A lithium-ion battery electrolyte for high-nickel ternary positive electrode materials and its application

Abstract

The present invention belongs to the technical field of lithium ion batteries, and relates to an electrolyte for a lithium ion battery with a high nickel ternary positive electrode material and its application, including an organic solvent, a lithium salt and an additive; the additive includes (5-cyanopyridine-3-yl) potassium trifluoroborate. The lithium ion battery electrolyte of the present invention can form a low-impedance interface film on the positive and negative electrode surfaces at the same time, improve the interface stability, and be applied to lithium ion batteries to obtain better cycle stability and lifespan.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium ion batteries, and in particular relates to a lithium ion battery electrolyte for high-nickel ternary positive electrode materials and applications thereof. Background Art

[0002] Lithium-ion batteries have the advantages of high energy density, long cycle life, low self-discharge, and wide operating temperature. Since their introduction in 1991, they have achieved rapid development and are widely used in mobile portable devices, electric vehicles, energy storage systems, etc. In order to further expand the application of lithium-ion batteries, lithium-ion batteries with higher energy density, longer cycle life and higher safety are urgently needed.

[0003] High nickel ternary (LiNi x Co y Mn z O2, x+y+z=1, x≥0.8, NCM) positive electrode material has the advantages of high specific capacity (180-250mAh / g), high voltage, low cost (low cobalt content), etc. It is an excellent high energy density positive electrode material. When matched with high specific capacity silicon negative electrode, it can increase the energy density of lithium-ion batteries to 300Wh / kg. It is an ideal material for the development of the next generation of commercial lithium-ion batteries.

[0004] However, high-nickel ternary cathode materials have disadvantages such as short cycle life and poor thermal stability. Paradoxically, the higher the nickel content, the higher the energy density, but the shorter the cycle life and the worse the thermal stability. The cycle performance and material stability of high-nickel ternary cathode materials can be improved by ion doping, surface coating and other methods, but there are problems such as complex operation and high cost. Fortunately, electrolyte optimization has been proven by the industry to be the simplest and most effective method.

[0005] Because of Ni 4+ Unstable and easily reduced, high-nickel ternary positive electrode materials will oxidize and decompose the electrolyte. At the same time, the reduction of nickel will also cause the dissolution of transition metals, destroying the stability of the electrolyte and positive electrode materials. Conventional carbonate electrolytes are mainly composed of ethylene carbonate, lithium hexafluorophosphate, etc. Ethylene carbonate has poor antioxidant properties and is prone to oxidative decomposition near high-nickel ternary positive electrode materials. Lithium hexafluorophosphate has poor stability and is easily decomposed to produce hydrofluoric acid under the catalysis of trace amounts of water. Hydrofluoric acid further attacks the interface film, affecting its stability and causing the battery cycle performance to decline. Therefore, a stable interface film becomes crucial in the optimization of the electrolyte. The electrolyte is composed of solvents, lithium salts, and additives. Researchers stabilize the interface film by introducing new additives. Summary of the invention

[0006] The purpose of the present invention is to provide an additive that is rarely reported in lithium-ion batteries, and to optimize the composition of lithium salts, solvents, and additives, so as to improve the battery cycle performance and extend the service life of lithium-ion batteries by forming low-impedance, high-stability CEI and SEI films on the surfaces of positive and negative electrodes.

[0007] Another object of the present invention is to apply the above electrolyte to lithium ion batteries to increase the cycle life of lithium ion batteries.

[0008] In order to solve the above technical problems, the present invention adopts the following technical solutions:

[0009] A lithium ion battery electrolyte for high-nickel ternary positive electrode materials comprises an organic solvent, a lithium salt and an additive; the additive comprises (5-cyanopyridine-3-yl) potassium trifluoroborate.

[0010] The additive is potassium (5-cyanopyridin-3-yl) trifluoroborate (KCPFB), and its structural formula is as follows Figure 1 As shown, the amount of addition is 0.5-10% of the total weight of the lithium ion battery electrolyte, preferably, the amount of addition is 3% of the total weight of the lithium ion battery electrolyte. The additive can form low-impedance CEI and SEI films on the positive and negative electrodes, thereby improving cycle stability.

[0011] Preferably, the mass fraction of the additive in the lithium-ion battery electrolyte is 0.5-10%.

[0012] Preferably, the mass fraction of the additive in the lithium-ion battery electrolyte is 3%.

[0013] Preferably, the following raw materials are included in parts by weight:

[0014] 75-90 parts of the organic solvent

[0015] 10 to 15 parts of the lithium salt

[0016] The additive is 0.5 to 10 parts.

[0017] A high-nickel ternary positive electrode material lithium-ion battery electrolyte, comprising an organic solvent, a lithium salt and an additive. The organic solvent accounts for 75% to 90% of the total weight of the lithium-ion battery electrolyte, the lithium salt accounts for 10% to 15% of the total weight of the lithium-ion battery electrolyte, and the additive accounts for 0.5% to 10% of the total weight of the lithium-ion battery electrolyte.

[0018] Preferably, the organic solvent includes one or more of a carbonate solvent and a carboxylate solvent; the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium difluorophosphate.

[0019] The lithium salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium tetrafluoroborate (LiBF4), and lithium difluorophosphate (LiPO2F2), and the lithium salt accounts for 10-15% of the total weight of the lithium-ion battery electrolyte.

[0020] Preferably, the organic solvent includes a carbonate solvent and a carboxylate solvent mixed in a mass ratio of 20-80:5-20; the carbonate solvent includes one or more of cyclic carbonates and linear carbonates; the carboxylate solvent includes one or more of ethyl acetate, ethyl propionate and propyl propionate.

[0021] In the above-mentioned lithium-ion battery electrolyte, the organic solvent is a mixture of carbonate and carboxylate solvents in a certain proportion, wherein the carbonate solvent accounts for 20-80% of the total weight of the lithium-ion battery electrolyte, and the carboxylate solvent accounts for 5-20% of the total weight of the lithium-ion battery electrolyte. The carbonate solvent includes cyclic carbonate and chain carbonate, wherein the cyclic carbonate includes at least one of ethylene carbonate (EC) and propylene carbonate (PC); the linear carbonate includes at least one of diethyl carbonate (DEC), ethyl methyl carbonate (EMC) and dimethyl carbonate (DMC). The carboxylate solvent includes at least one of ethyl acetate (EA), ethyl propionate (EP) and propyl propionate (PP).

[0022] Preferably, the cyclic carbonate includes one or more of ethylene carbonate and propylene carbonate; the chain carbonate includes one or more of diethyl carbonate, ethyl methyl carbonate and dimethyl carbonate.

[0023] An application of the above-mentioned lithium-ion battery electrolyte for high-nickel ternary positive electrode materials is characterized in that it is used to prepare lithium-ion batteries.

[0024] A lithium ion battery obtained by the above application.

[0025] Preferably, it includes the lithium-ion battery electrolyte, positive electrode, negative electrode, diaphragm, and shell; the positive electrode includes NCM; the negative electrode includes one or more of graphite, silicon carbon, and lithium metal; the diaphragm includes one or more of polypropylene film and polypropylene coated with alumina ceramic film; the shell includes one or more of a steel shell cylindrical shell, a square soft package shell, and a steel shell button battery shell.

[0026] The positive electrode can be a high nickel ternary positive electrode material such as NCM, for example, LiNi x Co y Mn 1-x-y O2, high nickel, that is, x≥0.8, 0.01≤y≤0.1, can achieve excellent results when used in conjunction with the battery electrolyte of the present invention.

[0027] The present invention also provides an application of the lithium ion battery electrolyte, which is a lithium ion battery, comprising an electrolyte, a positive electrode, a negative electrode, a separator and a shell. The positive electrode material is LiNi x Co y Mn 1-x-y O2,, x≥0.8, NCM; the negative electrode material is one of graphite, silicon carbon, and lithium metal negative electrode; the diaphragm is one of polypropylene (PP) film and polypropylene (PP) coated with alumina ceramic film; the shell is one of steel shell cylindrical, square soft pack or steel shell button battery.

[0028] Compared with the prior art, the present invention has the following beneficial effects:

[0029] As a new type of additive, KCPFB has a special atomic composition and chemical structure. It contains carbon atoms, nitrogen atoms, fluorine atoms, boron atoms, and potassium atoms, and forms cyano, pyridine, and boric acid-like structures. The special structure and steric hindrance of KCPFB are formed through a special connection method. The additive KCPFB can form insoluble inorganic components on the surface of the negative electrode, improving the stability of the SEI film; the additive KCPFB is easier to oxidize on the surface of the high-nickel ternary positive electrode material than organic solvents, and preferentially forms a CEI film. In addition, its steric hindrance is suitable, the membrane impedance is low, and the stability is higher, preventing the dissolution of transition metals.

[0030] Under high temperature environment, the electrolyte will accelerate decomposition and produce more HF, and the KCPFB additive can effectively eliminate HF, preventing it from further attacking the interface film and destroying the stability of the interface film, thus improving its high temperature performance.

[0031] The lithium ion battery electrolyte of the present invention can form a low-impedance interface film on the positive and negative electrode surfaces at the same time, thereby improving the interface stability. When applied to lithium ion batteries, better cycle stability and life can be obtained, while having good high-temperature performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 It is the chemical structure of the additive KCPFB in the present invention, and the CAS number of KCPFB is 1245906-68-6.

[0033] Figure 2 It is a comparison chart of the normal temperature and high temperature cycle stability of Example 1, Example 2, Example 3, Example 4, Example 5, Example 6 and Comparative Example 1, Comparative Example 2, Comparative Example 3. DETAILED DESCRIPTION

[0034] In order to make the purpose, technical solutions and advantages of the present invention more clear, the present invention will be further described in detail below in conjunction with specific embodiments.

[0035] Unless otherwise specified, the reagents used in the examples can be purchased from the market. The additive selected is potassium (5-cyanopyridin-3-yl) trifluoroborate (KCPFB), which has the structural formula Figure 1 shown.

[0036] The NMC811 / lithium half-cell assembled in the embodiment uses a 2016 model battery case, the positive electrode has no gasket and spring sheet, and the negative electrode uses a stainless steel gasket. The diameter of the NMC811 positive electrode is 14mm; the diameter of the lithium sheet is consistent with the stainless steel gasket (16mm), the thickness of the lithium sheet is 1mm, and the thickness of the gasket is 0.5mm; the amount of electrolyte used is 50μL, and the diaphragm used is a PP material diaphragm with a diameter of 19mm and a thickness of 25μm.

[0037] The button batteries assembled in the embodiment are all tested using the Xinwei test system, and constant current charge and discharge tests are performed at 25°C and 45°C to evaluate the cycle stability. The voltage range of the constant current charge and discharge test is: 2.3V-4.3V. First, 0.1C is used for the first three cycles of activation, and then 1C is used for long cycles.

[0038] Example 1

[0039] The present embodiment provides an electrolyte for a high-nickel ternary positive electrode material lithium ion battery and its application, which includes the following components, measured by mass percentage: LiPF6 / LiODFB / LiBOB (8 / 1 / 1) 12.5%; PC / EC / EMC / DMC / EP (2 / 2 / 2 / 2 / 2) 87%; KCPFB additive 0.5%; The present embodiment also provides an electrolyte for a high-nickel ternary positive electrode material lithium ion battery and its application preparation steps, which are as follows:

[0040] S1. In a glove box filled with high-purity argon, the moisture and oxygen contents in the glove box were controlled to be below 0.1ppm, and the above mass percentages of components were weighed;

[0041] S2. First, the organic solvent is mixed and stirred to form a uniform organic solvent;

[0042] S3. The lithium salt is then dissolved in an organic solvent and stirred to form a uniform solution;

[0043] S4. The KCPFB additive is added to the uniform solution of step S3 and stirred to obtain the electrolyte;

[0044] S5. Assemble NMC811 / lithium button cells with the electrolyte containing 0.5 wt% KCPFB obtained in S4, let it stand for 24 hours, perform 3 cycles of activation film formation at a rate of 0.1C, and then perform a long charge and discharge cycle test at a rate of 1C to evaluate the cycle stability of the lithium-ion battery containing the electrolyte.

[0045] Embodiment 2:

[0046] This embodiment provides an electrolyte for a high-nickel ternary positive electrode material lithium-ion battery and its application. The difference between this embodiment and Example 1 is that the mass percentage of each component is different, as shown in Table 1, and the other conditions are the same.

[0047] Embodiment 3:

[0048] This embodiment provides an electrolyte for a high-nickel ternary positive electrode material lithium-ion battery and its application. The difference between this embodiment and Example 1 is that the mass percentage of each component is different, as shown in Table 1, and the other conditions are the same.

[0049] Embodiment 4:

[0050] This embodiment provides an electrolyte for a high-nickel ternary positive electrode material lithium-ion battery and its application. The difference between this embodiment and Example 1 is that the mass percentage of each component is different, as shown in Table 1, and the other conditions are the same.

[0051] Embodiment 5:

[0052] This embodiment provides an electrolyte for a high-nickel ternary positive electrode material lithium-ion battery and its application. The difference between this embodiment and Example 1 is that the mass percentage of each component is different, as shown in Table 1, and the other conditions are the same.

[0053] Embodiment 6:

[0054] This embodiment provides an electrolyte for a high-nickel ternary positive electrode material lithium-ion battery and its application. The difference between this embodiment and Example 1 is that the mass percentage of each component is different, as shown in Table 1, and the other conditions are the same.

[0055] Comparative Example 1:

[0056] This comparative example provides an electrolyte for a high-nickel ternary positive electrode material lithium-ion battery and its application. The difference between this comparative example and Example 1 is that the KCPFB additive is not included, as shown in Table 1, and the other conditions are the same.

[0057] Comparative Example 2:

[0058] This comparative example provides an electrolyte for a high-nickel ternary positive electrode material lithium-ion battery and its application. The difference between this comparative example and comparative example 1 is that it includes 3% potassium trifluorophenylborate, as shown in Table 1, and the other conditions are the same.

[0059] Comparative Example 3:

[0060] This comparative example provides an electrolyte for a high-nickel ternary positive electrode material lithium-ion battery and its application. The difference between this comparative example and comparative example 1 is that it includes 3% (3-cyanophenyl) potassium trifluoroborate, as shown in Table 1, and the other conditions are the same.

[0061] Effect Example 1

[0062] The experimental results of Examples 1 to 6 and Comparative Examples 1 to 3 are summarized, and the structures are shown in Tables 1 and Figure 2 shown.

[0063] Table 1 Test results of embodiments and comparative examples

[0064]

[0065] From Table 1 and Figure 2 The test results show that the room temperature and high temperature cycle stability of the embodiment with KCPFB added are significantly better than those of the comparative example 1 without KCPFB added, the comparative example 2 with potassium phenyl trifluoroborate added, and the comparative example 3 with potassium (3-cyanophenyl) trifluoroborate added. Among them, the test result of embodiment 3 is the best and should be regarded as the preferred result, that is, the optimal addition ratio of KCPFB is 3%.

[0066] The above disclosure is only the preferred embodiment of the present invention, which cannot be used to limit the scope of the present invention. Therefore, equivalent changes made according to the claims of the present invention are still within the scope of the present invention.

Claims

1. A lithium ion battery electrolyte for high nickel ternary cathode material, characterized in that: The invention comprises an organic solvent, a lithium salt and an additive; the additive comprises potassium (5-cyanopyridine-3-yl) trifluoroborate; and the mass fraction of the additive in the lithium ion battery electrolyte comprises 0.5-10%.

2. The lithium-ion battery electrolyte for high-nickel ternary positive electrode materials according to claim 1, characterized in that: The mass fraction of the additive in the lithium-ion battery electrolyte includes 3%.

3. The lithium-ion battery electrolyte for high-nickel ternary positive electrode materials according to claim 1, characterized in that: The invention comprises the following raw materials in parts by weight: 75-90 parts of the organic solvent 10 to 15 parts of the lithium salt The additive is 0.5 to 10 parts.

4. The lithium-ion battery electrolyte for high-nickel ternary positive electrode materials according to claim 1, characterized in that: The organic solvent includes one or more of a carbonate solvent and a carboxylate solvent; the lithium salt includes one or more of lithium hexafluorophosphate, lithium bis(oxalatoborate), lithium difluorooxalatoborate, lithium tetrafluoroborate, and lithium difluorophosphate.

5. The lithium ion battery electrolyte for high nickel ternary cathode material according to claim 4, characterized in that: The organic solvent includes a carbonate solvent and a carboxylate solvent mixed in a mass ratio of 20-80:5-20; the carbonate solvent includes one or more of cyclic carbonates and chain carbonates; the carboxylate solvent includes one or more of ethyl acetate, ethyl propionate, and propyl propionate.

6. The lithium-ion battery electrolyte for high-nickel ternary positive electrode materials according to claim 5, characterized in that: The cyclic carbonate includes one or more of ethylene carbonate and propylene carbonate; the chain carbonate includes one or more of diethyl carbonate, ethyl methyl carbonate and dimethyl carbonate.

7. An application of a lithium-ion battery electrolyte for high-nickel ternary positive electrode materials as claimed in claim 1, characterized in that: Used to prepare lithium-ion batteries.

8. A lithium ion battery obtained by the use as claimed in claim 7.

9. The lithium ion battery according to claim 8, characterized in that: It includes the lithium-ion battery electrolyte, positive electrode, negative electrode, diaphragm, and shell; the positive electrode includes NCM; the negative electrode includes one or more of graphite, silicon carbon, and lithium metal; the diaphragm includes one or more of polypropylene film and polypropylene coated with alumina ceramic film; the shell includes one or more of steel shell cylindrical shell, square soft package shell, and steel shell button battery shell.

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