633465A uses vinyl sulfate (DTD) as a functional additive. The additive is reduced at a higher potential and forms a dense and stable SEI film after the first charge and discharge, reducing the interface impedance, inhibiting the solvent decomposition on the electrode surface, and improving the cycle performance of lithium-ion batteries under high pressure. However, the chemical properties of vinyl sulfate itself are unstable, and the properties of the electrolyte containing the additive are also unstable, which significantly increases the storage and transportation costs of the additive and the electrolyte. In addition, the additive is easy to discolor the electrolyte and affect the battery performance.

[0004] For example, patent CN113964385A provides an electrolyte, a preparation method and use thereof. The electrolyte includes a non-aqueous solvent, a lithium salt and an additive, wherein the additive includes an alkenyl silane additive. The invention also provides a method for preparing the electrolyte; the non-aqueous solvent, lithium salt and additive are mixed to obtain the electrolyte. The electrolyte provided by the invention undergoes an oxidative polymerization reaction at the positive electrode through the alkenyl silane additive, thereby forming a dense solid electrolyte interface protective film to inhibit the reaction between the electrolyte and the positive electrode; the lithium-ion battery including the electrolyte has excellent high-temperature storage performance and rate performance. However, the problems of the first-cycle coulomb efficiency and active lithium consumption of the battery of the invention need to be solved.

[0005] For another example, patent CN114142091A provides a non-aqueous electrolyte for lithium-ion batteries and a lithium-ion battery. The non-aqueous electrolyte for lithium-ion batteries includes a composite lithium salt, a non-aqueous solvent and an additive, wherein the additive includes a lithium salt additive, a silane additive and a sulfite additive, and the composite lithium salt includes lithium bis(fluorosulfonyl)imide and an auxiliary salt. By regulating the electrolyte formula, the invention not only synergizes the lithium salt additive and the silane additive to solve the problem of corrosion of aluminum foil caused by high-content lithium bis(fluorosulfonyl)imide during battery cycling, but also forms a stable SEI film on the surface of the positive electrode material. In order to further reduce the film formation impedance and change the SEI film structure, the present invention introduces sulfite additives so that the ternary positive electrode material system meets the performance requirements of low-temperature power, high-temperature cycling and high-temperature storage. However, the problem of active lithium consumption in this invention needs to be solved.

[0006] In view of this, the present invention selects component A, component B, and component C as a combined additive. Component A can reduce and inhibit the hydrofluoric acid in the electrolyte, and at the same time can effectively form a positive electrode passivation film, protect the positive electrode material, and avoid the dissolution of transition metals leading to aggravation of electrolyte side reactions. Component B has stable storage performance at room temperature, and will not affect the storage performance of the electrolyte after being added to the electrolyte. In addition, the additive can be reduced and decomposed at a higher potential to form a dense and thin low-impedance solid electrolyte layer at the negative electrode, effectively improving the first cycle coulomb efficiency of the battery, reducing the consumption of active lithium, and thus improving the cycle performance of the battery. The combined use of components A and B can form a solid electrolyte layer with excellent performance at both the positive and negative electrodes of the battery, effectively inhibiting the occurrence of side reactions during the battery charging and discharging process, and greatly improving the battery cycle life. Summary of the invention

[0007] Based on the problems existing in the prior art, the present invention provides a non-aqueous lithium-ion battery electrolyte formula and its application, aiming to solve the problems that the commonly used sulfur-containing additives must be stored at low temperatures and their own chemical properties are unstable, and to improve the service life of lithium iron phosphate batteries. The combined additives used in the present invention have no significant effect on the storage performance of the electrolyte, and can undergo redox decomposition before the solvent, forming a dense and thin low-impedance solid electrolyte layer at the positive and negative electrodes, effectively inhibiting the decomposition of the electrolyte, reducing the consumption of active lithium, and thus improving the high and low temperature cycle performance, high temperature storage performance and low temperature discharge performance of the battery.

[0008] To achieve the above purpose, the technical solution adopted by the present invention is as follows:

[0009] In one aspect, the present invention provides a non-aqueous lithium-ion battery electrolyte formulation, comprising the following components: a lithium salt, an organic solvent, and an additive.

[0010] Preferably, the additive comprises component A, component B and component C;

[0011] Preferably, component A is any one of tris(trimethylsilyl)phosphate (TMSP), tris(trimethylsilyl)phosphite (TMSPI) or tris(trimethylsilyl)borate (TMSB).

[0012] Preferably, component B is one of the compounds represented by formula (I), wherein R1, R2, R3, and R4 are independently hydrogen atoms, halogen elements, or C 1-4 An alkyl group, wherein the halogen element is one of F, Cl, Br, and I.

[0013]

[0014] Preferably, component B is a compound represented by formula (II), denoted as B1.

[0015]

[0016] Preferably, component C is a combination of vinylene carbonate (VC) and fluoroethylene carbonate (FEC).

[0017] Preferably, component A accounts for 0.2%-0.5% in the electrolyte, component B accounts for 0.5%-1% in the electrolyte, and component C accounts for 2.2%-4% in the electrolyte.

[0018] The mass ratio of vinylene carbonate to fluoroethylene carbonate in component C is 2-3:0.2-1.

[0019] Preferably, component A accounts for 0.3% of the electrolyte, component B accounts for 0.7% of the electrolyte, vinylene carbonate in component C accounts for 2.4% of the electrolyte, and fluoroethylene carbonate in component C accounts for 0.6% of the electrolyte.

[0020] Preferably, the lithium salt is selected from one or more of lithium hexafluorophosphate (LiPF6), lithium bis(trifluoromethyl)sulfonyl imide (LiFSI), and lithium bis(trifluoromethyl)sulfonyl imide (LiTFSI).

[0021] Preferably, the lithium salt accounts for 12.5% ​​in the electrolyte.

[0022] Preferably, the organic solvent is selected from one or more of cyclic carbonates and chain carbonates.

[0023] Preferably, the cyclic carbonate solvent accounts for 23%-28% in the electrolyte; the linear carbonate solvent accounts for 55%-65% in the electrolyte.

[0024] Preferably, the cyclic carbonate solvent accounts for 25.95% in the electrolyte; the linear carbonate solvent accounts for 57.55% in the electrolyte.

[0025] Preferably, the cyclic carbonate is one or more of ethylene carbonate, propylene carbonate, vinylene carbonate, and diethyl carbonate, preferably ethylene carbonate (EC).

[0026] Preferably, the linear carbonates are selected from one or more of dimethyl carbonate, diethyl carbonate, and ethyl methyl carbonate, preferably ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC).

[0027] Preferably, the proportion of ethyl methyl carbonate in the electrolyte is 31.6%, and the proportion of dimethyl carbonate in the electrolyte is 25.95%.

[0028] Preferably, the mass ratio of ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate is 3:4:3.

[0029] Preferably, the mass ratio of the lithium salt, the organic solvent and the combined additive is 3.125:20.875:1.

[0030] The present invention also provides a method for preparing a non-aqueous lithium ion battery electrolyte, comprising the following steps:

[0031] (1) mixing carbonate esters in an organic solvent, and then dissolving a lithium salt in the organic solvent to obtain a mixed solution;

[0032] (2) Adding additives to the mixed solution obtained in step (1) and stirring and mixing the mixture to obtain a non-aqueous lithium-ion battery electrolyte.

[0033] In addition, the present invention also provides an application of a non-aqueous lithium ion battery electrolyte in the preparation of a non-aqueous lithium ion battery.

[0034] Preferably, the non-aqueous lithium-ion battery comprises a positive electrode, a negative electrode, a separator and the above-mentioned battery electrolyte.

[0035] Preferably, the positive electrode active material is lithium iron phosphate (LiFePO4), and the negative electrode active material is a composite of one or more of artificial graphite, natural graphite, composite graphite, silicon-carbon composite material and silicon-oxygen composite material, preferably artificial graphite.

[0036] The present invention also provides a method for preparing a non-aqueous lithium ion battery, which specifically comprises the following steps:

[0037] The non-aqueous lithium-ion battery electrolyte obtained above was injected into the fully dried soft-pack battery. After the injection, primary sealing, formation and secondary sealing processes, the battery was divided into different capacities, and the qualified batteries were used as experimental samples.

[0038] Preferably, the positive and negative active materials of the soft-pack battery are lithium iron phosphate and artificial graphite.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The component B used in the present invention has stable chemical properties and can be stored at room temperature without low temperature. In addition, the addition of additives will not change the original storage temperature of the electrolyte and will not cause the electrolyte to change color during storage, which greatly reduces the storage cost, transportation cost and production cost of the sulfur-containing special additive.

[0041] (2) The combined additives used in the present invention can form a stable solid electrolyte layer at both the positive electrode and the negative electrode, effectively reducing the decomposition of the electrolyte.

[0042] (3) The combined additives used in the present invention can effectively inhibit battery gas production, improve the high-temperature cycle performance and low-temperature performance of the battery, and at the same time improve the high-temperature storage performance of the battery. DETAILED DESCRIPTION

[0043] The technical scheme of the present invention is clearly and completely described below with specific implementation methods. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in the field without creative work are within the scope of protection of the present invention. The materials, reagents, etc. used, if not otherwise specified, are reagents and materials available from commercial sources.

[0044] Unless otherwise indicated, the following terms have the following meanings. Any undefined term has its generally accepted meaning in the field. "Percentage" as described in the text refers to "mass percentage".

[0045] B1 used below is the compound represented by formula (II) of the present invention, and its structural formula is:

[0046]

[0047] The component contents of Examples 1-3 and Comparative Examples 1-6 are shown in Table 1.

[0048] Table 1 Components and percentages of electrolytes in various embodiments and comparative examples

[0049]

[0050] The non-aqueous lithium-ion battery electrolyte is prepared according to the following steps:

[0051] (1) The organic solvents in the embodiment and the comparative example are mixed according to the formula content, and then the lithium salt in the formula content is dissolved in the organic solvent to obtain a mixed solution;

[0052] (2) Adding the additives in the formula content to the mixed solution obtained in step (1), and then stirring and mixing, to obtain a non-aqueous lithium ion battery electrolyte.

[0053] The non-aqueous lithium-ion battery is prepared according to the following steps:

[0054] The non-aqueous lithium ion battery electrolyte is injected into a fully dried soft-pack battery, and after the steps of liquid injection, primary sealing, formation and secondary sealing, the battery is divided into different volumes to obtain the non-aqueous lithium ion battery.

[0055] Effect Experiment

[0056] 1. Electrolyte discoloration test at 25℃:

[0057] The electrolyte was divided into four aluminum bottles and placed in a 25°C constant temperature oven. After a specified time, the electrolyte was taken out to observe whether it changed color and record it. The experimental results are shown in Table 2.

[0058] Table 2 Discoloration time of electrolytes of various embodiments and comparative examples stored at 25°C

[0059] 5 days 10 days 15 days 30 days Example 1 none none none none Comparative Example 1 none none none Change Comparative Example 2 none Change Change Change Example 2 none none none none Comparative Example 3 none none none Change Comparative Example 4 none Change Change Change Example 3 none none none none Comparative Example 5 none none none Change Comparative Example 6 none Change Change Change

[0060] It can be seen from the table that the electrolyte prepared in the embodiment of the present invention has good stability and is not easy to change color.

[0061] 2. Electrolyte battery performance test

[0062] 25℃ / 45℃ cycle performance:

[0063] The lithium-ion battery prepared above was charged to 3.65V at 25℃ / 45℃ and 1C current, then charged at 3.65V until the current reached 0.05C; then discharged to 2.5V at 1C current, which was recorded as one cycle. The discharge capacity of the first cycle was recorded as DC1. After 500 cycles of charge and discharge, the discharge capacity of the 500th cycle was recorded as DC 500 , the capacity retention rate after the 500th cycle is calculated as follows:

[0064]

[0065] 60℃ Storage Performance:

[0066] The thickness of the newly installed battery is measured as d1, and the first discharge capacity is recorded as C1; after the battery is fully charged, the lithium-ion battery is placed in a 60°C high-temperature oven for 14 days; after 14 days, the battery is taken out and discharged once at 1C to 2.5V, and the discharge capacity is recorded as C2; the thickness is measured as d2, and the thickness change rate and capacity retention rate of 60°C storage for 14 days are calculated according to the following two formulas:

[0067]

[0068] -10℃ low temperature discharge performance:

[0069] The prepared lithium-ion battery was charged to 3.65V at 25°C and 1C current, and then charged at 3.65V until the current reached 0.05C; then discharged to 2.5V at 25°C and 1C current, and the discharge capacity was recorded as DC1. At 25°C and 1C current, the battery was charged to 3.65V, and then charged at 3.65V until the current reached 0.05C; then discharged to 2.5V at -10°C and 1C current, and the discharge capacity was recorded as DC2. The low-temperature discharge capacity retention rate was calculated according to the following formula:

[0070]

[0071] Table 3 Initial performance of batteries prepared in various embodiments and comparative examples

[0072]

[0073] Table 4 Battery performance test results of each embodiment and comparative example

[0074]

[0075]

[0076] It can be seen from Table 3 and Table 4 that the sulfur-containing additive added to the electrolyte prepared in the embodiment of the present invention will not affect the original storage performance of the electrolyte, and greatly reduce the storage and transportation costs of the electrolyte; the combined additive used in the present invention can bring excellent room temperature / high temperature cycle performance, high temperature storage performance and low temperature discharge performance to the battery prepared with lithium iron phosphate as the positive electrode material. Compared with MMDS and DTD, the sulfur-containing additive used in the embodiment of the present invention can bring more excellent room temperature / high temperature cycle performance, high temperature storage performance and low temperature discharge performance.

Claims

1. A non-aqueous lithium ion battery electrolyte, characterized in that: Includes the following components: Lithium salts, organic solvents and additives; The additives include component A, component B and component C; Component A is any one of tris(trimethylsilyl)phosphate, tris(trimethylsilyl)phosphite or tris(trimethylsilyl)borate; Component B is one of the compounds represented by formula (I), wherein R1, R2, R3, and R4 are independently hydrogen atoms, halogen elements, or C 1-4 An alkyl group, wherein the halogen element is one of F, Cl, Br, and I; Component C is a combination of vinylene carbonate and fluoroethylene carbonate.

2. The non-aqueous lithium ion battery electrolyte according to claim 1, characterized in that: The component B is a compound represented by formula (II), denoted as B1; 3. The non-aqueous lithium ion battery electrolyte according to claim 1, characterized in that: Calculated by percentage content of the non-aqueous lithium-ion battery electrolyte, the component A accounts for 0.2%-0.5%, the component B accounts for 0.5%-1%, the component C accounts for 2.2%-4%, and the mass ratio of vinylene carbonate to fluoroethylene carbonate in component C is 2-3:0.2-1.

4. The non-aqueous lithium ion battery electrolyte according to claim 1, characterized in that: The lithium salt is selected from one or more of lithium hexafluorophosphate, lithium bis(trifluoromethyl)sulfonyl imide and lithium bis(trifluoromethyl)sulfonyl imide.

5. The non-aqueous lithium ion battery electrolyte according to claim 1, characterized in that: The organic solvent is selected from cyclic carbonate organic solvents and / or chain carbonate organic solvents.

6. The method for preparing a non-aqueous lithium ion battery electrolyte according to any one of claims 1 to 5, characterized in that: The steps include: (1) mixing carbonate esters in an organic solvent, and then dissolving a lithium salt in the organic solvent to obtain a mixed solution; (2) Adding additives to the mixed solution obtained in step (1), and then stirring and mixing, to obtain a non-aqueous lithium-ion battery electrolyte.

7. Use of the non-aqueous lithium ion battery electrolyte according to any one of claims 1 to 5 or the non-aqueous lithium ion battery electrolyte prepared by the preparation method according to claim 6 in the preparation of a non-aqueous lithium ion battery.

8. A non-aqueous lithium ion battery, characterized in that: The invention comprises a positive electrode, a negative electrode, a separator and the non-aqueous lithium ion battery electrolyte according to any one of claims 1 to 5 or the non-aqueous lithium ion battery electrolyte prepared by the preparation method of claim 6.

9. The non-aqueous lithium ion battery according to claim 8, characterized in that: The active material of the positive electrode is lithium iron phosphate; the active material of the negative electrode is one or more of artificial graphite, natural graphite, composite graphite, silicon-carbon composite material and silicon-oxygen composite material.

10. The method for preparing a non-aqueous lithium ion battery according to any one of claims 8 to 9, characterized in that: The specific steps include: The nonaqueous lithium ion battery electrolyte according to any one of claims 1 to 5 or the nonaqueous lithium ion battery electrolyte prepared by the preparation method according to claim 6 is injected into a fully dried soft-pack battery, and after the steps of liquid injection, primary sealing, formation and secondary sealing, the battery is divided into volumes to obtain the nonaqueous lithium ion battery.

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