A method for determining and controlling the pre-lithium amount of a negative electrode lithium replenishment electrode sheet

Abstract

The present invention discloses a method for determining and controlling the pre-lithium amount of a negative electrode lithium replenishment pole piece, and the method can be used to accurately determine the lithium replenishment capacity and control the lithium replenishment amount. The method is to pre-de-lithiate the lithium replenishment pole piece through a small current to obtain the active lithium content that can be deintercalated in the pole piece, and then charge and discharge the pole piece at a small rate to obtain the first coulomb efficiency of the lithium replenishment negative electrode, and calculate the effective lithium amount consumed by the lithium replenishment pole piece to form the SEI film through the first coulomb efficiency of the non-lithium replenishment pole piece. After determining the lithium replenishment efficiency, the surface density of the lithium foil required for the whole battery is calculated, and the surface density of the metal lithium foil is controlled by mechanically punching holes in the lithium foil, so as to accurately replenish the lithium for the whole battery. Through this method, the positive electrode capacity can be fully utilized without excessive lithium replenishment, thereby improving the energy density of the battery.

Description

Technical Field

[0001] The present invention belongs to the field of lithium-ion batteries, and in particular relates to a method for determining and controlling the pre-lithium amount of a negative electrode lithium replenishing pole piece. Background Art

[0002] To meet the needs of long-range power batteries and large-scale energy storage batteries, the new generation of lithium-ion batteries requires higher weight energy density and volume energy density. However, during the first lithium insertion process of the negative electrode active material, the electrolyte will undergo a reduction reaction on the particle surface to form a solid electrolyte interface (SEI), thereby consuming the positive electrode active lithium, affecting the gram capacity of the positive electrode active material, and reducing the energy density of the battery.

[0003] In order to compensate for the loss of irreversible active lithium, the most promising industrial method is to use metal lithium powder / lithium foil or lithium source sputtering to achieve direct lithium replenishment on the negative electrode sheet. However, one of the technical difficulties in the lithium replenishment process is the determination of the amount of lithium replenishment. Metal lithium is a highly chemically active substance that will react chemically with O2, H2O, N2 in the air and electrolyte, making it difficult to determine the amount of lithium replenishment, and at the same time having a negative impact on the efficiency of lithium replenishment. Chinese patent CN 112993213 A discloses a method for calculating the negative electrode pre-lithiation lithium replenishment capacity and its application. The method uses the difference between the first lithium insertion capacity and the lithium removal capacity of the negative electrode minus the difference between the first lithium removal capacity and the lithium insertion capacity of the positive electrode as the lithium replenishment capacity, and then calculates the amount of metal lithium required to be loaded on the negative electrode sheet based on the theoretical specific capacity of metal lithium of 3860mAh / g. This method does not take into account the oxidation reaction of metal lithium during the pre-lithiation process, and the actual gram capacity of the lithium replenishment material will be less than 3860mAh / g, resulting in insufficient lithium replenishment capacity. Chinese patent CN112067672 A discloses a method for testing the specific capacity of pre-lithiation lithium powder and its application. The method uses the method of making metal lithium powder into a slurry to test the actual delithiation capacity to obtain the actual gram capacity of the lithium supplement material. However, it does not take into account that after the negative electrode active material is added, a SEI film will be formed on the surface of the active material, thereby consuming the active capacity in the lithium supplement material, so that the actual gram capacity will be low.

[0004] At present, the estimation of the pre-lithiation amount of negative electrode plates includes gas production and drainage method, potentiometric titration method and electrochemical method. Among them, gas production and drainage method is only applicable to graphite negative electrode. When the active material contains silicon, silicon reacts with water to generate hydrogen, which will cause interference. The potentiometric titration method can determine the Li element content through acid-base titration, but cannot determine the metal lithium content. The electrochemical method can accurately determine the amount of lithium replenishment and the efficiency of lithium replenishment by deintercalating and inserting lithium in the lithium replenishment plate, which is the preferred solution. Summary of the invention

[0005] In view of the problem that it is difficult to determine the amount of lithium replenishment in existing lithium replenishment technologies, the purpose of the present invention is to provide a method for determining and controlling the pre-lithium amount of a negative electrode lithium replenishment electrode plate, develop a method for calculating the effective lithium replenishment capacity of a pre-lithiated negative electrode, and accurately calculate the lithium replenishment efficiency of the negative electrode after lithium replenishment.

[0006] The technical solution adopted by the present invention is as follows:

[0007] A method for determining and controlling the pre-lithium amount of a negative electrode lithium replenishment electrode sheet comprises the following steps:

[0008] S1. Test the first lithium deintercalation capacity of the unreplenished negative electrode and calculate the first lithium intercalation capacity C 负1 and the first lithium removal capacity C 负2 , the first coulombic efficiency of the unsupplemented negative electrode was obtained

[0009] S2, using negative electrode lithium supplement material metal lithium foil / lithium powder or lithium source sputtering to transfer metal lithium to the negative electrode sheet, at this time the corresponding capacity of the metal lithium is C0, to obtain a lithium supplement negative electrode sheet;

[0010] S3, immersing the lithium-supplemented negative electrode sheet in the electrolyte and leaving it to stand for a certain period of time;

[0011] S4, assemble the lithium-supplemented negative electrode sheet into a button or soft-pack half-battery, and charge the battery with a small current to obtain the initial lithium removal capacity C of the lithium-supplemented negative electrode sheet. 补锂0 , and then charge and discharge in the same way as in S1, and calculate the first lithium insertion capacity C 补锂1 and secondary lithium removal capacity C 补锂2 ;

[0012] S5. The effective lithium replenishment of the lithium replenishment negative electrode plate consists of two parts. One part is the active lithium capacity C that can be removed for the first time. 补锂0 ; Part of it is the amount of lithium consumed when the metal lithium and the negative electrode active material form SEI in advance after the electrode is injected. SEI That is, the active lithium capacity required by the electrode before lithium supplementation is the first lithium removal capacity divided by the first coulomb efficiency, C SEI =C 补锂2 / η1-C 补锂1 , the effective lithium replenishment capacity is: C 有效补锂 =C 补锂0 +C 补锂2 / η1-C 补锂1 ; Thus, the actual gram capacity of the lithium supplement material is obtained: C'=C 有效补锂 / m, m is the mass of lithium supplement;

[0013] S6. Test the first lithium removal capacity C of the positive electrode 正1 and lithium insertion capacity C 正2 , thus the accurate lithium supplement surface density is obtained as: Where S is the pole piece area;

[0014] S7. If the required lithium supplement amount is low, pores are formed on the lithium foil, and the pore forming rate is Among them, M0 is the surface density of 5um-1mm thick lithium foil. In order to ensure the uniformity of lithium replenishment, the spacing between holes should be consistent and the pore diameter should be moderate.

[0015] The present invention can accurately calculate the actual gram capacity of the lithium supplement material in the battery through an electrochemical method, and can effectively improve the lithium supplement efficiency of the lithium supplement material by controlling the electrolyte immersion time; by changing the assembly method of the button half-cell, the lithium supplement negative electrode sheet is preferentially immersed in the electrolyte for a certain time, which can greatly reduce the gas production in the button battery, thereby improving the yield rate of the button battery. The actual gram capacity of the lithium supplement material can accurately determine the lithium supplement mass required for the battery, realize the full use of the gram capacity of the positive electrode active material, and greatly improve the energy density of the battery.

[0016] Preferably, the negative electrode lithium supplementation can be lithium supplementation by metal lithium foil, lithium supplementation by metal lithium powder, lithium supplementation by lithium alloy, or lithium supplementation by magnetron sputtering.

[0017] Preferably, the thickness of the lithium supplement is 0.1 um to 50 um.

[0018] Preferably, the negative electrode active material includes at least one of graphite, graphite-based negative electrode materials, silicon-based materials, silicon, silicon-carbon composite materials, tin-based materials, metal oxides, lithium titanate, and the like.

[0019] Preferably, in S3, the immersion time of the lithium-supplemented negative electrode sheet in the electrolyte is 10 minutes to 24 hours. To ensure that the gas production of the lithium-supplemented negative electrode sheet is completed and lithium loss is reduced, the immersion time is further preferably 2 to 4 hours.

[0020] Preferably, the delithiation current density in S4 is 0.01C-0.5C. To reduce the reaction time between the metallic lithium and the electrolyte, the delithiation current density is further preferably 0.1C-0.2C.

[0021] Preferably, the positive electrode material in S6 includes one of lithium iron phosphate, lithium manganese oxide, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, and a ternary positive electrode, or a modified material thereof.

[0022] Preferably, the punching method in S7 includes one or more of mechanical punching and laser punching. The shape of the hole can be one or more of a circle, a square, a rectangle, a diamond, a triangle, and a hexagon. The hole area can be 0.1um. 2 -1cm 2 .

[0023] The beneficial effects of the present invention are:

[0024] The method of the present invention can accurately determine the lithium replenishment capacity and control the amount of lithium replenishment. The method is to pre-de-lithiate the lithium replenishment electrode through a small current to obtain the active lithium content that can be deintercalated in the electrode, and then charge and discharge the electrode at a small rate to obtain the first coulomb efficiency of the lithium replenishment negative electrode, and calculate the effective lithium amount consumed by the lithium replenishment electrode to form the SEI film through the first coulomb efficiency of the unreplenished lithium electrode. After determining the lithium replenishment efficiency, the surface density of the lithium foil required for the whole battery is calculated, and the surface density of the metal lithium foil is controlled by mechanically punching holes in the lithium foil, so as to accurately replenish the lithium for the whole battery. Through this method, the positive electrode capacity can be fully utilized without excessive lithium replenishment, thereby improving the energy density of the battery. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The lithium foil with porosity in Example 9 of the present invention;

[0026] Figure 2 The lithium foil with porosity in Example 10 of the present invention;

[0027] Figure 3 It is the lithium foil with porosity in Example 11 of the present invention. DETAILED DESCRIPTION

[0028] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings and embodiments. The specific embodiments described here are only used to explain the technical solution of the present invention and are not limited to the present invention.

[0029] Example 1

[0030] A method for determining and controlling the pre-lithium amount of a negative electrode lithium replenishment electrode sheet, the specific steps are as follows:

[0031] S1. Mix active material SiOx, artificial graphite, polyacrylic acid binder (PAA), single-arm carbon nanotubes and conductive carbon black in a ratio of 55:35:7:0.4:2.6. Coat the prepared slurry on a 10um copper foil, dry it in an oven at 110°C, roll the electrode to a compaction density of 1.6g / cc, and punch it into 1.5cm diameter discs for standby use.

[0032] S2. Assemble CR2032 button cells in a glove box, use the metal lithium sheet as the counter electrode, use a 1 mol / L LiPF6 electrolyte system as the electrolyte, and use an EC:EMC:DEC=1:1:1 solvent.

[0033] S3. After injection, the battery was left to stand for 4 hours, charged at a constant current of 0.1C to a cut-off voltage of 0.05V, and then discharged at a constant current of 0.1C to 1.5V. The first discharge capacity was 7.81mAh, the first charge capacity was 6.23mAh, and the first coulombic efficiency was 79.8%.

[0034] S4, the thickness is 5um, the surface density is 2.70g / m 2 The metal lithium foil is transferred to the negative electrode sheet in S1 by roller pressing at a pressure of 0.2Mpa. The whole process is carried out with the ambient dew point kept below -40℃ or completed in an inert atmosphere.

[0035] S5. Punch out the lithium-supplemented electrode and immerse it in the electrolyte used in S2. Let it stand for 2 hours for later use.

[0036] S6. Assemble the lithium-supplemented electrodes into button batteries in a glove box, following the same steps as S2.

[0037] S7, the button battery assembled with lithium supplemented electrode is first charged to 1.5V at 0.1C times to obtain the reversible active lithium capacity C 补锂0 =1.01mAh, and then discharge to 0.05V at 0.1C rate, and get the first discharge capacity C 补锂1 =7.16mAh, then charge to 1.5V at 0.1C rate, get the first charge capacity C 补锂2 =6.25mAh, according to the formula: C 有效补锂 =C 补锂0 +C 补锂2 / η1-C 补锂1 , and get C 有效补锂 =1.68 mAh. The surface density of a 5 um thick lithium foil is 2.70 mg / cm 2 Therefore, the effective gram capacity of the lithium supplement material is 3559.3 mAh / g.

[0038] Example 2

[0039] The standing time in the electrolyte in step S5 of Example 1 was increased to 4 hours, and the other steps remained unchanged. The effective gram capacity of the lithium supplement material was calculated to be 3021.5 mAh / g.

[0040] Example 3

[0041] The standing time in the electrolyte in step S5 of Example 1 was increased to 8 hours, and the other steps remained unchanged. The effective gram capacity of the lithium supplement material was calculated to be 2673.4 mAh / g.

[0042] Example 4

[0043] The standing time in the electrolyte in step S5 of Example 1 was increased to 12 hours, and the other steps remained unchanged. The effective gram capacity of the lithium supplement material was calculated to be 2280.1 mAh / g.

[0044] Example 5

[0045] The standing time in the electrolyte in step S5 of Example 1 was increased to 24 hours, and the other steps remained unchanged. The effective gram capacity of the lithium supplement material was calculated to be 2056.8 mAh / g.

[0046] Example 6

[0047] The standing time in the electrolyte in step S5 of Example 1 was increased to 48 hours, and the other steps remained unchanged. The effective gram capacity of the lithium supplement material was calculated to be 1422.7 mAh / g.

[0048] Example 7

[0049] The standing time in the electrolyte in step S5 of Example 1 was increased to 72 hours, and the other steps remained unchanged. The effective gram capacity of the lithium supplement material was calculated to be 1420.9 mAh / g.

[0050] Example 8

[0051] The standing time in the electrolyte in step S5 of Example 1 was increased to 0.5 hours, and the other steps remained unchanged, and the prepared button battery failed.

[0052] The actual lithium replenishment gram capacity of the lithium replenishment material can be obtained by changing the infiltration time of the electrolyte of Examples 1-8 on the electrode. The results are shown in Table 1.

[0053] Table 1

[0054]

[0055]

[0056] It can be seen from Examples 1-8 that the actual gram capacity of the lithium replenishing material is related to the electrolyte immersion time. If the immersion time is too short, the button battery will fail directly, and if the immersion time is too long, the lithium replenishment efficiency will be reduced. Therefore, according to the effective lithium replenishment value of the battery at different aging times, the lithium replenishment of the whole battery can be accurately calculated.

[0057] Example 9

[0058] A lithium-ion full battery, including a positive electrode, a separator, a lithium-supplemented negative electrode, and an electrolyte, wherein the electrolyte immersion time is 4 hours, and the full battery is packaged with an aluminum-plastic film. The specific steps are as follows:

[0059] S1. Preparation of positive electrode sheet. LiCoO2, PVDF and CNT were dissolved in NMP solvent at a ratio of 98:1:1 and mixed evenly. The slurry was coated on 12um aluminum foil with a surface density of 196.7g / m 2 , dry and set aside.

[0060] S2. Make the positive electrode into a button half-battery and measure the first charge capacity C at a 0.1C rate. 正1 : 5.85mAh, first discharge capacity C 正2 : 5.56mAh.

[0061] S3, the negative electrode sheet is the negative electrode sheet in Example 1, and the first discharge capacity C is obtained. 负1 : 7.81mAh, first charge capacity C 负2 : 6.23mAh.

[0062] S4. Substitute the actual gram capacity C' of the lithium supplement material in Example 1: 3559.3 mAh / g into the formula The lithium supplement surface density M is 2.05 g / m 2 .

[0063] S5, the die-cutting size of the negative electrode is 58mm*45mm, and the die-cutting size of the positive electrode is 57mm*44mm.

[0064] S6. According to the formula, the pore formation rate of lithium foil with a thickness of 5um is calculated to be ε=24%. A circular punching needle with a radius of 3mm is selected to make 20 holes at equal distances on the metal lithium foil of the same size as the negative electrode sheet. Figure 1 , and then the pore-formed metal lithium foil is transferred to the negative electrode sheet by roller pressing to obtain a lithium-supplemented electrode sheet.

[0065] S7. Assemble the positive electrode, lithium-supplemented negative electrode and separator into a lithium-ion battery through a stacked battery manufacturing process, and obtain a negative electrode pre-lithiation lithium-ion battery after baking, liquid injection, standing for 4 hours and 0.1C formation.

[0066] Example 10

[0067] Different from Example 9, a circular hole needle with a radius of 4 mm was used to make 12 holes at equal distances on the metal lithium foil of the same size as the negative electrode sheet. Figure 2 , the remaining steps are the same as those in Example 9.

[0068] Embodiment 11

[0069] Different from Example 9, a circular hole needle with a radius of 2 mm was used to make 48 holes at equal distances on a metal lithium foil of the same size as the negative electrode sheet. Figure 3 , the remaining steps are the same as those in Example 9.

[0070] Comparative Example 1

[0071] Different from Example 9, the electrode is not supplemented with lithium, and the remaining steps are the same as Example 9.

[0072] The above-mentioned Examples 9-11 and Comparative Example 1 were subjected to capacity determination under the same conditions, and the performance of the positive electrode gram capacity is shown in Table 2.

[0073] Table 2

[0074]

[0075] The above only expresses the preferred embodiments of the present invention, and the description is relatively specific and detailed, but it cannot be understood as limiting the scope of the patent of the present invention. It should be pointed out that for ordinary technicians in this field, several modifications, improvements and substitutions can be made without departing from the concept of the present invention, which all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be based on the attached claims.

Claims

1. A method for determining and controlling the pre-lithium amount of a negative electrode lithium replenishment electrode sheet, characterized in that: The following steps are involved: S1. Test the first lithium deintercalation capacity of the unreplenished negative electrode and calculate the first lithium intercalation capacity C 负1 and the first lithium removal capacity C 负2 , the first coulombic efficiency of the unsupplemented negative electrode was obtained S2, using negative electrode lithium supplement material metal lithium foil / lithium powder or lithium source sputtering to transfer metal lithium to the negative electrode sheet, at this time the corresponding capacity of the metal lithium is C0, to obtain a lithium supplement negative electrode sheet; S3, immersing the lithium-supplemented negative electrode sheet in the electrolyte and leaving it to stand for a certain period of time; S4, assemble the lithium-supplemented negative electrode sheet into a button or soft-pack half-battery, charge the battery with a small current, and obtain the initial lithium removal capacity C of the lithium-supplemented negative electrode sheet. 补锂0 , and then charge and discharge in the same way as in S1, and calculate the first lithium insertion capacity C 补锂1 and secondary lithium removal capacity C 补锂2 ; S5. The effective lithium replenishment of the lithium replenishment negative electrode plate consists of two parts. One part is the active lithium capacity C that can be removed for the first time. 补锂0 ; Part of it is the amount of lithium consumed when the metal lithium and the negative electrode active material form SEI in advance after the electrode is injected. SEI That is, the active lithium capacity required by the electrode before lithium supplementation is the first lithium removal capacity divided by the first coulomb efficiency, C SEI =C 补锂2 / η1-C 补锂1 , the effective lithium replenishment capacity is: C 有效补锂 =C 补锂0 +C 补锂2 / η1-C 补锂1 ; Thus, the actual gram capacity of the lithium supplement material is obtained: C′=C 有效补锂 / m, m is the mass of lithium supplement; S6. Test the first lithium removal capacity C of the positive electrode 正1 and lithium insertion capacity C 正2 , thus the accurate lithium supplement surface density is obtained as: Where S is the pole piece area; S7. If the required lithium supplement amount is low, pores are made on the lithium foil, and the pore making rate is Among them, M0 is the surface density of 5um-1mm thick lithium foil. In order to ensure the uniformity of lithium replenishment, the spacing between holes should be consistent and the pore size should be moderate.

2. A method for determining and controlling the amount of lithium in a negative electrode lithium replenishment electrode sheet according to claim 1, characterized in that: The negative electrode lithium replenishment is one of metal lithium foil lithium replenishment, metal lithium powder lithium replenishment, lithium alloy lithium replenishment, and magnetron sputtering lithium replenishment.

3. A method for determining and controlling the amount of lithium in a negative electrode lithium replenishment electrode sheet according to claim 1, characterized in that: The thickness of lithium supplement is 0.1um~50um.

4. A method for determining and controlling the pre-lithium amount of a negative electrode lithium replenishment electrode sheet according to claim 1, characterized in that: The negative electrode active material includes at least one of graphite, graphite-based negative electrode materials, silicon-based materials, silicon, silicon-carbon composite materials, tin-based materials, metal oxides, and lithium titanate.

5. The method for determining and controlling the pre-lithium amount of a negative electrode lithium replenishment electrode sheet according to claim 1, characterized in that: In S3, the lithium-supplemented negative electrode sheet is immersed in the electrolyte for 10 minutes to 24 hours.

6. A method for determining and controlling the pre-lithium amount of a negative electrode lithium replenishment electrode sheet according to claim 1, characterized in that: The delithiation current density in S4 is 0.01C~0.5C.

7. The method for determining and controlling the pre-lithium amount of a negative electrode lithium replenishment electrode sheet according to claim 1, characterized in that: The positive electrode material in S6 includes one of lithium iron phosphate, lithium manganese oxide, lithium manganese iron phosphate, lithium cobalt oxide, lithium nickel oxide, and a ternary positive electrode or a modified material thereof.

8. The method for determining and controlling the pre-lithium amount of a negative electrode lithium replenishment electrode sheet according to claim 1, characterized in that: The punching methods in S7 include one or more of mechanical punching and laser punching. The hole shape is one or more of circular, rectangular, diamond, triangular, and hexagonal. The hole area is 0.1um 2 -1cm 2 .

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