Battery cell and energy storage device

Abstract

The application provides an electric core and an energy storage device. The electric core is wound by materials including a negative electrode sheet, a diaphragm and a positive electrode sheet. The diaphragm is arranged between the negative electrode sheet and the positive electrode sheet. The negative electrode sheet includes a first corner section, and the positive electrode sheet includes a second corner section. The electric core further includes a polymer layer. The polymer layer is arranged on the surface of at least one of the first corner section and the second corner section. The swelling rate of the polymer layer in electrolyte is 10% to 150%.

Description

Technical Field

[0001] This application relates to the field of energy storage technology, and more particularly to a battery cell and an energy storage device. Background Technology

[0002] Energy storage devices such as lithium-ion batteries and sodium-ion batteries are widely used in consumer electronics, electric vehicles, and energy storage systems. During the fabrication of battery cells for energy storage devices, the electrodes in the cells are frequently bent. After bending, the active material of the electrodes, being relatively hard, can puncture the separator, easily leading to short circuits in the resulting battery cells. Utility Model Content

[0003] The purpose of this application is to provide a battery cell and an energy storage device, which uses a battery cell with a low short-circuit failure rate.

[0004] This application provides a battery cell, which is formed by winding a material including a negative electrode, a separator, and a positive electrode. The separator is disposed between the negative electrode and the positive electrode. The negative electrode includes a first corner segment, and the positive electrode includes a second corner segment. The battery cell also includes a polymer layer, which is coated on the surface of at least one of the first corner segment and the second corner segment. The swelling rate of the polymer layer in the electrolyte is 10% to 150%.

[0005] This application provides a battery cell by providing a polymer layer on the surface of at least one of the first corner segment of the negative electrode and the second corner segment of the positive electrode. On the one hand, by wrapping the first or second corner segment, the polymer layer can prevent the negative or positive electrode from puncturing the separator after bending, thereby preventing short circuits in the battery cell. On the other hand, during the winding process of battery cell preparation, the negative electrode is prone to shedding powder at the first corner segment or the positive electrode at the second corner segment. The polymer layer can adsorb the active material powder that falls off the negative or positive electrode, preventing the powder from scattering after shedding, thereby reducing the defect rate (i.e., Hipot defect rate) of battery cell caused by short circuits due to winding. At the same time, it avoids the problem of edge powder shedding or even exposure of the current collector when the electrode (negative or positive electrode) is die-cut during the preparation of battery cell using the stacking process.

[0006] On the other hand, the polymer layer has a swelling rate for the electrolyte, allowing it to absorb and retain the electrolyte. Ions released from the positive electrode active material, such as lithium or sodium ions, can pass through the polymer layer and migrate to the negative electrode via the electrolyte absorbed within it. The presence of the polymer layer does not affect the function of the active material on the positive or negative electrode covered by the polymer layer, thus avoiding energy loss in the battery cell. Furthermore, the polymer layer provides a space for the active material of the positive or negative electrode to be scratched, and after being scratched, it can further release insulating polymer material, ensuring the stability of the battery cell.

[0007] Furthermore, compared to the limitation that insulating tape can only be applied to the positive electrode and that applying it to the negative electrode would cause a short circuit in the cell, the polymer layer in the cell of this application embodiment can be applied to both the negative and / or positive electrode, without limiting the type of electrode to which it is applied. Its advantages are even more obvious in energy storage devices with more rigid and brittle negative electrodes, such as sodium-ion batteries.

[0008] In one possible implementation, the polymer layer is used for insulation.

[0009] In one possible implementation, the glass transition temperature of the polymer layer is Tg, where Tg ≤ 0℃.

[0010] In one possible implementation, the first corner segment includes a negative current collector and a negative active layer covering the surface of the negative current collector, and the second corner segment includes a positive current collector and a positive active layer covering the surface of the positive current collector. Along the thickness direction of the polymer layer, the polymer layer includes a first adhesive surface and a second adhesive surface. The first adhesive surface is bonded to the negative active layer of the first corner segment, and the second adhesive surface is bonded to the separator. And / or the first adhesive surface is bonded to the positive active layer of the second corner segment, and the second adhesive surface is bonded to the separator.

[0011] In one possible implementation, the battery cell includes a flat region and two bending regions. Along the width direction of the battery cell, the two bending regions are connected to opposite sides of the flat region. Along the winding direction of the battery cell, the polymer layer includes a first end face and a second end face disposed opposite to each other, both of which are located in the bending regions.

[0012] In one possible implementation, the polymer layer extends for a length of L along the winding direction of the battery cell, where L ≤ 10 mm.

[0013] In one possible implementation, the thickness of the polymer layer is D, where D ≤ 2 mm.

[0014] In one possible implementation, the polymer layer can be configured in one of the following three ways: The polymer layer is disposed on the negative electrode sheet, and the number of turns of the polymer layer on the negative electrode sheet along the winding direction of the negative electrode sheet is ≥1 turn; Alternatively, the polymer layer is disposed on the positive electrode sheet, and the number of turns of the polymer layer on the positive electrode sheet along the winding direction of the positive electrode sheet is ≥1 turn; Alternatively, the polymer layer is disposed on both the negative electrode and the positive electrode. Along the winding direction of the negative electrode, the number of turns of the polymer layer on the negative electrode is ≥1, and along the winding direction of the positive electrode, the number of turns of the polymer layer on the positive electrode is ≥1.

[0015] In one possible implementation, when the polymer layer is disposed on the negative electrode, the number of polymer layers disposed on the negative electrode is 1 to 3. Alternatively, when the polymer layer is placed on the positive electrode, the second layer is placed on the positive electrode with 1 to 3 turns along the winding direction of the positive electrode.

[0016] This application also provides an energy storage device, including a housing and a battery cell as described above, wherein the battery cell is installed inside the housing. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This application scenario diagram illustrates the use of the energy storage device in an energy storage system, as provided in the embodiments of this application. Figure 2 for Figure 1 A schematic diagram of the cross-sectional structure of the energy storage device shown; Figure 3 for Figure 2 The diagram shows a cross-sectional view of the battery cell in the energy storage device in the first embodiment.

[0019] Reference numerals: 5000, energy storage system; 1000, energy storage device; 2000, high-voltage cable; 3000, first power conversion device; 4000, second power conversion device; 100, outer casing; 300, battery cell; 210, straight area; 230, bending area; 310, negative electrode plate; 301, negative current collector; 303, negative active layer; 10, first corner section; 30, second corner section; 330, positive electrode plate; 305, positive current collector; 307, positive active layer; 350, separator; 370, polymer layer; 381, first end face; 383, second end face. Detailed Implementation

[0020] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0021] Because the energy we need is highly time- and space-dependent, in order to utilize energy rationally and improve energy efficiency, it is necessary to store one form of energy in the same way or by converting it into another, and then release it in a specific energy form for future applications. Currently, the main way to generate green electricity is to develop green energy sources such as photovoltaics and wind power to replace fossil fuels. Currently, the generation of green electricity generally relies on solar, wind, and hydropower. However, wind and solar power are generally characterized by strong intermittency and large fluctuations, which can cause grid instability, insufficient power during peak demand periods, and excessive power during off-peak periods. Unstable voltage can also damage the power grid. Therefore, insufficient electricity demand or insufficient grid capacity may lead to the problem of "wind and solar curtailment." Solving these problems requires energy storage. This involves converting electrical energy into other forms of energy through physical or chemical means and storing it. When needed, this energy can be converted back into electrical energy and released. Simply put, energy storage is like a large "power bank," storing electrical energy when solar and wind power are abundant and releasing the stored electricity when needed.

[0022] Taking electrochemical energy storage as an example, this application provides an energy storage device for use in an energy storage system. The energy storage device is equipped with a set of chemical batteries, which mainly use the chemical elements in the batteries as energy storage medium. The charging and discharging process is accompanied by the chemical reaction or change of the energy storage medium. Simply put, the electrical energy generated by wind and solar energy is stored in the chemical batteries. When the use of external electrical energy reaches its peak, the stored electrical energy is released for use, or transferred to places with a shortage of electricity for use.

[0023] Current energy storage applications are quite widespread, including generation-side energy storage, grid-side energy storage, and consumption-side energy storage. The corresponding types of energy storage devices include: (1) Large-scale energy storage power stations (including multiple prefabricated energy storage modules) applied to wind power and photovoltaic power stations can help renewable energy power generation meet grid connection requirements and improve the utilization rate of renewable energy. As a high-quality active / reactive power regulation power source on the power supply side, energy storage power stations can achieve load matching of power in time and space, enhance the renewable energy absorption capacity, reduce instantaneous power changes, reduce the impact on the power grid, improve the absorption of new energy power generation, and are of great significance in power grid system backup, alleviating peak load power supply pressure and peak regulation and frequency regulation. (2) The energy storage prefabricated cabin applied on the grid side mainly functions as peak regulation, frequency regulation and grid congestion relief. In terms of peak regulation, it can realize peak shaving and valley filling of electricity load, that is, charging the energy storage battery when the electricity load is low and releasing the stored electricity during the peak electricity load period, thereby achieving a balance between power production and consumption. Small-scale energy storage cabinets applied to the electricity consumption side primarily function to facilitate self-consumption of electricity, peak-valley price arbitrage, capacity cost management, and improve power supply reliability. Depending on the application scenario, electricity consumption-side energy storage can be categorized into commercial and industrial energy storage cabinets, residential energy storage devices, and energy storage charging piles, generally used in conjunction with distributed photovoltaic (PV) systems. Commercial and industrial users can utilize energy storage for peak-valley price arbitrage and capacity cost management. In electricity markets implementing peak-valley pricing, charging the energy storage system during low electricity prices and discharging it during high electricity prices allows for arbitrage, reducing electricity costs. Furthermore, industrial enterprises subject to two-part tariffs can use energy storage systems to store energy during off-peak hours and discharge it during peak load periods, thereby reducing peak power and the maximum declared demand, ultimately lowering capacity costs. Residential PV systems combined with energy storage can improve self-consumption levels. High electricity prices and poor power supply stability drive demand for residential PV installations. Given that photovoltaic power generation occurs during the day, while user load is generally higher at night, configuring energy storage can better utilize photovoltaic power, improve self-consumption levels, and reduce electricity costs. Furthermore, energy storage is needed in areas such as communication base stations and data centers for backup power.

[0024] Please see Figure 1 , Figure 1 This diagram illustrates an application scenario where the energy storage device 1000 provided in this embodiment is used in an energy storage system 5000. It is understood that... Figure 1 The application scenario shown is illustrated using a shared energy storage scenario on the power generation / distribution side as an example. The energy storage device 1000 provided in this application embodiment is not limited to a prefabricated energy storage module in a power generation / distribution energy storage scenario.

[0025] This application provides an energy storage system 5000, which includes an energy storage device 1000, a high-voltage cable 2000, a first power conversion device 3000, and a second power conversion device 4000. In some embodiments on the power generation side, the second power conversion device 4000 can be a wind power conversion device. Since the electricity generated by wind power conversion is volatile, random, and intermittent, the unstable electricity output from the wind power conversion device can be stored in the energy storage device 1000 via grid connection. The energy storage device 1000 is connected to the high-voltage cable 2000 and outputs smooth electricity to the power distribution network, achieving peak shaving and frequency regulation, and ensuring stable grid operation. Alternatively, the wind power conversion device is always connected to the high-voltage cable 2000, and under normal power generation conditions, the wind power is converted through the high-voltage cable. The electrical energy output from the energy conversion device is supplied to the power consumption side of the distribution network. When the current power load is low and the wind power conversion device generates excess electricity, the excess electricity is first stored in the energy storage device 1000 to reduce the curtailment rate of wind and solar power and improve the problem of new energy power generation consumption. When the power load is high, the power grid issues an instruction to transmit the electricity stored in the energy storage device 1000 together with the high-voltage cable 2000 in grid-connected mode to supply the power consumption side. This provides the power grid with various services such as peak shaving, frequency regulation, and backup, giving full play to the peak shaving role of the power grid, promoting peak shaving and valley filling, and alleviating the power supply pressure of the power grid.

[0026] In some embodiments on the distribution network side, the first power conversion device 3000 can be a photovoltaic panel, and the energy storage device 1000 is connected to the high-voltage cable 2000 and installed downstream of the high-voltage cable 2000 and between the user load. The electrical energy output by the photovoltaic power conversion device is stored in the energy storage device 1000, which can respond in a timely manner to act as a backup power source when the power grid / distribution network fails; or, it can provide power supply support to alleviate line congestion when the high-voltage cable 2000 transmission line is blocked, and to delay the economic pressure caused by the expansion of the power grid / distribution capacity when the power grid is planned to be expanded.

[0027] Optionally, the first power conversion device 3000 may include, but is not limited to, a photovoltaic panel, and the second power conversion device 4000 may include, but is not limited to, a wind power conversion device. The first power conversion device 3000 and the second power conversion device 4000 can convert at least one of solar energy, light energy, wind energy, thermal energy, tidal energy, biomass energy and mechanical energy into electrical energy.

[0028] Optionally, the energy storage device 1000 may include, but is not limited to, energy storage applications such as energy storage power stations, hydropower / thermal / wind power generation systems, solar power generation systems, mobile power systems, smart home systems, or temporary power supply systems, and may also be applied in multiple fields such as data centers, military equipment, aerospace, charging piles, and electric vehicles.

[0029] Optionally, the energy storage device 1000 may include, but is not limited to, single-cell batteries, or battery modules, battery packs, battery clusters, power banks, energy storage cabinets / prefabricated energy storage compartments, and other battery integrated systems composed of single-cell batteries. The actual application form of the energy storage device 1000 provided in this application embodiment may be, but is not limited to, the listed products, and may also be other application forms. This application embodiment does not strictly limit the application form of the energy storage device 1000. This application embodiment only uses a multi-cell battery as an example for illustration.

[0030] Optionally, when the energy storage device 1000 is a single battery cell, the energy storage device 1000 can be, but is not limited to, at least one of cylindrical, square, prismatic, or other shaped batteries.

[0031] Optionally, the single cell can be a rechargeable battery, which refers to a single cell that can be recharged after discharge to activate the active materials and continue to be used. The single cell can be a lithium-ion battery, sodium-ion battery, sodium-lithium-ion battery, lithium metal battery, sodium metal battery, lithium-sulfur battery, magnesium-ion battery, nickel-metal hydride battery, nickel-cadmium battery, lead-acid battery, etc., and this application does not specifically limit it.

[0032] Please see Figure 2 and Figure 3 , Figure 2 for Figure 1 The diagram shows a cross-sectional structure of the energy storage device 1000. Figure 3 for Figure 2 A schematic diagram of the cross-sectional structure of the battery cell 300 in the first embodiment of the energy storage device 1000 shown.

[0033] For ease of description, the following definitions are provided. Figure 2 The length direction of the energy storage device 1000 shown is the X-axis direction, the width direction is the Y-axis direction, and the thickness direction is the Z-axis direction. The X-axis direction, Y-axis direction, and Z-axis direction are perpendicular to each other.

[0034] Energy storage device 1000 includes a housing 100, a battery cell 300, and an electrolyte ( Figure 2 and Figure 3 (Not shown in the text). The battery cell 300 is installed inside the casing 100, and the electrolyte is filled inside the casing 100. Exemplarily, the energy storage device 1000 includes individual batteries, battery modules, or battery packs. In this embodiment, a sodium-ion battery is used as an example for illustration.

[0035] Specifically, the outer casing 100 can be an aluminum casing. There can be one or more battery cells 300. When there are multiple battery cells 300, the assembled energy storage device 1000 forms a multi-JR (jelly roll) structure.

[0036] The length direction of the battery cell 300 is the X-axis direction, the width direction is the Y-axis direction, and the thickness direction is the Z-axis direction. The battery cell 300 is formed by winding a material including a negative electrode 310, a positive electrode 330, and a separator 350. The battery cell 300 includes a flat region 210 and two bending regions 230. Along the width direction of the battery cell 300, the two bending regions 230 are located on opposite sides of the flat region 210.

[0037] The negative electrode 310 includes a negative electrode current collector 301 and a negative electrode active layer 303 covering the surface of the negative electrode current collector 301. The negative electrode active layer 303 covers at least one surface of the negative electrode current collector 301 along its thickness direction. In this embodiment, the negative electrode active layer 303 covers both sides of the negative electrode current collector 301 along its thickness direction. The negative electrode current collector 301 collects the current generated by the negative electrode active material in the negative electrode active layer 303 to form a larger current output. Therefore, the negative electrode current collector 301 should have sufficient contact with the negative electrode active material in the negative electrode active layer 303, and its internal resistance should be as low as possible. The negative electrode current collector 301 can be made of a material with good conductivity and mechanical strength. For example, the negative electrode current collector 301 is a copper foil.

[0038] The negative electrode active layer 303 includes a negative electrode active material and a second additive. Exemplarily, the negative electrode active material includes carbon materials, such as hard carbon and graphite, and may also include non-carbon materials, such as nitrides, PAS, tin-based oxides, tin alloys, nano-anode materials, and other intermetallic compounds. Exemplarily, the negative electrode active material includes one or more of graphite, mesocarbon microbeads (MCMB), hard carbon, and soft carbon. Preferably, the negative electrode active material includes hard carbon. The second additive includes at least one of a conductive agent, a binder, and a thickener. This application does not specifically limit the types of conductive agents, binders, and thickeners; those skilled in the art can select them according to actual needs. Exemplarily, the conductive agent may be one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers. The binder may be one or more of the following: polyacrylic acid (PAA), sodium polyacrylate (PAAS), polyvinyl alcohol (PVA), polymerized styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), sodium alginate (SA), polymethacrylic acid (PMAA), and carboxymethyl chitosan (CMCS). The thickener may be sodium carboxymethyl cellulose (CMC).

[0039] The negative electrode 310 includes multiple first corner segments 10, all of which are located in the bending region 230 of the cell 300. According to the winding direction of the negative electrode 310, the multiple first corner segments 10 are respectively the first corner segment of the negative electrode, the second corner segment of the negative electrode, ..., the nth corner segment of the negative electrode. Each first corner segment 10 includes a negative electrode current collector 301 and a negative electrode active layer 303 covering the surface of the negative electrode current collector 301.

[0040] The positive electrode 330 includes a positive current collector 305 and a positive active layer 307 coated on the surface of the positive current collector 305. The positive active layer 307 is coated on at least one surface of the positive current collector 305 along its thickness direction. In this embodiment, the positive active layer 307 is coated on both sides of the positive current collector 305 along its thickness direction. The positive current collector 305 can be made of a material with good conductivity and mechanical strength. For example, the positive current collector 305 is an aluminum foil.

[0041] The positive electrode active layer 307 includes a positive electrode active material and a first additive. In this embodiment, the specific type of positive electrode active material in the positive electrode active layer 307 is not specifically limited; materials capable of reversible insertion / extraction of active ions can be used, and those skilled in the art can select according to actual needs. For example, the positive electrode active material in the positive electrode active layer 307 can be selected from sodium transition metal oxides and their modified materials. The modified material can be a sodium transition metal oxide that has undergone doping modification and / or coating modification. Preferably, the sodium transition metal oxide can be selected from one or more of sodium cobalt oxide, sodium nickel oxide, sodium manganese oxide, sodium nickel manganese oxide, sodium nickel cobalt manganese oxide, and sodium nickel cobalt aluminum oxide.

[0042] The first additive includes a binder and / or a conductive agent. This application does not specifically limit the types of binders and conductive agents; those skilled in the art can select them according to actual needs. For example, the binder used for the positive electrode active layer 307 may include one or more of polyvinylidene fluoride (PVDF) and polytetrafluoroethylene (PTFE); the conductive agent may include one or more of graphite, superconducting carbon, acetylene black, carbon black, Ketjen black, carbon dots, carbon nanotubes, graphene, and carbon nanofibers.

[0043] The positive electrode 330 includes multiple second corner segments 30, all located in the bending region 230 of the cell 300. According to the winding direction of the positive electrode 330, the multiple second corner segments 30 are respectively the first corner segment, the second corner segment, ..., the nth corner segment. Each second corner segment 30 includes a positive current collector 305 and a positive active layer 307 covering the surface of the positive current collector 305.

[0044] A separator 350 is disposed between the negative electrode 310 and the positive electrode 330. The separator 350 serves as a separator between the negative electrode 310 and the positive electrode 330. This application embodiment does not impose any particular limitation on the material of the separator 350; any known porous structure separator with good chemical and mechanical stability can be selected. For example, the material of the separator 350 can be one or more of glass fiber, non-woven fabric, polyethylene, polypropylene, and polyvinylidene fluoride. The separator 350 can be a single-layer film or a multi-layer composite film. When the separator 350 is a multi-layer composite film, the materials of each layer can be the same or different.

[0045] This application does not specifically limit the type of electrolyte; it can be selected according to requirements. The electrolyte can be selected from at least one of solid electrolytes and liquid electrolytes (i.e., electrolyte solutions). In this embodiment, the electrolyte is an electrolyte solution, which wets the battery cell 300. The electrolyte solution includes an electrolyte salt and a solvent.

[0046] For example, the electrolyte salt may be selected from one or more of LiPF6 (sodium hexafluorophosphate), LiBF4 (sodium tetrafluoroborate), LiClO4 (sodium perchlorate), LiAsF6 (sodium hexafluoroarsenate), LiFSI (sodium bis(fluorosulfonyl)imide), LiTFSI (sodium bis(trifluoromethanesulfonyl)imide), LiTFS (sodium trifluoromethanesulfonate), LiDFOB (sodium difluorooxalate borate), LiBOB (sodium dioxalate borate), LiPO2F2 (sodium difluorophosphate), LiDFOP (sodium difluorodioxalate phosphate), and LiTFOP (sodium tetrafluorooxalate phosphate).

[0047] For example, the solvent may be one or more of the following: dimethyl ethylene glycol (DME), dioxolane (DOL), ethylene carbonate (EC), propylene carbonate (PC), methyl ethyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butenyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE).

[0048] The electrolyte may optionally include additives. This application embodiment does not specifically limit the type of additives; they can be selected according to requirements. For example, additives may include negative electrode film-forming additives, positive electrode film-forming additives, and additives that can improve certain performance characteristics of the energy storage device 1000, such as additives that improve the overcharge performance of the energy storage device 1000, additives that improve the high-temperature performance of the energy storage device 1000, and additives that improve the low-temperature performance of the energy storage device 1000.

[0049] Continue reading Figure 3 In this embodiment of the application, the battery cell 300 further includes a polymer layer 370, which is coated on the surface of at least one of the first corner segment 10 and the second corner segment 30 in the negative electrode 310. Specifically, the polymer layer 370 may be coated on the surface of the first corner segment 10, or on the surface of the second corner segment 30, or simultaneously on the surfaces of the first corner segment 10 and the second corner segment 30.

[0050] The battery cell 300 includes at least one polymer layer 370. Along the winding direction of the battery cell 300, each polymer layer 370 includes a first end face 381 and a second end face 383 disposed opposite to each other, both located in the bending region 230 of the battery cell 300. For example, along the winding direction of the battery cell 300, the extension length of the polymer layer 370 is L, where L ≤ 10 mm. If the extension length L of the polymer layer 370 is too long, it will introduce additional resistance; furthermore, if the extension length L of the polymer layer 370 is greater than the extension length of the first corner segment 10 or the second corner segment 30, it will result in waste and increase manufacturing costs. In this embodiment, the extension length L of the polymer layer 370 is ≤ 3 mm.

[0051] If the polymer layer 370 is too thick, the absorption of electrolyte by the polymer layer 370 will result in an excessively long transport path for lithium or sodium ions, which may cause the active material of the negative electrode 310 or positive electrode 330 covered by the polymer layer 370 to lose its function. In this embodiment, the thickness of the polymer layer 370 is D, where D≤2mm.

[0052] In this embodiment, the polymer layer 370 has adhesive properties. Along the thickness direction of the polymer layer 370, the polymer layer 370 includes a first adhesive surface and a second adhesive surface. For example... Figure 3As shown in the illustration, this embodiment uses the example of a polymer layer 370 covering the surface of the first corner segment 10 in the negative electrode 310. The first adhesive surface of the polymer layer 370 is bonded to the negative electrode active layer 303 of the first corner segment 10, and the second adhesive surface is bonded to the separator 350, so that the polymer layer 370 covers the surface of the first corner segment 10. Utilizing the adhesive properties of the polymer layer 370, it is easier to adhere the active material powder that falls off the negative electrode 310 or the positive electrode 330, preventing the powder from scattering after the negative electrode 310 or the positive electrode 330 sheds powder.

[0053] In this embodiment, the polymer layer 370 is disposed on the negative electrode 310. Along the winding direction of the negative electrode 310, the polymer layer 370 is disposed on the negative electrode 310 with ≥1 turn, that is, the polymer layer 370 covers at least one segment of the first corner segment, the second corner segment, the third corner segment, etc. of the negative electrode. For example, along the winding direction of the negative electrode 310, the polymer layer 370 is disposed on the negative electrode 310 with 1 to 3 turns.

[0054] It is understood that in other embodiments, the first adhesive surface of the polymer layer 370 may also be bonded to the positive electrode active layer 307 of the second corner segment 30, and the second adhesive surface may be bonded to the separator 350, so that the polymer layer 370 covers the surface of the second corner segment 30. In this case, the polymer layer 370 is disposed on the positive electrode sheet 330, and along the winding direction of the positive electrode sheet 330, the polymer layer 370 is disposed on the positive electrode sheet 330 with ≥1 turn, that is, the polymer layer 370 covers at least one segment of the first corner segment, the second corner segment, the third corner segment, etc. of the positive electrode sheet. For example, along the winding direction of the positive electrode sheet 330, the polymer layer 370 is disposed on the positive electrode sheet 330 with 1 to 3 turns. It is understood that in other embodiments, the polymer layer 370 may also be disposed on both the negative electrode 310 and the positive electrode 330. In this case, the number of turns of the polymer layer 370 on the negative electrode 310 along the winding direction of the negative electrode 310 is ≥1, and the number of turns of the polymer layer 370 on the positive electrode 330 along the winding direction of the positive electrode 330 is ≥1.

[0055] In this embodiment, the polymer layer 370 is insulating, and its swelling rate in the electrolyte is 10%~150%. The swelling rate of the polymer layer 370 in the electrolyte can be calculated as follows: Weigh the dried polymer layer 370 as m1, immerse the polymer layer 370 in the electrolyte and then weigh the polymer layer 370 after immersion as m2, and the swelling rate of the polymer layer 370 in the electrolyte = (m2-m1) / m1.

[0056] In this embodiment, the glass transition temperature of the polymer layer 370 is Tg, where Tg ≤ 0℃. On the one hand, the lower the glass transition temperature Tg of the polymer layer 370, the softer the polymer layer 370 will be, avoiding the problem of the polymer layer 370 being too hard and prone to cracking. On the other hand, the lower the Tg, the larger the swelling ratio of the polymer layer 370 will generally be, which is beneficial to increasing the amount of electrolyte stored in the polymer layer 370, thereby improving the performance of the battery cell 300.

[0057] For example, the material of polymer layer 370 can be an acrylic resin polymer compound polymerized from two or more of the following monomers: isooctyl acrylate, butyl acrylate, methyl methacrylate, vinyl acetate, acrylic acid, hydroxyethyl methacrylate, toluene diisocyanate, diphenylmethane diisocyanate, polyester polyol, polyether polyol, N-hydroxymethyl methacrylate amine, etc.

[0058] In this embodiment, the polymer layer 370 is a polymer formed by the polymerization of isooctyl acrylate, butyl acrylate, and methyl methacrylate, and can be prepared according to the following steps: 1. Preparation of pre-emulsion: Nucleus-phase pre-emulsion: Mix isooctyl acrylate (20g), butyl acrylate (15g), methyl methacrylate (5g), divinylbenzene (0.5g), sodium dodecyl sulfate (1g), polyoxyethylene octylphenol ether (0.3g), and deionized water (60g), and stir at high speed (1000rpm) for 30 minutes to prepare a stable emulsion.

[0059] Shell phase pre-emulsion: Mix isooctyl acrylate (20g), butyl acrylate (15g), methyl methacrylate (5g), hydroxyethyl methacrylate (5g), acrylic acid (3g), N-hydroxymethylacrylamide (5g), vinyl acetate (7g), trimethylolpropane triacrylate (0.5g), allyloxynonylphenol polyoxyethylene ether ammonium sulfate (1g), and deionized water (60g), and stir at high speed for 30 minutes.

[0060] 2. Polymerization reaction: (1) Seed emulsion preparation: Add deionized water (100g), NaHCO3 (0.5g), and disodium ethylenediaminetetraacetate (0.05g) to the reactor, purge with nitrogen for 30 minutes to remove oxygen, and then heat to 75℃.

[0061] Add 10% (about 14g) of the nucleus pre-emulsion and ammonium persulfate solution (0.3g ammonium persulfate dissolved in 10g water), and keep warm for 30 minutes to form a seed emulsion (particle size about 50nm).

[0062] (2) Core-layer aggregation: Simultaneously add the remaining nucleus preemulsion and NaHSO3 solution (0.15g dissolved in 10g water), controlling the dropping rate to complete the process within 2 hours, while maintaining the temperature at 75℃.

[0063] (3) Shell aggregation: After the core layer was added, the mixture was kept at a constant temperature for 1 hour. Then, the shell pre-emulsion and the remaining ammonium persulfate solution (0.3 g dissolved in 10 g of water) were added dropwise. The addition was completed within 3 hours, and the temperature was raised to 80°C.

[0064] (4) Curing treatment: After the addition is complete, heat to 85°C and keep warm for 2 hours to eliminate residual monomers, then cool to below 40°C.

[0065] 3. Post-treatment: Filter with a 200-mesh filter to remove condensates. Adjust the pH to 8-9 with ammonia to improve storage stability, finally obtaining the material with polymer layer 370.

[0066] Currently, when insulating tape (such as PET (polyester) adhesive tape) is used to apply adhesive to the corner sections of the electrode plates in the battery cell 300, the electrolyte cannot wet the insulating tape. When the insulating tape is adhered to the positive electrode plate 330, the positive active material of the positive electrode plate 330 cannot pass through the insulating tape and release ions such as lithium ions or sodium ions, rendering the positive active material covered by the insulating tape ineffective and causing energy loss in the battery cell. When the insulating tape is adhered to the negative electrode plate 310, the ions such as lithium ions or sodium ions released from the positive active material of the positive electrode plate 330 pass through the separator 350, but cannot pass through the insulating tape and therefore cannot be embedded in the negative electrode plate 310. As a result, they will precipitate and crystallize on the insulating tape (such as forming lithium dendrites or sodium dendrites), which can easily cause a short circuit in the battery cell.

[0067] In the battery cell 300 provided in this application embodiment, by providing a polymer layer 370 on the surface of at least one of the first corner segment 10 and the second corner segment 30 of the negative electrode 310, on the one hand, it can prevent the negative electrode 310 or the positive electrode 330 from puncturing the separator 350 after bending by wrapping the first corner segment 10 or the second corner segment 30, thereby preventing the battery cell 300 from short-circuiting; on the other hand, during the winding process of preparing the battery cell 300, the negative electrode 310 at the first corner segment 10 or the positive electrode 330 at the second corner segment 350 can be wrapped with a polymer layer 370. Corner segment 30 is prone to powder shedding. The polymer layer 370 can adsorb the active material powder that falls off the negative electrode 310 or positive electrode 330, preventing the powder from scattering after the negative electrode 310 or positive electrode 330 falls off. This reduces the defect rate of the cell 300 due to short circuit caused by winding (i.e., the Hipot defect rate). At the same time, it avoids the problem of edge powder shedding or even exposure of the current collector when the electrode (negative electrode 310 or positive electrode 330) is die-cut during the preparation of the cell 300 using the stacking process.

[0068] On the other hand, the polymer layer 370 has a swelling ratio for the electrolyte, allowing it to absorb the electrolyte. Ions such as lithium ions or sodium ions released from the positive electrode active material of the positive electrode 330 can pass through the polymer layer 370 and migrate to the negative electrode 310 through the electrolyte absorbed in the polymer layer 370, where they are deposited. The presence of the polymer layer 370 does not affect the function of the active material of the negative electrode 310 or positive electrode 330 covered by the polymer layer 370, thus avoiding energy loss in the cell 300. In addition, the polymer layer 370 provides a space for the active material of the negative electrode 310 or positive electrode 330 to be scratched, and after being scratched, it can further release insulating polymer material, ensuring the stability of the cell 300.

[0069] Furthermore, compared to insulating tape, which can only be applied to the positive electrode 330 and whose application to the negative electrode 310 would cause a short circuit in the cell, the polymer layer 370 in the cell 300 of this application embodiment can be applied to both the negative electrode 310 and / or the positive electrode 330, without limiting the type of electrode. Its advantages are even more pronounced in energy storage devices 1000 such as sodium-ion batteries where the negative electrode 310 is more rigid and brittle. It should be noted that when a solid electrolyte is used in the cell, the polymer layer 370 cannot exhibit swelling properties; however, the polymer layer 370 can still be used in place of insulating tape to avoid powder shedding caused by frequent bending of the electrode.

[0070] Furthermore, the flat area 210 of the battery cell 300 typically does not shed powder during hot or cold pressing. By setting the first end face 381 and the second end face 383 of the polymer layer 370 to be located in the bending area 230 of the battery cell 300, on the one hand, the polymer layer 370 is prevented from extending too far into the flat area 210 of the battery cell 300, thus avoiding cost waste. On the other hand, it can also prevent the polymer layer 370 from extending into the flat area 210 of the battery cell 300 during hot or cold pressing, which would cause blockage of the separator 350, resulting in closed pores in the separator 350 and thus increasing the impedance of the battery cell 300.

[0071] This application also provides a battery cell 300 according to a second embodiment. The difference between the battery cell 300 of the second embodiment and the battery cell 300 of the first embodiment is that the polymer layer 370 of the battery cell 300 of the second embodiment is disposed on the surface of the first corner segment 10 of the negative electrode 310 and on the surface of the second corner segment 30 of the positive electrode 330.

[0072] Specifically, the polymer layer 370 includes a first layer and a second layer. The first layer is disposed on the surface of the first corner segment 10 of the negative electrode 310, and the second layer is disposed on the surface of the second corner segment 30 of the positive electrode 330. Along the winding direction of the cell 300, the extension length of the first layer is L1, where L1 ≤ 10 mm, and the extension length of the second layer is L2, where L2 ≤ 10 mm. The thickness of the first layer is D1, where D1 ≤ 2 mm, and the thickness of the second layer is D2, where D2 ≤ 2 mm.

[0073] The performance of the energy storage device 1000 provided in the embodiments of this application will be described below in conjunction with the effect experiment.

[0074] Comparative Examples 1 to 2 and Examples 1 to 4 all provide an energy storage device 1000, which is a sodium-ion battery, and is prepared according to the following steps: Preparation of negative electrode 310: The negative electrode can be prepared according to conventional methods in the art. The negative electrode active material and optional conductive agent, binder and thickener are dispersed in a solvent, which can be deionized water, to form a uniform negative electrode slurry. The negative electrode slurry is coated on the negative electrode current collector, and after drying, cold pressing and other processes, the negative electrode 310 is obtained. The negative electrode active material is a hard carbon material.

[0075] Preparation of positive electrode 330: The above-mentioned positive electrode can be prepared according to conventional methods in the art. The positive electrode active material and optional conductive agent and binder are dispersed in a solvent (e.g., N-methylpyrrolidone, abbreviated as NMP) to form a uniform positive electrode slurry. The positive electrode slurry is coated on the positive electrode current collector, and after drying, cold pressing and other processes, the positive electrode 330 is obtained.

[0076] Sodium-ion battery fabrication: Sodium-ion batteries can be fabricated using methods known in the art. Specifically, the positive electrode 330, separator 350, and negative electrode 310 are sequentially wound (or stacked), with the separator 350 positioned between the positive electrode 330 and the negative electrode 310 to provide insulation. The winding process yields the battery cell. The wound battery cell is then hot-pressed, and finally assembled with the casing and electrolyte to obtain the sodium-ion battery. Comparative Example 1 uses a normal winding method, without the application of insulating tape and polymer layer 370. Comparative Example 2 uses a method where insulating tape is applied to the second corner segment 30 of the positive electrode 330, with the tape extending 15 mm. In Examples 1 to 4, the sodium-ion batteries all involve coating a polymer layer 370 on the first corner segment 10 of the negative electrode 310. The extension length L of the polymer layer 370 is 4 mm. The swelling rate of the polymer layer 370 in the electrolyte is 10% in Example 1, 50% in Example 2, 100% in Example 3, and 150% in Example 2.

[0077] Sodium-ion batteries from Comparative Examples 1 to 2 and Examples 1 to 4 were tested, and the performance results of the sodium-ion batteries are shown in Table 1.

[0078] Table 1 Performance of sodium-ion batteries in Comparative Examples 1, 2 and 1

[0079] As shown in Table 1, in the sodium-ion battery of Comparative Example 1, the hard carbon material used as the negative electrode active material is quite hard and brittle due to its high specific surface area and defective structure. When the sodium-ion battery cell is prepared by winding, the negative electrode is frequently bent, especially at the innermost corner, where the corner is the smallest. This amplifies the hard and brittle characteristics of the hard carbon material, weakening the bonding force between the negative electrode active layer and the negative electrode current collector. This leads to frequent powder shedding from the negative electrode, resulting in a short-circuit rate as high as 54% for the wound cell. This makes it difficult to mass-produce the sodium-ion battery of Comparative Example 1, greatly limiting the application of sodium-ion batteries.

[0080] By comparing Comparative Example 1 and Examples 1 to 4, compared with the sodium-ion battery of Comparative Example 1, the sodium-ion batteries of Examples 1 to 4, by setting a polymer layer 370 in the cell, can significantly reduce the short-circuit defect rate (Hipot defect rate) of the hot-pressed cell after winding. The short-circuit defect rate of the cell formed after winding is reduced to <1%, while the cell capacity remains basically unchanged. Experimental results show that, in this embodiment, by setting a polymer layer 370 on the surface of the first corner segment 10 of the negative electrode 310 or the second corner segment 30 of the positive electrode 330, and utilizing the swelling rate of the polymer layer 370 to the electrolyte, the powder scattering caused by the shedding of hard and brittle active materials can be avoided, thereby reducing the short-circuit defect rate of the cell after winding. At the same time, the polymer layer 370 does not affect the function of the negative electrode active material in the covered negative electrode 310 or the positive electrode active material in the positive electrode 330, avoiding energy loss of the cell and ensuring the cell capacity.

[0081] Furthermore, by comparing Comparative Example 2 and Examples 1 to 4, the sodium-ion batteries of Examples 1 to 4 and the sodium-ion battery of Comparative Example 2 both exhibited lower cell hit-pot failure rates, but had higher cell capacities compared to the sodium-ion battery in Comparative Example 2. Experimental results show that by using polymer layer 370 instead of insulating tape, the embodiments of this application can improve cell capacity while ensuring a reduced cell hit-pot failure rate. Additionally, the polymer layer 370 used in Examples 1 to 4 has a swelling rate of 10% to 150% for the electrolyte, and can be used in both the negative electrode 310 and the positive electrode 330, avoiding the problem in the sodium-ion battery of Comparative Example 2 where the insulating tape could only be used on the positive electrode 330, and its use on the negative electrode 310 would cause a cell short circuit.

[0082] The above-disclosed embodiments are merely preferred embodiments of this application and should not be construed as limiting the scope of this application. Those skilled in the art will understand that all or part of the processes for implementing the above embodiments and equivalent variations made in accordance with the claims of this application are still within the scope of this application.

Claims

1. A battery cell, characterized in that, The battery cell is formed by winding a material including a negative electrode, a separator, and a positive electrode. The separator is disposed between the negative electrode and the positive electrode. The negative electrode includes a first corner segment, and the positive electrode includes a second corner segment. The battery cell also includes a polymer layer, which covers the surface of at least one of the first corner segment and the second corner segment. The swelling rate of the polymer layer in the electrolyte is 10% to 150%.

2. The battery cell according to claim 1, characterized in that, The polymer layer is insulating.

3. The battery cell according to claim 1, characterized in that, The glass transition temperature of the polymer layer is Tg, where Tg ≤ 0℃.

4. The battery cell according to claim 1, characterized in that, The first corner segment includes a negative current collector and a negative active layer covering the surface of the negative current collector. The second corner segment includes a positive current collector and a positive active layer covering the surface of the positive current collector. Along the thickness direction of the polymer layer, the polymer layer includes a first adhesive surface and a second adhesive surface. The first adhesive surface is bonded to the negative active layer of the first corner segment, and the second adhesive surface is bonded to the separator. And / or the first adhesive surface is bonded to the positive active layer of the second corner segment, and the second adhesive surface is bonded to the separator.

5. The battery cell according to any one of claims 1 to 4, characterized in that, The battery cell includes a flat region and two bending regions. Along the width direction of the battery cell, the two bending regions are connected to opposite sides of the flat region. Along the winding direction of the battery cell, the polymer layer includes a first end face and a second end face disposed opposite to each other. Both the first end face and the second end face are located in the bending region.

6. The battery cell according to claim 5, characterized in that, Along the winding direction of the battery cell, the extension length of the polymer layer is L, where L≤10mm.

7. The battery cell according to any one of claims 1 to 4, characterized in that, The thickness of the polymer layer is D, where D≤2mm.

8. The battery cell according to any one of claims 1 to 4, characterized in that, The polymer layer may be configured in one of the following three ways: The polymer layer is disposed on the negative electrode sheet, and the number of turns of the polymer layer on the negative electrode sheet along the winding direction of the negative electrode sheet is ≥1 turn; Alternatively, the polymer layer is disposed on the positive electrode sheet, and the number of turns of the polymer layer on the positive electrode sheet along the winding direction of the positive electrode sheet is ≥1 turn; Alternatively, the polymer layer is disposed on the negative electrode and the positive electrode, with the polymer layer having ≥1 turn on the negative electrode along the winding direction of the negative electrode, and the polymer layer having ≥1 turn on the positive electrode along the winding direction of the positive electrode.

9. The battery cell according to claim 8, characterized in that, When the polymer layer is disposed on the negative electrode sheet, the number of turns of the polymer layer on the negative electrode sheet along the winding direction of the negative electrode sheet is 1 to 3. Alternatively, when the polymer layer is disposed on the positive electrode sheet, the number of turns of the polymer layer on the positive electrode sheet along the winding direction of the positive electrode sheet is 1 to 3.

10. An energy storage device, characterized in that, It includes a housing and a battery cell as described in any one of claims 1 to 9, wherein the battery cell is mounted inside the housing.

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