Bipolar sodium ion battery pole piece, battery cell and dry preparation method and application thereof

Abstract

The invention relates to a bipolar sodium-ion battery pole piece, a battery cell and a dry preparation method and application of the bipolar sodium-ion battery pole piece. The preparation method of the battery pole piece comprises the following steps: mixing a sodium ion battery positive electrode material, a conductive agent and a binder according to a mass ratio, carrying out dry stirring, pressing the obtained positive electrode dry powder mixture into a film to obtain an initial diaphragm, and thinning the initial diaphragm to obtain a positive diaphragm with a target thickness; the method comprises the following steps: mixing a sodium ion battery negative electrode material, a conductive agent and a binder according to a mass ratio, carrying out dry stirring, pressing the obtained negative electrode dry powder mixture into a film to obtain an initial film, and thinning the initial film to obtain a negative electrode film with a target thickness; and respectively thermally compounding the positive electrode membrane and the negative electrode membrane onto the first surface and the second surface of the current collector, carrying out rolling treatment, and respectively carrying out region cutting to form a plurality of independent positive electrode functional sections and negative electrode functional sections, so as to obtain the bipolar sodium ion battery pole piece.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of sodium ion batteries, in particular to a bipolar sodium ion battery electrode sheet, a battery cell and a dry method for preparing the same and applications thereof. BACKGROUND

[0002] As an important alternative to lithium ion batteries, sodium ion batteries have attracted extensive attention in recent years due to their abundant sodium resources, low cost and environmental friendliness. Sodium ion batteries have shown good application prospects in the fields of energy storage and electric transportation, but their commercialization still faces many technical and process challenges. Currently, traditional wet process is mainly used for the preparation of sodium ion batteries. This process relies on a large amount of organic solvents, which has the disadvantages of incomplete solvent volatilization, serious environmental pollution, complex production process and high cost, thereby limiting the development of large-scale production and green manufacturing.

[0003] The bipolar battery structure has multiple advantages such as improving energy density, saving space and simplifying manufacturing process due to the shared current collector. In recent years, it has become an important direction to improve the performance of batteries. However, the existing manufacturing process of bipolar electrode sheets has great bottlenecks. The preparation of bipolar electrode sheets requires high precision control, including uniform coating of positive and negative electrode materials, thickness consistency and firmness of interlayer bonding during thermal compounding. The traditional wet process has problems such as solvent residue, complex process and long cycle, and the mechanical flexibility and electrochemical performance of the electrode sheet are difficult to balance, which limits the overall performance of the battery. In addition, the bipolar electrode sheet has higher requirements for the mechanical strength and structural integrity of the material during winding and assembly, and the existing wet process preparation cannot meet these multiple preparation requirements.

[0004] Therefore, there is an urgent need for an efficient, precise and stable bipolar sodium ion battery electrode sheet preparation technology that can achieve good matching and firm combination of positive and negative electrode materials, improve the mechanical properties and electrochemical properties of the electrode sheet, meet the large-scale industrial production and application requirements, and promote the further development and market application of bipolar sodium ion battery technology. SUMMARY

[0005] The present application aims to solve the problems existing in the prior art and provides a bipolar sodium ion battery electrode sheet, a battery cell and a dry method for preparing the same and applications thereof. By combining the dry preparation process with the thermal compounding roller pressing technology, a bipolar sodium ion battery electrode sheet with high structural integrity and excellent mechanical properties is successfully prepared. This method effectively avoids the problems of solvent residue and environmental pollution in the traditional wet process, and realizes green environmental protection and process simplification.

[0006] To achieve the above-mentioned purpose, in a first aspect, the present application provides a preparation method of a bipolar sodium ion battery electrode sheet, comprising:

[0007] Mixing and dry stirring sodium ion battery positive electrode material, conductive agent, binder according to mass ratio, obtain positive electrode dry powder mixture;The positive electrode dry powder mixture is pressed into a film to obtain an initial film sheet, and the initial film sheet is thinned to a target thickness of the positive electrode film sheet, and is wound for standby use;

[0008] Mixing and dry stirring sodium ion battery negative electrode material, conductive agent, binder according to mass ratio, obtain negative electrode dry powder mixture;The negative electrode dry powder mixture is pressed into a film to obtain an initial film sheet, and the initial film sheet is thinned to a target thickness of the negative electrode film sheet, and is wound for standby use;

[0009] The positive electrode film sheet and the negative electrode film sheet are respectively hot compounded to the first surface and the second surface of the current collector and are subjected to roll pressing treatment to obtain a double-sided composite electrode sheet;

[0010] The positive electrode film sheet and the negative electrode film sheet of the double-sided composite electrode sheet are respectively formed into a plurality of independent positive electrode functional segments and negative electrode functional segments by area cutting to obtain a bipolar sodium ion battery electrode sheet;The length of the negative electrode functional segment is greater than the length of the corresponding positive electrode functional segment;The length of the positive electrode functional segment is greater than the interval length between the adjacent two positive electrode functional segments.

[0011] Preferably, in the positive electrode dry powder mixture, the sodium ion battery positive electrode material includes one or more of layered oxide positive electrode material, polyanion compound positive electrode material or prussian blue compound positive electrode material;

[0012] The conductive agent includes one or more of acetylene black, conductive carbon black, carbon nanotube CNTs or graphene material;

[0013] The binder includes one or more of polytetrafluoroethylene PTFE, polyvinylidene fluoride PVDF, sodium carboxymethyl cellulose CMC-Na or polyacrylic acid PAA;

[0014] The mass ratio of the sodium ion battery positive electrode material, the conductive agent and the binder is 70-98:1-20:1-10.

[0015] Preferably, in the negative electrode dry powder mixture, the sodium ion battery negative electrode material includes one or more of hard carbon, soft carbon, sodium titanate, lithium titanate or tin-based material;

[0016] The conductive agent includes one or more of acetylene black, conductive carbon black, carbon nanotube CNTs or graphene material;

[0017] The binder includes one or more of polytetrafluoroethylene PTFE, polyvinylidene fluoride PVDF, sodium carboxymethyl cellulose CMC-Na or polyacrylic acid PAA;

[0018] The mass ratio of the sodium ion battery negative electrode material, the conductive agent and the binder is 70-98:1-20:1-10.

[0019] Preferably, the areal density of the positive electrode film piece of the target thickness is 15-80 mg / cm 3 , and the areal density of the negative electrode film piece of the target thickness is 8-40 mg / cm 3 .

[0020] The heat-combining of the positive electrode film piece and the negative electrode film piece to the first surface and the second surface of the current collector respectively and the roll processing specifically include: heat-combining the positive electrode film piece to the first surface of the current collector, roll processing the positive electrode film piece once after winding, heat-combining the negative electrode film piece to the second surface of the current collector, roll processing the negative electrode film piece once after winding, or heat-combining the positive electrode film piece and the negative electrode film piece to the first surface and the second surface of the current collector respectively, roll processing both surfaces after winding.

[0021] The current collector includes one of a metal foil, a metal mesh or a carbonized metal foil, a carbonized metal mesh, and specifically includes one or more of a copper foil, an aluminum foil, a stainless steel foil, a nickel foil, a nickel mesh, an aluminum mesh, a carbon-coated aluminum foil and a carbon-coated copper foil.

[0022] Preferably, the ratio of the negative electrode compaction density to the positive electrode compaction density after the roll processing is greater than 50%.

[0023] In a second aspect, the present application provides a bipolar sodium ion battery electrode piece prepared by the preparation method of the first aspect.

[0024] The bipolar sodium ion battery electrode piece includes a current collector and a plurality of positive electrode functional segments and negative electrode functional segments arranged on both sides of the current collector respectively, the plurality of positive electrode functional segments are sequentially distributed on the first surface along the length direction of the current collector, the plurality of negative electrode functional segments are sequentially distributed on the second surface along the length direction of the current collector, and each positive electrode functional segment corresponds to a negative electrode functional segment at a corresponding position in the thickness direction.

[0025] The length of the negative electrode functional segment is greater than the length of the corresponding positive electrode functional segment, and the length of the positive electrode functional segment is greater than the interval length between two adjacent positive electrode functional segments.

[0026] In a third aspect, the present application provides a preparation method of a bipolar sodium ion battery cell, which includes: after the bipolar sodium ion battery electrode piece of the second aspect is subjected to tab welding, a separator is covered, the bipolar sodium ion battery electrode piece and the separator are wound together to form a cylindrical winding core, and a bipolar sodium ion battery cell with a plurality of electrochemical units connected in series is obtained; and the plurality of electrochemical units are sequentially connected in series through the current collector.

[0027] Preferably, the preparation method further comprises: welding the tab of the bipolar sodium-ion battery electrode sheet before winding;

[0028] The tab welding mode comprises: respectively arranging tabs at both ends of the electrode sheet in the length direction and welding the tabs to the current collector; or, arranging multiple tabs along the length direction of the electrode sheet and welding the tabs to the current collector, so as to shorten the transmission path of the current on the current collector and reduce the internal resistance of the battery cell.

[0029] In a fourth aspect, an embodiment of the present application provides a bipolar sodium-ion battery cell, which is formed by winding the bipolar sodium-ion battery electrode sheet prepared by the preparation method of the first aspect or the bipolar sodium-ion battery electrode sheet of the second aspect and covering a separator thereon; or, the bipolar sodium-ion battery cell is prepared by the preparation method of the third aspect.

[0030] In a fifth aspect, an embodiment of the present application provides a sodium-ion battery, which comprises the bipolar sodium-ion battery electrode sheet of the second aspect or the bipolar sodium-ion battery cell of the fourth aspect.

[0031] The preparation method of the bipolar sodium-ion battery electrode sheet provided by the embodiment of the present application can precisely control the thickness and the compaction density of the electrode film sheet by means of solvent-free dry mixing and film pressing, significantly improves the mechanical strength and toughness of the electrode sheet, and meets the high requirements for the mechanical properties of the electrode sheet in the winding and assembling processes. After the positive electrode film sheet and the negative electrode film sheet are hot-combined with the current collector on both sides and are subjected to roller pressing treatment, the electrode sheet and the current collector are firmly combined, the stability of the interlayer structure is ensured, the delamination and falling-off phenomena are effectively avoided, and the overall electrochemical performance and the cycle stability of the electrode sheet are improved. In addition, by reasonably designing the length and the interval relationship of the positive electrode functional section and the negative electrode functional section, the effective formation of multiple electrochemical units in series is ensured, the current distribution and the structural stress of the electrode sheet are optimized, and the working efficiency and the service life of the battery are improved. Overall, the technical scheme of the present application not only improves the preparation precision and the product quality of the bipolar sodium-ion battery electrode sheet, but also reduces the manufacturing cost and the environmental impact, and has good industrial application prospects. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The preparation method of the bipolar sodium-ion battery electrode sheet provided by the embodiment of the present application is shown in the flowchart;

[0033] Figure 2 The structure of the bipolar sodium-ion battery electrode sheet provided by the embodiment of the present application is shown in the schematic diagram;

[0034] Figure 3The normal temperature charge-discharge comparison chart of the bipolar sodium ion battery cell of Example 1 of the present application and the sodium ion battery cell of Comparative Example 1. DETAILED DESCRIPTION

[0035] The technical solutions of the present application will be further described in detail below with the aid of the accompanying drawings and examples.

[0036] The present application provides a bipolar sodium ion battery electrode sheet, a battery cell, and a dry method for preparing the same and applications thereof.

[0037] Figure 1 The preparation method flow chart of the bipolar sodium ion battery electrode sheet provided by the present application, Figure 2 The structure schematic diagram of the bipolar sodium ion battery electrode sheet provided by the present application is shown in the following. Figure 1 and Figure 2 The bipolar sodium ion battery electrode sheet and the preparation method thereof are described.

[0038] Firstly, as shown in Figure 2 The bipolar sodium ion battery electrode sheet provided by the present application comprises a current collector, and a plurality of positive functional segments and negative functional segments arranged on both sides of the current collector, respectively. The plurality of positive functional segments are sequentially distributed on the first surface along the length direction of the current collector, and the plurality of negative functional segments are sequentially distributed on the second surface along the length direction of the current collector. Each positive functional segment corresponds to a negative functional segment at a corresponding position in the thickness direction. The length of the negative functional segment is greater than that of the corresponding positive functional segment. The length of the positive functional segment is greater than the interval length between two adjacent positive functional segments.

[0039] The bipolar sodium ion battery electrode sheet is prepared by the method flow shown in Figure 1

[0040] In step 110, the sodium ion battery positive electrode material, the conductive agent, and the binder are mixed in a certain mass ratio and dry stirred to obtain a positive electrode dry powder mixture. The positive electrode dry powder mixture is pressed into a film to obtain an initial film sheet. The initial film sheet is thinned to a positive electrode film sheet with a target thickness, and then wound for standby use.

[0041] ​Specifically, the sodium-ion battery cathode material, conductive agent, and binder are put into a solvent-free mixing device in a mass ratio of 70-98:1-20:1-10, and dry stirring is performed in a dry environment. The specific sodium-ion battery cathode material that can be selected includes one or more of a layered oxide cathode material, a polyanion compound cathode material, or a Prussian blue compound cathode material. The conductive agent includes one or more of acetylene black, conductive carbon black, carbon nanotubes (CNTs), or graphene material. The binder includes one or more of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC-Na), or polyacrylic acid (PAA). A high-speed mixer, a V-shaped mixer, or a planetary mixer can be used in the stirring process to ensure uniform dispersion of the components and avoid agglomeration, and to obtain a cathode dry powder mixture. The speed and time during stirring can use conventional parameters, as long as the components are uniformly dispersed and agglomeration is avoided. The obtained cathode dry powder mixture is then sent to a film forming machine through a powder feeding system, and is pressed into an initial film sheet with preliminary structural strength by rolling or molding. The initial film sheet is further adjusted to the target thickness by a precision rolling machine or thinning equipment, to ensure that the area density is between 15-80 mg / cm 3 After completion, the cathode film sheet is wound for use, and dustproof and moisture-proof treatment is performed.

[0042] Step 120, the sodium-ion battery cathode material, conductive agent, and binder are mixed in a mass ratio and dry stirring is performed to obtain a negative electrode dry powder mixture; the negative electrode dry powder mixture is pressed into a film to obtain an initial film sheet, and the initial film sheet is further thinned to a target thickness of a negative electrode film sheet, which is wound for use.

[0043] Specifically, the sodium-ion battery negative electrode material, the conductive agent, and the binder are put into a solvent-free mixing device in a mass ratio of 70-98:1-20:1-10, and dry stirring is performed in a dry environment. The specific sodium-ion battery negative electrode material that can be selected includes one or more of hard carbon, soft carbon, sodium titanate, lithium titanate, or tin-based material, etc.; the conductive agent includes one or more of acetylene black, conductive carbon black, carbon nanotubes (CNTs), or graphene material, etc.; and the binder includes one or more of polytetrafluoroethylene (PTFE), polyvinylidene fluoride (PVDF), sodium carboxymethyl cellulose (CMC-Na), or polyacrylic acid (PAA), etc. A high-speed mixer, a V-shaped mixer, or a planetary stirrer can be used in the stirring process to ensure uniform dispersion of the components and avoid agglomeration, and a negative electrode dry powder mixture is obtained. The speed and time during the stirring process can use conventional parameters as long as the components are uniformly dispersed and agglomeration is avoided. The obtained negative electrode dry powder mixture is then sent to a film forming machine through a powder feeding system, and is pressed into an initial film sheet with preliminary structural strength by rolling or molding. The initial film sheet is further adjusted to the target thickness by a precision rolling machine or thinning equipment to ensure that the area density is between 8-40 mg / cm 3 After completion, the negative electrode film sheet is wound for use, and dustproof and moisture-proof treatment is performed.

[0044] Step 130, the positive electrode film sheet and the negative electrode film sheet are respectively hot-composed to the first surface and the second surface of the current collector and are subjected to rolling treatment, and a double-sided composite electrode sheet is obtained.

[0045] Specifically, the current collector includes one of a metal foil, a metal mesh, or a carbonized metal foil, a carbonized metal mesh, and specifically includes one or more of a copper foil, an aluminum foil, a stainless steel foil, a nickel foil, a nickel mesh, an aluminum mesh, a carbon-coated aluminum foil, a carbon-coated copper foil, etc.

[0046] Rolling can be performed multiple times in a single-sided coating and single-sided rolling manner, or can be performed in a double-layer coating and double-sided rolling manner.

[0047] For example, the positive electrode film sheet is hot-composed to the first surface of the current collector, is rolled once after winding, the negative electrode film sheet is hot-composed to the second surface of the current collector, and is rolled once after winding.

[0048] For example, the positive electrode film sheet and the negative electrode film sheet are respectively hot-composed to the first surface and the second surface of the current collector, are rolled after winding, and are subjected to double-sided rolling.

[0049] In this step, whether single-sided rolling or double-sided rolling is adopted, the order of “hot-composition-winding-rolling” is adopted, which mainly takes into account the following aspects:

[0050] First, this method facilitates continuous production: after thermal compounding is completed, the film directly enters the winding process, facilitating production line scheduling; if thermal compounding and rolling are directly connected in series, once the rolling machine malfunctions, it will affect the continuous operation of the front-end thermal compounding production line.

[0051] Second, the surface temperature of the film after thermal compounding is relatively high, and there may be thermal stress inside. If rolling is performed immediately, uneven thickness, local wrinkles, or even coating micro-cracks may occur. After winding and storage, the material size is more stable, and the density after rolling is more uniform, allowing precise control of the compaction density.

[0052] In a preferred embodiment, the ratio of the negative electrode compaction density to the positive electrode compaction density is greater than 50% after the rolling process. Such parameter settings can balance the structure and electrochemical performance of the bipolar sodium-ion battery electrode sheet. On the one hand, in the bipolar structure, the positive and negative electrodes are on the same current collector, and the mechanical coupling is very tight. If the negative electrode compaction density is too low, the negative electrode will have insufficient surface capacity, and the negative electrode capacity will be depleted first during cycling, causing sodium deposition (sodium metal deposition) at high battery state of charge (SOC), which poses a safety risk. By setting the ratio of the negative electrode compaction density to the positive electrode compaction density to be greater than 50%, the active material accumulation on the unit area of the negative electrode is sufficient, and the capacity of the positive electrode is reasonably matched, avoiding sodium deposition due to insufficient negative electrode capacity at high state of charge, thereby improving the safety of the battery cell; on the other hand, in the bipolar structure, the current path not only exists within a single electrochemical cell, but also is transmitted in series along the current collector, and the internal resistance of the electrode sheet has a more significant impact on the power of the entire string at high rates. Increasing the negative electrode compaction density appropriately can reduce the in-plane resistance of the electrode sheet, reduce internal resistance loss in the bipolar series structure, and improve high-rate charge and discharge performance. At the same time, maintaining a certain ratio between the negative electrode compaction density and the positive electrode compaction density can also improve the mechanical strength of the electrode sheet. When winding the bipolar electrode sheet, the mechanical strength and flexibility of the electrode sheet on both sides are closest to the optimal. If the negative electrode compaction density is too low, the mechanical strength will be insufficient, and wrinkles, pulverization, or shedding may occur during winding and cycling. Setting the compaction ratio to be greater than 50% can make the negative electrode and the positive electrode more matched in terms of stress and ductility, making the deformation and stress distribution of the positive and negative electrodes during winding more balanced, improving the stability of the wound core structure, and thereby prolonging the cycle life of the battery cell.

[0053] Step 140, the positive electrode film and the negative electrode film of the double-sided composite electrode sheet are respectively cut by area cutting to form a plurality of independent positive electrode functional sections and negative electrode functional sections, obtaining a bipolar sodium-ion battery electrode sheet.

[0054] Specifically, the step is implemented by a laser cleaning process. The three-layer structure of the positive electrode film, the current collector and the negative electrode film is scanned by laser to remove the positive electrode film and the negative electrode film in the predetermined area, so that the current collector is exposed to realize the separation of the electrode functional section. During the laser cleaning process, by adjusting the process parameters such as laser power, scanning interval, pulse width, scanning times and scanning speed, the edge of the cutting area can be clean, the residual area of the cleaning area is less than 1%, the removal thickness of the current collector is not more than 1μm on the positive electrode side and not more than 0.5μm on the negative electrode side, and the deviation of the cleaning area size from the design size is not more than 0.5mm.

[0055] The preparation method of the bipolar sodium ion battery electrode sheet provided by the embodiment of the application realizes accurate control of the thickness and the compaction density of the electrode film by means of solvent-free dry mixing and film pressing, significantly improves the mechanical strength and toughness of the electrode sheet, and meets the high requirements for the mechanical properties of the electrode sheet in the winding and assembling processes. After the positive electrode film and the negative electrode film are heat-combined with the current collector on both sides, the electrode sheet and the current collector are firmly combined through roller pressing treatment, the stability of the interlayer structure is ensured, the delamination and falling-off phenomena are effectively avoided, and the overall electrochemical performance and the cycle stability of the electrode sheet are improved.

[0056] In addition, the length of the negative electrode functional section in the bipolar sodium ion battery electrode sheet is set to be greater than the length of the corresponding positive electrode functional section, so as to ensure that the negative electrode sheet can cover or extend to the edge of the positive electrode sheet during winding, avoid the short circuit risk caused by the exposure of the positive electrode in the battery, and ensure the good electrical contact and safety between the electrodes. The length of the positive electrode functional section is set to be greater than the interval length between the adjacent two positive electrode functional sections, so as to ensure that there is enough overlapping or contact area between the positive electrode sections after winding, thereby ensuring the stability and conductive continuity of the internal structure of the battery. That is, through the above length and interval design, it is ensured that the electrode sections can be reasonably connected after winding, so that the battery structure is compact and the electrical performance is reliable.

[0057] On the basis of the preparation method of the bipolar sodium ion battery electrode sheet, the bipolar sodium ion battery electrode sheet is further welded with tabs, covered with a separator, and wound together with the separator to form a cylindrical winding core, so that a bipolar sodium ion battery cell with multiple series-connected electrochemical units can be obtained; wherein the multiple electrochemical units are sequentially electrically connected through the current collector to form a series connection structure.

[0058] The tab welding mode includes: setting a tab at each end of the tab length direction and welding connection with the current collector; or, setting multiple tabs along the tab length direction and welding connection with the current collector, so as to shorten the transmission path of current on the current collector and reduce the internal resistance of the battery cell. Specifically, the setting mode of the tab can be flexibly adjusted according to the design requirements of the battery cell. When the two-end tab arrangement is adopted, the tabs are respectively located at both ends of the tab length direction and are welded with the corresponding current collector to ensure smooth conduction of current; the multi-tab design can uniformly distribute multiple tabs along the tab length direction, thereby shortening the transmission distance of current on the current collector, reducing the internal resistance of the battery cell, and improving the current carrying capacity and overall performance of the battery. This design scheme takes into account the optimization of electrical performance and manufacturing process, and is suitable for the preparation of high-power and high-energy-density bipolar sodium-ion battery cells.

[0059] The separator can be specifically selected from any one of a polyethylene (PE) separator, a polypropylene (PP) separator, a ceramic-coated separator, a polyvinylidene fluoride (PVDF) based separator, or an inorganic-organic composite separator.

[0060] After the tab welding and the separator covering are completed, the bipolar sodium-ion battery tab and the separator are tightly combined to form a cylindrical winding core structure through a winding process. In the winding core, multiple electrochemical units are electrically connected in sequence through the current collector arranged on the tab to form a series circuit, thereby effectively improving the output voltage of the battery cell.

[0061] The present application optimizes the current distribution and structural stress of the tab by reasonably designing the length and spacing relationship of the positive and negative functional sections, which helps to improve the working efficiency and service life of the battery. Overall

[0062] The bipolar sodium-ion battery tab or battery cell formed by the above-mentioned mode of the present application can be applied in the fields of energy storage systems, electric vehicles, smart grids, portable electronic devices, etc. The multi-unit series connection structure not only improves the overall voltage output of the battery, but also optimizes the internal current distribution, enhances the safety and cycle stability of the battery, and the bipolar design simplifies the battery assembly process, which helps to reduce the manufacturing cost and improve the production efficiency.

[0063] In order to make the purpose, technical scheme and advantages of the present application clearer, the present application will be described in further detail below with reference to the drawings. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative labor fall within the scope of protection of the present application.

[0064] Example 1

[0065] The embodiment provides a bipolar sodium ion battery pole piece prepared by a dry method and a sodium ion battery preparation method, and comprises the following steps.

[0066] (1) A positive electrode active material of sodium vanadium manganese phosphate, a conductive agent SP and a binder PTFE are proportioned according to a mass ratio of 95:2:3, and are fully mixed by using a dry mixing stirrer under a solvent-free condition to prepare a positive electrode dry powder mixture.

[0067] (2) The positive electrode dry powder mixture is pressed into a film by using a film forming machine, the thickness of the primary film piece is about 300 μm, and the area density is about 30 mg / cm 2 , so that the film forming is smooth. Then, the primary film piece is thinned multiple times until the thickness of the film piece reaches 250 μm, and the area density is about 25 mg / cm 2 .

[0068] (3) A hard carbon negative electrode active material, a conductive agent SP and a binder PTFE are proportioned according to a mass ratio of 94:2:4, and are fully mixed by using a dry mixing stirrer under a solvent-free condition to prepare a negative electrode dry powder mixture.

[0069] (4) The negative electrode dry powder mixture is pressed into a film by using a film forming machine, the thickness of the primary film piece is about 150 μm, and the area density is about 15 mg / cm 2 , so that the film forming is smooth. Then, the primary film piece is thinned multiple times until the thickness of the film piece reaches 120 μm, and the area density is about 12 mg / cm 2 .

[0070] (5) The film piece prepared by the film forming machine is further processed by using a thermal compounding device. First, the positive electrode film piece prepared in the step (2) is thermally compounded to the A surface of a 12 μm carbon-coated aluminum foil, and after winding, the single-sided pole piece is rolled to press the positive electrode of the sodium vanadium manganese phosphate to a compactness of about 1.45 g / cm 3 ; then the negative electrode film piece prepared in the step (4) is thermally compounded to the B surface of the 12 μm carbon-coated aluminum foil, and after winding, the single-sided pole piece is rolled to press the hard carbon negative electrode to a compactness of about 0.9 g / cm 3 , so as to form a bipolar sodium ion electrode pole piece.

[0071] (6) The bipolar sodium ion electrode pole piece is subjected to laser treatment, and the A / B surface positive / negative electrode film piece is divided into multiple functional sections, while ensuring that the length of the negative electrode functional section is greater than that of the corresponding positive electrode functional section, so as to realize the design effect of the negative electrode covering the positive electrode. Then, the bipolar pole piece is welded with a tab, and is wound into a cylindrical core together with a diaphragm. The core is subjected to baking treatment, moisture reaches the standard, and then a shell is assembled, liquid is injected and packaged to prepare a sodium ion battery cell.

[0072] (7) The encapsulated cylindrical sodium-ion battery cell is subjected to aging, formation, aging, and capacity test, and finally a sodium-ion battery is obtained.

[0073] Example 2

[0074] The present embodiment provides a dry-method electrode-prepared bipolar sodium-ion battery electrode sheet and a sodium-ion battery preparation method, comprising the following steps:

[0075] (1) A positive electrode dry powder mixture is prepared by mixing sodium vanadium manganese phosphate positive electrode active material, conductive agent SP, and binder PTFE in a mass ratio of 92:3:5 under solvent-free conditions using a dry mixing stirrer.

[0076] (2) The above-mentioned positive electrode dry powder mixture is pressed into a film by a film forming machine, and the thickness of the primary film is about 300 μm, and the area density is about 30 mg / cm 2 to ensure smooth film formation. Subsequently, the primary film is thinned multiple times until the film thickness reaches 250 μm, and the area density is about 25 mg / cm 2 The prepared positive electrode film is wound for later use in thermal compounding.

[0077] (3) A negative electrode dry powder mixture is prepared by mixing hard carbon negative electrode active material, conductive agent SP, and binder PTFE in a mass ratio of 94:2:4 under solvent-free conditions using a dry mixing stirrer.

[0078] (4) The above-mentioned negative electrode dry powder mixture is pressed into a film by a film forming machine, and the thickness of the primary film is about 150 μm, and the area density is about 15 mg / cm 2 to ensure smooth film formation. Subsequently, the primary film is thinned multiple times until the film thickness reaches 120 μm, and the area density is about 12 mg / cm 2 The prepared negative electrode film is wound for later use in thermal compounding.

[0079] (5) The film prepared by the film forming machine is further processed using a thermal compounding device. First, the positive electrode film prepared in step (2) is thermally compounded to the A side of a 12 μm carbon-coated aluminum foil, and after winding, the single-sided electrode sheet is rolled to a phosphorus vanadium manganese sodium positive electrode compaction density of about 1.45 g / cm 3 ; then the negative electrode film prepared in step (4) is thermally compounded to the B side of a 12 μm carbon-coated aluminum foil, and after winding, the single-sided electrode sheet is rolled to a hard carbon negative electrode compaction density of about 0.9 g / cm 3 , thereby forming a bipolar sodium-ion electrode sheet.

[0080] (6) The bipolar sodium ion electrode tab is subjected to laser treatment, and the A / B surface positive and negative electrode films are divided into multiple functional segments, while ensuring that the length of the negative functional segment is greater than that of the corresponding positive functional segment, to achieve the design effect of negative electrode covering positive electrode. Then the bipolar tab is welded with the tab, and the cylindrical core is wound with the separator. The core is subjected to baking treatment, and after the moisture reaches the standard, the shell assembly, liquid injection and packaging are carried out to prepare the sodium ion battery cell.

[0081] (7) The packaged cylindrical sodium ion battery cell is subjected to aging, formation, aging and capacity distribution processes, and finally obtains a sodium ion battery.

[0082] Example 3

[0083] The present embodiment provides a dry-process electrode prepared bipolar sodium ion battery tab and a sodium ion battery preparation method, comprising the following steps:

[0084] (1) According to the mass ratio of 92:3:5, P2 type positive active material Na 0.67 Ni 0.25 Mn 0.75 O2, conductive agent SP and binder PTFE are mixed to prepare a positive dry powder mixture.

[0085] (2) The above positive dry powder mixture is pressed into a film by a film forming machine, and the initial film thickness is about 300 μm, and the surface density is about 30 mg / cm 2 , to ensure smooth film formation. Then the initial film is thinned multiple times until the film thickness reaches 250 μm, and the surface density is about 25 mg / cm 2 , and the prepared positive electrode film is wound for later use.

[0086] (3) According to the mass ratio of 94:2:4, hard carbon negative active material, conductive agent SP and binder PTFE are mixed to prepare a negative dry powder mixture.

[0087] (4) The above negative dry powder mixture is pressed into a film by a film forming machine, and the initial film thickness is about 150 μm, and the surface density is about 15 mg / cm 2 , to ensure smooth film formation. Then the initial film is thinned multiple times until the film thickness reaches 120 μm, and the surface density is about 12 mg / cm 2 , and the prepared negative electrode film is wound for later use.

[0088] (5) The film prepared by the film forming machine is further processed by a thermal compounding device. First, the positive electrode film prepared in step (2) is thermally compounded to the A side of a 12 μm carbon-coated aluminum foil, and after winding, the single-sided electrode is rolled to press the positive electrode of sodium vanadium phosphate, with a compacted density of about 1.45 g / cm 3 ; then the negative electrode film prepared in step (4) is thermally compounded to the B side of a 12 μm carbon-coated aluminum foil, and after winding, the single-sided electrode is rolled to press the hard carbon negative electrode, with a compacted density of about 0.9 g / cm 3 , thereby forming a bipolar sodium ion electrode.

[0089] (6) The bipolar sodium ion electrode is laser processed to divide the A / B side positive and negative electrode films into multiple functional segments, while ensuring that the length of the negative functional segment is greater than that of the corresponding positive functional segment, to achieve the design effect of the negative electrode covering the positive electrode. Then the bipolar electrode is welded with the tab, and the tab is wound together with the separator into a cylindrical core. The core is baked, and after the moisture reaches the standard, the shell is assembled, liquid is injected, and the package is prepared to prepare a sodium ion battery cell.

[0090] (7) The packaged cylindrical sodium ion battery cell undergoes aging, formation, aging, and capacity distribution processes, and finally obtains a sodium ion battery.

[0091] Example 4

[0092] The present embodiment provides a bipolar sodium ion battery electrode prepared by a dry method and a sodium ion battery preparation method, comprising the following steps:

[0093] (1) P2-type positive electrode active material Na 0.67 Ni 0.25 Mn 0.75 O2, conductive agent SP, conductive agent CNTs, and binder PTFE are mixed in a solvent-free condition by using a dry mixing stirrer to prepare a positive electrode dry powder mixture.

[0094] (2) The above positive electrode dry powder mixture is pressed into a film by a film forming machine, and the thickness of the primary film is about 300 μm, and the area density is about 30 mg / cm 2 to ensure smooth film formation. Then the primary film is thinned multiple times until the film thickness reaches 250 μm, and the area density is about 25 mg / cm 2 , and the prepared positive electrode film is wound for later use.

[0095] (3) Hard carbon negative electrode active material, conductive agent SP, and binder PTFE are mixed in a solvent-free condition by using a dry mixing stirrer to prepare a negative electrode dry powder mixture.

[0096] (4) The above negative dry powder mixture is pressed into a film by a film forming machine, and the initial film thickness is about 150 μm, and the surface density is about 15 mg / cm 2 . The film forming is ensured to be smooth. Then the initial film is thinned multiple times until the film thickness reaches 120 μm, and the surface density is about 12 mg / cm 2 . The prepared negative electrode film is wound for later use in thermal compounding.

[0097] (5) The film prepared by the film forming machine is further processed by a thermal compounding device. First, the positive electrode film prepared in step (2) is thermally compounded to the A side of a 12 μm carbon-coated aluminum foil, and after winding, the single-sided electrode is rolled to press the positive electrode of sodium vanadium phosphate manganese to a compactness of about 1.45 g / cm 3 ; then the negative electrode film prepared in step (4) is thermally compounded to the B side of the 12 μm carbon-coated aluminum foil, and after winding, the single-sided electrode is rolled to press the hard carbon negative electrode to a compactness of about 0.9 g / cm 3 , thereby forming a bipolar sodium ion electrode.

[0098] (6) The bipolar sodium ion electrode is subjected to laser treatment to divide the A / B side positive and negative electrode films into multiple functional segments, while ensuring that the length of the negative electrode functional segment is greater than that of the corresponding positive electrode functional segment, achieving the design effect of the negative electrode covering the positive electrode. Then the bipolar electrode is welded with the tab, and the tab is wound together with the separator into a cylindrical core. The core is subjected to baking treatment, and after the moisture reaches the standard, the shell assembly, liquid injection and packaging are carried out to prepare a sodium ion battery cell.

[0099] (7) The packaged cylindrical sodium ion battery cell is subjected to aging, formation, aging and capacity distribution processes, and finally a sodium ion battery is obtained.

[0100] Comparative Example 1

[0101] (1) Sodium vanadium phosphate manganese positive electrode material, conductive agent SP, conductive agent CNTs, and binder PVDF are mixed in a mass ratio of 94:2:1:3, and NMP solvent is used for homogenization. After the preparation of the slurry, wet coating is carried out on the surface of a 12 μm aluminum foil, and the double-sided surface density is 27 mg / cm 2 . The above sodium vanadium phosphate manganese positive electrode is rolled to a compactness of 1.45 g / cm 3 ; the rolled positive electrode is slitted and cut to prepare the required positive electrode. The positive electrode has a peeling force of 12 N / m and a film resistance of 38 Ω·cm.

[0102] (2) The hard carbon negative electrode material, conductive agent SP, conductive agent CNTs, and binder PVDF are mixed in a mass ratio of 92:3.6:0.4:4, and deionized water is used as a solvent for homogenization. After the slurry is prepared, it is wet coated on the surface of a 12 μm aluminum foil, and the double-sided area density is 12 mg / cm 2 . The dried hard carbon negative electrode sheet is rolled, and the compacted density is 0.9 g / cm 3 . The rolled negative electrode sheet is slitted and cut to prepare the required negative electrode sheet.

[0103] (3) The positive electrode sheet of sodium vanadium manganese phosphate prepared in step (1) is compounded with a separator to ensure that the separator completely covers the surface of the positive electrode sheet and is tightly attached. At the same time, the hard carbon negative electrode sheet prepared in step (2) is compounded with a separator to ensure that the separator uniformly covers the negative electrode sheet and avoids gaps and wrinkles. The compounded positive electrode-separator sheet and negative electrode-separator sheet are respectively wound for standby use.

[0104] (4) The positive electrode sheet and the negative electrode sheet that have been respectively compounded with a separator are tightly stacked and wound into a cylindrical core structure in the designed order by using a winding device. During the winding process, the tension and electrode alignment are reasonably controlled to ensure uniform stacking and good electrical contact between the layers.

[0105] (5) The cylindrical core wound is baked to remove residual moisture, and after reaching the moisture content standard required by the process, the shell assembly, liquid injection, and packaging are performed to finally prepare a sodium ion battery cell.

[0106] (6) The packaged cell is subjected to aging, formation, aging, and capacity distribution processes to ensure stable cell performance and meet application requirements.

[0107] The good sodium ion cells prepared in the examples and comparative examples are tested.

[0108] 1. Single cell capacity test

[0109] The sodium ion batteries prepared in Examples 1-4 and Comparative Example 1 are subjected to charge and discharge at 0.5C / 0.5C rate in a 25℃ oven, and the energy density of the cell is tested. The test results are shown in Table 1.

[0110] Numbering Test temperature Crate-in coefficient 0.5C cell capacity / Ah Example 1 25 0.93 2.1 Example 2 25 0.93 2.0 Example 3 25 0.93 2.1 Example 4 25 0.93 2.2 Comparative Example 25 0.93 1.9

[0111] Table 1

[0112] As can be seen from the data in Table 1 above, under the same shell filling coefficient and the same test temperature, the capacity of the bipolar sodium ion battery of the present application is significantly better than that of the comparative example.

[0113] Figure 3The figure is a comparison of the charge-discharge at room temperature of the bipolar sodium-ion battery of Example 1 of the present application and the sodium-ion battery of Comparative Example 1. It can be seen that:

[0114] The voltage range of the bipolar sodium-ion battery of Example 1 of the present application is about 6.5V to 8.3V, which is significantly higher than the voltage range of the conventional sodium-ion battery of Comparative Example 1, which is about 2.5V to 4.2V. This shows that the series structure of the bipolar sodium-ion battery effectively improves the working voltage of the overall battery, which is beneficial to improve the output power and energy density of the single battery. Compared with the conventional single sodium-ion battery, the bipolar structure is more suitable for application scenarios that require higher voltage output.

[0115] 2. Cell voltage platform

[0116] The sodium-ion batteries prepared in Examples 1-4 and Comparative Example 1 were subjected to charge-discharge at 0.5C / 0.5C, 1C / 1C rate in a 45℃ oven, and the cycle life of the cells was tested, and the test results are shown in Table 2 below.

[0117]

[0118] Table 2

[0119] As can be seen from the data in Table 2 above, the voltage of the bipolar sodium-ion battery of the present application is significantly higher than that of the comparative example, breaking through the voltage limitation of the conventional method for preparing the cell.

[0120] The above specific embodiments further illustrate the purpose, technical solutions and beneficial effects of the present application. It should be understood that the above description is only a specific embodiment of the present application and is not intended to limit the protection scope of the present application. Any modification, equivalent replacement, improvement, etc. within the spirit and principles of the present application should be included in the protection scope of the present application.

Claims

1. A method of making a bipolar sodium-ion battery electrode sheet, characterized by, The preparation method comprises: The sodium ion battery positive electrode material, the conductive agent and the binder are mixed according to the mass ratio and dry stirring to obtain a positive electrode dry powder mixture; the positive electrode dry powder mixture is pressed into a film to obtain an initial film sheet, and the initial film sheet is thinned to a target thickness of a positive electrode film sheet for winding; The sodium ion battery negative electrode material, the conductive agent and the binder are mixed according to the mass ratio and dry stirring to obtain a negative electrode dry powder mixture; the negative electrode dry powder mixture is pressed into a film to obtain an initial film sheet, and the initial film sheet is thinned to a target thickness of a negative electrode film sheet for winding; The positive electrode film sheet and the negative electrode film sheet are respectively hot-composed to the first surface and the second surface of the current collector and subjected to roll pressing treatment to obtain a double-sided composite electrode sheet; The positive electrode film sheet and the negative electrode film sheet of the double-sided composite electrode sheet are respectively formed into a plurality of independent positive electrode functional sections and negative electrode functional sections through area cutting to obtain a bipolar sodium ion battery electrode sheet; wherein the length of the negative electrode functional section is greater than the length of the corresponding positive electrode functional section; the length of the positive electrode functional section is greater than the interval length between adjacent two positive electrode functional sections.

2. The production method according to claim 1, characterized by, The sodium ion battery positive electrode material comprises one or more of a layered oxide positive electrode material, a polyanion compound positive electrode material or a Prussian blue compound positive electrode material; The conductive agent comprises one or more of acetylene black, conductive carbon black, carbon nanotubes CNTs or graphene material; The binder comprises one or more of polytetrafluoroethylene PTFE, polyvinylidene fluoride PVDF, sodium carboxymethyl cellulose CMC-Na or polyacrylic acid PAA; The mass ratio of the sodium ion battery positive electrode material, the conductive agent and the binder is 70-98:1-20:1-10.

3. The method of claim 1, wherein, The sodium ion battery negative electrode material comprises one or more of hard carbon, soft carbon, sodium titanate, lithium titanate or tin-based material; The conductive agent comprises one or more of acetylene black, conductive carbon black, carbon nanotubes CNTs or graphene material; The binder comprises one or more of polytetrafluoroethylene PTFE, polyvinylidene fluoride PVDF, sodium carboxymethyl cellulose CMC-Na or polyacrylic acid PAA; The mass ratio of the sodium ion battery negative electrode material, the conductive agent and the binder is 70-98:1-20:1-10.

4. The method of claim 1, wherein, The areal density of the positive electrode film of the target thickness is 15 to 80 mg / cm 3 The areal density of the negative electrode film of the target thickness is 8 to 40 mg / cm 3 ; The hot-composition of the positive electrode film sheet and the negative electrode film sheet to the first surface and the second surface of the current collector and the roll pressing treatment specifically comprise: hot-composing the positive electrode film sheet to the first surface of the current collector, winding, and then roll pressing the positive electrode film sheet once, and then hot-composing the negative electrode film sheet to the second surface of the current collector, winding, and then roll pressing the negative electrode film sheet once; or hot-composing the positive electrode film sheet and the negative electrode film sheet to the first surface and the second surface of the current collector respectively, winding, and then double-sided roll pressing; The current collector comprises one of a metal foil, a metal mesh or a carbonized metal foil, a carbonized metal mesh, and specifically comprises one or more of a copper foil, an aluminum foil, a stainless steel foil, a nickel foil, a nickel mesh, an aluminum mesh, a carbon-coated aluminum foil and a carbon-coated copper foil.

5. The preparation method according to claim 1, characterized in that, The ratio of the negative electrode compaction density to the positive electrode compaction density is greater than 50% after the roll-pressing treatment.

6. A bipolar sodium-ion battery pole piece prepared by the method of any one of claims 1-5, characterized in that, The bipolar sodium-ion battery electrode sheet comprises a current collector and a plurality of positive functional segments and negative functional segments arranged on both sides of the current collector, respectively, the plurality of positive functional segments are sequentially distributed on a first surface along the length direction of the current collector, the plurality of negative functional segments are sequentially distributed on a second surface along the length direction of the current collector, and each positive functional segment corresponds to a negative functional segment at a corresponding position in the thickness direction. The length of the negative functional segment is greater than the length of the corresponding positive functional segment, and the length of the positive functional segment is greater than the interval length between two adjacent positive functional segments.

7. A method of making a bipolar sodium-ion battery cell, characterized in that, The preparation method comprises the following steps: after the bipolar sodium-ion battery electrode sheet of claim 6 is subjected to tab welding, a separator is covered, and the bipolar sodium-ion battery electrode sheet is wound together with the separator to form a cylindrical winding core, thereby obtaining a bipolar sodium-ion battery cell with a plurality of electrochemical units connected in series; wherein the plurality of electrochemical units are sequentially connected in series through the current collector.

8. The production method according to claim 7, characterized by, The preparation method further comprises: tab welding the bipolar sodium-ion battery electrode sheet before winding. The tab welding method comprises the following steps: arranging tabs at both ends of the electrode sheet in the length direction and welding the tabs to the current collector; or arranging a plurality of tabs along the length direction of the electrode sheet and welding the tabs to the current collector, so as to shorten the transmission path of the current on the current collector and reduce the internal resistance of the cell.

9. A bipolar sodium-ion battery cell, characterized in that, The bipolar sodium-ion battery cell is prepared from the bipolar sodium-ion battery electrode sheet prepared by the preparation method of any one of claims 1-5 or from the bipolar sodium-ion battery electrode sheet of claim 6, which is covered with a separator and wound; or the bipolar sodium-ion battery cell is the bipolar sodium-ion battery cell prepared by the preparation method of claim 7.

10. A sodium-ion battery, characterized in that, The sodium-ion battery comprises the bipolar sodium-ion battery electrode sheet of claim 6 or the bipolar sodium-ion battery cell of claim 9.

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