Lithium ion battery and preparation method thereof

Abstract

The invention discloses a lithium ion battery and a preparation method thereof, and the preparation method comprises the following steps: S1, providing a positive plate, a negative plate, a diaphragm and an electrolyte, assembling the positive plate, the negative plate and the diaphragm to obtain a battery cell, injecting the electrolyte into the battery cell, and packaging to obtain an assembly; and S2, performing formation and capacity grading on the assembly obtained in the step S1 to obtain the lithium ion battery: performing constant-voltage and constant-current charging to the SOC with the capacity of 15-30% according to a system of 0.01-0.03 C. The preparation method disclosed by the invention can be used for solving a lithium precipitation phenomenon of a pole piece interface, and improving the cycle life and the safety performance of the lithium ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of secondary batteries, and in particular to a lithium ion battery and a preparation method thereof. Background Art

[0002] During the charge and discharge process, existing new energy lithium-ion batteries can experience lithium deposition at the electrode interface due to factors such as insufficient negative electrode residual capacity and abnormal charging conditions. This interfacial lithium deposition not only affects battery performance but can also pose a safety hazard. Therefore, it is crucial to provide a lithium-ion battery that can mitigate lithium deposition at the electrode interface, as well as a lithium-ion battery produced using this method. Summary of the Invention

[0003] The purpose of the present invention is to solve the above problems and provide a lithium ion battery and a preparation method thereof, which can resolve the lithium plating phenomenon at the electrode interface and improve the cycle life and safety performance of the lithium ion battery.

[0004] In order to solve the above technical problems, the technical solutions adopted by the present invention are as follows:

[0005] In a first aspect, the present invention provides a method for preparing a lithium ion battery, comprising the steps of:

[0006] S1. Providing a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, assembling the positive electrode sheet, the negative electrode sheet, and the separator to obtain a battery cell, injecting the electrolyte into the battery cell, and then encapsulating the cell to obtain an assembly;

[0007] S2. The assembly obtained in step S1 is subjected to fractionation to obtain the lithium-ion battery: the battery is charged at a constant voltage and constant current at a rate of 0.01-0.03C to a SOC of 15-30%.

[0008] Optionally, the compaction density of the negative electrode sheet is 3-3.2 g / cm3.

[0009] Optionally, the negative electrode sheet includes a negative electrode material coated on a negative electrode current collector; in terms of mass percentage, the negative electrode material includes 40-45% of a negative electrode active material, 20-23% of a binder, 13-15% of an additive, and the balance a conductive agent.

[0010] Optionally, the method for preparing the negative electrode sheet includes the steps of: mixing the negative electrode active material, the binder and the additive to obtain a negative electrode slurry, coating the negative electrode slurry on both sides of the negative electrode current collector, and drying and rolling to obtain the negative electrode sheet.

[0011] Optionally, the water content of the electrolyte is within 0.02%.

[0012] Optionally, the electrolyte includes, by mass percentage, 28-30% of ethylene carbonate (EC), 19.8-20% of propylene carbonate (PC), 14.8-15.01% of diethyl carbonate (DEC), 9.5-11% of dimethyl carbonate (DMC), 10-20% of lithium salt and the balance of water.

[0013] Optionally, the positive electrode sheet includes a positive electrode material coated on a positive electrode current collector; in parts by mass, the ratio of the added amount of the positive electrode material to the added amount of the negative electrode material is 3:1-4:1.

[0014] Optionally, in a second aspect, the present invention provides a lithium-ion battery, which is manufactured using the lithium-ion battery manufacturing method described above.

[0015] The beneficial effects produced by the present invention include at least:

[0016] The preparation method of the lithium-ion battery described in the present invention adopts a low-current, low-rate charging mechanism by changing the magnitude of the charge and discharge current to avoid excessive lithium ions from being deintercalated from the positive electrode, thereby avoiding excessive lithium ion adsorption on the negative electrode, which is beneficial to the negative electrode excess, thereby reducing the deposition of lithium ions on the negative electrode surface to form lithium metal, reducing high voltage, and preventing lithium deposition on the negative electrode surface caused by battery overcharging, which is beneficial to improving the cycle life and safety of the battery; without affecting the original test function, the test current of the process step is adaptively adjusted to improve the electrode interface of the fixed battery cell to meet standard requirements and achieve the test purpose. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 The figure is a comparison of the surface morphology of the negative electrode sheet of a lithium ion battery obtained by the preparation method of the present invention after charge and discharge with that of the negative electrode sheet of a lithium ion battery in the prior art.

[0018] Among them, 1-lithium deposition interface, 2-electrode. DETAILED DESCRIPTION

[0019] To facilitate understanding of the present invention, the present invention will be described more fully below with reference to the accompanying drawings. Preferred embodiments of the present invention are shown in the accompanying drawings. However, the present invention may be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided to provide a more thorough and comprehensive understanding of the present disclosure.

[0020] Unless otherwise defined, all technical and scientific terms used herein have the same meanings as commonly understood by those skilled in the art to which this invention pertains. The terms used in this specification are for the purpose of describing specific embodiments only and are not intended to limit the invention. Unless otherwise specified, all raw materials used in this invention were prepared using conventional methods or purchased directly.

[0021] In the present invention, descriptions such as “first”, “second”, etc. are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features.

[0022] Example:

[0023] A method for preparing a lithium ion battery comprises the following steps:

[0024] S1. Providing a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, assembling the positive electrode sheet, the negative electrode sheet, and the separator to obtain a battery cell, injecting the electrolyte into the battery cell, and then encapsulating the cell to obtain an assembly;

[0025] S2. The assembly obtained in step S1 is subjected to fractionation to obtain the lithium-ion battery: the battery is charged at a constant voltage and constant current at a rate of 0.01-0.03C to a SOC of 15-30%.

[0026] The preparation method of the lithium-ion battery described in the present invention adopts a low-current, low-rate charging mechanism by changing the magnitude of the charge and discharge current to avoid excessive lithium ions from being deintercalated from the positive electrode, thereby avoiding excessive lithium ion adsorption on the negative electrode, which is beneficial to the negative electrode excess, thereby reducing the deposition of lithium ions on the negative electrode surface to form lithium metal, reducing high voltage, and preventing lithium deposition on the negative electrode surface caused by battery overcharging, which is beneficial to improving the cycle life and safety of the battery; according to the control of the charging current of 0.01C, the liquid phase lithium ion concentration between the positive and negative electrodes can be reduced by 0.21% during the charge and discharge process; without affecting the original test function, the test current of the process step is adaptively adjusted to improve the electrode interface of the fixed battery cell to meet standard requirements and achieve the test purpose.

[0027] Optionally, the compaction density of the negative electrode sheet is 3-3.2 g / cm3.

[0028] Optionally, the negative electrode sheet includes a negative electrode material coated on a negative electrode current collector; in terms of mass percentage, the negative electrode material includes 40-45% of a negative electrode active material, 20-23% of a binder, 13-15% of an additive, and the balance a conductive agent.

[0029] The negative electrode sheet material provided by the present invention is conducive to the excess of negative electrode, improves the negative electrode margin, provides sufficient embedding sites for lithium ions, and allows more lithium ions to be reversibly deintercalated and deintercalated, thereby having a higher specific capacity; thereby avoiding the precipitation of lithium ions on the negative electrode surface, thereby improving the lithium precipitation phenomenon at the negative electrode interface; the structure is relatively stable during the charge and discharge process, and has a long cycle life; it can form a stable solid electrolyte membrane with the electrolyte, ensuring a high coulombic efficiency.

[0030] Optionally, the negative electrode active material includes one or more carbon materials or non-carbon materials; further, the negative electrode active material is a silicon-carbon composite material. Silicon has an ultra-high theoretical specific capacity of up to 4200mAh / g, which is 10 times higher than that of traditional graphite materials, and has a lower delithiation potential. Since its voltage platform is higher than that of graphite, it is more difficult to cause surface lithium ion precipitation during charging, and the overall safety performance of the battery is better.

[0031] Optionally, the method for preparing the negative electrode sheet includes the steps of: mixing the negative electrode active material, the binder, and the additive to obtain a negative electrode slurry; applying the negative electrode slurry to both sides of a negative electrode current collector; and drying and rolling to obtain the negative electrode sheet. The negative electrode current collector includes copper foil.

[0032] Optionally, the water content of the electrolyte is within 0.02% to avoid exceeding the water content standard, so as to ensure that the amount of electrolyte is sufficient and fully infiltrates the electrode.

[0033] Optionally, the electrolyte comprises, by mass percentage, 28-30% of ethylene carbonate, 19.8-20% of propylene carbonate, 14.8-15.01% of diethyl carbonate, 9.5-11% of dimethyl carbonate, 10-20% of lithium salt and the balance of water.

[0034] The electrolyte described in the present invention is an organic-inorganic hybrid system, specifically comprising five organic solvents and an inorganic lithium salt. Ethylene carbonate, propylene carbonate, diethyl carbonate, and dimethyl carbonate are organic solvents that provide ionic conductivity and electrochemical stability in the electrolyte. The lithium salt is an inorganic salt that provides ionic conductivity and participates in the battery reaction.

[0035] Optionally, the positive electrode sheet comprises a positive electrode material coated on a positive electrode current collector; the ratio of the amount of the positive electrode material added to the amount of the negative electrode material added is 3:1-4:1 in parts by mass. The positive electrode current collector comprises aluminum foil.

[0036] In a second aspect, an embodiment of the present invention provides a lithium-ion battery, which is manufactured using the lithium-ion battery manufacturing method described above.

[0037] Example 1:

[0038] A lithium-ion battery was prepared using the preparation method described above; wherein the negative electrode sheet in the embodiment of the present invention had a compacted density of 3.2 g / cm3; the negative electrode material comprised, by mass percentage, 45% of a negative electrode active material, 23% of a binder, and 15% of an additive; the water content of the electrolyte was controlled within 0.02%; and during the capacity separation process, constant voltage and constant current charging was adopted at a rate of 0.01C to a SOC of approximately 30%.

[0039] The inhibition rate of lithium plating of the prepared battery cell is above 50%, and the lithium plating phenomenon can be reduced by another 15% after 1,000 cycles. This is beneficial to prevent the deposition of lithium on the negative electrode surface caused by overcharging of the battery, which is beneficial to improving the cycle life and safety of the battery and improving the overall preparation process of the battery cell.

[0040] Comparative Example 1:

[0041] Compared with Example 1, the difference of Comparative Example 1 is that the charge and discharge current used in the capacity division process in Comparative Example 1 is greater than the charging current listed in the present invention. After the same number of cycles, the surface morphology of the negative electrode sheet is shown in FIG. Figure 1 As shown, Figure 1 The upper middle part is the negative electrode sheet of the present invention, and the lower part is the negative electrode sheet obtained in comparative example 1. It can be seen intuitively that a large number of lithium deposition interfaces 1 appear on the electrode sheet 2 in the prior art, that is, compared with the prior art, the negative electrode sheet obtained in the present invention is smoothly embedded in the negative electrode during the charge and discharge process, and lithium deposition is not easy to occur.

[0042] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0043] The above embodiments merely represent preferred embodiments of the present invention. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the present invention. It should be noted that a person skilled in the art would be able to make various modifications and improvements without departing from the spirit of the present invention, all of which fall within the scope of protection of the present invention. Therefore, the scope of protection of the present invention shall be determined by the appended claims.

Claims

1. A method for preparing a lithium ion battery, characterized in that: Including steps: S1. Providing a positive electrode sheet, a negative electrode sheet, a separator, and an electrolyte, assembling the positive electrode sheet, the negative electrode sheet, and the separator to obtain a battery cell, injecting the electrolyte into the battery cell, and then encapsulating the cell to obtain an assembly; S2. The assembly obtained in step S1 is subjected to fractionation to obtain the lithium-ion battery: the battery is charged at a constant voltage and constant current at a rate of 0.01-0.03C to a capacity of 15-30% SOC.

2. The method for preparing a lithium-ion battery according to claim 1, wherein The compaction density of the negative electrode sheet is 3-3.2 g / cm3.

3. The method for preparing a lithium-ion battery according to claim 1, wherein: The negative electrode sheet comprises a negative electrode material coated on a negative electrode current collector; in terms of mass percentage, the negative electrode material comprises 40-45% of a negative electrode active material, 20-23% of a binder, 13-15% of an additive and the balance a conductive agent.

4. The method for preparing a lithium-ion battery according to claim 3, wherein: The preparation method of the negative electrode sheet comprises the steps of: mixing the negative electrode active material, the binder and the additive to obtain a negative electrode slurry, coating the negative electrode slurry on both sides of the negative electrode current collector respectively, and drying and rolling to obtain the negative electrode sheet.

5. The method for preparing a lithium-ion battery according to claim 1, wherein: The water content of the electrolyte is within 0.02%.

6. The method for preparing a lithium-ion battery according to claim 1, wherein: Calculated by mass percentage, the electrolyte includes 28-30% of ethylene carbonate, 19.8-20% of propylene carbonate, 14.8-15.01% of diethyl carbonate, 9.5-11% of dimethyl carbonate, 10-20% of lithium salt and the balance of water.

7. The method for preparing a lithium-ion battery according to claim 3, wherein: The positive electrode sheet includes a positive electrode material coated on a positive electrode current collector; in terms of mass, the ratio of the added amount of the positive electrode material to the added amount of the negative electrode material is 3:1-4:

1.

8. A lithium ion battery, characterized in that: The lithium-ion battery is prepared by the method for preparing a lithium-ion battery according to any one of claims 1 to 7.

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