A low-temperature-resistant lithium-ion battery negative electrode slurry and its preparation method and application

Abstract

The present invention discloses a low-temperature-resistant lithium-ion battery negative electrode slurry, its preparation method, and application, belonging to the field of lithium-ion battery technology. The low-temperature-resistant lithium-ion battery negative electrode slurry is composed of the following components, calculated by mass percentage: 42-48.5% negative electrode material, 0.1-3.0% polyacrylate binder, 1-2.0% conductive agent, 0.6-1.5% sodium carboxymethyl cellulose, and 45-55% deionized water. The negative electrode slurry of the present invention improves the compatibility of the electrolyte and the negative electrode material at low temperatures, increases the ion transfer rate, and reduces the internal resistance, effectively ensuring the low-temperature discharge performance of the lithium-ion battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium ion batteries, and in particular to a low-temperature resistant lithium ion battery negative electrode slurry, a preparation method thereof, and an application thereof. Background Art

[0002] The working principle of lithium-ion battery is: Li + Diffusion in the electrolyte and Li + The intercalation and deintercalation between the positive and negative electrodes realizes the mutual conversion of electrical energy and chemical energy. With the rapid development of the electronic cigarette industry, the requirements for the low temperature resistance of electronic cigarette batteries are getting higher and higher, while the low temperature performance of lithium-ion batteries is affected by Li + Movement rate in positive and negative electrode materials, Li + The impact of factors such as the movement rate in the electrolyte, the electrolyte / electrolyte interface film impedance, and the charge transfer rate. Currently, most electrolytes on the market increase in viscosity in low-temperature environments, reducing the ion transfer rate; even the solvent components crystallize at low temperatures, resulting in increased internal resistance of the battery and reduced discharge efficiency.

[0003] Therefore, it is very necessary to develop a low-temperature resistant lithium-ion battery negative electrode slurry and its preparation method that can improve the compatibility of the electrolyte and the negative electrode material at low temperatures, increase the ion transfer rate, and reduce the internal resistance, so as to solve the problem that existing lithium-ion batteries are difficult to transport and store at low temperatures and difficult to discharge at low temperatures. Summary of the Invention

[0004] In order to overcome the shortcomings of the prior art, the purpose of the present invention is to provide a low-temperature resistant lithium-ion battery negative electrode slurry and a preparation method thereof. The negative electrode slurry can improve the compatibility of the electrolyte and the negative electrode material at low temperatures, increase the ion transfer rate, and reduce the internal resistance, thereby effectively ensuring the low-temperature discharge performance of the lithium-ion battery.

[0005] In order to solve the above problems, the technical solutions adopted by the present invention are as follows:

[0006] A low-temperature-resistant lithium-ion battery negative electrode slurry consists of the following components in percentage by mass: 42-48.5% of a negative electrode material, 0.1-3.0% of a polyacrylate binder, 1-2.0% of a conductive agent, 0.6-1.5% of sodium carboxymethyl cellulose, and 45-55% of deionized water.

[0007] As a preferred embodiment of the present invention, the negative electrode material is one of artificial graphite, natural graphite, lithium titanate, lithium alloy, and nano silicon carbon powder.

[0008] As a preferred embodiment of the present invention, the conductive agent is one of conductive carbon black, carbon nanotubes, graphene, and carbon fiber.

[0009] A second object of the present invention is to provide a method for preparing the low-temperature resistant lithium-ion battery negative electrode slurry as described above, which specifically comprises the following steps:

[0010] S1. Mix the formulated amount of sodium carboxymethyl cellulose with a portion of deionized water and stir evenly to form a first glue solution;

[0011] S2, adding the negative electrode material in the formula amount to the first glue solution, stirring evenly to form a second glue solution;

[0012] S3. Add the conductive agent and the remaining deionized water in the formula amount to the second glue solution, and stir evenly to obtain a third glue solution;

[0013] S4, adding polyacrylate binder to the third glue solution, controlling the solid content to 44-48%, stirring evenly and then vacuuming to obtain a slurry;

[0014] S5. Defoaming the obtained slurry, filling it with air and releasing the vacuum to obtain the negative electrode slurry for lithium-ion batteries.

[0015] As a preferred embodiment of the present invention, the vacuum degree in step S4 is -0.08 MPa.

[0016] A third object of the present invention is to provide a low-temperature resistant lithium-ion battery, which includes a positive electrode sheet, a negative electrode sheet made of the above-mentioned negative electrode slurry, a separator, and a low-temperature electrolyte.

[0017] As a preferred embodiment of the present invention, the low-temperature electrolyte comprises the following components by mass percentage: 10-15% electrolyte salt, 73-88% non-aqueous organic solvent, and 1-12% additives.

[0018] As a preferred embodiment of the present invention, the electrolyte salt is a mixture of lithium tetrafluoroborate and lithium bis(oxalatoborate).

[0019] As a preferred embodiment of the present invention, the non-aqueous organic solvent is selected from at least one of ethyl acetate, ethylene carbonate, propylene carbonate or ethyl methyl carbonate.

[0020] As a preferred embodiment of the present invention, the additive is selected from at least one of triphenyl phosphate, monofluoromethylethylene carbonate, difluoromethylethylene carbonate or trifluoromethylethylene carbonate.

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] By adding a polyacrylic acid binder to the negative electrode slurry, the present invention forms a good solid electrolyte interface layer on the negative electrode surface, improving the compatibility of the low-temperature electrolyte with the negative electrode material, while ensuring strong adhesion between the negative electrode material and the current collector, thereby improving the mechanical properties of the electrode sheet. Furthermore, by optimizing the ratio of the low-temperature electrolyte and combining it with the negative electrode slurry of the present invention, the ion transfer rate of the resulting lithium-ion battery is increased, the internal resistance is reduced, and transportation and storage in cold regions are facilitated. Furthermore, the rate discharge capacity can be quickly restored at -10°C, improving the low-temperature storage performance and low-temperature rate discharge performance of the lithium battery, thereby resolving the problem of the battery's difficulty in transportation, storage, and discharge at low temperatures. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a low-temperature discharge performance test curve of the lithium-ion battery provided in Example 2 of the present invention. DETAILED DESCRIPTION

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0025] A low-temperature-resistant lithium-ion battery negative electrode slurry is composed of the following components, calculated by mass percentage: 42-48.5% negative electrode material, 0.1-3.0% polyacrylate binder, 1-2.0% conductive agent, 0.6-1.5% sodium carboxymethyl cellulose, and 45-55% deionized water. The negative electrode material is selected from artificial graphite, natural graphite, lithium titanate, lithium alloy, or nano-silicon-carbon powder; and the conductive agent is selected from conductive carbon black, carbon nanotubes, graphene, or carbon fiber. The preparation method comprises the following steps:

[0026] S1. Mix the formulated amount of sodium carboxymethyl cellulose with part of the deionized water, stir for 5 to 10 minutes at a revolution of 5 r / min and a rotation speed of 200 r / min, and then stir for 120 minutes at a revolution of 35 r / min and a rotation speed of 1700 r / min to form a first glue solution;

[0027] S2. Add the formulated amount of negative electrode material to the first glue solution, and stir at a revolution speed of 35 r / min and a rotation speed of 1700 r / min for 120 min to form a second glue solution;

[0028] S3. Add the conductive agent and the remaining deionized water in the formula amount to the second glue solution, and stir at a revolution speed of 35 rpm and a rotation speed of 1700 rpm for 90 min to obtain a third glue solution;

[0029] S4. Add polyacrylate binder to the third glue solution, control the solid content to 44-48%, stir at a revolution speed of 25 r / min and a rotation speed of 900 r / min for 30 min, and evacuate to a vacuum degree of -0.08 MPa to obtain a slurry;

[0030] S5. Defoaming the obtained slurry, filling it with air and releasing the vacuum to obtain the negative electrode slurry for lithium-ion batteries.

[0031] A low-temperature-resistant lithium-ion battery comprises a positive electrode sheet, a negative electrode sheet made from the above-mentioned negative electrode slurry, a separator, and a low-temperature electrolyte. The low-temperature electrolyte comprises the following components, by mass percentage: 10-15% electrolyte salt, 73-88% non-aqueous organic solvent, and 1-12% additives. The electrolyte salt is a mixture of lithium tetrafluoroborate and lithium bis(oxalatoborate). The non-aqueous organic solvent is selected from at least one of ethyl acetate, ethylene carbonate, propylene carbonate, or ethyl methyl carbonate. The additive is selected from at least one of triphenyl phosphate, monofluoromethylethylene carbonate, difluoromethylethylene carbonate, or trifluoromethylethylene carbonate.

[0032] Embodiment 1:

[0033] A low-temperature-resistant lithium-ion battery comprises a negative electrode plate and a low-temperature electrolyte.

[0034] Among them, the negative electrode sheet is made of low-temperature resistant lithium-ion battery negative electrode slurry, which is composed of the following components by mass percentage: 43% natural graphite, 1% conductive carbon black, 1% sodium carboxymethyl cellulose CMC, 54.9% deionized water, and 0.1% polyacrylate adhesive.

[0035] The method for preparing the negative electrode slurry comprises the following steps:

[0036] S1. Mix the formulated amount of sodium carboxymethyl cellulose with part of the deionized water, stir for 5 to 10 minutes at a revolution of 5 r / min and a rotation speed of 200 r / min, and then stir for 120 minutes at a revolution of 35 r / min and a rotation speed of 1700 r / min to form a first glue solution;

[0037] S2. Add the formulated amount of negative electrode material to the first glue solution, and stir at a revolution speed of 35 r / min and a rotation speed of 1700 r / min for 120 min to form a second glue solution;

[0038] S3. Add the conductive agent and the remaining deionized water in the formula amount to the second glue solution, and stir at a revolution speed of 35 rpm and a rotation speed of 1700 rpm for 90 min to obtain a third glue solution;

[0039] S4. Add polyacrylate binder to the third glue solution, control the solid content to 45.4%, stir at a revolution of 25 r / min and a rotation speed of 900 r / min for 30 min, and evacuate to a vacuum degree of -0.08 MPa to obtain a slurry;

[0040] S5. Defoaming the obtained slurry, filling it with air and releasing the vacuum to obtain the negative electrode slurry for lithium-ion batteries.

[0041] The low-temperature electrolyte consists of the following components, calculated by mass: 10% lithium tetrafluoroborate, 2% lithium bis(oxalatoborate), 83% non-aqueous organic solvent, and 5% triphenyl phosphate. Prior to preparation, the solid components were dried with 3A molecular sieves to ensure the electrolyte's moisture content was below 150 ppm. The preparation process is as follows: ethyl acetate, ethylene carbonate, propylene carbonate, and ethyl methyl carbonate were mixed in a mass ratio of 3:2:2:3 to prepare the non-aqueous organic solvent. Triphenyl phosphate was then added, followed by lithium tetrafluoroborate and lithium bis(oxalatoborate) to form the low-temperature electrolyte. All preparation steps were completed in a glove box filled with an argon atmosphere.

[0042] Preparation of lithium-ion batteries: The above-mentioned negative electrode slurry is used to prepare lithium-ion batteries through the following steps: coating, rolling, slitting, sheeting, winding, packaging, liquid injection, aging, formation, secondary sealing, capacity adjustment, and full inspection. The electrolyte used for liquid injection is the above-mentioned low-temperature electrolyte, which accounts for 25% of the battery weight.

[0043] Example 2:

[0044] A low-temperature-resistant lithium-ion battery includes a negative electrode plate and a low-temperature electrolyte. This embodiment differs from Example 1 in that the negative electrode slurry used for the low-temperature-resistant lithium-ion battery comprises the following components, calculated by mass percentage: 43% natural graphite, 1% conductive carbon black, 1% sodium carboxymethyl cellulose (CMC), 53% deionized water, and 2% polyacrylate binder. All other components are the same as in Example 1.

[0045] The discharge performance of lithium-ion batteries was measured at room temperature 25°C and low temperature -10°C. The results are as follows: Figure 1 As shown. Figure 1 It can be seen that the lithium ion battery prepared in the present invention has a discharge platform of 3.2V at both low temperature and room temperature at a low temperature of -10°C, a low temperature discharge capacity of 659.8mAh, a room temperature discharge capacity of 789.2mAh, and a low temperature / room temperature discharge capacity ratio of 83%. It can be seen that the lithium ion battery prepared in this embodiment has good low temperature discharge capability.

[0046] Example 3:

[0047] A low-temperature-resistant lithium-ion battery includes a negative electrode plate and a low-temperature electrolyte. This embodiment differs from Example 1 in that the negative electrode slurry used for the low-temperature-resistant lithium-ion battery comprises the following components, calculated by mass percentage: 43% artificial graphite, 1% graphene, 1% sodium carboxymethyl cellulose (CMC), 52% deionized water, and 3% polyacrylate binder. All other components are the same as in Example 1.

[0048] Comparative Example 1:

[0049] This comparative example differs from Example 2 in that the electrolyte used in the electrolyte solution is different. Specifically, the room-temperature electrolyte solution comprises the following components, calculated by mass percentage: 12% lithium hexafluorophosphate, 83% nonaqueous organic solvent, and 5% triphenyl phosphate. All other conditions are the same as in Example 1.

[0050] Comparative Example 2:

[0051] The difference between this comparative example and Example 1 is that the adhesive used is styrene-butadiene rubber (SBR). All other aspects are the same as those of Example 1.

[0052] Comparative Example 3:

[0053] The difference between this comparative example and Example 2 is that the adhesive used is styrene-butadiene rubber (SBR). All other aspects are the same as those of Example 2.

[0054] Comparative Example 4:

[0055] The difference between this comparative example and Example 3 is that the adhesive used is styrene-butadiene rubber (SBR). All other aspects are the same as those of Example 3.

[0056] Bonding effect verification experiment:

[0057] The bonding effect and mechanical strength of the negative electrode sheets prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were tested. The results are shown in Table 1.

[0058] Table 1 Comparison of bonding effect and mechanical strength results of Examples 1 to 3 and Comparative Examples 1 to 4

[0059] project Type and dosage of adhesive Pole bonding effect Electrode mechanical strength Example 1 Polyacrylate 0.1% Difference Difference Example 2 Polyacrylate 2% excellent excellent Example 3 Polyacrylate 3% good good Comparative Example 1 Polyacrylate 2% excellent excellent Comparative Example 2 Styrene butadiene rubber 0.1% Difference Difference Comparative Example 3 Styrene butadiene rubber 2% good good Comparative Example 4 Styrene butadiene rubber 3% good good

[0060] From the analysis of Table 1, it can be seen that whether the addition ratio of styrene-butadiene rubber or polyacrylate binder is low, the bonding effect will be poor. The reason is that the small amount of binder added makes the active material on the electrode sheet and the binder unevenly dispersed. When the addition ratio is 2%, the electrode sheet bonding effect of polyacrylate is better than that of styrene-butadiene rubber. This is because at this ratio, the polyacrylate binder can form a good solid electrolyte interface layer on the negative electrode surface, which can improve the compatibility between the low-temperature electrolyte and the negative electrode material. When the addition ratio of polyacrylate is 3%, the bonding effect decreases because it is difficult to disperse by stirring, which makes the negative electrode slurry easily agglomerated. It can be seen that the present invention, by selecting a specific polyacrylate binder and screening its dosage, enables the negative electrode slurry to obtain better compatibility between the low-temperature electrolyte and the negative electrode material.

[0061] Low temperature discharge performance verification experiment:

[0062] The lithium-ion batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were subjected to a low-temperature charging test. The specific operation was as follows: the lithium-ion batteries were fully charged at 1C constant current and constant voltage at room temperature, the batteries were placed in a low-temperature box at -10±2°C for 4 hours, and then discharged to 3.0V at a current of 3A. The batteries were taken out and placed at 25±5°C for 2 hours. The appearance was observed. The results are shown in Table 2.

[0063] Table 2 Comparison of low temperature discharge performance test results of Examples 1 to 3 and Comparative Examples 1 to 4

[0064]

[0065] From the analysis of Table 2, it can be seen that the internal resistance of Examples 1 to 3 is lower than that of Comparative Examples 1 to 4, indicating that the polyacrylate adhesive combined with the low-temperature electrolyte can effectively reduce the contact impedance, reduce electrode polarization, and improve the electrochemical performance. After the test, the residual (discharge) capacity and median voltage of the batteries of Examples 1 to 3 are higher than those of the corresponding Comparative Examples 1 to 4, indicating that the lithium-ion battery prepared by the present invention forms a thin and dense SEI film on the negative electrode, ensuring the Li + It has a large diffusion coefficient in the active material, thus ensuring the discharge capacity of the battery at low temperatures. It will not deform, explode or leak during low-temperature discharge, and has good safety performance.

[0066] Low temperature storage performance verification experiment:

[0067] The lithium-ion batteries prepared in Examples 1 to 3 and Comparative Examples 1 to 4 were subjected to a low-temperature storage test. The specific operation was as follows: the battery was fully charged according to the standard, the voltage and internal resistance were recorded, and the battery was placed at -40±2°C for 24 hours, the voltage and internal resistance were recorded, and then the battery was placed at -10±2°C for 2 hours and then discharged at 3A to 3.0V. The battery was observed to see whether it could be discharged at -10°C. The results are shown in Table 3.

[0068] Table 3 Comparison of low temperature storage performance test results of Examples 1 to 3 and Comparative Examples 1 to 4

[0069]

[0070] Analysis of Table 3 shows that after storage at -40±2°C for 24 hours, the lithium-ion batteries of Examples 1 to 3 have an internal resistance increase rate of ≤5%, a pressure drop rate of ≤1%, no bloating, and no leakage, and can be well discharged at -10°C. In contrast, the internal resistance increase rates of Comparative Examples 1 to 4 mostly exceed 5%, and the pressure drop rates mostly exceed 1%. It can be seen that the lithium-ion batteries of Examples 1 to 3 can be stored at -40°C.

[0071] In summary, the lithium-ion battery provided by the present invention uses a polyacrylate adhesive to replace the original water-based adhesive styrene-butadiene rubber SBR, and the lithium-ion battery prepared using a low-temperature electrolyte has superior low-temperature storage performance and low-discharge performance than the lithium-ion battery using styrene-butadiene rubber SBR as a binder. The lithium battery prepared can be stored at -40°C and can be discharged at a rate of 3A when the temperature returns to -10°C.

[0072] The above embodiments are only preferred embodiments of the present invention and cannot be used to limit the scope of protection of the present invention. Any non-substantial changes and replacements made by technicians in this field on the basis of the present invention fall within the scope of protection required by the present invention.

Claims

1. A low-temperature-resistant lithium-ion battery, characterized in that: The lithium-ion battery includes a positive electrode sheet, a negative electrode sheet, a separator, and a low-temperature electrolyte; The negative electrode sheet includes a negative electrode slurry, which is composed of the following components in percentage by mass: 42-48.5% of negative electrode material, 0.1-3.0% of polyacrylate binder, 1-2.0% of conductive agent, 0.6-1.5% of sodium carboxymethyl cellulose, and 45-55% of deionized water; The low-temperature electrolyte includes the following components by mass percentage: 10-15% electrolyte salt, 73-88% non-aqueous organic solvent, and 1-12% additives; the electrolyte salt is a mixture of lithium tetrafluoroborate and lithium bis(oxalatoborate).

2. The low-temperature-resistant lithium-ion battery according to claim 1, characterized in that: The negative electrode material is one of artificial graphite, natural graphite, lithium titanate, lithium alloy, and nano silicon carbon powder.

3. The low-temperature-resistant lithium-ion battery according to claim 1, wherein: The conductive agent is one of conductive carbon black, carbon nanotubes, graphene, and carbon fiber.

4. The low-temperature-resistant lithium-ion battery according to claim 1, wherein: The non-aqueous organic solvent is selected from at least one of ethyl acetate, ethylene carbonate, propylene carbonate or ethyl methyl carbonate.

5. The low-temperature-resistant lithium-ion battery according to claim 1, characterized in that: The additive is selected from at least one of triphenyl phosphate, monofluoromethylethylene carbonate, difluoromethylethylene carbonate or trifluoromethylethylene carbonate.

Images