Calculation method for metal lithium utilization rate of pre-lithiated negative plate

Abstract

The invention provides a method for calculating the metal lithium utilization rate of a pre-lithiated negative plate, and relates to the technical field of batteries, the method comprises the following steps: S1, punching a negative plate into a wafer with the area of S, assembling the wafer and a metal lithium plate into a button battery 1, and testing the first lithium embedding capacity of the negative plate as C1mAh and the first lithium removing capacity as C2mAh; s2, performing pre-lithiation on the same group of negative plates in the S1, soaking the negative plates in an electrolyte, punching the negative plates into wafers with the area of S, assembling the wafers with metal lithium plates to form a button battery 2, firstly testing the lithium removal capacity of the negative plates as C3mAh, then testing the lithium insertion capacity as C4mAh, and finally testing the secondary lithium removal capacity as C5mAh; s3, the pre-lithiation degree beta = metal lithium effective capacity / negative electrode capacity, and a negative electrode material comprises one or a combination of more of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbon, silica, lithium titanate and the like, through the detection method, the pre-lithiation degree of the pole piece can be accurately detected, and effective data support is provided for cell design.

Description

Technical Field

[0001] The present invention relates to the field of batteries, and in particular to a method for calculating the utilization rate of metallic lithium in a pre-lithium negative electrode sheet. Background Art

[0002] In recent years, the rapid development of portable electronic products, new energy vehicles, smart grids, distributed energy storage, and the Internet of Things has continuously put forward higher requirements for the performance of lithium-ion batteries, among which the improvement of battery cycle performance and energy density is the most urgent. During the formation process of lithium-ion batteries, lithium ions generate SEI films on the surface of the negative electrode, consuming active lithium, resulting in battery capacity loss. By introducing lithium ions in advance, active lithium can be compensated to achieve the effect of improving the energy density of lithium-ion batteries. The irreversible capacity loss of the most widely used graphite negative electrode is greater than 6%, while for silicon-based negative electrodes with high gram capacity, the irreversible capacity loss is even as high as 10% to 20%. The introduction of lithium ions in advance can improve the shortcomings of low first efficiency, give full play to its high capacity advantages, further improve battery cycle performance and energy density, and greatly promote the development of lithium-ion batteries.

[0003] Since metal lithium has a high gram capacity (3860mAh / g) and will not introduce other substances, it is the most ideal material for replenishing lithium ions, including metal lithium powder, metal lithium foil, metal lithium bar, metal lithium block, etc. At present, the more mature technology is to add a layer of metal lithium to the negative electrode through calendering and vacuum evaporation process. However, part of the supplemented metal lithium will be oxidized in the air, and will have side reactions with the electrolyte, causing failure; the other part will have a self-short-circuit lithium insertion reaction with graphite during the injection stage, and at the same time generate SEI film and lithium insertion reaction, which can improve the performance of lithium-ion batteries.

[0004] The utilization rate of metal lithium is very important for battery design. Excessive pre-lithium will cause lithium deposition in the battery, generate lithium dendrites, and cause rapid battery performance degradation and safety hazards. If the pre-lithium amount is too low, the effect will not be significantly improved. Therefore, determining the utilization rate of metal lithium on the negative electrode is important for battery pre-lithiation. Summary of the invention

[0005] The purpose of the present invention is to provide a method for calculating the utilization rate of metal lithium in a pre-lithium negative electrode sheet to solve the above technical problems. To achieve this purpose, the present invention adopts the following technical solutions: A method for calculating the utilization rate of metallic lithium in a pre-lithium negative electrode sheet comprises the following steps: S1, take the negative electrode sheet and punch it into a disc with an area of ​​S, assemble it with a metal lithium sheet into a button battery 1, and test the negative electrode sheet's first lithium insertion capacity to be C1mAh, and the first lithium removal capacity to be C2mAh; S2, take the negative electrode sheets of the same group in S1, perform pre-lithiation, soak in electrolyte, and then punch and cut into discs with an area of ​​S and assemble with metal lithium sheets to buckle 2. First test the negative electrode sheet lithium removal capacity of C3mAh, then test the lithium insertion capacity of C4mAh, and finally test the lithium removal capacity of C5mAh; S3. Pre-lithiation degree β = effective capacity of metallic lithium / negative electrode capacity.

[0006] A further preferred solution: in step S1, the negative electrode material includes one or more combinations of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbon, silicon oxygen, lithium titanate, etc.

[0007] A further preferred embodiment: in step S1, C1 is the total capacity of lithium ions first embedded in the negative electrode material and forming the SEI film, with a current of 0.05-1.0C; C2 is the capacity of lithium ions released, with a current of 0.05-1.0C, and C1-C2 is the capacity of lithium ions in the negative electrode that is not pre-lithiated to form the SEI film.

[0008] A further preferred embodiment: in step S2, the pre-lithiation method includes one or a combination of two of calendering chemical pre-lithiation, electrochemical pre-lithiation, and metal lithium contact pre-lithiation; The metal lithium contact pre-lithiation includes two processes: evaporation and rolling. The metal lithium is a combination of one or more of lithium foil, lithium belt, lithium bar, lithium block, perforated lithium foil, lithium alloy, etc.

[0009] A further preferred embodiment: in step S2, the electrolyte is immersed for 0.5-6 hours.

[0010] A further preferred solution: In the step S2, during the electrolyte immersion stage, the metallic lithium is divided into three parts: S21. Side reactions occur with the electrolyte; S22 is embedded in graphite to generate LiXC compound, and this part of the capacity is C3; S23. Generate SEI film, the capacity of this part is (C1-C2)-(C4-C5).

[0011] A further preferred embodiment: in step S3, the effective capacity of metallic lithium = C3 + [(C1-C2)-(C4-C5)], and the negative electrode capacity = C2.

[0012] A further preferred embodiment: in step S3, the pre-lithiation degree β of the negative electrode is 1%-100%.

[0013] Beneficial effects of the present invention: Figure 1It can be seen that if the pre-lithiation degree is too low, the performance of the battery cell will not be significantly improved; if the pre-lithiation degree of the battery cell is excessive, lithium will be deposited in the battery cell, resulting in deterioration of the battery cell cycle and a drop in battery performance. Only when the pre-lithiation degree of the electrode is within a reasonable range can the performance of the battery cell be effectively improved. The detection method of the present invention can accurately detect the pre-lithiation degree of the electrode, providing effective data support for battery cell design. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 is a process flow chart of the present invention; Figure 2 This is a test performance table of the power-on 1-5 embodiments of the present invention; Figure 3 Graph showing the cycle performance of battery cells 1-5 according to embodiments of the present invention. DETAILED DESCRIPTION

[0015] See also Figure 1-Figure 3 , a method for calculating the utilization rate of metal lithium in a pre-lithium negative electrode sheet, comprising the following steps: S1, take the negative electrode sheet and punch it into a disc with an area of ​​S, assemble it with a metal lithium sheet into a button battery 1, and test the negative electrode sheet's first lithium insertion capacity to be C1mAh, and the first lithium removal capacity to be C2mAh; Preferably, the negative electrode material includes one or more combinations of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbon, silicon oxygen, lithium titanate, etc.; C1 is the total capacity of lithium ions first embedded in the negative electrode material and forming the SEI film, and the current size is 0.05-1.0C; C2 is the released lithium ion capacity, the current size is 0.05-1.0C, and C1-C2 is the lithium ion capacity of the SEI film generated by the negative electrode without pre-lithiation.

[0016] S2, take the negative electrode sheets of the same group in S1, perform pre-lithiation, soak in electrolyte, and then punch and cut into discs with an area of ​​S and assemble with metal lithium sheets to buckle 2. First test the negative electrode sheet lithium removal capacity of C3mAh, then test the lithium insertion capacity of C4mAh, and finally test the lithium removal capacity of C5mAh; The pre-lithiation method includes one or a combination of two of calendering chemical pre-lithiation, electrochemical pre-lithiation, and metal lithium contact pre-lithiation; The metal lithium contact pre-lithiation process includes two processes: evaporation and rolling. The metal lithium is a combination of one or more of lithium foil, lithium ribbon, lithium bar, lithium block, lithium foil with holes, lithium alloy, etc. Wherein, the electrolyte soaking time is 0.5-6h; Furthermore, during the electrolyte immersion stage, metallic lithium will be divided into three parts: S21. Side reactions occur with the electrolyte; S22 is embedded in graphite to generate LiXC compound, and this part of the capacity is C3; S23. Generate SEI film, the capacity of this part is (C1-C2)-(C4-C5).

[0017] S3, pre-lithiation degree β = effective capacity of metal lithium / negative electrode capacity; The effective capacity of lithium metal = C3 + [(C1-C2)-(C4-C5)], the negative electrode capacity = C2; The degree of pre-lithiation of the negative electrode β is 1%-100%.

[0018] Example 1, preparation of negative electrode sheet: S1. Prepare a negative electrode sheet 1 by taking graphite: binder: dispersant: conductive agent according to a formula of 95%:3.1%:0.4%:1.5%; S2. Take the negative electrode sheet 1, and the punching area is 1.534cm 2 The disc and the metal lithium sheet are assembled into a button battery 1, the button battery discharge capacity is 7.581mAh, and the button battery charge capacity is 6.576mAh; S3. Take the negative electrode 1, roll and coat it with 2um lithium to prepare the pre-lithiated electrode 2, soak it in electrolyte for 2h, and punch out the area of ​​1.534cm 2 The wafer and the metal lithium sheet are assembled into a button battery 2. The first charging capacity of the button battery is 0.807mAh, the first discharging capacity is 7.315mAh, and the second charging capacity is 6.189mAh.

[0019] S4. Take the negative electrode 1, roll and coat it with 3um lithium to prepare the pre-lithiated electrode 3, soak it in electrolyte for 2h, and punch out the area of ​​1.534cm 2 The wafer and the metal lithium sheet are assembled into a button battery 3. The first charging capacity of the button battery is 0.987mAh, the first discharging capacity is 7.198mAh, and the second charging capacity is 6.378mAh.

[0020] S5. Take the negative electrode 1, roll and coat it with 4um lithium to prepare the pre-lithiated electrode 4, soak it in electrolyte for 2h, and punch out the area of ​​1.534cm 2 The disc and the metal lithium sheet are assembled into a button battery 4. The first charging capacity of the button battery is 1.142mAh, the first discharging capacity is 7.026mAh, and the second charging capacity is 6.550mAh.

[0021] S6. Take the negative electrode 1, roll and coat it with 5um lithium to prepare the pre-lithiated electrode 5, soak it in electrolyte for 2h, and punch out the area of ​​1.534cm 2 The disc and the metal lithium sheet are assembled into a button battery 5. The first charging capacity of the button battery is 1.687mAh, the first discharging capacity is 6.525mAh, and the second charging capacity is 6.531mAh.

[0022] S7. Take negative electrode sheet 1, negative electrode sheet 2, negative electrode sheet 3, negative electrode sheet 4, and negative electrode sheet 5 and match them with the lithium iron phosphate positive electrode sheet, respectively, to prepare soft-pack batteries named battery cell 1, battery cell 2, battery cell 3, battery cell 4, and battery cell 5, and perform cycle testing; The button battery and the battery cell of the above embodiment 1 were tested and analyzed, and the results are shown in Table 1 and Figure 1 As shown in Table 1, the degree of pre-lithiation can be accurately calculated by the method of the present application. From the data, it can be calculated that as the thickness of the lithium-filled rolled sheet increases, the degree of pre-lithiation also increases from 10.4% to 41.0%; Figure 1 It can be seen that if the pre-lithiation degree is too low, the performance of the battery cell will not be significantly improved; if the pre-lithiation degree of the battery cell is excessive, lithium will be deposited in the battery cell, resulting in deterioration of the battery cell cycle and a drop in battery performance. Only when the pre-lithiation degree of the electrode is within a reasonable range can the performance of the battery cell be effectively improved. The detection method of the present invention can accurately detect the pre-lithiation degree of the electrode, providing effective data support for battery cell design.

Claims

1. A method for calculating the utilization rate of metallic lithium in a pre-lithium negative electrode sheet, characterized in that: The following steps are involved: S1, take the negative electrode sheet and punch it into a disc with an area of ​​S, assemble it with a metal lithium sheet into a button battery 1, and test the negative electrode sheet's first lithium insertion capacity to be C1mAh, and the first lithium removal capacity to be C2mAh; S2, take the negative electrode sheets of the same group in S1, perform pre-lithiation, soak in electrolyte, and then punch and cut into discs with an area of ​​S and assemble with metal lithium sheets to buckle 2. First test the negative electrode sheet lithium removal capacity of C3mAh, then test the lithium insertion capacity of C4mAh, and finally test the lithium removal capacity of C5mAh; S3. Pre-lithiation degree β = effective capacity of metallic lithium / negative electrode capacity.

2. The method for calculating the utilization rate of metal lithium in a pre-lithium negative electrode sheet according to claim 1, characterized in that: In the step S1, the negative electrode material includes one or more combinations of artificial graphite, natural graphite, soft carbon, hard carbon, silicon carbon, silicon oxygen, lithium titanate, etc.

3. The method for calculating the utilization rate of metal lithium in a pre-lithium negative electrode sheet according to claim 1, characterized in that: In step S1, C1 is the total capacity of lithium ions first embedded in the negative electrode material and forming the SEI film, and the current size is 0.05-1.0C; C2 is the capacity of lithium ions released, and the current size is 0.05-1.0C, and C1-C2 is the capacity of lithium ions in the negative electrode that is not pre-lithiated to form the SEI film.

4. The method for calculating the utilization rate of metal lithium in a pre-lithium negative electrode sheet according to claim 1, characterized in that: In step S2, the pre-lithiation method includes one or a combination of two of calendering chemical pre-lithiation, electrochemical pre-lithiation, and metal lithium contact pre-lithiation; The metal lithium contact pre-lithiation includes two processes: evaporation and rolling. The metal lithium is a combination of one or more of lithium foil, lithium belt, lithium bar, lithium block, perforated lithium foil, lithium alloy, etc.

5. The method for calculating the utilization rate of metal lithium in a pre-lithium negative electrode sheet according to claim 1, characterized in that: In step S2, the electrolyte is immersed for 0.5-6 hours.

6. The method for calculating the utilization rate of metal lithium in a pre-lithium negative electrode sheet according to claim 1, characterized in that: In step S2, during the electrolyte soaking stage, the metallic lithium is divided into three parts: S21. Side reactions with the electrolyte; S22 is embedded in graphite to generate LiXC compound, and this part of the capacity is C3; S23. Generate SEI film, the capacity of this part is (C1-C2)-(C4-C5).

7. The method for calculating the utilization rate of metal lithium in a pre-lithium negative electrode sheet according to claim 6, characterized in that: In step S3, the effective capacity of metallic lithium = C3 + [(C1-C2)-(C4-C5)], and the negative electrode capacity = C2.

8. The method for calculating the utilization rate of metal lithium in a pre-lithium negative electrode sheet according to claim 1, characterized in that: In the step S3, the pre-lithiation degree β of the negative electrode is 1%-100%.

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