Electrode plate and preparation method thereof, battery and power utilization device

Abstract

The invention relates to an electrode plate and a preparation method thereof, a battery and an electric device, the electrode plate comprises a current collector and an active material layer arranged on at least one surface of the current collector, the active material layer comprises a pore-forming agent, and the pore-forming agent comprises polycyclic aromatic hydrocarbon and derivatives thereof. The pore-forming agent in the active material layer of the electrode plate can be dissolved in the organic solvent, pores are generated in the active material layer, transmission of active ions in the active material layer is facilitated, the rate capability of the battery is improved, the pore-forming agent dissolved in the electrolyte basically has no negative influence on the battery, and an additional removal process is not needed. And the pore-forming agent can react with the metal lithium after being dissolved in the electrolyte, so that the bad lithium deposition phenomenon can be eliminated, and the safety of the battery is improved. The preparation method of the electrode plate can adapt to an existing process, a pore-forming device does not need to be additionally adopted or transformed, the pore-forming cost of the electrode plate is reduced, and the risk of active substance loss caused by an etching type pore-forming means is also reduced.

Description

Technical Field

[0001] The present application relates to the field of electrochemical energy storage, and in particular to an electrode sheet and a preparation method thereof, a battery and an electrical device. Background Art

[0002] Secondary batteries (such as lithium-ion batteries) are widely used in power batteries and 3C electronic products. In order to improve the energy density of lithium-ion batteries, increasing the thickness of the electrode sheet is an effective measure, but too thick an electrode will make the active material at the bottom unusable and reduce the dynamic performance of the electrode sheet at high rate charge and discharge. Therefore, how to improve the fast charging performance of thick electrodes has become an urgent problem to be solved. Summary of the invention

[0003] In view of this, the present application provides an electrode sheet and a preparation method thereof, a battery and an electrical device to solve at least one of the above technical problems.

[0004] To achieve the above objectives, in a first aspect, the present application provides an electrode sheet, comprising a current collector and an active material layer disposed on at least one surface of the current collector, wherein the active material layer comprises an active substance, the active material layer comprises a pore former, and the pore former comprises polycyclic aromatic hydrocarbons and their derivatives.

[0005] The present application uses polycyclic aromatic hydrocarbons and their derivatives as pore formers for electrode sheets. The pore formers are added to the electrode sheet slurry to form an active material layer. The pore formers in the active material layer can be dissolved in an organic solvent (such as an electrolyte) to generate pores in the active material layer. These pores are conducive to the transmission of active ions (such as lithium ions) in the active material layer, thereby improving the fast charging performance of the battery; and the pore formers dissolved in the electrolyte have basically no negative impact on the battery, and no additional removal process is required. After the pore former of the present application is dissolved in the electrolyte, it can accept electrons in lithium metal through electron transfer to form lithium ions and free radicals, so that lithium can be dissolved in the electrolyte, which helps to eliminate the undesirable lithium deposition phenomenon and improve the safety of the battery; and polycyclic aromatic hydrocarbons and their derivatives can also be used as overcharge protection agents for the battery. For example, when the battery is overcharged, polycyclic aromatic hydrocarbons and their derivatives will polymerize at high potential, causing local micro-short circuits in the battery, reducing the cell voltage, and reducing the risk of overcharging the cell. In addition, the electrode sheet of the present application can adapt to the existing electrode sheet preparation process, without the need for additional pore-making devices or modifications to the pore-making devices, thereby reducing the cost of electrode sheet pore-making and the risk of active material loss caused by etching-type pore-making methods.

[0006] Based on the first aspect, in some possible implementations, the polycyclic aromatic hydrocarbons and their derivatives include one or more of biphenyl, naphthalene, phenanthrene, anthracene, tetracene, pyrene and perylene. The above polycyclic aromatic hydrocarbons and their derivatives can leave pores on the electrode sheet by dissolving in an organic solvent, and can also react with metallic lithium to help eliminate undesirable lithium deposition and improve the safety of the battery. They can also be used as overcharge protection agents for the battery to reduce the safety risks of the electrode sheet caused by overcharging.

[0007] Based on the first aspect, in some possible implementations, the mass content of polycyclic aromatic hydrocarbons and their derivatives in the active material layer is 0.1% to 20%. Controlling the mass content of the pore former within this range is conducive to forming an appropriate amount of pores in the active material layer, and is also conducive to the pore former being dissolved in the electrolyte and reacting with metallic lithium, which helps to eliminate undesirable lithium deposition and improve the safety of the battery. It is also conducive to the pore former dissolved in the electrolyte acting as an overcharge protection agent for the battery, reducing the safety risk of the electrode sheet caused by overcharging.

[0008] Based on the first aspect, in some possible implementations, the active material layer includes a first surface facing the current collector and a second surface arranged opposite to the first surface, and the mass content of the pore former in the active material layer gradually increases along the direction from the first surface to the second surface. In thick electrodes, it is difficult to wet the bottom of the electrode sheet. If too much pore former is added, it may be difficult to completely dissolve. By setting the mass content relationship of the pore former in the active material layer, it is beneficial to control or promote the porosity of the surface layer of the electrode sheet after the pore former is dissolved to be higher, which is beneficial for the electrolyte to better contact with the underlying active material, and achieve a state similar to the contact between the surface of the electrode without a pore former and the electrolyte, thereby improving the electrolyte wettability of the underlying active material, while controlling the porosity of the electrode sheet within an appropriate range, which is beneficial to maintaining a good energy density.

[0009] Based on the first aspect, in some possible implementations, the thickness of the active material layer on any surface of the current collector is 20 μm to 300 μm. By setting the thickness of the active material layer, the fast charging performance of the lithium-ion battery and the liquid retention of the electrode sheet can be improved while increasing the energy density of the electrode sheet.

[0010] In a second aspect, the present application provides a method for preparing an electrode sheet, the method comprising: providing an active material layer on at least one surface of a current collector, the active material layer comprising a pore former, and the pore former comprising polycyclic aromatic hydrocarbons and derivatives thereof.

[0011] Based on the second aspect, in some possible implementations, the preparation method further includes: contacting the active material layer with an organic solvent to dissolve the pore former in the organic solvent; and drying the active material layer to obtain an electrode sheet.

[0012] Based on the second aspect, in some possible implementations, the organic solvent includes one or more of an electrolyte solvent, acetone, toluene, dichloromethane, chloroform, ethyl acetate, acetonitrile, methanol, and petroleum ether. The organic solvent is selected from the above substances to dissolve the pore former and is conducive to reducing the dissolution of the binder in the active material layer.

[0013] The present application uses polycyclic aromatic hydrocarbons and their derivatives as pore formers for electrode sheets. The electrode sheets can adapt to the existing electrode sheet preparation process, and there is no need to use an additional pore former or to modify the pore former, which reduces the cost of electrode sheet pore making and also reduces the loss of active substances caused by etching-type pore making methods. In the above preparation method, the electrode sheet containing the pore former in the active material layer is contacted with an organic solvent (such as soaking), so that the pore former is dissolved in the organic solvent, and pores are reserved on the electrode sheet. The pore making method is simple.

[0014] In a third aspect, the present application provides a battery, which includes the above-mentioned electrode sheet, or includes an electrode sheet prepared by the above-mentioned electrode sheet preparation method.

[0015] After the above-mentioned electrode sheets are assembled into a battery, on the one hand, the pore-forming agent in the active material layer of the electrode sheet will dissolve in the electrolyte in the battery to create pores in the electrode sheet, which is beneficial to shorten the transmission path of lithium ions, improve the fast charging performance of lithium-ion batteries, and also help to increase the liquid retention of the electrode sheet, thereby helping to extend the life of the battery; on the other hand, the pore-forming agent can also react with metallic lithium after dissolving in the electrolyte to eliminate undesirable lithium deposition phenomena and improve the safety of the battery; and, polycyclic aromatic hydrocarbons can also serve as overcharge protection agents for batteries to reduce battery safety risks caused by overcharging.

[0016] In a fourth aspect, the present application provides an electrical device, which includes the above-mentioned battery. DETAILED DESCRIPTION

[0017] The embodiments of the present application are described in detail below. The embodiments described below are exemplary and are only used to explain the present application, and cannot be understood as limiting the present application; it should be noted that, unless otherwise defined, all technical and scientific terms used herein have the same meaning as those generally understood by technicians in the technical field of the present application; in the absence of conflict, the embodiments of the present application and the features in the embodiments can be combined with each other; many specific details are explained in the following description to facilitate a full understanding of the present application, and the described embodiments are only part of the embodiments of the present application, not all of the embodiments.

[0018] The present application has found that setting appropriate pores on the electrode sheet is an effective way to improve the fast charging performance of the battery. In the related art, electrode pores are mostly made by laser or roller pressing to make pores on the electrode sheet. However, the efficiency of laser pore making is not high, and precision control is difficult. Laser ablation may also cause the loss of active substances and also involve the modification of manufacturing equipment. Roller pressing pore making involves the fine manufacturing of roller pressing equipment, which has high requirements for processing accuracy, and the service life of the mold used for rolling is also an issue that needs to be considered in production costs. Therefore, there is a need for an electrode sheet whose preparation method is simple and easy, is basically compatible with the current production process or has low cost, to make up for the shortcomings of the existing electrode pore making method and achieve the purpose of improving the electrochemical performance of the resulting battery.

[0019] Based on this, an embodiment of the present application provides a battery, including a housing, an electrode assembly and an electrolyte. The battery can be a lithium ion battery, a sodium ion battery or a potassium ion battery. The electrode assembly and the electrolyte are both located in the housing.

[0020] The outer shell may be a packaging bag encapsulated by an encapsulation film (such as an aluminum-plastic film), for example, a soft-pack battery. In other embodiments, it may also be a steel shell battery, an aluminum shell battery, etc.

[0021] The electrode assembly includes an electrode sheet and a separator, the electrode sheet includes a positive electrode sheet and a negative electrode sheet, and the separator is used to separate the positive electrode sheet and the negative electrode sheet, and can be arranged between the positive electrode sheet and the negative electrode sheet. In some embodiments, the electrode assembly can be a laminated structure, for example, it is formed by alternatingly stacking the positive electrode sheet, the separator and the negative electrode sheet in sequence. In other embodiments, the electrode assembly can also be a winding structure, for example, it is formed by stacking the positive electrode sheet, the separator and the negative electrode sheet in sequence and then winding them.

[0022] Electrode sheet The electrode sheet includes a current collector and an active material layer disposed on at least one surface of the current collector. In the present application, the active material layer of the electrode sheet includes a pore former, and the pore former includes polycyclic aromatic hydrocarbons and derivatives thereof.

[0023] The present application uses polycyclic aromatic hydrocarbons and their derivatives as pore formers for electrode sheets. By adding the pore formers to the electrode sheet slurry to form an active material layer, the pore formers in the active material layer can be dissolved in an organic solvent (such as an electrolyte) to generate pores in the active material layer. These pores are conducive to the transmission of active ions (such as lithium ions) in the active material layer, thereby improving the rate performance of the battery; and the pore formers dissolved in the electrolyte have basically no negative impact on the battery, and no additional removal process is required. After the pore former of the present application is dissolved in the electrolyte, it can accept electrons in lithium metal through electron transfer to form lithium ions and free radicals, so that lithium can be dissolved in the electrolyte, which helps to eliminate the undesirable lithium deposition phenomenon and improve the safety of the battery; and polycyclic aromatic hydrocarbons and their derivatives can also be used as overcharge protection agents for the battery. For example, when the battery is overcharged, polycyclic aromatic hydrocarbons and their derivatives will polymerize at high potential, causing local micro-short circuits in the battery, reducing the cell voltage, and reducing the risk of overcharging the cell. In addition, the electrode sheet of the present application can adapt to the existing electrode sheet preparation process, without the need for additional pore-making devices or modifications to the pore-making devices, thereby reducing the cost of electrode sheet pore-making and the risk of active material loss caused by etching-type pore-making methods.

[0024] In some embodiments, the polycyclic aromatic hydrocarbons and their derivatives include one or more of biphenyl, naphthalene, phenanthrene, anthracene, tetracene, pyrene and perylene. The above polycyclic aromatic hydrocarbons and their derivatives can leave pores on the electrode sheet by dissolving in an organic solvent, and can also react with metallic lithium to help eliminate undesirable lithium deposition and improve battery safety. They can also be used as overcharge protection agents for batteries to reduce the safety risks of electrode sheets caused by overcharging.

[0025] In some embodiments, the mass content of the pore former in the active material layer is 0.1% to 20%. For example, the mass content of polycyclic aromatic hydrocarbons and their derivatives can be 0.1%, 0.4%, 0.60%, 0.8%, 1%, 3%, 5%, 8%, 10%, 13%, 15%, 18%, 20%, or any value within the range formed by any two of the above values. The mass content of the pore former is controlled within this range, which is conducive to forming an appropriate amount of pores in the active material layer, and is also conducive to the pore former being dissolved in the electrolyte and reacting with metallic lithium, which helps to eliminate the undesirable lithium deposition phenomenon and improve the safety of the battery. It is also conducive to the pore former dissolved in the electrolyte as an overcharge protector for the battery, reducing the safety risk of the electrode sheet caused by overcharging.

[0026] In some embodiments, the active material layer includes a first surface facing the current collector and a second surface arranged opposite to the first surface, and the mass content of the pore former in the active material layer gradually increases along the direction from the first surface to the second surface. In thick electrodes, it is difficult to wet the bottom of the electrode sheet. If too much pore former is added, it may be difficult to completely dissolve. By setting the mass content relationship of the pore former in the active material layer, it is beneficial to control or promote the porosity of the surface of the electrode sheet after the pore former is dissolved to be higher, which is beneficial for the electrolyte to better contact with the underlying active material, and achieve a state similar to the contact between the surface of the electrode without a pore former and the electrolyte, thereby facilitating the improvement of the electrolyte wettability of the underlying active material, while controlling the porosity of the electrode sheet within a suitable range, which is beneficial to maintaining a good energy density. It can be understood that when the mass content of the pore former in the active material layer exceeds the preset relationship, the porosity of the bottom layer of the electrode sheet may increase, which may cause the overall pores of the electrode sheet to be more, resulting in a decrease in energy density.

[0027] In some embodiments, the thickness of the active material layer on any surface of the current collector is 20 μm to 300 μm. For example, the thickness of the active material layer can be 20 μm, 40 μm, 60 μm, 80 μm, 100 μm, 150 μm, 200 μm, 250 μm, 300 μm, or any value within the range formed by any two of the above values. The thickness of the active material layer is controlled within the above range, which is beneficial to improve the energy density of the electrode sheet, such as forming a thick electrode. The present application uses small molecule quinone organic compounds and their derivatives as pore-forming agents for electrode sheets, which can improve the rate performance of lithium-ion batteries and the liquid retention of electrode sheets while increasing the energy density of the electrode sheets.

[0028] The electrode sheet may be a positive electrode sheet and / or a negative electrode sheet.

[0029] The negative electrode sheet includes a negative electrode current collector and a negative electrode active material layer disposed on at least one surface of the negative electrode current collector. The negative electrode current collector may be at least one of copper foil, nickel foil, stainless steel foil, titanium foil or a carbon-based current collector, or may be any composite current collector disclosed in the prior art, such as but not limited to a current collector formed by combining the aforementioned conductive foil and a polymer substrate.

[0030] The negative electrode active material layer includes a negative electrode material, and the negative electrode material includes graphite, mesophase microcarbon beads (MCMB), hard carbon, soft carbon, silicon, silicon-carbon composite, SiOx (0.5<x<1.6), Li-Sn alloy, Li-Sn-O alloy, Sn, SnO, SnO2, spinel structured lithium titanate, lithiated TiO2-Li4Ti5O 12 , Li-Al alloy and at least one of metallic lithium.

[0031] The negative electrode active material layer also includes a binder to bind the negative electrode active material particles to facilitate the formation of a film layer, and can also improve the binding force between the negative electrode active material layer and the negative electrode current collector. In some embodiments, the binder may include but is not limited to polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene butadiene rubber, acrylic (ester) styrene butadiene rubber, epoxy resin or nylon, etc.

[0032] The negative electrode active material layer may also include a conductive material, including but not limited to a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof. In some embodiments, the carbon-based material may include but is not limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material may include but is not limited to metal powder or metal fiber, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0033] The positive electrode sheet includes a positive electrode current collector and a positive electrode active material layer disposed on at least one surface of the positive electrode current collector. The positive electrode current collector may be made of aluminum foil or nickel foil, or may be any composite current collector disclosed in the prior art, such as but not limited to the current collector formed by combining the aforementioned conductive foil and a polymer substrate. The positive electrode active material layer includes a positive electrode material, and the positive electrode material includes a compound that can reversibly embed and deintercalate lithium ions (i.e., a lithiated intercalation compound). In some embodiments, the positive electrode material may include a lithium transition metal composite oxide. The lithium transition metal composite oxide contains lithium and at least one element selected from cobalt, manganese and nickel. In some embodiments, the positive electrode material may include but is not limited to lithium cobalt oxide (LiCoO2), lithium nickel manganese cobalt ternary material (NCM), lithium manganese oxide (LiMn2O4), lithium nickel manganese oxide (LiNi 0.5 Mn 1.5 O4) or at least one of lithium iron phosphate (LiFePO4).

[0034] The positive electrode active material layer may also include a binder to bond the positive electrode active material particles to facilitate the formation of a film layer, and at the same time, to improve the bonding force between the positive electrode active material layer and the positive electrode current collector. In some embodiments, the binder may include but is not limited to at least one of polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinyl pyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylic (ester) styrene-butadiene rubber, epoxy resin or nylon.

[0035] The positive electrode active material layer may also include a conductive material, including but not limited to a carbon-based material, a metal-based material, a conductive polymer, or any combination thereof. In some embodiments, the carbon-based material may include but is not limited to natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based material may include but is not limited to metal powder or metal fiber, such as copper, nickel, aluminum, or silver. In some embodiments, the conductive polymer may be a polyphenylene derivative.

[0036] Isolation film The isolation membrane includes a membrane layer with a porous structure, and its material includes but is not limited to at least one of polyethylene, polypropylene, polyvinylidene fluoride, polyethylene terephthalate, polyimide or aramid. For example, the isolation membrane can be a polypropylene porous membrane, a polyethylene porous membrane, a polypropylene non-woven fabric, a polyethylene non-woven fabric or a polypropylene-polyethylene-polypropylene porous composite membrane.

[0037] Electrolyte The electrolyte has the function of conducting ions between the positive electrode sheet and the negative electrode sheet. In some embodiments, the electrolyte includes a lithium salt and an organic solvent. The lithium salt can be selected from but not limited to one or more of lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium tetraphenylborate (LiB(C6H5)4), lithium methanesulfonate (LiCH3SO3), lithium bis(trifluoromethanesulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiCF3SO3), lithium bis(trifluoromethylsulfonyl)imide (LiN(SO2CF3)2, tris(trifluoromethylsulfonyl)methyl lithium (LiC(SO2CF3)3), lithium bis(oxalatoborate) (LiBOB) and lithium difluorophosphate (LiPO2F2). For example, the lithium salt is selected from LiPF6 because it can give high ionic conductivity and improve cycle characteristics. The organic solvent can be a carbonate compound, a carboxylate compound, an ether compound, Compounds, nitrile compounds, other organic solvents or combinations thereof. Examples of carbonate compounds include, but are not limited to, diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methylpropyl carbonate (MPC), ethylpropyl carbonate (EPC), ethylmethyl carbonate (MEC), ethylene carbonate (EC), propylene carbonate (PC), butylene carbonate (BC), vinylethylene carbonate (VEC), fluoroethylene carbonate (FEC), 1,2-difluoroethylene carbonate, 1,1-difluoroethylene carbonate, 1,1,2-trifluoroethylene carbonate, 1,1,2,2-tetrafluoroethylene carbonate, 1-fluoro-2-methylethylene carbonate, 1-fluoro-1-methylethylene carbonate, 1,2-difluoro-1-methylethylene carbonate, 1,1,2-trifluoro-2-methylethylene carbonate, trifluoromethylethylene carbonate or combinations thereof.

[0038] An embodiment of the present application further provides a method for preparing an electrode sheet, comprising: Step 1: An active material layer is disposed on at least one surface of the current collector, wherein the active material layer includes a pore former, and the pore former includes polycyclic aromatic hydrocarbons and derivatives thereof.

[0039] In some embodiments, the active material layer can be provided in the following manner: providing the active material layer on the surface of the current collector includes applying a coating composition on at least one surface of the current collector, the coating composition includes a pore former, and the pore former includes polycyclic aromatic hydrocarbons and their derivatives. Then, the current collector coated with the coating composition can be preliminarily dried and rolled to obtain the active material layer. The present application uses polycyclic aromatic hydrocarbons and their derivatives as pore formers. After the coating composition including the pore former forms a coating, the pore former in the coating can be dissolved in an organic solvent to produce pores in the coating.

[0040] In some embodiments, the polycyclic aromatic hydrocarbons and their derivatives include one or more of biphenyl, naphthalene, phenanthrene, anthracene, tetracene, pyrene and perylene. The polycyclic aromatic hydrocarbons and their derivatives can leave pores on the coating by dissolving in an organic solvent.

[0041] In some embodiments, the coating composition further comprises one or more of a conductive agent, a binder and an active material, and the active material comprises one of a positive electrode material and a negative electrode material. The pore-forming agent of the present application is applied to the coating slurry of the electrode sheet, and can generate pores in the coating of the electrode sheet by dissolving in an organic solvent.

[0042] In some embodiments, the active material layer includes a first surface facing the current collector and a second surface disposed opposite to the first surface, and the mass content of the pore former in the active material layer gradually increases along the direction from the first surface to the second surface. It can be understood that the layered arrangement of the above-mentioned active material layer on the current collector can be achieved by configuring coating compositions with different mass contents of the pore former, first applying a coating composition with a lower mass content of the pore former on one surface of the current collector, and then applying a coating composition with a higher mass content of the pore former.

[0043] In some embodiments, the rolled structure can also be cut to obtain an electrode sheet. In the present application, small molecule quinone organic compounds and their derivatives are used as pore-forming agents for electrode sheets. The electrode sheet can adapt to the above-mentioned existing electrode sheet preparation process, without the need for additional pore-forming devices or modification of the pore-forming devices, thereby reducing the cost of electrode sheet pore-forming and reducing the loss of active substances caused by etching-type pore-forming methods.

[0044] In some embodiments, the method for preparing the electrode sheet further comprises: Step 2: contacting the active material layer with an organic solvent to dissolve the pore former in the organic solvent; drying the active material layer to obtain an electrode sheet.

[0045] During the above-mentioned contact (such as immersion) process, the pore-forming agent in the active material layer can be dissolved in an organic solvent to reserve pores on the electrode sheet, and the pore-forming method is simple; moreover, the pore-forming agent dissolved in the electrolyte has basically no negative impact on the battery cell, and no additional removal process is required.

[0046] In some embodiments, the organic solvent includes one or more of electrolyte solvent, acetone, toluene, dichloromethane, chloroform, ethyl acetate, acetonitrile, methanol and petroleum ether. The organic solvent selected from the above substances can dissolve the pore former and is conducive to reducing the dissolution of the binder in the active material layer.

[0047] In some embodiments, the electrode sheet prepared by the above preparation method can be directly used to assemble into a battery. The preparation process of adding polycyclic aromatic hydrocarbons and their derivatives as pore-forming agents in this application is basically adapted to the above-mentioned existing electrode sheet preparation process, and the battery assembly and liquid injection steps are consistent with the conventional process, and the infiltration, formation, secondary injection and volume separation processes are all consistent with the conventional process.

[0048] Another embodiment of the present application provides a battery, which includes the electrode sheet provided in the above embodiment, or includes an electrode sheet prepared by the method for preparing the electrode sheet provided in the above embodiment.

[0049] After the above-mentioned electrode sheets are assembled into a battery, on the one hand, the pore-forming agent in the active material layer of the electrode sheet will dissolve in the electrolyte in the battery to create pores in the electrode sheet, which is beneficial to shorten the transmission path of lithium ions, improve the rate performance of lithium-ion batteries, and also help to increase the liquid retention of the electrode sheet, thereby helping to extend the life of the battery; on the other hand, the pore-forming agent can also react with metallic lithium after being dissolved in the electrolyte, eliminating undesirable lithium deposition phenomena, reducing lithium dendrite phenomena, and improving battery safety; and polycyclic aromatic hydrocarbons can also serve as overcharge protectors for batteries to reduce the safety risks of electrode sheets caused by overcharging.

[0050] Another embodiment of the present application also provides an electrical device, including the above-mentioned battery. In some embodiments, the battery of the present application can be used for but not limited to the following electrical devices: laptop computers, pen-input computers, mobile computers, e-book players, portable phones, portable fax machines, portable copiers, portable printers, head-mounted stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini-discs, transceivers, electronic notepads, calculators, memory cards, portable recorders, radios, backup power supplies, motors, cars, motorcycles, power-assisted bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, large household batteries or lithium-ion capacitors, etc.

[0051] The scheme of the present application will be explained below in conjunction with the embodiments. Those skilled in the art will understand that the following examples are only used to explain the present application and cannot be construed as limiting the present application. Unless otherwise stated, the reagents, software and instruments not specifically stated in the following embodiments are all conventional commercial products or open source.

[0052] Embodiment 1: A soft pack battery, the preparation method of which comprises: S1, select LiFePO4 as the positive electrode material, mix LiFePO4, Super P and polyvinylidene fluoride (PVDF) in a mass ratio of 96:2:2, apply it on the aluminum foil current collector, dry it in an oven, and then roll it to obtain the required positive electrode sheet.

[0053] S2, select graphite as the negative electrode material, use double-layer coating, mix graphite, styrene butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), biphenyl and Super P in a mass ratio of 97.2:1.2:0.8:0.4:0.4, and apply it on the copper foil current collector as the lower layer; mix graphite, styrene butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC), biphenyl and Super P in a mass ratio of 96.8:1.2:0.8:0.8:0.4 as the upper layer slurry, dry it in an oven, and then roll it to obtain the required negative electrode sheet.

[0054] S3, a 2.5 Ah small soft-pack battery was made by the Z-shaped stacking method. The electrolyte was injected into the argon glove box with an injection coefficient of 2.6 and left to stand at 45 °C for 48 h.

[0055] Embodiment 2: S1, select LiFePO4 as the positive electrode material, use double-layer coating, mix LiFePO4, biphenyl, Super P and polyvinylidene fluoride (PVDF) in a mass ratio of 95.6:0.4:2:2, and apply it on the aluminum foil current collector as the lower layer, mix LiFePO4, biphenyl, Super P and polyvinylidene fluoride (PVDF) in a mass ratio of 95.2:0.8:2:2 as the upper layer slurry, dry it in an oven, and then roll it to obtain the required positive electrode sheet.

[0056] S2, graphite is selected as the negative electrode material, graphite, styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC) and Super P are evenly mixed in a mass ratio of 97.6:1.2:0.8:0.4, coated on a copper foil current collector, dried in an oven, and then roll-pressed to obtain the desired negative electrode sheet.

[0057] S3, a 2.5 Ah small soft-pack battery was made by the Z-shaped stacking method. The electrolyte was injected into the argon glove box with an injection coefficient of 2.6 and left to stand at 45 °C for 48 h.

[0058] Embodiment 3: S1, same as Example 2.

[0059] S2, same as Example 1.

[0060] S3, a 2.5 Ah small soft-pack battery was made by the Z-shaped stacking method. The electrolyte was injected into the argon glove box with an injection coefficient of 2.6 and left to stand at 45 °C for 48 h.

[0061] Embodiment 4: The difference from Example 3 is that in S1, LiNi 0.8 Co 0.1 Mn 0.1 O2 is used as the positive electrode material.

[0062] Embodiment 5: The difference from Example 3 is that in S1, biphenyl is replaced by naphthalene; in S2, biphenyl is replaced by naphthalene.

[0063] Embodiment 6: The difference from Example 3 is that in S2, biphenyl is replaced by naphthalene.

[0064] Embodiment 7: The difference from Example 3 is that in S1, biphenyl is replaced by phenanthrene; in S2, biphenyl is replaced by phenanthrene.

[0065] Embodiment 8: The difference from Example 3 is that in S1, biphenyl is replaced by anthracene; in S2, biphenyl is replaced by anthracene.

[0066] Embodiment 9: The difference from Example 3 is that in S1, biphenyl is replaced by pyrene; in S2, biphenyl is replaced by pyrene.

[0067] Comparative Example 1: S1, select LiFePO4 as the positive electrode material, mix LiFePO4, Super P and polyvinylidene fluoride (PVDF) in a mass ratio of 96:2:2, apply it on the aluminum foil current collector, dry it in an oven, and then roll it to obtain the required positive electrode sheet.

[0068] S2, graphite is selected as the negative electrode material, graphite, styrene-butadiene rubber (SBR), sodium carboxymethyl cellulose (CMC) and Super P are evenly mixed in a mass ratio of 97.6:1.2:0.8:0.4, coated on a copper foil current collector, dried in an oven, and then roll-pressed to obtain the desired negative electrode sheet.

[0069] S3, a 2.5 Ah small soft-pack battery was made by the Z-shaped stacking method. The electrolyte was injected into the argon glove box with an injection coefficient of 2.6 and left to stand at 45 °C for 48 h.

[0070] The soft pack batteries of Examples 1-9 and Comparative Example 1 of the present application were subjected to performance tests, including: 1. Capacity test of soft-pack batteries: 3 C capacity test is carried out through step charging, non-constant current charging and discharging, and 3 C is the equivalent rate; 5 C capacity test is carried out through step charging, non-constant current charging and discharging, and 5 C is the equivalent rate.

[0071] 2. Capacity retention rate test of soft-pack batteries: The capacity retention rate is calculated based on the discharge capacity of the first cycle.

[0072] 3. DC impedance test of soft-pack battery: DC impedance is measured at 25% SOC and discharged at a rate of 2 C for 10 s.

[0073] 4. Lithium deposition risk assessment: Perform a step charge test at -10°C, discharge at 0.33 C, and cycle 50 times. After standing for 24 hours, disassemble the battery and observe whether there is lithium deposition on the negative electrode surface. If the lithium deposition area occupies 0 to 5% of the entire negative electrode area, it is judged as low, 5 to 10% as medium, and greater than 10% as high.

[0074] Please refer to Table 1 for the above performance test results.

[0075] Table 1. Performance test results of Examples 1-9 and Comparative Example 1 of the present application It can be seen from the electrochemical performance test that in the preparation process of the electrode sheets of Examples 1-9 of the present application, polycyclic aromatic hydrocarbons and their derivatives are used as pore formers and added to the surface coating of the current collector. The pore formers in the coating are dissolved in the electrolyte to generate pores on the electrode sheets, which is beneficial to shorten the transmission path of lithium ions and improve the rate performance of the soft-pack battery, which is reflected in the higher ratio of 5 C capacity (Ah) to 1 C capacity (Ah) of the batteries of Examples 1-9, and the lower DC impedance of the batteries after cycling. It is also beneficial to increase the liquid retention of the electrode sheets, thereby improving the capacity cycle retention rate of the soft-pack batteries.

[0076] Compared with the embodiments of the present application, Comparative Example 1 is a conventional electrode sheet, and its 3 C capacity retention rate and the ratio of 5 C capacity (Ah) to 1 C capacity (Ah) are significantly lower, and the DC impedance is significantly higher, indicating that its rate performance is not as good as the embodiments of the present application. The electrode sheet of the present application has improved rate performance.

[0077] It can be seen from the lithium plating risk assessment that in the soft-pack batteries of Examples 1-9 of the present application, the pore-forming agent can react with metallic lithium after being dissolved in the electrolyte, thereby eliminating undesirable lithium deposition phenomena, such as lithium plating at the negative electrode, reducing lithium dendrite phenomena, and enhancing the safety of the battery cell or battery.

[0078] Compared with the embodiments of the present application, Comparative Example 1 does not use polycyclic aromatic hydrocarbons and their derivatives as pore-forming agents, and its lithium plating risk is relatively high, and the safety of the battery cell and battery is relatively low.

[0079] The above implementation modes are only used to illustrate the technical solutions of the present application and are not intended to limit the present application. Although the present application has been described in detail with reference to the above preferred implementation modes, a person skilled in the art should understand that the technical solutions of the present application may be modified or replaced by equivalents without departing from the spirit and scope of the technical solutions of the present application.

Claims

1. An electrode sheet, comprising a current collector and an active material layer disposed on at least one surface of the current collector, wherein the active material layer comprises an active substance, characterized in that: The active material layer includes a pore former, and the pore former includes polycyclic aromatic hydrocarbons and derivatives thereof.

2. The electrode sheet according to claim 1, characterized in that: The polycyclic aromatic hydrocarbons and their derivatives include one or more of biphenyl, naphthalene, phenanthrene, anthracene, tetracene, pyrene and perylene.

3. The electrode sheet according to claim 1, characterized in that: The mass content of the pore former in the active material layer is 0.1% to 20%.

4. The electrode sheet according to claim 1, characterized in that: The active material layer includes a first surface facing the current collector and a second surface opposite to the first surface, and the mass content of the pore former in the active material layer gradually increases along a direction from the first surface to the second surface.

5. The electrode sheet according to claim 4, characterized in that: The thickness of the active material layer on any one surface of the current collector is 20 μm to 300 μm.

6. A method for preparing an electrode sheet, characterized in that: include: An active material layer is disposed on at least one surface of the current collector, wherein the active material layer includes a pore former, and the pore former includes polycyclic aromatic hydrocarbons and derivatives thereof.

7. The method for preparing an electrode sheet according to claim 6, characterized in that: Also includes: contacting the active material layer with an organic solvent to dissolve the pore former in the organic solvent; The active material layer is dried to obtain the electrode sheet.

8. The method for preparing an electrode sheet according to claim 7, characterized in that: The organic solvent includes one or more of electrolyte solvent, acetone, toluene, dichloromethane, chloroform, ethyl acetate, acetonitrile, methanol and petroleum ether.

9. A battery, characterized in that: The battery comprises the electrode sheet according to any one of claims 1 to 5, or comprises an electrode sheet prepared by the method for preparing the electrode sheet according to any one of claims 6 to 8.

10. An electrical device, characterized in that: The electric device comprises the battery as claimed in claim 9.

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