Lithium ion battery electrolyte additive, electrolyte and lithium battery

Abstract

The invention relates to the technical field of lithium ion batteries, in particular to a lithium ion electrolyte additive, a lithium ion battery electrolyte and a lithium battery. The lithium ion electrolyte additive provided by the invention has a structure as shown in a formula (I) and / or a formula (II), and R1 and R2 are independently selected from one of the following groups. The additive adopted by the invention can change the solvation composition of lithium ions, so that the HOMO energy of a solvation structure is higher, the electrolyte is easier to oxidize and decompose on the surface of the positive electrode, and then a layer of positive electrode interface film containing Si-O is generated on the surface of the positive electrode, so that the cycling stability of the positive electrode material is effectively improved.

Description

TECHNICAL FIELD

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

[0002] With the promotion of lithium ion batteries in the field of new energy vehicles and energy storage, the demand for lithium ion battery electrolyte is huge. As the carrier of lithium ions, electrolyte transports lithium ions during charging and discharging, so it needs to have great ionic conductivity and small electronic conductivity, and is called the "blood" of lithium batteries. As the "blood" of lithium batteries, electrolyte not only has an important influence on the cycle life and specific capacity of the battery, but also directly determines the stable electrochemical window (ESPWs), high and low temperature performance, safety performance, redox mechanism, etc. Therefore, in recent years, people pay more and more attention to the research and development of electrolyte.

[0003] The common positive electrode materials of lithium ion batteries at present mainly include LCO, NCM, NCA, LFP, LMO and the like, and the common problems of the positive electrode materials mainly include catalysis of electrolyte, dissolution of transition metal elements and the like. The surface of the layered positive electrode material is usually covered by residual lithium compound (RLC). With the passage of time, RLC gradually forms a dense resistance layer covering the surface of the positive electrode particles, which hinders the ion flow between the positive electrode and the electrolyte and the electron flow between the positive electrode and the conductive carbon. The positive electrode film-forming additive can prevent the decomposition of electrolyte on the surface of the positive electrode and reduce the dissolution of transition metal elements. Although the commonly used NCM positive electrode material has high capacity, its cycle stability is also poor. Surface coating and element doping are effective methods to improve the structural stability of NCM material. In addition, forming a layer of CEI film on the surface of the positive electrode through electrolyte additive is also a feasible method to improve the performance of NCM material. At present, there is an urgent need to provide a new type of lithium ion battery electrolyte additive. SUMMARY

[0004] In order to solve the above technical problems, the present application provides a lithium ion battery electrolyte additive, electrolyte and lithium battery. The present application can change the solvation of lithium ions, so that the HOMO energy of the solvation structure is higher, the electrolyte is more likely to oxidize and decompose on the surface of the positive electrode, and then a positive electrode interfacial film containing Si-O is generated on the surface of the positive electrode, thereby effectively improving the cycle stability of the positive electrode material.

[0005] In the first aspect, the present application provides a lithium ion battery electrolyte additive, which has a structure as shown in formula (I) and / or formula (II): wherein R1, R2 are each independently selected from one of the following groups: wherein, · is the connecting site of the lithium ion and the host.

[0006] The additive used in the application is a surface silicon-containing additive. The specific compound can change the solvation structure of lithium ions, so that the HOMO energy of the solvation structure is higher, and the electrolyte is more likely to be oxidized and decomposed on the surface of the positive electrode, thereby generating a positive electrode interface film containing Si-O on the surface of the positive electrode, thereby effectively improving the cycle stability of the positive electrode material.

[0007] As preferred, one or more of the following structures M1-M12 are included: .

[0008] In the application, the specific compound used as the lithium ion battery electrolyte additive can better play the role of the matrix in the system, and significantly improve the cycle stability and comprehensive performance of the battery.

[0009] In a second aspect, the application provides the use of the above-mentioned lithium ion battery electrolyte additive in a lithium ion battery.

[0010] In a third aspect, the application provides an electrolyte comprising the above-mentioned lithium ion battery electrolyte additive, a lithium salt, and a solvent.

[0011] As preferred, the amount of the lithium ion battery electrolyte additive is 0.1% to 2% of the total mass of the electrolyte, preferably 0.5% to 1%. The effect is better at the preferred concentration, further improving the capacity retention rate.

[0012] As preferred, an auxiliary additive is further included, and the amount of the auxiliary additive is 0% to 2% of the total mass of the electrolyte, preferably 0.5% to 1%; the auxiliary additive comprises vinylene carbonate (VC). The application of a certain proportion of other additives such as VC can cooperate with the silicon-containing additive of the application to synergistically optimize the interface film and regulate the solvation structure, further improving the cycle stability.

[0013] As preferred, the solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, fluoromethyl ethyl carbonate, dipropyl carbonate, methyl ethyl carbonate, butyl acetate, methyl propionate, methyl butyrate, ethyl acetate, and ethyl butyrate.

[0014] Further preferably, the solvent comprises at least two of methyl ethyl carbonate, ethylene carbonate, dimethyl carbonate, dimethylether, butyl acetate. The effect is better with the preferred kinds of solvent.

[0015] Further preferably, in the electrolyte, the mass fraction of the ethylene carbonate is 20-30%, the mass fraction of the methyl ethyl carbonate is 20-30%, and the mass fraction of the diethyl carbonate is 40-60%. The preferred kinds of solvent and the preferred proportions form a synergistic effect with the silicon-containing additive of the present application, further significantly improving the comprehensive performance of the electrolyte in terms of cycle stability, ion conductivity, etc. For example, the mass fraction of the ethylene carbonate can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc., the mass fraction of the methyl ethyl carbonate can be 20%, 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, etc., and the mass fraction of the diethyl carbonate can be 40%, 42%, 44%, 46%, 48%, 50%, 52%, 54%, 56%, 58%, 60%, etc., but is not limited to the listed values. Other values not listed within the value range are also applicable.

[0016] As a preference, the lithium salt is selected from at least one of LiPF6, LiBOB, LiDFB and LiFSI; the concentration of the lithium salt is 0.4-2.2 M, and other values not listed within the value range are also applicable.

[0017] In a fourth aspect, the present application provides a lithium battery using the above-mentioned electrolyte.

[0018] The present application has at least the following beneficial effects: the novel lithium-ion battery electrolyte additive provided by the present application can change the solvation of lithium ions, so that the HOMO energy of the solvation structure is higher, and the electrolyte is more likely to be oxidized and decomposed on the surface of the positive electrode, thereby generating a positive electrode interfacial film containing Si-O on the surface of the positive electrode, thereby effectively improving the cycle stability of the positive electrode material. DETAILED DESCRIPTION

[0019] To make the objectives, technical solutions and advantages of the present application clearer, the technical solutions in the present application will be described clearly and completely below. Obviously, the described embodiments are only some of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative labor fall within the scope of protection of the present application.

[0020] The endpoints of the ranges and any values stated in the present disclosure are not limited to the precise values stated. The ranges and values should be construed to be approximations that allow for significant variation. It is noted that various ranges have been presented for values list as being heartier or together, and that some of the published range can be thus divided, to the same end.

[0021] Any embodiment described herein as "example" is not necessarily to be construed as preferred over other embodiments. The use of any of the found aspects of the embodiments in the drawings is not meant to limit that aspect of the embodiment to that figure alone, but that every aspect of the embodiment can occur in each and every one of the drawings.

[0022] The reagents, materials, and instruments used in the embodiments of the present application, comparative examples, if not specifically stated, are conventional reagents, materials, and instruments, and can be obtained by purchase, wherein the reagents involved can also be obtained by purchase and conventional synthesis method.

[0023] In the following examples of the present application, the raw materials such as VC, DTD, etc. are purchased from Jiujiang Tianci High-tech Materials Co., Ltd.

[0024] (I) Preparation of lithium ion battery electrolyte additive Preparation of compound M2 The intermediate tris (trimethylsilyl) phosphate and pyrrole used are purchased from Angene Chemicals.

[0025] Under nitrogen protection, 31.5 g (0.1 moL) of TMSP, 22.1 g (0.33 moL) of imidazole, 10.0 g of sodium ethoxide, and 150.0 g of dichloroethane were sequentially weighed into a 500 mL three-necked flask, and the system was heated at 45°C for 10-24 h, and the system changed from white turbid liquid to yellow turbid liquid.

[0026] After the reaction of the system was completed, filtration was performed, and the filtrate was obtained as yellow liquid by removing the solvent under reduced pressure, with a GC purity of 99.88% and a yield of 90.0%.

[0027] Preparation of compound M9 Under nitrogen protection, 31.5 g (0.1 moL) of TMSP, 22.1 g (0.33 moL) of imidazole, 10.0 g of sodium ethoxide, and 150.0 g of dichloroethane were sequentially weighed into a 500 mL three-necked flask, and the system was heated at 45°C for 10-24 h, and the system changed from white turbid liquid to yellow turbid liquid.

[0028] After the reaction is completed, filter, and remove the solvent from the filtrate under reduced pressure to obtain 38 g of a dark yellow liquid, with a GC purity of 99.45% and a yield of 79.33%.

[0029] Preparation of compound M13 Under nitrogen protection, 27.8 g (0.1 moL) of TMSB, 22.1 g (0.33 moL) of imidazole, 10.0 g of sodium ethoxide, and 150.0 g of dichloroethane were sequentially weighed into a 500 mL three-necked flask, and the system was heated at 45°C for 10-24 h, during which the white turbid liquid changed into a dark yellow turbid liquid.

[0030] After the reaction was completed, the system was filtered, and the solvent was removed from the filtrate under reduced pressure to obtain 38 g of a dark yellow liquid, with a GC purity of 99.45% and a yield of 79.33%.

[0031] Preparation of compound M20 Under nitrogen protection, 27.8 g (0.1 moL) of TMSB, 22.1 g (0.33 moL) of imidazole, 10.0 g of sodium ethoxide, and 150.0 g of dichloroethane were sequentially weighed into a 500 mL three-necked flask, and the system was heated at 45°C for 10-24 h, during which the white turbid liquid changed into a dark yellow turbid liquid.

[0032] After the reaction was completed, the system was filtered, and the solvent was removed from the filtrate under reduced pressure to obtain 38 g of a dark yellow liquid, with a GC purity of 99.45% and a yield of 79.33%.

[0033] Other compounds (M18, M21, etc.) in the present application can also be obtained by the method of the above preparation example, and the preparation methods are basically the same, and the reaction conditions, such as the length of the reaction time, are different.

[0034] (II) Preparation of lithium ion batteries The formulations of the lithium ion battery electrolytes listed in Examples 1-9 and Comparative Examples 1-3 and the corresponding battery positive electrode materials are shown in Table 1.

[0035] Table 1 Lithium ion battery electrolytes of Examples 1-9 and Comparative Examples 1-3

[0036] The method for preparing lithium ion batteries using the lithium ion battery electrolytes listed in Examples 1-6 and Comparative Examples 1-3 is as follows: (1) Preparation of electrolyte In an argon glove box with water content <1 ppm, EC, EMC, DMC organic solvents are mixed in a certain proportion, lithium salt is dissolved in the above organic solvent, then the corresponding additive is added in the organic solvent, completely dissolved, mixed uniformly, to obtain the electrolyte. Among them, EC needs to be preheated and melted at a temperature of 45℃, the concentration of lithium salt is 1 moL / L / 0.5 moL / L, the weight ratio of ethylene carbonate (EC), methyl ethyl carbonate (EMC), dimethyl carbonate (DMC) is EC: EMC: DMC = 4:13:3, wherein the content of the new type of lithium ion battery electrolyte additive provided by the application is 0.5% of the total weight of the electrolyte.

[0037] (2) Preparation of the battery cell The battery cell adopts a standard process battery cell (NCM) of Guoxuan Hi-tech.

[0038] (3) Packaging of the battery cell The liquid injection and primary packaging are carried out in an argon glove box, and the secondary packaging is carried out after 30h of standing, 22h of aging, and the use of a Shenzhen Kexing vacuum secondary packaging machine.

[0039] The lithium ion batteries corresponding to the electrolytes in the above examples and comparative examples are subjected to cycle performance determination, and the determination results are shown in Table 2.

[0040] Table 2: Capacity retention rate of lithium ion batteries of examples and comparative examples

[0041] As can be seen from Table 2, at 25℃, the cycle performance of the lithium ion battery of the application using the additive in the application is far superior to that of Comparative Example 3 without the additive; even for Comparative Examples 1 and 2 which added other excellent performance additives in the art, the application also shows obvious advantages in cycle performance, and the additive and electrolyte of the application can improve the cycle stability of the overall battery by forming a positive electrode interface film.

[0042] Finally, it should be noted that the above examples are only used to illustrate the technical solutions of the application, and not to limit them; although the application has been described in detail with reference to the foregoing examples, those skilled in the art should understand that they can still modify the technical solutions described in the foregoing examples, or make equivalent substitutions for some of the technical features; and these modifications or substitutions do not make the essence of the corresponding technical solutions deviate from the spirit and scope of the technical solutions of the embodiments of the application.

Claims

1. A lithium ion battery electrolyte additive, characterized in that The structure shown in formula (I) and / or formula (II): Wherein, R1 and R2 are each independently selected from one of the following groups: Wherein, · is the connection site with the main body.

2. The lithium-ion battery electrolyte additive according to claim 1, characterized in that Includes one or more of the following structures M1-M12: 。 3. Use of the lithium ion battery electrolyte additive according to claim 1 or 2 in a lithium ion battery.

4. An electrolyte, characterized in that The invention comprises the lithium-ion battery electrolyte additive according to claim 1 or 2, a lithium salt and a solvent.

5. The electrolyte according to claim 4, characterized in that The amount of the lithium-ion battery electrolyte additive is 0.1% to 2% of the total mass of the electrolyte.

6. The electrolyte according to claim 4 or 5, characterized in that The electrolyte further comprises an auxiliary additive, the amount of which is 0% to 2% of the total mass of the electrolyte; preferably, the auxiliary additive comprises vinylene carbonate.

7. The electrolyte according to any one of claims 4 to 6, characterized in that The solvent is selected from at least one of dimethyl carbonate, diethyl carbonate, ethylene carbonate, propylene carbonate, ethyl methyl fluorocarbonate, dipropyl carbonate, ethyl methyl carbonate, butyl acetate, methyl propionate, methyl butyrate, ethyl acetate and ethyl butyrate.

8. The electrolyte according to claim 7, characterized in that The solvent includes at least two of ethyl methyl carbonate, ethylene carbonate, dimethyl carbonate, dimethyl ether, and butyl acetate.

9. The electrolyte according to any one of claims 4 to 8, characterized in that The lithium salt is selected from at least one of LiPF6, LiBOB, LiDFB and LiFSI.

10. A lithium battery, characterized in that: The electrolyte according to any one of claims 4 to 9 is used.

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