Low-temperature sodium-ion battery pole piece, battery cell and preparation method of low-temperature sodium-ion battery pole piece

Abstract

The invention belongs to the technical field of battery preparation, and particularly relates to a low-temperature sodium-ion battery pole piece, a battery cell and a preparation method thereof. The battery pole piece is composed of a porous current collector and active substance slurry, the active substance slurry adopts a gradient coating mode, and the current collector is sequentially provided with a first active substance slurry coating and a second active substance slurry coating from inside to outside; the first active material slurry coating and the second active material slurry coating are arranged on the reverse side of the substrate. As the content of the conductive agent near the current collector side is high, more conductive networks are created, the electron transmission resistance of the pole piece is low, and the dynamic and cycling stability of the battery is improved. The low-temperature sodium-ion battery system constructed by matching the gradient layered pole piece with the porous current collector and the super-current electrolyte can effectively improve the dynamics inside the battery, and the low-temperature sodium-ion battery has excellent low-temperature rate performance and cycle performance, and is simple in preparation method and low in cost.

Description

Technical Field

[0001] The present invention belongs to the technical field of battery preparation, and in particular relates to a low-temperature sodium ion battery pole piece, a battery core and a preparation method thereof. Background Art

[0002] With the development of the new energy economy, power batteries and 3C consumer batteries have developed most rapidly, and product updates and iterations have been rapid. At the same time, higher requirements are placed on low-temperature performance for power batteries and 3C consumer batteries. Usually, the main design environment for secondary batteries is 0~45℃ to meet the needs under typical environments. However, with the transformation of the application market, higher requirements are placed on the low-temperature performance of batteries. For example, in the field of transportation, batteries are required to provide stable energy output at -40℃, the military defense field needs to provide communication equipment with batteries that can work at -40℃, the polar scientific research field needs batteries that can work at -80℃, and the field of extraterrestrial exploration needs batteries that can withstand extreme cold conditions of -100℃ or even lower. Traditional secondary batteries have low ion and electron conductivity and poor system kinetics in low-temperature environments, which causes the battery to show a significant performance degradation.

[0003] Therefore, there is an urgent need to provide a sodium ion battery cell with stable performance under low temperature conditions, long cycle life, good safety, simple process, low cost, and suitable for industrial production.

[0004] The sodium ion battery disclosed in CN 111525099 B provides a higher initial coulombic efficiency and rate performance by adopting a positive electrode material-hard carbon system constructed by controlling the particle size of the positive and negative electrode materials. However, it is not matched with a low-temperature electrolyte, so the low-temperature performance of the system needs to be verified. Summary of the invention

[0005] The technical problem to be solved by the present invention is to overcome the problem of poor kinetic performance of secondary batteries under low temperature conditions and provide a sodium ion battery system constructed by a porous current collector-step coating-superfluid electrolyte with high conductivity, rapid mass transfer and low cost under low temperature conditions.

[0006] The technical problem further to be solved by the present invention is to overcome the defects of the prior art and provide a method for preparing a low-temperature sodium ion battery cell with simple process, low cost and suitable for industrial production.

[0007] In order to achieve the above-mentioned purpose, the present invention provides a low-temperature sodium ion battery pole piece, which adopts a porous current collector; a first active material slurry coating and a second active material slurry coating are sequentially arranged on both sides of the current collector from the inside to the outside, and a first active material slurry coating and a second active material slurry coating are arranged on the reverse side thereof; wherein the type and / or content of the conductive agent in the first active material slurry coating is different from that in the second active material slurry coating, and the ionic conductivity and electronic conductivity of the first active material slurry coating close to the current collector are higher than those of the second active material slurry coating, the battery pole piece includes a positive pole piece and a negative pole piece, and the low temperature is a temperature below zero degrees.

[0008] The present invention also provides a low-temperature sodium ion battery cell, which comprises the battery pole piece and superfluid electrolyte described above.

[0009] The present invention also provides a method for preparing a low-temperature sodium ion battery cell as described above, which comprises the following steps: (1) Preparation of battery slurry: The positive electrode material, the negative electrode material, the conductive agent and the binder are dissolved in a solvent and dispersed into a uniform slurry to obtain positive electrode active material slurry and negative electrode active material slurry respectively; (2) Coating of battery slurry: The positive electrode active material slurry and the negative electrode active material slurry obtained in step (1) are respectively coated on the two sides of the corresponding porous current collector by a coating machine; and the first active material slurry coating and the second active material slurry coating are sequentially arranged on both sides of the current collector from the inside to the outside, and the first active material slurry coating and the second active material slurry coating are arranged on the reverse side thereof, so as to obtain a positive electrode coating and a negative electrode coating, respectively; wherein the type and content of the conductive agent in the first active material slurry coating are different from those in the second active material slurry coating, and the ionic conductivity and electronic conductivity of the first active material slurry coating close to the current collector are higher than those of the second active material slurry coating; (3) Electrode sheet rolling: The positive electrode coating sheet and the negative electrode coating sheet obtained in step (2) are respectively pressed into dense electrode sheets with uniform thickness by a roller press, and then cut into positive electrode sheets and negative electrode sheets respectively; (4) Winding, tab welding, and baking: The positive electrode sheet and the negative electrode sheet tabs obtained in step (3) are welded, and then the positive electrode sheet, the separator, and the negative electrode sheet are wound into a bare cell in the order of the positive electrode sheet, the separator, and the negative electrode sheet, and then the cell is placed in a shell and baked in an oven; (5) Liquid injection: Test the water content of the battery cell prepared in step (4). If the test is qualified, inject the superfluid electrolyte and seal the cell. (6) Chemical formation and capacity separation: The battery obtained in step (5) is formed at room temperature with a small current, aged at high temperature, and then capacity separated to obtain a sodium ion battery cell.

[0010] Preferably, the mass percentages of the positive electrode material, the conductive agent and the binder in the positive electrode active material slurry are 90%~97%: 1%~4%: 2%~4%; the mass percentages of the negative electrode material, the conductive agent and the binder in the negative electrode active material slurry are 90%~98%: 2%~4%: 1%~4%.

[0011] Preferably, the positive electrode material includes at least one of sodium copper manganate, sodium nickel iron manganate, sodium vanadium phosphate, sodium iron pyrophosphate, sodium iron sulfate positive electrode materials and modified positive electrode materials thereof.

[0012] Preferably, the negative electrode material is at least one of biomass hard carbon, coal-based hard carbon, and resin-based hard carbon negative electrode materials.

[0013] Preferably, the solvent in step (1) is at least one of water, acetone, N-methylpyrrolidone, N,N-dimethylformamide, dimethylacetamide and difluoromethane.

[0014] Preferably, the conductive agent is at least one of a carbon black conductive agent, a graphite conductive agent, a fiber conductive agent, a nanotube conductive agent, and a graphene conductive agent.

[0015] Preferably, the sodium salt in the superfluid electrolyte is at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium trifluoromethylsulfonate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide; the additive is at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, 1,3-propane sultone, sodium difluorooxalatoborate, and sodium bis(oxalatoborate); and the solvent is at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethyl propionate, and ethyl acetate.

[0016] Compared with the prior art, the present invention has the following beneficial effects: (1) The present invention uses a porous current collector. The porous structure increases the contact area between the electrode material and the electrolyte, allowing the electrochemical reaction to proceed more quickly and fully. At the same time, the pores provide a channel for rapid transmission of the electrolyte and reactants, which helps to reduce concentration polarization and improve the performance of batteries or electrochemical devices. In some cases, the porous current collector can also enhance the stability of the electrode by providing additional mechanical support and extend the service life of the device. Finally, in some cases, the porous current collector can replace the traditional solid current collector, thereby saving material costs and improving the energy density of the battery.

[0017] (2) The present invention adopts gradient coating, and the content and / or type of the conductive agent in the active material slurry of the first layer coated with the current collector is different from that of the active material slurry of the second layer. The conductive agent performance in the active material slurry near the current collector is better than that on the far side of the current collector, and the conductive agent content in the active material slurry near the current collector is higher than that on the far side of the current collector. The high content of the conductive agent near the current collector can create more conductive networks, the electron transfer resistance of the electrode is low, and the battery dynamics and cycle stability at low temperatures are improved.

[0018] (3) When the content of the conductive agent remains unchanged, the performance of the gradient layered pole piece with a high content of the conductive agent in the lower layer close to the current collector is better than that of the gradient layered pole piece with a high content of the conductive agent in the upper layer, or compared with only a single layer of the conductive agent. This makes it possible to reduce costs by using less conductive agent by setting a gradient layered pole piece with a high content of the conductive agent in the lower layer close to the current collector. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0020] Figure 1 A schematic diagram of a low-temperature sodium ion battery electrode provided by the present invention; Figure 2 This is a -10°C cycle diagram of the battery of Example 1 of the present invention; Figure 3 This is the -10°C charge and discharge diagram of the battery in Example 1 of the present invention; Figure 4 This is a -10°C low temperature charging diagram of the battery in Example 1 of the present invention; Figure 5 This is a -20°C low temperature charging diagram of the battery in Example 1 of the present invention; Figure 6 This is a -20°C low-temperature discharge diagram of the battery in Example 1 of the present invention; Figure 7 This is a -30°C low-temperature discharge diagram of the battery in Example 1 of the present invention; Figure 8 This is a -40°C low-temperature discharge diagram of the battery in Example 1 of the present invention; Fig. 9 This is a cycle diagram of the battery of Comparative Example 1 of the present invention at -10°C; Fig.10The diagram shows the influence of different distribution of conductive agent on electron conduction, among which (a) is a gradient layered electrode with a high content of conductive agent in the upper layer, (b) is a single layer of conductive agent with uniform distribution, and (c) is a gradient layered electrode with a high content of conductive agent in the lower layer.

[0021] Logo Description: 1-1 is the first active material slurry coating on the A side of the pole piece; 1-2 is the second active material slurry coating on the A side of the pole piece; 2-1 is the porous current collector coating; 3-1 is the first active material slurry coating on the B side of the pole piece; 3-2 is the second active material slurry coating on the B side of the pole piece. DETAILED DESCRIPTION

[0022] In order to facilitate the understanding of the present invention, the present invention will be described more comprehensively and meticulously below in conjunction with the accompanying drawings and preferred embodiments of the present invention, but the protection scope of the present invention is not limited to the following specific embodiments.

[0023] Unless otherwise defined, all professional terms used below have the same meanings as those generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention.

[0024] Unless otherwise specified, various raw materials, reagents, instruments and equipment used in the present invention can be purchased from the market or prepared by existing methods.

[0025] In order to improve the low-temperature performance of sodium-ion batteries, the present application designs a low-temperature sodium-ion electrode, which is composed of a porous current collector and an active material slurry, wherein the active material slurry adopts a gradient coating mode, specifically, the first active material slurry coating and the second active material slurry coating are sequentially arranged from the inside to the outside on both sides of the current collector; and the first active material slurry coating and the second active material slurry coating on the reverse side thereof. The type and / or content of the conductive agent in the first active material slurry coating close to the current collector is different from that in the second active material slurry coating.

[0026] The embodiment of the present invention also provides a low-temperature sodium ion battery cell, which includes the above-mentioned battery pole piece, specifically including a low-temperature sodium ion battery system constructed by a gradient layered pole piece, a porous current collector and a superfluid electrolyte. The present invention also provides a method for preparing the low-temperature sodium ion battery cell, comprising the following steps: (1) Preparation of battery slurry: The positive and negative electrode materials are respectively dissolved with the conductive agent and the binder in the solvent to obtain the positive and negative electrode active material slurries. In this process, the mass percentages of the positive electrode material, the conductive agent and the binder in the positive electrode active material slurry are 90%~97%: 1%~4%: 2%~4%; the mass percentages of the negative electrode material, the conductive agent and the binder in the negative electrode active material slurry are 90%~98%: 2%~4%: 1%~4%. The positive electrode material includes at least one of sodium nickel iron manganese oxide, sodium vanadium phosphate, sodium pyrophosphate iron phosphate, and sodium ferric sulfate positive electrode; the negative electrode material includes at least one of biomass hard carbon, coal-based hard carbon, and resin-based hard carbon negative electrode; the solvent is at least one of water, acetone, N-methylpyrrolidone, N,N-dimethylformamide, dimethylacetamide, and difluoromethane; the conductive agent is at least one of carbon black conductive agent, graphite conductive agent, fiber conductive agent, nanotube conductive agent, and graphene conductive agent.

[0027] (2) Coating of battery slurry: The positive electrode active material slurry and the negative electrode active material slurry obtained in step (1) are coated on the two sides of the corresponding porous current collector by a coating machine, and the slurry on the two sides of the porous current collector is coated in a gradient manner to obtain a positive electrode coating and a negative electrode coating, respectively.

[0028] (3) Electrode sheet rolling: The positive electrode coating sheet and the negative electrode coating sheet obtained in step (2) are respectively pressed into dense electrode sheets with uniform thickness by a roller press, and then cut into positive electrode sheets and negative electrode sheets respectively.

[0029] (4) Winding, tab welding, and baking: The positive electrode sheet and the negative electrode sheet tabs obtained in step (3) are welded, and then the positive electrode sheet, the separator, and the negative electrode sheet are wound into a bare cell in the order of the positive electrode sheet, the separator, and the negative electrode sheet, which are then placed in a shell and baked in an oven.

[0030] (5) Liquid injection: Test the water content of the battery cell prepared in step (4). If the test is qualified, inject the superfluid electrolyte and seal the cell.

[0031] (6) Formation and capacity division: The cylindrical battery obtained in step (5) is formed at room temperature with a small current, aged at high temperature for 48 hours, and then capacity division is performed.

[0032] In order to objectively illustrate the technical effects produced by the present application, the following embodiments and comparative examples will be used for description.

[0033] Example 1 A method for preparing a low-temperature sodium ion battery pole piece and a battery cell thereof comprises the following steps: (1) Preparation of battery slurry: The positive and negative electrode materials of the battery, the conductive agent and the binder are dissolved in a solvent and dispersed into a uniform slurry. The positive electrode material in the positive electrode first active material slurry coating slurry is Na 0.67 Cu 0.33 Mn0.67 O2 (Ti / Al dual doping), the conductive agent is conductive carbon nanotubes CNT and conductive carbon black SP, the binder is polyvinylidene fluoride PVDF, and its main material (i.e. Na 0.67 Cu 0.33 Mn 0.67 O2 (Ti / Al dual doping): CNT: SP: PVDF ratio is 94%: 1%: 1%: 4%, the positive electrode material in the positive electrode second active material slurry coating slurry is Na 0.67 Cu 0.33 Mn 0.67 O2 (Ti / Al dual doping), the conductive agent is SP, the binder is PVDF, and the main material: SP: PVDF ratio is 95%: 3%: 2%, among which the conductivity of CNT is greater than SP, the negative electrode first active material slurry coating slurry in which the negative electrode material is biomass hard carbon, the conductive agent is SP, the binder is sodium carboxymethyl cellulose CMC and styrene butadiene rubber SBR, and the main material: SP: CMC: SBR ratio is 95%: 2%: 1.5%: 1.5%, the negative electrode second active material slurry coating slurry in which the negative electrode material is biomass hard carbon, the conductive agent is SP, the binder is CMC and SBR, and the main material: SP: CMC: SBR ratio is 95%: 1.2%: 1.5%: 2.3%.

[0034] (2) Coating of battery slurry: The positive electrode active material slurry is coated on the porous current collector by a coating machine, wherein the coating surface density of the positive electrode first coating layer is 90 g / m 2 The surface density of the second coating layer of the positive electrode is 90g / m 2 The reverse side is coated in the same manner to obtain a positive electrode coating; the negative electrode active material slurry is coated on the porous current collector by a coating machine, wherein the surface density of the negative electrode first coating layer is 70g / m 2 The second coating layer of the negative electrode has a coating surface density of 70 g / m 2 The reverse side is coated in the same manner to obtain a negative electrode coating.

[0035] (3) Electrode sheet rolling: The positive electrode coating sheet and the negative electrode coating sheet obtained in step (2) are respectively pressed into dense electrode sheets with uniform thickness by a roller press, and then cut into positive electrode sheets and negative electrode sheets respectively.

[0036] (4) Winding, tab welding, and baking: The positive electrode sheet and the negative electrode sheet tabs obtained in step (3) are welded, and then the positive electrode sheet, the separator, and the negative electrode sheet are wound into a bare cell in the order of the positive electrode sheet, the separator, and the negative electrode sheet, which are then placed in a shell and baked in an oven.

[0037] (5) Liquid injection: After the water content of the battery cell in step (4) is tested to be qualified, inject the superfluid electrolyte, whose formula is: sodium hexafluorophosphate NAPF6: ethylene carbonate EC: propylene carbonate PC: ethyl methyl carbonate EMC: diethyl carbonate DEC: propenyl-1,3-sultone PST: 1,3-propane sultone PS: vinyl sulfate DTD: fluoroethylene carbonate FEC = 11.13: 7.11: 25.99: 28.14: 20.7: 0.42: 1.46: 1.41: 1.04, and seal the bottle.

[0038] (6) Capacity separation: The cylindrical battery obtained in step (5) is formed at room temperature with a small current, aged at high temperature for 48 h, and then capacity separation is performed to obtain a low-temperature sodium ion battery.

[0039] Example 2 A method for preparing a low-temperature sodium ion battery pole piece and a battery cell thereof comprises the following steps: (1) Preparation of battery slurry: The positive and negative electrode materials of the battery, the conductive agent and the binder are dissolved in a solvent and dispersed into a uniform slurry. The positive electrode material in the positive electrode first active material slurry coating slurry is Na 0.67 Cu 0.33 Mn 0.67 O2 (Ti / Al dual doping), the conductive agent is SP, the binder is PVDF, the main material: SP: PVDF ratio is 95%: 3%: 2%, the positive electrode material in the positive electrode second active material slurry coating slurry is Na 0.67 Cu 0.33 Mn 0.67 O2 (Ti / Al dual doping), the conductive agent is SP, the binder is PVDF, and the main material: SP: PVDF ratio is 96%: 2%: 2%, the negative electrode first active material slurry coating slurry in which the negative electrode material is biomass hard carbon, the conductive agent is SP: the binder is CMC and SBR, and the main material: SP: CMC: SBR ratio is 95%: 2%: 1.5%: 1.5%, the negative electrode second active material slurry coating slurry in which the negative electrode material is biomass hard carbon, the conductive agent is SP: the binder is CMC and SBR, and the main material: SP: CMC: SBR ratio is 95%: 1.2%: 1.5%: 2.3%.

[0040] (2) Coating of battery slurry: The positive electrode active material slurry is coated on the porous current collector by a coating machine, wherein the coating surface density of the positive electrode first coating layer is 90 g / m 2 The surface density of the second coating layer of the positive electrode is 80g / m 2 The reverse side is coated in the same manner to obtain a positive electrode coating; the negative electrode active material slurry is coated on the porous current collector by a coating machine, wherein the surface density of the negative electrode first coating layer is 70g / m 2 The negative electrode second coating layer has a coating surface density of 60 g / m2 The reverse side is coated in the same manner to obtain a negative electrode coating.

[0041] (3) Electrode sheet rolling: The positive electrode coating sheet and the negative electrode coating sheet obtained in step (2) are respectively pressed into dense electrode sheets with uniform thickness by a roller press, and then cut into positive electrode sheets and negative electrode sheets respectively.

[0042] (4) Winding, tab welding, and baking: The positive electrode sheet and the negative electrode sheet tabs obtained in step (3) are welded, and then the positive electrode sheet, the separator, and the negative electrode sheet are wound into a bare cell in the order of the positive electrode sheet, the separator, and the negative electrode sheet, which are then placed in a shell and baked in an oven.

[0043] (5) Liquid injection: After the water content of the battery cell in step (4) is tested and qualified, inject the superfluid electrolyte, whose formula is: NAPF6:EC:PC:EMC:DEC:PST:PS:DTD:FEC=11.13:7.11:25.99:28.14:20.7:0.42:1.46:1.41:1.04, and seal it.

[0044] (6) Capacity separation: The cylindrical battery obtained in step (5) is formed at room temperature with a small current, aged at high temperature for 48 h, and then capacity separation is performed to obtain a low-temperature sodium ion battery.

[0045] Comparative Example 1 A method for preparing a low-temperature sodium ion battery pole piece and a battery cell thereof comprises the following steps: (1) Preparation of battery slurry: The positive and negative electrode materials of the battery, the conductive agent, and the binder are dissolved in a solvent and dispersed into a uniform slurry. The positive electrode material is Na 0.67 Cu 0.33 Mn 0.67 O2 (Ti / Al dual doping), the conductive agent is SP, the binder is PVDF, and the main material: SP: PVDF ratio is 95%: 3%: 2%. The negative electrode material is biomass hard carbon, the conductive agent is SP: the binder is CMC and SBR, and the main material: SP: CMC: SBR ratio is 95%: 1.2%: 1.5%: 2.3%.

[0046] (2) Coating of battery slurry: The positive electrode active material slurry is coated on the aluminum foil current collector by a coating machine, wherein the positive electrode coating surface density is 180 g / m 2 , obtain a positive electrode coating; coat the above negative electrode active material slurry on the aluminum foil current collector by a coating machine, wherein the negative electrode coating surface density is 140g / m 2 , and obtain the negative electrode coating.

[0047] (3) Electrode sheet rolling: The positive electrode coating sheet and the negative electrode coating sheet obtained in step (2) are respectively pressed into dense electrode sheets with uniform thickness by a roller press, and then cut into positive electrode sheets and negative electrode sheets respectively.

[0048] (4) Winding, tab welding, and baking: The positive electrode sheet and the negative electrode sheet tabs obtained in step (3) are welded, and then the positive electrode sheet, the separator, and the negative electrode sheet are wound into a bare cell in the order of the positive electrode sheet, the separator, and the negative electrode sheet, which are then placed in a shell and baked in an oven.

[0049] (5) Liquid injection: After the water content of the battery cell in step (4) is tested and qualified, inject the superfluid electrolyte, whose formula is: NAPF6:EC:PC:EMC:DEC:PST:PS:DTD:FEC=11.13:7.11:25.99:28.14:20.7:0.42:1.46:1.41:1.04, and seal it.

[0050] (6) Formation and capacity division: The cylindrical battery obtained in step (5) is formed at room temperature with a small current, aged at high temperature for 48 hours, and then capacity division is performed.

[0051] Performance Testing The batteries obtained in Examples 1-2 and Comparative Example 1 were subjected to cycle life tests and low-temperature charge and discharge tests. The low-temperature charge and discharge test standard was in accordance with GB / T 31486-2015 Electrical performance requirements and test methods for power batteries for electric vehicles. The low-temperature cycle test conditions were: temperature: -10°C, charge and discharge rate 0.1C / 0.1C, voltage range: 2-4V. The test results are shown in Table 1. Figure 2-Figure 9 shown.

[0052] Depend on Figure 2-Figure 8 It can be seen that in Example 1, the low-temperature sodium ion battery cell constructed by matching the battery pole piece prepared by the innovative method of porous current collector-gradient coating with a superfluid electrolyte has a capacity retention rate of 100% after 50 cycles of -10°C, 0.1C / 0.1C, a -10°C low-temperature charging capacity retention rate of 90%, a -10°C low-temperature discharge capacity retention rate of 89.5%, a -20°C low-temperature discharge capacity retention rate of 90.2%, a -30°C low-temperature discharge capacity retention rate of 86.4%, and a -40°C low-temperature discharge capacity retention rate of 81.2%.

[0053] Fig. 9 It can be seen that the battery electrode prepared by the traditional aluminum foil and uniform coating method on both sides of the current collector in Comparative Example 1 is matched with the low-temperature sodium ion battery cell constructed with superfluid electrolyte. The capacity retention rate is 93.8% at -10°C, 0.1C / 0.1C for 50 cycles.

[0054] from Fig.10 It can be seen that when the total conductive agent content remains unchanged, compared with a higher conductive agent content in the upper layer and compared with a uniform distribution of the conductive agent, a higher conductive agent content in the lower layer can form more conductive pathways, reduce the electron transfer resistance of the electrode, and improve the battery rate performance and cycle stability.

[0055] Depend on Figure 2-Figure 8It can be seen that the low-temperature sodium ion battery pole piece and battery cell constructed by porous current collector-gradient coating-superfluid electrolyte can effectively improve the low-temperature cycle performance of the battery and improve the low-temperature charge and discharge performance of the battery. The solution within the scope of the claims of the present invention can meet the above requirements in all aspects, obtain the most optimized solution, and obtain a low-temperature sodium ion battery with the best performance.

[0056] The above contents are further detailed descriptions of the present invention in combination with specific preferred embodiments, and it cannot be determined that the specific implementation of the present invention is limited to these descriptions. For ordinary technicians in the field to which the present invention belongs, several simple deductions or substitutions can be made without departing from the concept of the present invention, which should be regarded as falling within the scope of protection of the present invention.

Claims

1. A low-temperature sodium ion battery pole piece, characterized in that: A porous current collector is used; a first active material slurry coating and a second active material slurry coating are sequentially arranged on both sides of the current collector from the inside to the outside, and a first active material slurry coating and a second active material slurry coating are arranged on the reverse side thereof; wherein the type and / or content of the conductive agent in the first active material slurry coating is different from that in the second active material slurry coating, and the ionic conductivity and electronic conductivity of the first active material slurry coating close to the current collector are higher than those of the second active material slurry coating, the battery pole piece includes a positive pole piece and a negative pole piece, and the low temperature is a temperature below zero degrees.

2. A low-temperature sodium ion battery cell, characterized in that: It comprises the battery electrode sheet and superfluid electrolyte as described in claim 1.

3. A method for preparing a low-temperature sodium ion battery cell as claimed in claim 2, characterized in that: The following steps are involved: (1) Preparation of battery slurry: The positive electrode material, the negative electrode material, the conductive agent and the binder are dissolved in a solvent and dispersed into a uniform slurry to obtain positive electrode active material slurry and negative electrode active material slurry respectively; (2) Coating of battery slurry: The positive electrode active material slurry and the negative electrode active material slurry obtained in step (1) are respectively coated on the two sides of the corresponding porous current collector by a coating machine; and the first active material slurry coating and the second active material slurry coating are sequentially arranged on both sides of the current collector from the inside to the outside, and the first active material slurry coating and the second active material slurry coating are arranged on the reverse side thereof, so as to obtain a positive electrode coating and a negative electrode coating, respectively; wherein the type and content of the conductive agent in the first active material slurry coating are different from those in the second active material slurry coating, and the ionic conductivity and electronic conductivity of the first active material slurry coating close to the current collector are higher than those of the second active material slurry coating; (3) Electrode sheet rolling: The positive electrode coating sheet and the negative electrode coating sheet obtained in step (2) are respectively pressed into dense electrode sheets with uniform thickness by a roller press, and then cut into positive electrode sheets and negative electrode sheets respectively; (4) Winding, tab welding, and baking: The positive electrode sheet and the negative electrode sheet tabs obtained in step (3) are welded, and then the positive electrode sheet, the separator, and the negative electrode sheet are wound into a bare cell in the order of the positive electrode sheet, the separator, and the negative electrode sheet, and then the cell is placed in a shell and baked in an oven; (5) Liquid injection: Test the water content of the battery cell prepared in step (4). If the test is qualified, inject the superfluid electrolyte and seal the cell. (6) Chemical formation and capacity separation: The battery obtained in step (5) is formed at room temperature with a small current, aged at high temperature, and then capacity separated to obtain a sodium ion battery cell.

4. The method according to claim 3, characterized in that The mass percentages of the positive electrode material, the conductive agent and the binder in the positive electrode active material slurry are 90%~97%: 1%~4%: 2%~4%; the mass percentages of the negative electrode material, the conductive agent and the binder in the negative electrode active material slurry are 90%~98%: 2%~4%: 1%~4%.

5. The method according to claim 3, characterized in that: The positive electrode material includes at least one of sodium copper manganate, sodium nickel iron manganate, sodium vanadium phosphate, sodium iron pyrophosphate, sodium iron sulfate positive electrode materials and modified positive electrode materials thereof.

6. The method according to claim 3, characterized in that The negative electrode material is at least one of biomass hard carbon, coal-based hard carbon, and resin-based hard carbon negative electrode materials.

7. The method according to claim 3, characterized in that The solvent in step (1) is at least one of water, acetone, N-methylpyrrolidone, N,N-dimethylformamide, dimethylacetamide and difluoromethane.

8. The method according to claim 3, characterized in that The conductive agent is at least one of a carbon black conductive agent, a graphite conductive agent, a fiber conductive agent, a nanotube conductive agent, and a graphene conductive agent.

9. The method according to claim 3, characterized in that: The sodium salt in the superfluid electrolyte is at least one of sodium hexafluorophosphate, sodium perchlorate, sodium tetrafluoroborate, sodium trifluoromethylsulfonate, sodium bis(fluorosulfonyl)imide, and sodium bis(trifluoromethylsulfonyl)imide; the additive is at least one of vinylene carbonate, fluoroethylene carbonate, vinyl sulfate, 1,3-propane sultone, sodium difluorooxalatoborate, and sodium bis(oxalatoborate); and the solvent is at least one of ethylene carbonate, propylene carbonate, dimethyl carbonate, diethyl carbonate, ethyl methyl carbonate, tetrahydrofuran, ethylene glycol dimethyl ether, diethylene glycol dimethyl ether, ethyl propionate, and ethyl acetate.

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