A half-cell, a preparation method thereof, and a method for detecting open-circuit voltage

Abstract

The application discloses a kind of half battery and its preparation method, the detection method of open-circuit voltage.The preparation method of the half battery includes the following steps: lithium sheet, separator and graphite pole piece are stacked in sequence, and sealing, standing are carried out, and half battery is obtained;Before stacking the separator, first electrolyte is added to the lithium sheet;Before stacking the graphite pole piece, second electrolyte is added to the separator;The volume ratio of the first electrolyte and the second electrolyte is 1: (1-5).When the half battery prepared by the half battery preparation method of the application is detected by open-circuit voltage, the reliability and stability of the obtained open-circuit voltage are better, and can be used to judge the performance of battery and / or electrode material.

Description

Technical Field

[0001] This invention relates to a half-cell and its preparation method, as well as a method for detecting open-circuit voltage. Background Technology

[0002] The open-circuit voltage of a half-cell is a key indicator for evaluating battery performance, and its magnitude and stability are of great significance in battery research and development, application and management.

[0003] The stability of open-circuit voltage reflects the ability of electrode materials to maintain their structure during cycling. Small open-circuit voltage fluctuations indicate fewer side reactions and more stable interfaces in the electrode materials, contributing to extended battery life. Open-circuit voltage drift or decay may indicate electrode material degradation, while excessive open-circuit voltage fluctuations may trigger localized overheating or dendrite growth, affecting battery safety. A stable open-circuit voltage helps maintain internal battery equilibrium and reduces risk. Therefore, monitoring the stability of open-circuit voltage can help identify the battery's health status at an early stage.

[0004] However, current technologies do not cover the detection of open-circuit voltage of half-cells made from graphite materials, so the performance of half-cells and / or electrode materials cannot be evaluated by open-circuit voltage. Summary of the Invention

[0005] The technical problem this invention aims to solve is to overcome the deficiency in existing technologies that do not address the control of open-circuit voltage in half-cells made from graphite materials, thus making it impossible to evaluate the performance of batteries and / or electrode materials based on open-circuit voltage. This invention provides a half-cell, its preparation method, and an open-circuit voltage detection method. When the open-circuit voltage of a half-cell prepared using the method of this invention is tested, the obtained open-circuit voltage exhibits better reliability and stability, and can be used to evaluate the performance of batteries and / or electrode materials.

[0006] The present invention solves the above-mentioned technical problems through the following technical solution:

[0007] This invention provides a method for preparing a half-cell, comprising the following steps:

[0008] Lithium sheets, separators, and graphite electrodes are stacked sequentially, then sealed and left to stand to obtain a half-cell.

[0009] Before stacking the separator, a first electrolyte is added to the lithium sheet; before stacking the graphite electrode, a second electrolyte is added to the separator; the volume ratio of the first electrolyte to the second electrolyte is 1:(1-5).

[0010] In this invention, the inventors discovered during their research that the process of preparing half-cells using graphite materials involves numerous steps, most of which cannot be fully automated, and the charge / discharge plateau is <0.1V. This results in poor stability during fabrication and testing, leading to poor open-circuit voltage stability of the prepared half-cells. Consequently, the performance of the battery and materials cannot be evaluated based on open-circuit voltage, and the stability of test data is also affected. In this invention, the inventors creatively discovered parameters affecting the open-circuit voltage stability of half-cells during fabrication and rationally controlled the range of these parameters, resulting in half-cells with superior open-circuit voltage reliability and stability.

[0011] In this invention, the half-cell is preferably prepared in a glove box where the water and oxygen content is less than 1 ppm, for example, in a glove box where the water and oxygen content is less than 0.01 ppm.

[0012] In this invention, the diameter of the lithium sheet can be 15-25 mm, preferably 16-21 mm, for example 19 mm. The thickness of the lithium sheet is preferably 1.0-1.5 mm, for example 1.1 mm.

[0013] In this invention, the surface of the lithium sheet is preferably free of impurities. The impurities are preferably oxide films.

[0014] When the surface of the lithium sheet contains impurities, it is preferable to use a brush to remove the impurities from the surface of the lithium sheet.

[0015] Before brushing away impurities from the surface of the lithium sheet, it is preferable to also perform a step of fixing the lithium sheet. The fixing tool can be conventional in the art, such as a stainless steel plate with grooves or a lint-free cloth.

[0016] The length of the grooved stainless steel plate is preferably 5-15 cm, for example, 10 cm. The width of the grooved stainless steel plate is preferably 5-15 cm, for example, 10 cm. The thickness of the grooved stainless steel plate is preferably 1-10 mm, for example, 5 mm. The difference between the diameter of the groove and the diameter of the lithium sheet is preferably 0-3 mm, for example, 1 mm. The difference between the depth of the groove and the thickness of the lithium sheet is preferably 0.1-0.3 mm, for example, 0.2 mm.

[0017] The cleanroom cloth is preferably made of 100% polyester fiber. The size of the cleanroom cloth is preferably not smaller than the size of the lithium sheet. The length of the cleanroom cloth is preferably 10-30cm, for example, 20cm. The width of the cleanroom cloth is preferably 10-30cm, for example, 20cm.

[0018] The diameter of each bristle of the brush can be 0.05mm-0.20mm, preferably 0.05-0.15mm, for example 0.15, 0.10, or 0.05mm. The length of each bristle can be 0.3-1.9cm, preferably 0.6-1.3cm, for example 0.6 or 1.1cm. The thickness of the brush is preferably 0.3-1.1cm, for example 0.5cm. The width of the brush is preferably 1-2cm, for example 1.1cm.

[0019] In a preferred embodiment, each bristle of the brush has a diameter of 0.15 mm and a length of 0.6 cm; the brush has a thickness of 0.5 cm and a width of 1.1 cm.

[0020] In a preferred embodiment, each bristle of the brush has a diameter of 0.05 mm and a length of 1.1 cm; the brush has a thickness of 0.5 cm and a width of 1.1 cm.

[0021] In this invention, the type of diaphragm can be conventional in the art, such as a polyethylene diaphragm. The thickness of the diaphragm is preferably 15-25 μm, for example, 20 μm. The diameter of the diaphragm is preferably 20-30 mm, for example, 22 mm.

[0022] In this invention, the preferred method for preparing the graphite electrode sheet includes the following steps: coating a graphite-containing slurry onto a current collector, and then rolling and drying it to obtain the graphite electrode sheet.

[0023] The graphite-containing slurry preferably comprises graphite material, dispersant, solvent, binder, and conductive agent. The graphite material is preferably artificial graphite and / or natural graphite, such as artificial graphite. The dispersant can be of a type conventional in the art, such as carboxymethyl cellulose. The solvent can be of a type conventional in the art, such as water. The binder can be of a type conventional in the art, such as styrene-butadiene rubber. The conductive agent can be of a type conventional in the art, such as conductive carbon black. The preferred mass ratio of the graphite material, dispersant, solvent, binder, and conductive agent is (92-98):1:(125-135):(1-3):1, for example, 95:1:130:2:1.

[0024] The current collector can be of a type conventional in the art, such as copper foil. The thickness of the current collector can also be conventional in the art, preferably 5-12 μm, for example 9 μm.

[0025] The coating equipment can be conventional in the art, such as a transfer coating machine.

[0026] The coating speed is preferably 1000-3000 mm / min, for example 1500 mm / min.

[0027] The rolling operation can be conventional in the art, and the rolling speed is preferably 1-6 m / min, for example 3 m / min. The distance between the roll gaps is preferably 20-40 μm, for example 30 μm. The rolling pressure is preferably 15-25 MPa, for example 19 MPa.

[0028] The drying temperature can be conventional in the art, preferably 70-95°C, for example 90°C.

[0029] The areal density of the graphite electrode is preferably 5-15 mg / cm³. 2 For example, 9mg / cm 2 The compaction density of the graphite electrode sheet is preferably 1-2 g / cm³. 3 For example, 1.5g / cm 3 .

[0030] The porosity of the graphite electrode sheet is preferably 20-40%, for example 31%.

[0031] The diameter of the graphite electrode sheet is preferably 10-20 mm, for example, 16 mm.

[0032] In this invention, the types of the first electrolyte and the second electrolyte can be independent of each other, preferably the same or different, for example, the same. The concentrations of the first electrolyte and the second electrolyte can also be independent of each other, preferably the same or different, for example, the same.

[0033] In a preferred embodiment, the first electrolyte and the second electrolyte are of the same type and concentration.

[0034] In this invention, the first electrolyte and the second electrolyte can be of conventional types in the art, generally including lithium salts, solvents and additives.

[0035] The preferred type of lithium salt is lithium hexafluorophosphate.

[0036] The solvent preferably includes one or more of ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, and vinylene carbonate, for example, any of the following: ① ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate; ② ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, and vinylene carbonate.

[0037] When the solvent is ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate, the volume ratio of ethylene carbonate, methyl ethyl carbonate and dimethyl carbonate is preferably (0.5-1.5):(0.5-1.5):(0.5-1.5), for example 1:1:1.

[0038] When the solvent is ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, and vinylene carbonate, the volume ratio of ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, and vinylene carbonate is preferably (2-3):(3-4):(2-3):1:(0.1-0.2), for example, 2.8:3.2:2.8:1:0.18.

[0039] The additive is preferably one or more of pentafluorophenol sulfonate, vinylene carbonate, borate ester, and sulfite ester, such as pentafluorophenol sulfonate, borate ester, and sulfite ester, or vinylene carbonate. The mass percentage of pentafluorophenol sulfonate is preferably 0.5%-1.5%, for example, 1.0%. The mass percentage of borate ester is preferably 0.5%-1.5%, for example, 0.8%. The mass percentage of pentafluorophenol sulfonate is preferably 0.5%-1.5%, for example, 0.7%. The mass percentage of vinylene carbonate is preferably 0.5%-1.5%, for example, 1.0%. The mass percentages represent the percentage of each additive component by the total mass of the electrolyte.

[0040] The molar concentration of lithium salt in the first electrolyte or the second electrolyte is preferably 0.5M-1.5M, for example 1M.

[0041] In a preferred embodiment, the first electrolyte and the second electrolyte are of the same type and concentration, and the concentration of both the first electrolyte and the second electrolyte is 1M, comprising lithium hexafluorophosphate, solvent, and additive; the solvent in the solution is ethylene carbonate, ethyl methyl carbonate, and dimethyl carbonate in a volume ratio of 1:1:1; the additive is 1.0% vinylene carbonate.

[0042] In a preferred embodiment, the first electrolyte and the second electrolyte are of the same type and concentration, and both the first electrolyte and the second electrolyte have a concentration of 1M, comprising lithium hexafluorophosphate, solvent, and additives; the solvent is ethylene carbonate, ethyl methyl carbonate, dimethyl carbonate, fluoroethylene carbonate, and vinylene carbonate in a volume ratio of 2.8:3.2:2.8:1:0.18; the additives are 1.0% pentafluorophenol sulfonate, 0.8% borate ester, and 0.7% sulfite ester.

[0043] In this invention, the volume ratio of the first electrolyte to the second electrolyte is preferably 1:(1-4), for example, 1:3. The total volume of the first electrolyte and the second electrolyte is preferably 20-60 μL, for example, 30 or 40 μL. During battery assembly, electrolyte is typically added twice: once on the lithium sheet and once on the separator. The lithium sheet hardly absorbs electrolyte, and adding too much electrolyte to the lithium sheet will increase the battery's internal resistance. Graphite electrodes have good liquid absorption capacity, and adding less electrolyte to the separator will also increase the battery's internal resistance. Therefore, the amount of electrolyte on the lithium sheet should be less, while the amount of electrolyte on the separator, used for liquid absorption by the graphite electrodes, should be more. This arrangement can reduce the battery's internal resistance and improve the consistency of open-circuit voltage.

[0044] In a preferred embodiment, the volume of the first electrolyte is 10 μL, and the volume of the second electrolyte is 10 μL.

[0045] In a preferred embodiment, the volume of the first electrolyte is 15 μL, and the volume of the second electrolyte is 15 μL.

[0046] In a preferred embodiment, the volume of the first electrolyte is 30 μL, and the volume of the second electrolyte is 30 μL.

[0047] In a preferred embodiment, the volume of the first electrolyte is 10 μL and the volume of the second electrolyte is 30 μL.

[0048] In this invention, the sealing process conditions can be conventional in the art, and the sealing pressure is preferably 5-8 kg / cm². 2 For example, 6.5 kg / cm 2 .

[0049] In this invention, the settling time can be ≥3 hours, preferably 19-40 hours, such as 25, 30, or 35 hours. A certain amount of time is required for the electrolyte to distribute evenly in the electrode. If the battery settling time is insufficient, some particles in the electrode will not be wetted by the electrolyte, causing the working electrode state to deviate from the ideal working state, and the open-circuit voltage to deviate significantly from the theoretical value. Increasing the settling time can improve the uniformity of electrolyte wetting and improve the consistency of the open-circuit voltage.

[0050] In this invention, the method for preparing the half-cell preferably includes the following steps: sequentially stacking a negative electrode shell, a support, a lithium sheet, a separator, a graphite electrode sheet, and a positive electrode shell; and sealing and allowing it to stand to obtain a half-cell;

[0051] Before stacking the separator, a first electrolyte is added to the lithium sheet; before stacking the graphite electrode, a second electrolyte is added to the separator; the volume ratio of the first electrolyte to the second electrolyte is 1:(1-5).

[0052] The negative electrode shell can be of a conventional type in the art, such as CR2430.

[0053] The type of support can be conventional in the art, such as nickel foam.

[0054] The positive electrode shell can be of a type commonly used in the field, such as CR2430.

[0055] This invention provides a half-cell, which is prepared using the half-cell preparation method described above.

[0056] The present invention provides a method for detecting open-circuit voltage, which includes the following steps: detecting the open-circuit voltage of a half-cell as described above.

[0057] In this invention, the detection of the open-circuit voltage is preferably performed at room temperature, for example, 25±1℃.

[0058] The positive and progressive effects of this invention are as follows:

[0059] The open-circuit voltage obtained when the half-cell prepared by the method of the present invention is tested has good reliability and stability, and can be used to evaluate the performance of the battery and / or electrode materials. Detailed Implementation

[0060] The present invention will be further illustrated by way of embodiments below, but the present invention is not limited to the scope of the embodiments described herein.

[0061] In the following examples and comparative examples, CMC was purchased from Jiangmen Hercules Chemical Co., Ltd., and the product name was Bondwell. TM BVH8; SBR was purchased from BASF Paper Chemicals (Jiangsu) Co., Ltd., model Binder 21-11.

[0062] In the following embodiments and comparative examples, the range of open-circuit voltage is obtained by the following calculation formula: Range of open-circuit voltage = Maximum value of open-circuit voltage obtained by testing - Minimum value of open-circuit voltage obtained by testing;

[0063] The mean absolute error of the open-circuit voltage is obtained by the following formula: Mean Absolute Error of Open-Circuit Voltage The mean absolute error of the open circuit voltage is calculated by taking the absolute value of the difference between the measured open circuit voltage of each group and the theoretical open circuit voltage of 3.045V, summing all the absolute values, and then dividing by the number of test groups.

[0064] Example 1-1

[0065] Graphite electrode production:

[0066] (1) A graphite slurry is prepared by mixing artificial graphite, carboxymethyl cellulose (CMC), water, styrene-butadiene rubber (SBR), and conductive carbon black (SP) in a mass ratio of 95:1:130:2:1.

[0067] (2) The above-mentioned graphite slurry was coated onto a copper foil current collector with a thickness of 9 μm using a transfer coating machine. After rolling and drying, a graphite electrode sheet was obtained. The coating speed was 1500 mm / min, the rolling speed was 3 m / min, the distance between the roller gaps was 30 μm, the rolling pressure was 19 MPa, and the drying temperature of the transfer coating machine was 90 °C. The areal density of the graphite electrode sheet was 9 mg / cm³. 2 The compaction density of this graphite electrode is 1.5 g / cm³. 3 The porosity of the graphite electrode is 31%.

[0068] Assembly of button cell:

[0069] Required materials: graphite electrode sheet (Φ16mm), lithium sheet (Φ19mm, 1.1mm thick), separator (polypropylene (PP) material, Φ22mm, 20μm thick), positive electrode shell (CR2430), negative electrode shell (CR2430), first electrolyte and second electrolyte (including lithium hexafluorophosphate and solvent, additives, the solvent includes ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a volume ratio of 1:1:1; the additive is 1% vinylene carbonate (1% means the mass of vinylene carbonate to the total mass of the first electrolyte or the second electrolyte), the molar concentration of lithium hexafluorophosphate in the electrolyte is 1M), support (nickel foam);

[0070] Before assembly, the lithium sheets are pretreated to ensure their surface is free of impurities. The pretreatment method is as follows: the lithium sheets are fixed in place using a stainless steel plate with grooves (the stainless steel plate is 10cm long and wide, and 5mm thick; the grooves are 20mm in diameter and 1.3mm deep), and the oxide film formed on the surface of the lithium sheets due to contact with air is brushed off. The brush bristles are 0.15mm in diameter, 0.6cm long, 0.5cm thick, and 1.1cm wide.

[0071] In a glove box where the water and oxygen content are both <0.01ppm, the negative electrode shell, nickel foam, lithium sheet, separator, graphite electrode, and positive electrode shell are stacked sequentially, and then subjected to a pressure of 6.5 kg / cm². 2 Under the specified conditions, the cells were sealed and allowed to stand at room temperature (25±1℃) for 3 hours to obtain a coin cell. Before stacking the separator, 30μL of the first electrolyte was added to the lithium sheet; before stacking the graphite electrode, 30μL of the second electrolyte was added to the separator; the volume ratio of the first electrolyte to the second electrolyte was 1:1.

[0072] Ten button cells were produced in parallel following the steps described above.

[0073] The coin cell half-cells prepared above were placed in a room temperature environment (25±1℃), and a high-precision battery tester was used with the range set to voltage. The positive and negative probes of the high-precision battery tester were respectively connected to the positive and negative terminals of the obtained coin cell half-cells to avoid short circuits. After the voltage reading stabilized, the value was recorded as the open circuit voltage (OCV). The measured open circuit voltage range was 2.6-3.1V.

[0074] Examples 1-2

[0075] The only difference from Example 1-1 is that the standing time is 30 hours.

[0076] After being left to stand for 30 hours, the open-circuit voltage range of the button cell was 2.9±0.1V, which is narrower and more consistent.

[0077] Table 1. Test results of open-circuit voltage in Examples 1-1 and 1-2

[0078]

[0079] As can be seen from Examples 1-1 and 1-2 and Table 1, increasing the resting time can improve the OCV stability of coin cell half-cell detection.

[0080] Example 2-1

[0081] Graphite electrode production:

[0082] (1) A graphite slurry is prepared by mixing artificial graphite, carboxymethyl cellulose (CMC), water, styrene-butadiene rubber (SBR), and conductive carbon black (SP) in a mass ratio of 95:1:130:2:1.

[0083] (2) The above-mentioned graphite slurry was coated onto a copper foil current collector with a thickness of 9 μm using a transfer coating machine. After rolling and drying, a graphite electrode sheet was obtained. The coating speed was 1500 mm / min, the rolling speed was 3 m / min, the distance between the roller gaps was 30 μm, the rolling pressure was 19 MPa, and the drying temperature of the transfer coating machine was 90 °C. The areal density of the graphite electrode sheet was 9 mg / cm³. 2 The compaction density of this graphite electrode is 1.5 g / cm³. 3 The porosity of the graphite electrode is 31%.

[0084] Assembly of button cell:

[0085] Required materials: graphite electrode sheet (Φ16mm), lithium sheet (Φ19mm, 1.1mm thick), separator (polypropylene (PP) material, Φ22mm, 20μm thick), positive electrode shell (CR2430), negative electrode shell (CR2430), first electrolyte and second electrolyte (composed of lithium hexafluorophosphate and solvent, the solvent including ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a volume ratio of 1:1:1; the molar concentration of lithium hexafluorophosphate is 1M), support (nickel foam);

[0086] Before assembly, the lithium sheets are first pretreated to ensure that their surface is free of impurities. The pretreatment method is as follows: the lithium sheets are fixed with a lint-free cloth (100% polyester fiber), and the oxide film formed on the surface of the lithium sheets due to contact with air is brushed off. The diameter of each bristle of the brush is 0.05mm, the length of each bristle is 1.1cm, the thickness of the brush is 0.5cm, and the width of the brush is 1.1cm.

[0087] In a glove box where the water and oxygen content are both <0.01ppm, the negative electrode shell, nickel foam, lithium sheet, separator, graphite electrode, and positive electrode shell are stacked sequentially, and then subjected to a pressure of 6.5 kg / cm². 2 Under the specified conditions, the cells were sealed and allowed to stand at room temperature (25±1℃) for 3 hours to obtain a coin cell. Before stacking the separator, 30μL of the first electrolyte was added to the lithium sheet; before stacking the graphite electrode, 30μL of the second electrolyte was added to the separator; the volume ratio of the first electrolyte to the second electrolyte was 1:1.

[0088] Ten button cells were produced in parallel following the steps described above.

[0089] Place the coin cell at room temperature (25±1℃) and use a high-precision battery tester with the range set to voltage. Contact the positive and negative probes of the high-precision battery tester with the positive and negative terminals of the coin cell respectively to avoid short circuits. After the voltage reading stabilizes, record the value as the open circuit voltage (OCV).

[0090] Table 2. Test results of open-circuit voltage in Examples 1-1 and 2-1

[0091]

[0092] In the production of lithium wafers, it is impossible to guarantee that every process is under vacuum conditions. Therefore, an oxide film will form on the surface of the lithium wafer after it comes into contact with air, which affects the open circuit voltage of the resulting coin cell and the lithium insertion in the electrochemical reaction. So, before battery assembly, the oxide layer on the surface of the lithium wafer is brushed off. The tools for brushing off the oxide layer on the surface of the lithium wafer include brushes and tools for fixing the lithium wafer.

[0093] As shown in Examples 1-1 and 2-1 and Table 2, both the diameter and length of the brush bristles affect the cleaning effect. Coarser and shorter bristles result in greater scratches on the lithium sheet surface, while finer and longer bristles are less effective at cleaning the oxide layer on the lithium sheet surface. Experimental studies have shown that when the brush bristle diameter is 0.05-0.1 mm and the length is 1-1.3 cm, using a lint-free cloth to fix the lithium sheet results in better cleaning of the oxide layer on the lithium sheet surface, and the resulting coin cell half-cell exhibits better open-circuit voltage stability.

[0094] When cleaning the oxide layer on the surface of lithium sheets, lithium metal powder is inevitably swept off as well. In Example 1-1, if a stainless steel plate with grooves is used as a tool to fix the lithium sheets, the lithium metal powder deposited on the surface of the stainless steel plate will move with the movement of the plate due to its smooth surface. When the lithium powder is scattered on the surface of the graphite electrode, the battery will experience a self-reaction during the resting process, resulting in a decrease in the battery's open-circuit voltage. At the same time, because there is a lot of lithium metal powder around the grooves, the tweezers will also become contaminated when they pick up the cleaned lithium sheets. When the contaminated tweezers pick up the separator or electrode, the battery's open-circuit voltage will also decrease due to a self-reaction. When the tool for fixing the lithium sheets is changed from a stainless steel plate with grooves to a lint-free cloth, the deposited metal powder will stick to the lint-free cloth due to its greater friction. At the same time, when the tweezers pick up the lithium sheets, there will be no lithium metal powder on the surface of the tweezers.

[0095] Example 3-1

[0096] Graphite electrode production:

[0097] (1) A graphite slurry is prepared by mixing artificial graphite, carboxymethyl cellulose (CMC), water, styrene-butadiene rubber (SBR), and conductive carbon black (SP) in a mass ratio of 95:1:130:2:1.

[0098] (2) The above-mentioned graphite slurry was coated onto a copper foil current collector with a thickness of 9 μm using a transfer coating machine. After rolling and drying, a graphite electrode sheet was obtained. The coating speed was 1500 mm / min, the rolling speed was 3 m / min, the distance between the roller gaps was 30 μm, the rolling pressure was 19 MPa, and the drying temperature of the transfer coating machine was 90 °C. The areal density of the graphite electrode sheet was 9 mg / cm³. 2 The compaction density of this graphite electrode is 1.5 g / cm³. 3 The porosity of the graphite electrode is 31%.

[0099] Assembly of button cell:

[0100] Required materials: graphite electrode sheet (Φ16mm), lithium sheet (Φ19mm, 1.1mm thick), separator (polypropylene (PP) material, Φ22mm, 20μm thick), positive electrode shell (CR2430), negative electrode shell (CR2430), first electrolyte and second electrolyte (composed of lithium hexafluorophosphate and solvent, the solvent including ethylene carbonate, ethyl methyl carbonate and dimethyl carbonate in a volume ratio of 1:1:1; the molar concentration of lithium hexafluorophosphate is 1M), support (nickel foam);

[0101] Before assembly, the lithium sheets are first pretreated to ensure that their surface is free of impurities. The pretreatment method is as follows: the lithium sheets are fixed with a lint-free cloth (100% polyester fiber), and the oxide film formed on the surface of the lithium sheets due to contact with air is brushed off. The diameter of each bristle of the brush is 0.05mm, the length of each bristle is 1.1cm, the thickness of the brush is 0.5cm, and the width of the brush is 1.1cm.

[0102] In a glove box where the water and oxygen content are both <0.01ppm, the negative electrode shell, nickel foam, lithium sheet, separator, graphite electrode, and positive electrode shell are stacked sequentially, and then subjected to a pressure of 6.5 kg / cm². 2 Under the specified conditions, the cells were sealed and allowed to stand at room temperature (25±1℃) for 30 hours to obtain a coin cell. Before stacking the separator, 10μL of the first electrolyte was added to the lithium sheet; before stacking the graphite electrode, 10μL of the second electrolyte was added to the separator; the volume ratio of the first electrolyte to the second electrolyte was 1:1.

[0103] Six button cells were produced in parallel following the steps described above.

[0104] Place the coin cell at room temperature (25±1℃) and use a high-precision battery tester with the range set to voltage. Contact the positive and negative probes of the high-precision battery tester with the positive and negative terminals of the coin cell respectively to avoid short circuits. After the voltage reading stabilizes, record the value as the open circuit voltage (OCV).

[0105] Example 3-2

[0106] The only difference from Example 3-1 is that: before stacking the separator, 15 μL of the first electrolyte is added to the lithium sheet; before stacking the graphite electrode, 15 μL of the second electrolyte is added to the separator; the volume ratio of the first electrolyte to the second electrolyte is 1:1.

[0107] Example 3-3

[0108] The only difference from Example 3-1 is that: before stacking the separator, 30 μL of the first electrolyte is added to the lithium sheet; before stacking the graphite electrode, 30 μL of the second electrolyte is added to the separator; the volume ratio of the first electrolyte to the second electrolyte is 1:1.

[0109] Examples 3-4

[0110] The only difference from Example 3-1 is that: before stacking the separator, 10 μL of the first electrolyte is added to the lithium sheet; before stacking the graphite electrode, 30 μL of the second electrolyte is added to the separator; the volume ratio of the first electrolyte to the second electrolyte is 1:3.

[0111] Table 3. Test results of open-circuit voltage in Examples 3-1 to 3-4

[0112]

[0113] As can be seen from Examples 3-1 to 3-4 and Table 3, the open-circuit voltage of the assembled coin cell is more stable when the volumes of electrolyte added twice are 10 μL and 30 μL, respectively. When assembling the battery, electrolyte is added twice to allow the separator and positive and negative electrodes to fully absorb the electrolyte. The separator and negative electrode have high electrolyte absorption rates, while the lithium sheet hardly absorbs any electrolyte. Therefore, the volumes of electrolyte added twice should be different, with less electrolyte added for the lithium sheet and more electrolyte added for the electrode sheet.

[0114] Example 4

[0115] The difference from Examples 3-3 lies in the type and concentration of the first and second electrolytes. Specifically, the electrolyte (purchased from Xinya Shanshan New Material Technology (Quzhou) Co., Ltd., model number 16883) is composed of lithium hexafluorophosphate, solvent, and additives; the solvent is 28% ethylene carbonate + 32% methyl ethyl carbonate + 28% dimethyl carbonate + 10% fluoroethylene carbonate + 1.8% vinylene carbonate (% represents the percentage of each solvent component in the total volume of the solvent); the additives are 1.0% pentafluorophenol sulfonate, 0.8% borate ester, and 0.7% sulfite (% represents the percentage of each additive component in the total mass of the electrolyte); the molar concentration of lithium hexafluorophosphate is 1M.

[0116] Table 4. Test results of open-circuit voltage in Examples 3-4 and Example 4.

[0117]

[0118] As can be seen from Examples 3-3, Example 4 and Table 4, the stability and reliability of the open-circuit voltage of half-cells assembled with different electrolyte compositions vary greatly.

[0119] While specific embodiments of the present invention have been described above, those skilled in the art should understand that these are merely illustrative examples, and the scope of protection of the present invention is defined by the appended claims. Those skilled in the art can make various changes or modifications to these embodiments without departing from the principles and essence of the present invention, but all such changes and modifications fall within the scope of protection of the present invention.

Claims

1. A method for preparing a half-cell, characterized in that, It includes the following steps: Lithium sheets, separators, and graphite electrodes are stacked sequentially, then sealed and left to stand to obtain a half-cell. Before stacking the separator, a first electrolyte is added to the lithium sheet; before stacking the graphite electrode, a second electrolyte is added to the separator; the volume ratio of the first electrolyte to the second electrolyte is 1:(1-5).

2. The method for preparing a half-cell as described in claim 1, characterized in that, The method for preparing the half-cell satisfies one or more of the following conditions: (1) The diameter of the lithium sheet is 15-25 mm, preferably 16-21 mm, for example 19 mm; (2) The thickness of the lithium sheet is 1.0-1.5 mm, for example 1.1 mm; (3) The surface of the lithium sheet is free of impurities; the impurities are preferably oxide films; When the surface of the lithium sheet contains impurities, it is preferable to use a brush to remove the impurities from the surface of the lithium sheet. (4) The type of diaphragm is a polyethylene diaphragm; (5) The thickness of the diaphragm is 15-25 μm, for example 20 μm; (6) The diameter of the diaphragm is 20-30 mm, for example 22 mm; (7) The preparation method of the graphite electrode includes the following steps: coating a slurry containing graphite onto a current collector, and then rolling and drying it to obtain the graphite electrode.

3. The method for preparing a half-cell as described in claim 2, characterized in that, The method for preparing the half-cell satisfies one or more of the following conditions: (1) Before brushing away the impurities on the surface of the lithium sheet, a step of fixing the lithium sheet is also performed; The fixing tool is, for example, a stainless steel plate with grooves or a lint-free cloth; (2) The diameter of each bristle of the brush is 0.05mm-0.20mm, preferably 0.05-0.15mm, for example 0.15, 0.10 or 0.05mm; (3) The length of each bristle of the brush is 0.3-1.9cm, preferably 0.6-1.3cm, for example 0.6 or 1.1cm; (4) The thickness of the brush is 0.3-1.1cm, for example 0.5cm; (5) The width of the brush is 1-2cm, for example 1.1cm.

4. The method for preparing a half-cell as described in claim 3, characterized in that, The method for preparing the half-cell satisfies one or more of the following conditions: (1) The length of the stainless steel plate with the groove is 5-15cm, for example 10cm; (2) The width of the stainless steel plate with grooves is 5-15cm, for example 10cm; (3) The thickness of the stainless steel plate with grooves is 1-10mm, for example 5mm; (4) The difference between the diameter of the groove and the diameter of the lithium sheet is 0-3 mm, for example, 1 mm; (5) The difference between the depth of the groove and the thickness of the lithium sheet is 0.1-0.3 mm, for example 0.2 mm; (6) The cleanroom cloth is made of 100% polyester fiber; (7) The size of the cleanroom cloth is not smaller than the size of the lithium sheet; (8) The length of the cleanroom cloth is 10-30cm, for example 20cm; (9) The preferred size of the cleanroom cloth is 10-30cm, for example 20cm.

5. The method for preparing a half-cell as described in claim 2, characterized in that, The method for preparing the half-cell satisfies one or more of the following conditions: (1) The graphite-containing slurry includes graphite material, dispersant, solvent, binder and conductive agent; Wherein, the graphite material is preferably artificial graphite and / or natural graphite, such as artificial graphite; the dispersant is preferably carboxymethyl cellulose; the solvent is preferably water; the binder is preferably styrene-butadiene rubber; the conductive agent is preferably conductive carbon black; the mass ratio of the graphite material, dispersant, solvent, binder and conductive agent is preferably (92-98):1:(125-135):(1-3):1, for example 95:1:130:2:1; (2) The current collector is copper foil; (3) The thickness of the current collector is 5-12 μm, for example 9 μm; (4) The coating speed is 1000-3000 mm / min, for example 1500 mm / min; (5) The speed of the roller pressing is 1-6 m / min, for example 3 m / min; (6) The distance between the roll gaps during the rolling process is 20-40 μm, for example, 30 μm; (7) The pressure of the roller is 15-25 MPa, for example 19 MPa; (8) The drying temperature is 70-95℃, for example 90℃; (9) The areal density of the graphite electrode is 5-15 mg / cm³. 2 For example, 9mg / cm 2 ; (10) The compaction density of the graphite electrode sheet is 1-2 g / cm³. 3 For example, 1.5g / cm 3 ; (11) The porosity of the graphite electrode is 20-40%, for example 31%; (12) The diameter of the graphite electrode is 10-20 mm, for example 16 mm.

6. The method for preparing a half-cell as described in claim 1, characterized in that, The method for preparing the half-cell satisfies one or more of the following conditions: (1) The types of the first electrolyte and the second electrolyte are independent of each other, preferably the same or different, for example the same; (2) The concentrations of the first electrolyte and the second electrolyte are independent of each other, preferably the same or different, for example, the same; (3) The first electrolyte and the second electrolyte include lithium salt, solvent and additives; The lithium salt is preferably lithium hexafluorophosphate; the molar concentration of the lithium salt in the first electrolyte or the second electrolyte is preferably 0.5M-1.5M, for example 1M. The solvent includes one or more of ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, and vinylene carbonate, for example, any one of the following: ① ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate; ② ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, and vinylene carbonate. When the solvent is ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate, the volume ratio of ethylene carbonate, methyl ethyl carbonate, and dimethyl carbonate is preferably (0.5-1.5):(0.5-1.5):(0.5-1.5), for example, 1:1:1; When the solvent is ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, and vinylene carbonate, the volume ratio of ethylene carbonate, methyl ethyl carbonate, dimethyl carbonate, fluoroethylene carbonate, and vinylene carbonate is preferably (2-3):(3-4):(2-3):1:(0.1-0.2), for example 2.8:3.2:2.8:1:0.18; The additive is preferably one or more of pentafluorophenol sulfonate, vinylene carbonate, borate ester, and sulfite, such as pentafluorophenol sulfonate, borate ester, and sulfite, or vinylene carbonate; the mass percentage of pentafluorophenol sulfonate is preferably 0.5%-1.5%, for example 1.0%; the mass percentage of borate ester is preferably 0.5%-1.5%, for example 0.8%; the mass percentage of pentafluorophenol sulfonate is preferably 0.5%-1.5%, for example 0.7%; the mass percentage of vinylene carbonate is preferably 0.5%-1.5%, for example 1.0%; the mass percentage represents the percentage of each additive component in the total mass of the electrolyte; (4) The volume ratio of the first electrolyte to the second electrolyte is 1:(1-4), for example 1:3; (5) The total volume of the first electrolyte and the second electrolyte is 20-60 μL, for example 30 or 40 μL.

7. The method for preparing a half-cell as described in claim 1, characterized in that, The method for preparing the half-cell satisfies (1) and / or (2) of the following conditions: (1) The sealing pressure is 5-8 kg / cm². 2 For example, 6.5 kg / cm 2 ; (2) The settling time is ≥3h, preferably 19-40h, for example 25, 30 or 35h.

8. The method for preparing a half-cell as described in claim 1, characterized in that, The method for preparing the half-cell includes the following steps: sequentially stacking a negative electrode shell, a support, a lithium sheet, a separator, a graphite electrode sheet, and a positive electrode shell; and sealing and allowing it to stand to obtain a half-cell; The preferred type of the negative electrode shell is CR2430; The type of support is preferably nickel foam; The preferred type of the positive electrode shell is CR2430.

9. A half-cell, characterized in that, It is prepared by the method of any one of claims 1-8.

10. A method for detecting open-circuit voltage, characterized in that, It includes the following steps: detecting the open-circuit voltage of the half-cell as described in claim 9.

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