Battery cell desiccant and use thereof

Abstract

The application relates to a battery cell desiccant and application thereof. The battery cell desiccant comprises a carbonate compound, an alkyl silicate compound and a silazane solvent. The battery cell desiccant of the application is placed in an oven, the moisture of the battery cell is evaporated, the components of the desiccant are also evaporated, the water vapor and the chemical desiccant vapor meet and react, the water vapor in the gas phase is converted and removed, and the moisture of the battery cell can be continuously accelerated to be below 10 ppm. The battery cell desiccant of the application solves the technical problem that the moisture in the gas phase and the moisture of the battery cell are balanced during the battery cell drying process, and the moisture of the battery cell is not less than 60 ppm.

Description

Technical Field

[0001] This invention relates to the field of electrochemical energy storage technology, and in particular to a battery cell desiccant and its application. Background Technology

[0002] The electrode materials of battery cells, especially lithium-ion and lithium-metal batteries, such as NCM ternary materials, graphite anodes, electrolytes, and separators, are all hydrophilic or readily react with water. The moisture content inside the battery cell is controlled below 150 ppm, and for advanced cells, it is required to be below 100 ppm. The main purpose is to avoid thermodynamic instability and kinetic performance degradation caused by moisture, and to ensure the safety, lifespan, and electrochemical performance of the battery.

[0003] The moisture content of battery cells produced in a normal environment varies with the season, generally ranging from 600 to 900 ppm. Due to the heat resistance limitations of the separator, the temperature for vacuum drying is typically 85-90℃. After 48 hours of vacuum drying, it is difficult to reduce the moisture content of the battery cells to below 200 ppm. The total power distribution of a 10GWh lithium battery production line is approximately 40,000 kW, of which the power distribution of the drying and air conditioning system (including dehumidification, cooling, and heating functions) accounts for approximately 16,000 kW, or about 40%. If it operates continuously for 300 days a year, with a load of 0.85, the annual power consumption of the drying and air conditioning system is approximately: 16,000kW × 24 hours / day × 300 * 0.85 days / year = 97.92 million kWh / year. At an electricity price of 0.75 yuan / kWh, the annual electricity cost for the drying and air conditioning system is as high as 73.44 million yuan. The main reason is that most processes on the production line are carried out in the drying workshop, where the air dew point is ≤-36℃. The moisture content of the cells produced in this workshop is 350-500 ppm. After vacuum drying, the moisture content of the cells is reduced to below 150 ppm before electrolyte is added. In liquid batteries, the remaining moisture in the cells is converted into gas and removed during battery formation and capacity testing. However, it is difficult to remove moisture from solid-state battery cells during formation and capacity testing. During operation, the moisture is converted into gas, which creates pressure that separates the positive and negative electrodes. A pressure as high as 20 MPa is required to press the positive and negative electrodes together, hindering the industrialization of solid-state batteries.

[0004] Therefore, in order to save energy consumption and reduce costs in factories, how to develop a drying technology for producing battery cells under normal conditions has become an urgent technical problem to be solved in this field. Summary of the Invention

[0005] To address the aforementioned technical problems, the present invention aims to provide a battery cell desiccant and its application. The battery cell desiccant of the present invention is placed in an oven. As the moisture in the battery cell evaporates, the components of the desiccant also evaporate. The water vapor and the chemical desiccant vapor react, converting and removing the water vapor in the gas phase. The moisture in the battery cell continues to evaporate rapidly, reducing the battery cell moisture content to below 10 ppm. The battery cell desiccant of the present invention solves the technical problem of maintaining a battery cell moisture content of no less than 60 ppm due to the equilibrium between the moisture in the gas phase and the moisture in the battery cell during the drying process.

[0006] To achieve this objective, the present invention adopts the following technical solution: In a first aspect, the present invention provides a battery cell desiccant, the battery cell desiccant comprising carbonate compounds, alkyl silicate compounds, and silazane solvents.

[0007] In this invention, the drying mechanism of the battery cell desiccant using a combination of carbonate compounds, alkyl silicate compounds, and silazane solvents is as follows: H2O + SiM(OM)3 → SiM(OM)2(OH) + MOH (1) H2O + SiM2(OM)2 → SiM2(OM)(OH) + MOH (2) H2O + SiM3-NH-SiM3 → SiM3-O-SiM3 + NH3 (3) H2O + SiM3-NM-SiM3 → SiM3-O-SiM3 + NH2M (4) 2SiM(OM)2(OH) + SiM3-NH-SiM3 → 2SiM(OM)2(OSiM3) + NH3 (5) 2SiM(OM)2(OH) + SiM3-NM-SiM3 → 2SiM(OM)2(OSiM3) + NH2M (6) 2MOH + SiM3-NH-SiM3 → 2SiM3-OM+NH3 (7) 2MOH + SiM3-NM-SiM3 → 2SiM3-OM+NH2M (8) In the above reaction formula, M represents methyl. After the reaction, the hydrogen from the water is finally discharged from the system as ammonia and monomethylamine gaseous compounds at room temperature through a vacuum pump; some of the oxygen from the water is discharged from the vacuum pump as hexamethyldisiloxane, methoxytrimethylsilane, and methanol; and some of the oxygen from the water dissolves in the vacuum oil as trimethylsilyl-dimethoxy and methyl silane ether. Excess methyltrimethoxysilane and excess hexamethyldisiloxane dissolve in the vacuum oil to ensure that there is no trace amount of water in the vacuum oil.

[0008] Preferably, the carbonate compound includes any one or a combination of at least two of dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate.

[0009] In this invention, carbonate compounds are used to carry the light components generated by water conversion out of the vacuum system, thereby promoting water conversion and removal.

[0010] Preferably, the alkyl silicate compound includes any one or a combination of at least two of methyltrimethoxysilane (MTMS), dimethyldimethoxysilane (DMDS), or vinyltrimethoxysilane (VTMO).

[0011] In this invention, alkyl silicate compounds are the main components of the drying process.

[0012] Preferably, the silazane solvent includes hexamethyldisilazane (HMDS) and / or heptamethyldisilazane (HPMS).

[0013] In this invention, silazane solvents are used for drying and dehydration and to prevent alkyl silicates from hydrolyzing and polymerizing into polymeric products in vacuum oil.

[0014] Preferably, the molar ratio of the carbonate compound to the silazane solvent is (0.6-1.5):1, for example, it can be 0.8:1, 0.9:1, 1:1, 1.2:1 or 1.4:1, etc.

[0015] Preferably, the molar ratio of the alkyl silicate compound to the silazane solvent is (0.8-2.8):1, for example, it can be 1:1, 1.5:1, 1.8:1, 2:1 or 2.5:1, etc.

[0016] Preferably, the cell desiccant includes a secondary battery cell desiccant.

[0017] Secondly, the present invention provides a method for drying a battery cell, the drying method comprising the following steps: The battery cell desiccant as described in the first aspect is used to dry the battery cell under vacuum conditions to obtain the dried battery cell.

[0018] Preferably, in the battery cell desiccant, the molar number of alkyl silicate compounds is 1.0-2.2 times the molar number of water in the battery cell before drying, for example, it can be 1.2 times, 1.5 times, 1.6 times, 1.8 times or 2.0 times, etc.

[0019] Preferably, in the battery cell desiccant, the molar number of silazane solvent is 0.8-1.2 times the molar number of water in the battery cell before drying, for example, it can be 0.9 times, 0.95 times, 1.0 times, 1.05 times or 1.1 times, etc.

[0020] Preferably, in the battery cell desiccant, the number of moles of carbonate compounds is 0.8-1.2 times the number of moles of moisture in the battery cell before drying, for example, it can be 0.9 times, 0.95 times, 1.0 times, 1.05 times or 1.1 times, etc.

[0021] The moisture content of the battery cell before drying refers to the sum of the moisture content of the positive electrode, negative electrode, and separator of the battery cell before drying.

[0022] Preferably, the drying method includes the following steps: The battery cell desiccant as described in the first aspect and the battery cell before drying are placed in a vacuum oven, the vacuum is turned on, the temperature is increased in stages, the temperature is kept constant and the air is changed, the temperature is lowered, and the vacuum is broken with nitrogen to obtain the dried battery cell.

[0023] Compared with the prior art, the present invention has at least the following beneficial effects: The cell desiccant of this invention can reduce cell moisture to below 10 ppm. A production line with a capacity of 10 GWh lithium batteries per year consumes approximately 500 tons of desiccant annually, with a procurement cost of 8.5 million yuan. Adding the cost of exhaust gas absorption of 1.5 million yuan, the annual savings amount to 63.44 million yuan, reducing cell drying costs by 86.4%, improving battery performance, and eliminating the moisture barrier to the industrialization of solid-state batteries. Attached Figure Description

[0024] Figure 1 This is a schematic diagram of the oven vacuum tube connection in an application example and a comparative application example of the present invention. Detailed Implementation

[0025] To facilitate understanding of the present invention, the following embodiments are provided. Those skilled in the art should understand that these embodiments are merely illustrative and should not be construed as limiting the scope of the invention.

[0026] Examples 1-12, Comparative Examples 1-4 Each battery cell desiccant is provided. The composition of the battery cell desiccant is shown in Table 1. In Table 1, EMC / H2O, MTMS / H2O, HMDS / H2O, and TEOS / H2O represent the multiples of the molar number of EMC, MTMS, HMDS, and TEOS relative to the molar number of moisture in the battery cell before drying, respectively. TEOS is tetraethyl orthosilicate.

[0027] Table 1 Application Example 1-12, Comparison with Application Example 1-4 A method for drying a battery cell is provided. The battery cell consists of 150 1.8AH 811+graphite ternary lithium-ion cells, with a total energy of 150 × 1.8 × 3.7 ≈ 1 kWh. The moisture content of the battery cell is shown in Table 2. The total water content is 2.32 grams, or 0.13 moles.

[0028] Table 2 Laboratory oven vacuum tubes, such as Figure 1 As shown, the pipe size is 1-inch stainless steel pipe.

[0029] The drying method includes the following steps: (1) Mix the components of the battery cell desiccant to obtain a mixed solution, bottle it, transfer it into a vacuum oven, and open the cap.

[0030] (2) Place the battery cells on the tray and move them onto the rack of the oven. Close the oven door, turn on the vacuum pump, open valve 2, and open the oven vacuum valve. After the vacuum reaches -0.09~-0.1MPA, close the oven vacuum valve, close valve 2, and turn off the vacuum pump. Set the oven temperature to 50℃ and maintain it for 1.5 hours.

[0031] (3) Turn on the vacuum pump, open valve 2, and open the oven vacuum valve. After the vacuum degree reaches -0.09~-0.1MPA, close the oven vacuum valve, close valve 2, and turn off the vacuum pump. Set the oven temperature to 70℃ and maintain it for 1.5 hours.

[0032] (4) Turn on the vacuum pump, open valve 2, open the oven vacuum valve. After the vacuum degree reaches -0.1MPA, close the oven vacuum valve, close valve 2, and turn off the vacuum pump. Set the oven temperature to 90℃.

[0033] (5) After 2 hours, open the oven vacuum valve, open valve 1, observe the vacuum level drop to -0.02~-0.01MPA, then close valve 1. Turn on the vacuum pump, open valve 2, and after the vacuum level reaches -0.1MPA, close the oven vacuum valve, close valve 2, and turn off the vacuum pump.

[0034] (6) Repeat step (5) and maintain for 15 hours. Then set the oven to 20°C, turn off the oven power switch, and let the oven cool to room temperature. Open the oven vacuum valve and open valve 1 to purge the vacuum with nitrogen. After the vacuum level is 0, close valve 1.

[0035] (7) Open the oven door (the oven is in the drying room), take out the battery cells and put them into the aluminum bag. Heat seal the aluminum bag in the drying room and move it into the glove box.

[0036] (8) Cut open the aluminum packaging bag in the glove box, take out a piece of battery cell, break it open, scrape 0.15-0.2 grams of powder from the positive and negative electrodes respectively, put them into the moisture measuring bottle, and mark the positive and negative electrodes.

[0037] (9) The sample was sent to the drying room and the moisture content was measured using an 860 KF Thermoprep cartridge furnace. The furnace temperature was set to 180°C and the time for heating nitrogen to carry away the volatile moisture was set to 300 seconds. The moisture content of the positive and negative electrodes was obtained by operating the moisture meter program.

[0038] The test results are shown in Table 3.

[0039] Table 3 The test results show that: (1) As can be seen from Application Examples 1-12, the present invention solves the technical problem of the battery cell moisture content not being lower than 60 ppm due to the balance between the moisture in the gas phase and the moisture in the battery cell during the battery cell drying process by using a combination of carbonate compounds, alkyl silicate compounds and silazane solvents as battery cell desiccant.

[0040] (2) As can be seen from Application Examples 1-4, when the molar ratio of EMC / H2O is fixed at 1, the molar ratio of MTMS / H2O is fixed at 2, and the molar ratio of HMDS / H2O increases from 0.9 to 1.2, the moisture content of the positive and negative electrodes decreases, but the change is not significant. In contrast, when the molar ratio of HMDS / H2O in Application Example 1 is set to 0, the moisture content of the positive and negative electrodes increases sharply.

[0041] As can be seen from Application Examples 5-8, when the molar ratio of EMC / H2O is fixed at 1 and the molar ratio of HMDS / H2O is fixed at 1, and the molar ratio of MTMS / H2O increases from 1.5 to 2.2, the moisture content of both the positive and negative electrodes decreases, but the change is not significant. In contrast, in Application Example 2, where the molar ratio of MTMS / H2O is set to 0, the moisture content of both the positive and negative electrodes increases sharply.

[0042] As can be seen from Application Examples 9-12, when the molar ratio of MTMS / H2O is fixed at 2 and the molar ratio of HMDS / H2O is fixed at 1, and the molar ratio of EMC / H2O increases from 0.9 to 1.2, the moisture content of the positive and negative electrodes changes slightly. In contrast, in Application Example 3, when the molar ratio of EMC / H2O is set to 0, the moisture content of the positive and negative electrodes increases.

[0043] Data from Application Examples 1-12 show that when the composition ratio of the desiccant varies within the above range, the moisture content of the battery cell remains stable between 1.6 and 6.1 ppm, providing strong technical support for the uniformity of battery quality.

[0044] (3) By comparing the application examples 1-3, it can be seen that setting the EMC ratio to 0 has a smaller impact on the moisture content of the battery cell, while setting the MTMS and HMDS ratio to 0 has a larger impact on the moisture content of the battery cell.

[0045] (4) By comparing application examples 1-12 with comparative application example 4, it can be seen that the performance of the battery cell desiccant is significantly worse after MTMS is replaced with tetraethyl orthosilicate.

[0046] In summary, this invention solves the technical problem of maintaining a cell moisture content of no less than 60 ppm during the cell drying process by using a combination of carbonate compounds, alkyl silicate compounds, and silazane solvents as a cell desiccant.

[0047] The applicant declares that the above description is only a specific embodiment of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention fall within the protection and disclosure scope of the present invention.

Claims

1. A battery cell desiccant, characterized in that, The battery cell desiccant includes carbonate compounds, alkyl silicate compounds, and silazane solvents.

2. The battery cell desiccant according to claim 1, characterized in that, The carbonate compounds include any one or a combination of at least two of dimethyl carbonate, ethyl methyl carbonate, or diethyl carbonate.

3. The battery cell desiccant according to claim 1 or 2, characterized in that, The alkyl silicate compounds include any one or a combination of at least two of methyltrimethoxysilane, dimethyldimethoxysilane, or vinyltrimethoxysilane.

4. The battery cell desiccant according to any one of claims 1-3, characterized in that, The silazane solvents include hexamethyldisilazane and / or heptamethyldisilazane.

5. The battery cell desiccant according to any one of claims 1-4, characterized in that, The molar ratio of the carbonate compound to the silazane solvent is (0.6-1.5):

1.

6. The battery cell desiccant according to any one of claims 1-5, characterized in that, The molar ratio of the alkyl silicate compound to the silazane solvent is (0.8-2.8):

1.

7. A method for drying a battery cell, characterized in that, The drying method includes the following steps: The battery cell desiccant as described in any one of claims 1-6 is used to dry the battery cell under vacuum conditions to obtain the dried battery cell.

8. The drying method according to claim 7, characterized in that, In the battery cell desiccant, the molar number of alkyl silicate compounds is 1.0-2.2 times the molar number of water molecules in the battery cell before drying.

9. The drying method according to claim 7 or 8, characterized in that, In the battery cell desiccant, the molar number of silazane solvents is 0.8-1.2 times the molar number of water molecules in the battery cell before drying.

10. The drying method according to any one of claims 7-9, characterized in that, In the battery cell desiccant, the number of moles of carbonate compounds is 0.8-1.2 times the number of moles of moisture in the battery cell before drying.

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