Lithium ion battery electrolyte and lithium ion battery

Abstract

The invention discloses a lithium ion battery electrolyte and a lithium ion battery. The electrolyte comprises an organic solvent, a lithium salt and an additive, wherein the organic solvent comprises fluoroethylene carbonate, the lithium salt comprises LiPF6 and LiNO3 with a concentration of more than 1.3 mol / L, and further comprises at least one boron-containing lithium salt or fluorophosphite. The lithium ion battery provided by the invention has good charging and discharging cycle performance at room temperature and high temperature.

Description

Technical Field

[0001] The present invention belongs to the field of electrochemical technology, and in particular relates to a lithium battery electrolyte and a lithium ion battery. Background Art

[0002] When silicon material is used as the negative electrode of lithium-ion batteries, the reversible generation and decomposition of Li-Si alloys is accompanied by huge volume changes during the battery charge and discharge cycle, which will cause the alloy to pulverize or crack, leading to the collapse of the silicon material structure and the peeling of the electrode material, causing the electrode material to lose electrical contact, resulting in a sharp decline in the cycle performance of silicon negative electrode lithium-ion batteries. At the same time, due to the occurrence of side reactions, a large amount of gas will be generated during the charge and discharge process, which can easily cause bloating inside the battery.

[0003] LiNO3 can form a solid electrolyte interface film on the lithium metal negative electrode, thereby preventing the lithium polysulfide dissolved in the electrolyte from reacting with the lithium metal to cause reduction. LiNO3 can also inhibit the gas production of the battery. However, the solubility of LiNO3 in carbonate is not good, and the electrolyte with LiNO3 added does not improve the cycle performance of silicon negative electrode batteries very well. Summary of the invention

[0004] The technical problem to be solved by the present invention is to provide an electrolyte capable of improving the normal temperature and high temperature cycle performance of lithium ion batteries.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is:

[0006] In one aspect, the present invention provides a lithium-ion battery electrolyte, comprising an organic solvent, a lithium salt and an additive; wherein the organic solvent comprises fluoroethylene carbonate, and the lithium salt comprises LiPF6 and LiNO3 at a concentration of 1.3 mol / L or more; and the electrolyte further comprises at least one of the following components:

[0007] The lithium salt described in A also includes boron-containing lithium salts;

[0008] B. The additive described herein includes fluorophosphites.

[0009] Preferably, the fluoroethylene carbonate accounts for 5 to 30% of the total mass of the electrolyte, and more preferably 10 to 20%.

[0010] Preferably, the concentration of LiPF6 is 1.3 to 3 mol / L, more preferably 1.5 to 2 mol / L.

[0011] Preferably, the concentration of LiNO3 is 0.01 to 0.2 mol / L, more preferably 0.05 to 0.15 mol / L.

[0012] Preferably, the concentration of the boron-containing lithium salt is 0.1 to 0.5 mol / L, more preferably 0.1 to 0.3 mol / L.

[0013] Preferably, the fluorophosphite accounts for 0.01-5% of the total mass of the electrolyte; more preferably, it accounts for 0.1-2%.

[0014] Preferably, the boron-containing lithium salt is one or more of LiDFOB, LiBOB, and LiBF4.

[0015] Preferably, the organic solvent further comprises one or more of cyclic carbonate, chain carbonate and carboxylic acid ester.

[0016] Preferably, the electrolyte further comprises a dissolution promoter.

[0017] Further preferably, the dissolution promoter is CuF2.

[0018] Another aspect of the present invention provides a lithium-ion battery, comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte; wherein the electrolyte is any one of the electrolytes described above.

[0019] Preferably, the active material of the negative electrode is a composite negative electrode material of silicon carbon, or silicon dioxide and artificial graphite.

[0020] The present invention can improve the cycle performance of a lithium ion battery using silicon-carbon material as a negative electrode, as well as the gas generation and flatulence problems, by using the electrolyte.

[0021] Due to the application of the above technical solution, the present invention has the following advantages compared with the prior art:

[0022] In the present invention, by adding fluoroethylene carbonate, fluorophosphite, lithium nitrate, high-concentration lithium salt and boron-containing lithium salt to the silicon negative electrode lithium battery electrolyte, the SEI film formed on the surface of the silicon negative electrode is dense and has good toughness, can tolerate the volume expansion of the silicon negative electrode during the charge and discharge process, and significantly improves the room temperature cycle performance and high temperature performance of the silicon negative electrode battery. DETAILED DESCRIPTION

[0023] The present invention is further described below in conjunction with the examples. However, the present invention is not limited to the following examples. The implementation conditions used in the examples can be further adjusted according to the different requirements of specific use, and the implementation conditions not specified are conventional conditions in the industry. The technical features involved in each embodiment of the present invention can be combined with each other as long as they do not conflict with each other.

[0024] Preparation of electrolyte:

[0025] Ethylene carbonate, diethyl carbonate and ethyl methyl carbonate were uniformly mixed in a volume ratio of 1:1:1. The other components and amounts in the electrolyte are shown in Table 1 and Table 2.

[0026] Preparation of the battery:

[0027] The negative electrode is made of silicon-carbon material, and the positive electrode is made of 4.2V NCM523 material. The electrolyte, positive electrode and negative electrode are assembled into a lithium battery according to conventional processes.

[0028] After the lithium battery prepared by the electrolyte of each embodiment was cycled for 500 times at 1.0C at 25°C and 300 times at 1.0C at 45°C, the battery capacity percentage was tested. The results are shown in Tables 1 and 2. The test process was carried out using a Xinwei electrochemical test cabinet. The substances involved in the table are lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium bis(oxalatoborate) (LiBOB), lithium difluorooxalatoborate (LiODFB), lithium nitrate (LiNO3), fluoroethylene carbonate (FEC) and tris(2,2,2-trifluoroethyl)phosphite (TTFP).

[0029] Table 1

[0030]

[0031]

[0032] By analyzing the test results of Table 1, it can be seen from the comparison between Example 1 and Example 2 that the addition of LiNO3 can significantly increase the battery capacity percentage at 25°C and the battery capacity percentage at 45°C. By comparing Examples 2 to 6, it can be seen that the battery capacity percentage at 25°C and the battery capacity percentage at 45°C increase with the increase in the amount of LiNO3 added, and then decrease with the further increase in the amount of LiNO3 added. By comparing Example 5 and Example 11, it can be seen that the addition of TTFP can further increase the battery capacity percentage at 25°C and the battery capacity percentage at 45°C. By comparing Examples 7 to 10, it can be seen that the amount of FEC added should not be too much or too little, there is an optimal range, and it will affect the battery capacity percentage at 25°C and 45°C.

[0033] Table 2

[0034]

[0035]

[0036] By analyzing the test results in Table 2, it can be seen from the comparison of Examples 12 to 16 that there is an optimal range for the amount of LiPF6 added. By comparing Examples 17 to 19, it can be seen that the addition of boron-containing lithium salts LiBF4, LiBOB and LiODFB can significantly increase the battery capacity percentage at 25°C and 45°C, and the addition of LiBOB has a better effect on improving the battery capacity.

[0037] In summary, it can be seen that the electrolyte formula provided by the present invention significantly improves the room temperature and high temperature cycle performance of silicon negative electrode lithium ion batteries.

[0038] The above detailed description of the present invention is intended to enable persons familiar with the art to understand the contents of the present invention and implement them. It does not limit the protection scope of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the protection scope of the present invention.

Claims

1. A lithium ion battery electrolyte, which is composed of an organic solvent, a lithium salt and an additive, characterized in that: The organic solvent consists of fluoroethylene carbonate, ethylene carbonate, diethyl carbonate and ethyl methyl carbonate, the lithium salt consists of LiPF6, LiNO3 and boron-containing lithium salt, the additive is fluorophosphite, the fluoroethylene carbonate accounts for 10% to 20% of the total mass of the lithium-ion battery electrolyte, the concentration of LiPF6 is 1.5 to 2 mol / L, the concentration of LiNO3 is 0.05 to 0.15 mol / L, and the concentration of the boron-containing lithium salt is 0.1 to 0.3 mol / L; the fluorophosphite accounts for 0.1% to 2% of the total mass of the electrolyte.

2. The lithium-ion battery electrolyte according to claim 1, characterized in that: The boron-containing lithium salt is one or more of LiDFOB, LiBOB, and LiBF4.

3. A lithium-ion battery comprising a positive electrode, a negative electrode, a separator disposed between the positive electrode and the negative electrode, and an electrolyte, characterized in that: The electrolyte is the lithium ion battery electrolyte according to claim 1 or 2.

4. The lithium-ion battery according to claim 3, characterized in that: The active material of the negative electrode is a composite negative electrode material of silicon carbon, or silicon dioxide and artificial graphite.

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