A method for preparing a silicon negative electrode lithium ion battery

Abstract

The invention discloses a preparation method of a silicon negative electrode lithium ion battery, which relates to the technical field of new energy batteries, and comprises the following steps: S1, using nickel cobalt manganese acid NCM523 material as a positive electrode active material to prepare a positive electrode sheet of a battery core; using silicon negative electrode material as a negative electrode active material to prepare a negative electrode sheet of the battery core; S2, regulating the N / P ratio to be 1.04-1.12; S3, adding the nickel cobalt manganese acid material and the silicon negative electrode material and required raw materials into a stirrer respectively, stirring at a high speed to uniformly disperse the components to obtain a homogenate; S4, processing the homogenate obtained in step S3 to form a battery core; S5, sequentially heating, injecting liquid, standing and charging and discharging the battery core obtained in step S4 to obtain a silicon negative electrode lithium ion battery, and by simultaneously controlling the battery core N / P ratio and optimizing the formation process, the first efficiency of the battery core can be significantly improved and enhanced, and the high temperature storage and cycle performance of the battery core can be improved.

Description

Technical Field

[0001] The present invention relates to the technical field of new energy batteries, and in particular to a method for preparing a silicon negative electrode lithium ion battery. Background Art

[0002] At present, the negative electrode material of lithium-ion batteries is mainly graphite, but there is limited room for improving energy density, and the problems of fast charging and lithium precipitation are difficult to solve. Silicon-based negative electrodes have high specific capacity and excellent fast charging. The current mass-produced silicon-based negative electrode has a specific capacity of 1400-2500mAh / g, which is 4-7 times that of graphite. In addition, silicon can provide channels for lithium ion embedding and extraction from all directions, and has excellent fast charging performance. The development of fast charging technology and the anxiety about driving range have driven the demand for silicon-based negative electrodes.

[0003] In the prior art, patent document CN117080594A provides a method for improving the wrinkling problem of silicon-based negative electrodes in high-voltage soft-package lithium-ion batteries; patent document CN106684426A provides a variable current step formation method for soft-package lithium-ion batteries, mainly to improve the cycle performance of the battery; patent document CN111600062A provides a formation method for improving the cycle life of silicon-carbon soft-package lithium-ion batteries, which to a certain extent inhibits the expansion of silicon-carbon negative electrode materials during the cycle process and improves the battery cycle performance.

[0004] However, the series of methods in the above patents have no predictable and significant improvement effect on the first efficiency of silicon-based negative electrodes in lithium-ion batteries. The present invention is mainly a method for preparing silicon negative electrode lithium-ion batteries, which aims to improve the problem of low first efficiency of silicon negative electrode lithium-ion batteries from the perspectives of battery cell design and preparation process. Summary of the invention

[0005] The object of the present invention is to provide a method for preparing a silicon negative electrode lithium ion battery to solve the problem of low initial efficiency of existing negative electrode lithium ion batteries.

[0006] A method for preparing a silicon negative electrode lithium ion battery comprises the following steps:

[0007] S1. Using nickel cobalt manganese oxide LiNi0.5Co0.2Mn0.3O2 (NCM523) material as the positive electrode active material to prepare the positive electrode sheet of the battery cell; using silicon negative electrode material as the negative electrode active material to prepare the negative electrode sheet of the battery cell;

[0008] S2, adjust the N / P ratio to 1.04-1.12, the N / P ratio of the battery cell refers to the ratio of the positive electrode ternary to the silicon negative electrode;

[0009] S3, adding the nickel cobalt manganese oxide material and the silicon negative electrode material and the required raw materials into a stirrer, stirring at high speed to evenly disperse the components to obtain a homogenate;

[0010] S4, processing the homogenate obtained in step S3 to form a battery cell;

[0011] S5, heating, liquid injection and static treatment and charge and discharge treatment are sequentially performed on the battery cell obtained in step S4 to obtain a silicon negative electrode lithium ion battery. The battery cell is heated to remove moisture and residual solvent inside the battery cell, and the liquid injection and static treatment can ensure that the amount of electrolyte in the battery cell is moderate and the electrolyte fully infiltrates the internal materials of the battery cell. The formation operation of the first charge and discharge of the battery cell is convenient to activate the active material inside the battery cell and form a stable SEI film.

[0012] Preferably, the silicon negative electrode lithium ion battery obtained in step S5 is subjected to multiple charging tests until the silicon negative electrode lithium ion battery meets predetermined design requirements.

[0013] Preferably, the specific steps of the processing in step S4 are:

[0014] S41, coating operation: coating the slurry on the current collector to form a uniform coating, sending the coated current collector into an oven for drying and curing, so that the coating and the current collector are closely combined to obtain a pole piece;

[0015] S42, cold pressing operation: placing the electrode into a cold press and pressing it to improve the density and conductivity of the electrode;

[0016] S43, die-cutting and striping operation: according to the design requirements, the cold-pressed electrode is cut into the required shape and size, and the electrode is cut into multiple narrow strips for subsequent winding;

[0017] S44, winding operation: Wind the cut positive electrode sheet, negative electrode sheet and separator together in a certain order to form a battery cell, and weld the tabs of the battery cell to the external wire to ensure reliable connection.

[0018] Preferably, the specific steps of the charge and discharge process in step S5 are:

[0019] S51, first use 0.02-0.05C current, charge to the cut-off voltage of 3.0-3.5V, and leave it for 5-15 minutes;

[0020] S52, then use a current of 0.1-0.2C to charge to a cut-off voltage of 3.7-4.4V, and leave it for 5-15 minutes; finally, the SOC is controlled at 20-100%.

[0021] Preferably, the specific capacity of the silicon negative electrode material in step S1 is 450 mAh / g.

[0022] Preferably, the capacity of the silicon negative electrode lithium ion battery is 40Ah, and its shell material is aluminum.

[0023] The advantages of the present invention are: a preparation method of a silicon negative electrode lithium ion battery in the present invention controls the N / P ratio of the battery cell so that the positive electrode has a lower electrode potential, reduces the dissolution of transition metals and the occurrence of side reactions during the charging process of the battery, improves the first efficiency of the battery cell, and simultaneously improves the high-temperature storage and cycle performance of the battery cell. By comparing different formation voltages, formation SOCs, etc., it is found that the first efficiency of the battery cell is almost not improved by using a high SOC and a high-voltage formation process for deactivation, and the first efficiency of the low SOC slow formation is significantly improved and improved. By simultaneously controlling the N / P ratio of the battery cell and optimizing the formation process, the first efficiency of the battery cell can be significantly improved and enhanced. DETAILED DESCRIPTION

[0024] In order to make the technical means, creative features, objectives and effects achieved by the present invention easy to understand, the present invention is further explained below in conjunction with specific implementation methods.

[0025] Example 1

[0026] This embodiment uses nickel cobalt manganese oxide NCM523 material as the positive electrode and silicon negative electrode material with a specific capacity of 450mAh / g as the negative electrode to assemble into an aluminum shell lithium ion battery with a capacity of 40Ah, and provides the N / P ratio and formation method of the lithium ion battery. The specific steps are as follows:

[0027] Step 1: Cell design: Adjust the cell N / P ratio to 1.08;

[0028] Step 2: Homogenize, coat, cold press, die-cut, slit, wind, weld, vacuum bake, and inject liquid according to the design;

[0029] Step 3: Then let it stand and then form, control the formation temperature at 45±5℃, vacuum degree at –80±5kpa, the formation process requires two-step charging, the first step is to use a current of 0.04C, charge to a cut-off voltage of 3.4V, and the charging cut-off time is 600min; after charging, let it sit for 15min; the second step is to use a current of 0.2C, charge to a cut-off voltage of 3.75V, and the charging cut-off time is 600min; after charging, let it sit for 15min; the final formation SOC is controlled at about 67%.

[0030] Steps Current time Cut-off voltage SOC 1 Charge 0.04C 600min 3.4V 2 Shelf 15min 3 Charge 0.2C 600min 3.75V 4 Shelf 15min 5 Finish 67％

[0031] Step 4: Carry out capacity process technology to complete battery cell preparation.

[0032] Example 2

[0033] This embodiment uses nickel cobalt manganese oxide NCM523 material as the positive electrode and silicon negative electrode material with a specific capacity of 450mAh / g as the negative electrode to assemble into an aluminum shell lithium ion battery with a capacity of 40Ah, and provides the N / P ratio and formation method of the lithium ion battery. The specific steps are as follows:

[0034] Step 1: Battery cell design: Adjust the battery cell N / P ratio to 1.12;

[0035] Step 2: Homogenize, coat, cold press, die-cut, slit, wind, weld, vacuum bake, and inject liquid according to the design;

[0036] Step 3: Then let it stand and then form, control the formation temperature at 45±5℃, vacuum degree at –80±5kpa, the formation process requires two-step charging, the first step is to use a current of 0.04C, charge to a cut-off voltage of 3.4V, and the charging cut-off time is 600min; after charging, let it sit for 15min; the second step is to use a current of 0.2C, charge to a cut-off voltage of 3.75V, and the charging cut-off time is 600min; after charging, let it sit for 15min; the final formation SOC is controlled at 67%.

[0037] Steps Current time Cut-off voltage SOC 1 Charge 0.04C 600min 3.4V 2 Shelf 15min 3 Charge 0.2C 600min 3.75V 4 Shelf 15min 5 Finish 67％

[0038] Step 4: Carry out capacity process technology to complete battery cell preparation.

[0039] Example 3

[0040] This embodiment uses nickel cobalt manganese oxide NCM523 material as the positive electrode and silicon negative electrode material with a specific capacity of 450mAh / g as the negative electrode to assemble into an aluminum shell lithium ion battery with a capacity of 40Ah, and provides the N / P ratio and formation method of the lithium ion battery. The specific steps are as follows:

[0041] Step 1: Cell design: Adjust the cell N / P ratio to 1.08;

[0042] Step 2: Homogenize, coat, cold press, die-cut, slit, wind, weld, vacuum bake, and inject liquid according to the design;

[0043] Step 3: Then let it stand and then form, control the formation temperature at 45±5℃, vacuum degree at –80±5kpa, the formation process requires two-step charging, the first step is to use a current of 0.02C, charge to a cut-off voltage of 3.4V, and the charging cut-off time is 300min; after charging, let it sit for 15min; the second step is to use a current of 0.2C, charge to a cut-off voltage of 3.75V, and the charging cut-off time is 30min; after charging, let it sit for 15min; the final formation SOC is controlled at 20%.

[0044]

[0045]

[0046] Step 4: Carry out capacity process technology to complete battery cell preparation.

[0047] Example 4

[0048] This embodiment uses nickel cobalt manganese oxide NCM523 material as the positive electrode and silicon negative electrode material with a specific capacity of 450mAh / g as the negative electrode to assemble into an aluminum shell lithium ion battery with a capacity of 40Ah, and provides the N / P ratio and formation method of the lithium ion battery. The specific steps are as follows:

[0049] Step 1: Cell design: Adjust the cell N / P ratio to 1.08;

[0050] Step 2: Homogenize, coat, cold press, die-cut, slit, wind, weld, vacuum bake, and inject liquid according to the design;

[0051] Step 3: Then let it stand and then form, control the formation temperature at 45±5℃, vacuum degree at –80±5kpa, the formation process requires two-step charging, the first step is to use a current of 0.04C, charge to a cut-off voltage of 3.4V, and a charging cut-off time of 600min; after charging, let it sit for 15min; the second step is to use a current of 0.2C, charge to a cut-off voltage of 4.35V, and a charging cut-off time of 600min; after charging, let it sit for 15min; finally, the formation SOC is controlled at 100%.

[0052] Steps Current time Cut-off voltage SOC 1 Charge 0.04C 600min 3.4V 2 Shelf 15min 3 Charge 0.2C 600min 4.35V 4 Shelf 15min 5 Finish 100％

[0053] Step 4: Carry out capacity process technology to complete battery cell preparation.

[0054] Example 5

[0055] This embodiment uses nickel cobalt manganese oxide NCM523 material as the positive electrode and silicon negative electrode material with a specific capacity of 450mAh / g as the negative electrode to assemble into an aluminum shell lithium ion battery with a capacity of 40Ah, and provides the N / P ratio and formation method of the lithium ion battery. The specific steps are as follows:

[0056] Step 1: Cell design: Adjust the cell N / P ratio to 1.08;

[0057] Step 2: Homogenize, coat, cold press, die-cut, slit, wind, weld, vacuum bake, and inject liquid according to the design;

[0058] Step 3: Then let it stand and then form, control the formation temperature at 45±5℃, vacuum degree at –80±5kpa, the formation process requires two-step charging, the first step is to use a current of 0.04C, charge to a cut-off voltage of 3.4V, and the charging cut-off time is 600min; after charging, let it sit for 15min; the second step is to use a current of 0.2C, charge to a cut-off voltage of 4.40V, and the charging cut-off time is 600min; after charging, let it sit for 15min; finally, the formation SOC is controlled at 100%.

[0059] Steps Current time Cut-off voltage SOC 1 Charge 0.04C 600min 3.4V 2 Shelf 15min 3 Charge 0.2C 600min 4.40V 4 Shelf 15min 5 Finish 100％

[0060] Step 4: Carry out capacity process technology to complete battery cell preparation.

[0061] The performance test of the silicon negative electrode lithium ion battery prepared above was carried out: the battery cells prepared by controlling the N / P ratio of the battery cells in the above Examples 1-5 and at different formation SOCs and voltages were subjected to the first efficiency test, and the test results are recorded in Table 1.

[0062] Table 1:

[0063] Group Example 1 Example 2 Example 3 Example 4 Example 5 First effect 84.3％ 83.2％ 85.9％ 84.5％ 84.3％

[0064] It can be seen from the above table that the difference between Example 1 and Example 2 is that the N / P ratio of the battery cell is different. The N / P ratio of Example 1 is relatively low, so that the positive electrode has a lower electrode potential, reduces the dissolution of transition metals and the occurrence of side reactions during the charging process of the battery, and improves the initial efficiency of the battery cell.

[0065] The difference between Example 1 and Example 3 is that the first-step formation current of Example 3 is smaller, and the formation SOC is controlled to be lower. It is found that the first efficiency of slow formation at low SOC is significantly improved.

[0066] The difference between Example 1 and Example 4 and Example 5 is that the formation charge cut-off voltage of Example 4 and Example 5 is higher, and the charging SOC is higher. It is found that the first efficiency of the battery cell is hardly improved by using a high SOC and high voltage formation process for deactivation.

[0067] According to the control of the N / P ratio of the battery cell in Examples 1-5 of the present invention, and the comparison of different formation voltages, formation SOCs, etc., it is found that the first effect of slow formation with a lower NP ratio and a low SOC is significantly improved. The present invention controls the N / P ratio of the battery cell so that the positive electrode has a lower electrode potential, reduces the dissolution of transition metals and the occurrence of side reactions during the charging process of the battery, improves the first effect of the battery cell, and simultaneously improves the high-temperature storage and cycle performance of the battery cell. At the same time, by comparing different formation voltages, formation SOCs, etc., it is found that the first effect of the battery cell is almost not improved by using a high SOC and high-voltage formation process for deactivation; the first effect of slow formation with a low SOC is significantly improved. By controlling the N / P ratio of the battery cell and optimizing the formation process at the same time, the first effect of the battery cell can be significantly improved and enhanced.

[0068] It is known from common technical knowledge that the present invention can be implemented by other embodiments that do not deviate from its spirit or essential features. Therefore, the above disclosed embodiments are only illustrative in all respects and are not exclusive. All changes within the scope of the present invention or within the scope equivalent to the present invention are included in the present invention.

Claims

1. A method for preparing a silicon negative electrode lithium ion battery, characterized in that: The following steps are involved: S1. Using nickel cobalt manganese oxide LiNi0.5Co0.2Mn0.3O2 (NCM523) material as the positive electrode active material to prepare the positive electrode sheet of the battery cell; using silicon negative electrode material as the negative electrode active material to prepare the negative electrode sheet of the battery cell; S2, regulating the N / P ratio to 1.04-1.12; S3, adding the nickel cobalt manganese oxide material and the silicon negative electrode material and the required raw materials into a stirrer, stirring at high speed to evenly disperse the components to obtain a homogenate; S4, processing the homogenate obtained in step S3 to form a battery cell; S5. The battery cell obtained in step S4 is heated, filled with liquid, allowed to stand, and charged and discharged in sequence to obtain a silicon negative electrode lithium-ion battery.

2. The method for preparing a silicon negative electrode lithium ion battery according to claim 1, characterized in that: The silicon negative electrode lithium ion battery obtained in step S5 is subjected to multiple charging tests until the silicon negative electrode lithium ion battery meets the predetermined design requirements.

3. The method for preparing a silicon negative electrode lithium ion battery according to claim 1, characterized in that: The specific steps of the processing in step S4 are: S41, coating operation: coating the slurry on the current collector to form a uniform coating, and sending the coated current collector into an oven for drying and curing to obtain a pole piece; S42, cold pressing operation: placing the electrode into a cold press for pressing; S43, die-cutting and striping operation: according to the design requirements, the cold-pressed electrode is cut into the required shape and size, and the electrode is cut into multiple narrow strips; S44, winding operation: Wind the cut positive electrode sheet, negative electrode sheet and separator together in a certain order to form a battery cell.

4. The method for preparing a silicon negative electrode lithium ion battery according to claim 1, characterized in that: The specific steps of the charge and discharge process in step S5 are: S51, first use 0.02-0.05C current, charge to the cut-off voltage of 3.0-3.5V, and leave it for 5-15 minutes; S52, then use a current of 0.1-0.2C to charge to a cut-off voltage of 3.7-4.4V, and leave it for 5-15 minutes; finally, the SOC is controlled at 20-100%.

5. The method for preparing a silicon negative electrode lithium ion battery according to claim 1, characterized in that: The specific capacity of the silicon negative electrode material in step S1 is 450 mAh / g.

6. The method for preparing a silicon negative electrode lithium ion battery according to claim 1, characterized in that: The capacity of the silicon negative electrode lithium ion battery is 40Ah, and its shell material is aluminum.

7. A silicon negative electrode lithium ion battery, characterized in that: The battery is prepared by the method for preparing a silicon negative electrode lithium ion battery according to any one of claims 1 to 6.

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