Electrode and preparation method thereof, lithium ion battery and electric equipment

Abstract

The electrode comprises a current collector and a carbonized film, and a plurality of grooves are formed in the surface, parallel to the current collector, of the carbonized film at intervals; the electrode further comprises a solidified electrode material layer arranged between the carbonized film and the current collector. The invention also relates to a preparation method of the electrode, a lithium ion battery and electric equipment. The electrode provided by the invention is provided with the groove structure, so that the pore tortuosity of the electrode in the thickness direction of the electrode is reduced, the wettability of an electrolyte in an electrode piece is improved while the energy density of the electrode is ensured, and the influence of concentration polarization on the electrochemical performance of the electrode is reduced; meanwhile, the carbonized film coated on the surface of the cured electrode material layer of the electrode provided by the invention is used as a conductive interface, so that the transmission capability of electrons and ions is improved, the polarization of the pole piece is effectively reduced, and the rate capability of the battery is improved; the carbonization film covers the surface of the active material layer, so that the problems of cracking and falling of the active material layer can be relieved.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and specifically, relates to an electrode, a preparation method thereof, a lithium-ion battery, and an electrical device using the same. Background Art

[0002] As a cathode material for lithium batteries, phosphate polyanion salts have the advantages of stable structure, high safety, good cycle performance, etc., and are widely used in lithium-ion batteries for new energy vehicles. Currently, the cathode material of lithium manganese iron phosphate forms LiMn x Fe 1-x PO4 (0 < x < 1) by partially replacing iron with manganese to increase the voltage platform of LiFePO4 and further improve its energy density. However, the energy density of LiMn x Fe 1-x PO4 is still lower than that of high-nickel ternary batteries. Currently, the overall proportion of active components in the battery can be increased by adopting electrode design to achieve higher energy output. However, thicker electrodes are prone to cracking of the active material layer and falling off during the drying process. At the same time, similar to LiFePO4, LiMn x Fe 1-x PO4 also faces the problem of slow electron / ion conduction rate. And as the electrode coating amount increases, the Li + / e - transmission distance is extended, and the resistance to lithium-ion diffusion increases significantly, which is not conducive to the rate performance and electrochemical cycle performance of the battery. Therefore, improving the transmission efficiency of the electrode is an important method to improve the electrochemical performance of lithium manganese iron phosphate batteries. Summary of the Invention

[0003] The purpose of the present invention is to overcome the problems existing in the prior art, and provide an electrode, a preparation method thereof, a lithium-ion battery, and an electrical device using the same, which can enable the battery to have higher energy density and rate performance.

[0004] To achieve the above purpose, in the first aspect of the present invention, an electrode is provided. The electrode includes a current collector and a carbonized film. The carbonized film has a plurality of grooves arranged at intervals on the surface parallel to the current collector; the electrode further includes a cured electrode material layer disposed between the carbonized film and the current collector.

[0005] Optionally, the edge of the carbonized film is bonded to the current collector.

[0006] Optionally, the cured electrode material layer is provided with recesses, and the recesses of the cured electrode material layer match the grooves of the carbonized film; or, the cured electrode material layer is not provided with the recesses.

[0007] Optionally, the grooves are arranged in an array; and / or the shape of the grooves is sawtooth wave-shaped, square wave-shaped, trapezoidal wave-shaped or arc wave-shaped; and / or the width of the grooves is 50-200 μm, and the distance between two adjacent grooves is 100-500 μm; and / or the depth of the grooves is 20-80% of the thickness of the cured electrode material layer.

[0008] Optionally, the thickness of the carbonized film is 2-10 μm; the width of the contact surface between the carbonized film and the current collector ≤ 1 mm.

[0009] Optionally, the thickness of the current collector is 6-17 μm; the current collector is selected from at least one of copper foil and aluminum foil.

[0010] Optionally, the thickness of the cured electrode material layer is 100-200 μm, preferably 110-160 μm; the single-sided surface density of the electrode is 200-260 g / m 2 , preferably 220-240 g / m 2 .

[0011] Optionally, a convex arc surface is formed between adjacent grooves of the electrode.

[0012] Optionally, the active material in the cured electrode material layer is a lithium iron manganese phosphate cathode material; the chemical formula of the lithium iron manganese phosphate cathode material is LiMn x Fe 1-x PO4, where 0.5 ≤ x ≤ 0.9.

[0013] The second aspect of the present invention provides a method for preparing an electrode, the method comprising the following steps:

[0014] Bond an organic polymer film on the surface of the current collector to form a cavity between the surface of the current collector and the organic polymer film; wherein, the organic polymer film has a plurality of grooves arranged at intervals on the surface parallel to the current collector;

[0015] Inject the electrode slurry into the cavity to obtain a green body;

[0016] Perform heat treatment on the green body so that the electrode slurry is cured to obtain a cured electrode material layer, and the organic polymer film is carbonized to form a carbonized film.

[0017] Optionally, the grooves are arranged in an array; and / or the shape of the grooves is sawtooth wave-shaped, square wave-shaped, trapezoidal wave-shaped or arc wave-shaped; and / or the width of the grooves is 50-200 μm, and the distance between two adjacent grooves is 100-500 μm; and / or the depth of the grooves is 20-80% of the thickness of the cured electrode material layer of the electrode.

[0018] Optionally, the organic polymer film is polyvinyl alcohol with a molecular weight of 25,000 - 35,000; wherein, the heat distortion temperature of the polyvinyl alcohol with a molecular weight of 25,000 - 35,000 is 75 - 100°C, preferably 87 - 92°C, and the carbonization temperature is 200 - 250°C, preferably 200 - 220°C; the thickness of the organic polymer film is 2 - 10 μm; the width of the contact surface between the organic polymer film and the current collector ≤ 1 mm.

[0019] Optionally, the thickness of the current collector is 6 - 17 μm; the current collector is selected from at least one of copper foil and aluminum foil.

[0020] Optionally, the thickness of the solidified electrode material layer is 100 - 200 μm, preferably 110 - 160 μm; the single-sided areal density of the electrode is 200 - 260 g / m 2 , preferably 220 - 240 g / m 2 .

[0021] Optionally, an outwardly convex arc surface is formed between adjacent grooves of the electrode.

[0022] Optionally, the electrode paste includes a positive electrode paste or a negative electrode paste; the active material in the positive electrode paste is a lithium manganese iron phosphate positive electrode material; wherein, the chemical formula of the lithium manganese iron phosphate positive electrode material is LiMn x Fe 1-x PO4, where 0.5 ≤ x ≤ 0.9.

[0023] The third aspect of the present invention provides a lithium-ion battery, which includes the electrode described in the first aspect or the second aspect of the present invention.

[0024] The fourth aspect of the present invention provides an electrical equipment, which includes the aforementioned lithium-ion battery.

[0025] Through the above technical solutions, the solidified electrode material layer and the carbonized film of the electrode provided by the present invention have a groove structure, which reduces the pore tortuosity of the electrode in the electrode thickness direction, improves the wettability of the electrolyte in the electrode sheet while ensuring the energy density of the electrode, reduces the influence of concentration polarization on the electrochemical performance of the electrode, and thus enables the battery to have a higher energy density and rate performance. At the same time, the surface of the solidified electrode material layer of the electrode provided by the present invention is coated with a carbonized film, and the carbonized film serves as a conductive interface, increasing the electron and ion transport capabilities, further optimizing the conductive performance of the electrode, effectively reducing the polarization of the electrode sheet and increasing the rate performance of the battery; the carbonized film covers the surface of the active material layer, which can alleviate the problems of cracking and shedding of the active material layer.

[0026] Other features and advantages of the present invention will be described in detail in the subsequent specific implementation section. Brief Description of the Drawings

[0027] The drawings are used to provide a further understanding of the present invention and constitute a part of the specification. Together with the following specific embodiments, they are used to explain the present invention, but do not limit the present invention. In the drawings:

[0028] Figure 1 is a schematic structural diagram of the electrode provided by the present invention.

[0029] Figure 2 is a schematic structural diagram of the organic polymer film provided by the present invention bonded to the current collector.

[0030] Description of Reference Numerals in the Drawings

[0031] 11 Current collector; 12 Carbonized film; 13 Solidified electrode paste layer

[0032] 21 Current collector; 22 Organic polymer film; 23 Cavity; 24 Contact surface Specific Embodiments

[0033] The following provides a detailed description of the specific embodiments of the present invention. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention and are not used to limit the present invention.

[0034] The capacity and energy density output by the battery pack are related to the content of active substances in the electrode. Designing a thicker electrode means that higher energy output can be achieved. Therefore, designing a thicker electrode and a thinner electrolyte can effectively increase the proportion of active substances in the electrode, thereby obtaining a higher energy density. However, continuously increasing the electrode thickness will also bring some negative effects. For example, in actual applications, designing a thicker electrode is likely to cause electrode cracking and is prone to falling off during the drying process of the electrode paste. At the same time, as the electrode thickness increases, the Li + / e - transmission distance is extended (high-curvature Li + / etransmission channels), which means an increase in internal impedance; it is difficult for solid electrolytes to establish continuous Li - + / e - transmission channels, resulting in a decrease in the utilization rate of active materials and a low output capacity.

[0035] Currently, creating pores in the electrode is an efficient strategy to solve defects such as thick electrode sheets, low porosity, poor wettability, and long ion migration paths. The solutions for creating pores in the electrode include creating pores by adding pore-forming agents and creating pores using methods such as suction grooving. However, the solution of creating pores with pore-forming agents has various uncontrollable problems such as pore-forming agent residue, complex processing technology, and low production efficiency; the solution of suction grooving is prone to unstable grooving effects due to the accumulation of residual materials, and the suction equipment needs to be cleaned, reducing the production efficiency.

[0036] To solve the above problems, the present invention provides an electrode. Referring to Figure 1 the schematic structural diagram of the electrode shown, the electrode includes a current collector 11 and a carbonized film 12. The carbonized film 12 has a plurality of grooves arranged at intervals on the surface parallel to the current collector 11. A solidified electrode material layer 13 is provided between the carbonized film 12 and the current collector 11. Specifically, as Figure 1 shown, the grooves are provided on the surface of the carbonized film opposite to the current collector to shorten the transmission distance of lithium ions between the electrodes.

[0037] The plurality of grooves arranged at intervals on the solidified electrode material layer and the carbonized film of the electrode provided by the present invention shorten the transmission distance of lithium ions between the electrodes and improve the electrochemical performance of the electrode sheet; the carbonized film formed on the surface of the solidified electrode material layer can further strengthen the conductivity of the electrode and improve the transmission efficiency of the electrode.

[0038] In some embodiments of the present invention, the edge of the carbonized film 12 is bonded to the current collector 11. Bonding the edge of the carbonized film to the current collector can comprehensively protect the active material layer and avoid the problems of cracking and falling off during the drying process of the active material layer.

[0039] In some embodiments of the present invention, the solidified electrode material layer is provided with recesses. Specifically, the recesses of the solidified electrode material layer match the grooves of the carbonized film.

[0040] In some other embodiments of the present invention, the solidified electrode material layer is not provided with the recesses, and the grooves on the carbonized film may not extend to the solidified electrode material layer, that is, only exist on the carbonized film.

[0041] In some embodiments of the present invention, the grooves are arranged in an array. Specifically, the grooves are located on the surface of the carbonized film parallel to the current collector, and the shape of the grooves along the width direction of the grooves can be sawtooth wave-shaped, square wave-shaped, trapezoidal wave-shaped or arc wave-shaped.

[0042] In some embodiments of the present invention, the width W1 (referring to the maximum width of the groove), the depth D1 (referring to the maximum depth of the groove) and the spacing L1 between adjacent grooves (referring to the maximum spacing of the grooves) can also be designed. For example, in some embodiments of the present invention, the width of the groove is 50-200 μm, and the spacing between two adjacent grooves is 100-500 μm. Designing the size of the grooves, for example, when the width of the electrode sheet is fixed, reducing the width of the grooves can increase the electrolyte infiltration area to ensure efficient mass transfer of the positive electrode material during charge and discharge and optimize the rate performance of the electrode. To further improve the rate performance of the electrode, the depth of the groove is 20-80% of the thickness of the solidified electrode material layer of the electrode.

[0043] In some embodiments of the present invention, the thickness of the carbonized film is 2 - 10 μm; the width of the contact surface between the carbonized film and the current collector is ≤ 1 mm.

[0044] In some embodiments of the present invention, the thickness of the current collector is 6 - 17 μm; the current collector is selected from at least one of copper foil and aluminum foil.

[0045] In some embodiments of the present invention, the thickness of the solidified electrode paste layer is 100 - 200 μm, preferably 110 - 160 μm.

[0046] In the present invention, by first shaping the organic film to form an electrode with grooves, it can not only ensure the uniform distribution of the grooves on the electrode, but also control the fluidity of the electrode paste during the coating process, ensuring the uniformity of the solidified electrode paste layer.

[0047] In some embodiments of the present invention, the areal density of one side of the electrode can be 200 - 260 g / m 2 , preferably, it can be 220 - 240 g / m 2 .

[0048] In some embodiments of the present invention, an outwardly convex arc surface is formed between adjacent grooves of the electrode, increasing the contact area between the electrode plate and the electrolyte, which is beneficial to ion transport.

[0049] In some embodiments of the present invention, the active substance in the solidified electrode paste is lithium manganese iron phosphate cathode material; wherein, the chemical formula of the lithium manganese iron phosphate cathode material is LiMn x Fe 1-x PO4, where 0.5 ≤ x ≤ 0.9.

[0050] The present invention provides a method for preparing an electrode, and the method includes the following steps:

[0051] Bond an organic polymer film on the surface of the current collector to form a cavity between the surface of the current collector and the organic polymer film; wherein, the organic polymer film has a plurality of grooves arranged at intervals on the surface parallel to the current collector;

[0052] Inject the electrode paste into the cavity to obtain a green body;

[0053] Perform heat treatment on the green body to solidify the electrode paste to obtain a solidified electrode paste layer and carbonize the organic polymer film to form a carbonized film.

[0054] The preparation method of the electrode provided by the present invention combines an organic polymer film with a groove shape on the surface of the current collector to form a cavity for accommodating the electrode paste between the surface of the current collector and the organic polymer film. The embryo is heat-treated to cure the electrode paste and carbonize the organic polymer film. The solvent in the electrode paste volatilizes to form a stable shaped coating of the electrode paste, and a groove structure is formed in the shaped coating, reducing the pore tortuosity of the electrode in the electrode thickness direction, obtaining an electrode structure with good rate performance, improving the wettability of the electrolyte in the electrode sheet while ensuring the energy density of the electrode, and reducing the influence of concentration polarization on the electrochemical performance of the electrode. At the same time, the organic polymer film is carbonized to form a carbonized film, and the carbonized film has a nanoscale porous structure, which can further strengthen the conductivity of the lithium iron phosphate manganese material, neither hindering ion diffusion nor improving the conductivity, and also preventing excessive surface side reactions caused by direct contact between the electrolyte and the active material. The carbonized film covers the surface of the active material layer and can also alleviate the problems of cracking and peeling of the active material layer during the drying process.

[0055] In some embodiments of the present invention, the electrode paste completely fills the cavity.

[0056] In some other embodiments of the present invention, the grooves only exist on the organic polymer film. Correspondingly, there are grooves on the carbonized film but no recesses are formed on the cured electrode paste layer.

[0057] The present invention adopts a method of shaping and creating pores with an organic polymer film, and the groove structure on the formed electrode is uniform, which can not only meet the sufficient wetting of the electrolyte to the electrode in the electrode thickness direction, but also control the casting fluidity of the electrode to a certain extent, ensuring the uniformity of the electrode sheet coating.

[0058] In the present invention, during the heat treatment of the embryo, the organic polymer film reaches the thermal decomposition temperature and is carbonized to form an amorphous carbon coating structure, improving the rate performance of the positive electrode and being beneficial to further improving the conductivity of the electrode.

[0059] In the present invention, the groove is an arbitrary waveform with a designable aspect ratio.

[0060] In some embodiments of the present invention, the mass transfer channel grooves for forming the electrode can be square wave-shaped, sawtooth wave-shaped, trapezoidal wave-shaped or arc wave-shaped. For ease of implementation, the organic polymer film has a plurality of grooves arranged at intervals, such as square grooves, rounded grooves or grooves with a trapezoidal cross-section. In some embodiments, the groove can be a square groove, that is, the opening of the groove on the organic polymer film is rectangular. In some preferred embodiments, the opening of the groove on the organic polymer film (that is, the junction of the side of the organic binder film parallel and away from the current collector and the side of the groove perpendicular to the current collector) can also be designed to be rounded to weaken the influence of the tip on the separator.

[0061] Figure 2 The structural schematic diagram before the organic polymer film is coated with the electrode paste in an embodiment of the present invention is shown. As Figure 2 shown, an organic polymer film 22 with square grooves is bonded to the surface of the current collector 21, a cavity 23 is formed between the current collector 21 and the organic polymer film 22, and the part where the organic polymer film is bonded to the current collector is the contact surface 24.

[0062] Referring to Figure 2 , the distance at the maximum width of the grooves on the organic polymer film is the width W2, the distance at the maximum depth of the grooves is the depth D2, and the maximum distance between adjacent grooves is the spacing L2. Preferably, the width W2 of the grooves is 50 - 200 μm, the depth D2 of the grooves is 20 - 80% of the thickness of the cured electrode paste layer of the electrode, and the spacing L2 between two adjacent grooves is 100 - 500 μm.

[0063] Among them, the arrangement of the grooves on the organic polymer film can be designed. For example, multiple grooves are evenly spaced. In order to further increase the mass transfer effect of the electrode, the grooves can be arranged in an array.

[0064] In some embodiments of the present invention, a groove structure is formed on the organic polymer film by a thermoplastic method. Specifically, the thermoplastic method includes extrusion molding and / or hot pressing.

[0065] Among them, the organic polymer film can be a shaped resin or other olefin copolymers. Preferably, the organic polymer film is an organic compound that can be carbonized at low temperature.

[0066] Specifically, the organic polymer film is polyvinyl alcohol PVA, and the monomer of the polyvinyl alcohol is [C2H4O] n , and the organic polymer film is polyvinyl alcohol with a low degree of polymerization and a molecular weight of 25,000 - 35,000.

[0067] Specifically, the glass transition temperature of the polyvinyl alcohol is 75 - 85 °C and it starts to embrittle at 100 °C. Therefore, the heat distortion temperature of the organic polymer film is 75 - 100 °C. Considering that the electrode paste will not crack under high-temperature baking, the carbonization temperature of the organic polymer film is 200 - 250 °C. Preferably, the heat distortion temperature of the organic polymer film is 87 - 92 °C, and the carbonization temperature is 200 - 220 °C.

[0068] Specifically, the preparation method of the polyvinyl alcohol includes free radical polymerization, catalytic polymerization, and anionic polymerization. In addition, the polyvinyl alcohol film finished product can be obtained through solution casting, drying, peeling, and winding.

[0069] In some embodiments of the present invention, the temperature for heat-treating the embryo is 200 - 220 °C. The heat-treatment time is any time that enables the electrode paste to cure and the organic polymer film to carbonize without causing the cured electrode paste layer to crack. For example, in some embodiments, the heat-treatment time is 0.5 - 2 hours.

[0070] In some embodiments of the present invention, the thickness of the organic polymer film is 2 - 10 μm, so that the organic polymer film has a certain support strength while not hindering lithium-ion transmission.

[0071] In some embodiments of the present invention, the organic polymer film is formed on the current collector by hot pressing. The hot pressing temperature is the heat distortion temperature of the organic polymer film. For example, the heat distortion temperature of polyvinyl alcohol is 75 - 100 °C. Considering the comprehensive temperature effect and reducing the influence of the hot pressing contact surface on the amount of the coated electrode paste, the contact surface width between the organic polymer film and the current collector ≤ 1 mm.

[0072] Among them, the thickness of the current collector is 6 - 17 μm. Preferably, the current collector is selected from at least one of copper foil and aluminum foil.

[0073] Among them, the thickness of the cured electrode paste layer is 100 - 200 μm, and the areal density of one side of the electrode is 200 - 260 g / m 2 Preferably, to ensure the energy density of the electrode, the thickness of the cured electrode paste layer is 110 - 160 μm; the areal density of the electrode is 220 - 240 g / m 2

[0074] In some embodiments of the present invention, the organic polymer film has a certain hardness, so that after injecting the electrode paste into the cavity, the groove can still maintain the designed shape. Or, the organic polymer film has a certain elasticity. For example, after injecting the electrode paste into the cavity, the shape of the organic polymer film may change. For example, the organic polymer film forms an arc-shaped film due to elastic deformation, and a convex arc surface is formed between adjacent grooves of the electrode, further increasing the contact area between the electrode sheet and the electrolyte and being beneficial to ion transmission.

[0075] Among them, the electrode paste includes a positive electrode paste or a negative electrode paste; by injecting the positive electrode paste or the negative electrode paste into the cavity respectively to form an electrode with a groove structure and designing it into a staggered stack, the transmission distance of lithium ions between the electrodes can be further shortened, thereby improving the electrochemical performance of the battery.

[0076] In some embodiments of the present invention, the active substance in the positive electrode paste is a lithium iron manganese phosphate positive electrode material; among them, the chemical formula of the lithium iron manganese phosphate positive electrode material is LiMn x ​Fe 1-x PO4, where 0.5 ≤ x ≤ 0.9. Specifically, the positive electrode material may also be a material obtained by doping different elements into lithium iron manganese phosphate.

[0077] In some embodiments of the present invention, an electrode paste mixed in a certain proportion is used, which includes a positive electrode active material, a binder, a conductive agent, and a solvent, and a dispersant is used to make the paste disperse evenly and maintain a stable viscosity. The electrode paste further includes a conductive agent, a binder, a dispersant, and a solvent; the conductive agent is selected from at least one of conductive carbon black, carbon nanotubes, graphene, and acetylene black; the binder is selected from at least one of polyvinylidene fluoride, polyvinyl alcohol, hydroxypropyl methylcellulose, ethyl cellulose, polyvinyl butyral, and acrylic resin; the dispersant is selected from at least one of sodium dodecyl sulfate and fatty alcohol polyoxyethylene ether; the solvent is selected from at least one of N-methylpyrrolidone, acetone, ethanol, and water.

[0078] The present invention also provides a lithium-ion battery, which includes the electrode as described above.

[0079] The present invention also provides an electrical device, which includes the aforementioned lithium-ion battery. The positive electrode material provided by the present invention can be used in terminal consumer products, such as mobile phones, tablet computers, laptop computers, electronic watches, or other wearable and movable electronic devices, and can also be used in electrical devices such as electric vehicles and energy storage cabinets.

[0080] The present invention will be further described in detail below through examples, but the present invention is not limited to the following examples.

[0081] Example 1

[0082] In this example, the current collector used for preparing the electrode is aluminum foil, and the preparation method includes the following steps:

[0083] (1) An organic polymer film with a right-angled groove is prepared by an extrusion molding method, and the organic polymer film and the aluminum foil are hot-pressed at 90 °C to form a cavity closed on all sides. The width of the contact surface between the organic polymer film and the aluminum foil is 0.8 mm; among them, the organic polymer film is a polyvinyl alcohol film with a molecular weight of 25,000 - 35,000, the thickness of the organic polymer film is 8 μm, the width of the groove on the organic polymer film is 200 μm, the groove spacing is 200 μm, and the depth of the groove is 50% of the electrode thickness; and the single-sided surface density of the electrode is designed to be 220 g / m 2 , and the thickness is 110 μm;

[0084] (2) Lithium iron manganese phosphate positive electrode material, conductive agent carbon nanotubes, binder polyvinylidene fluoride, dispersant polyvinylpyrrolidone, and solvent NMP are added to a mixing tank and stirred evenly to obtain a positive electrode paste; among them, the lithium iron manganese phosphate positive electrode material LiMnx Fe 1-x In FePO4, x = 0.6; the weight ratio of lithium iron phosphate manganese phosphate cathode material, carbon nanotubes, polyvinylidene fluoride, polyvinylpyrrolidone and NMP is 100:3:5:0.5:80;

[0085] (3) Coat the above positive electrode paste into the cavity of step (1) by extrusion coating to obtain a green body;

[0086] (4) Bake the above green body at 200 °C for 2 hours, take out the product after cooling, and obtain the dried electrode sheet;

[0087] (5) Roll the above dried electrode sheet to obtain an electrode product, denoted as E1.

[0088] Example 2

[0089] The method for preparing the electrode in this example is carried out with reference to Example 1. The difference from Example 1 is that the width of the groove is 150 μm; the obtained electrode product is denoted as E2.

[0090] Example 3

[0091] The method for preparing the electrode in this example is carried out with reference to Example 1. The difference from Example 1 is that the width of the groove is 50 μm; the obtained electrode product is denoted as E3.

[0092] Example 4

[0093] The method for preparing the electrode in this example is carried out with reference to Example 1. The difference from Example 1 is that the depth of the groove is 30% of the electrode thickness; the obtained electrode product is denoted as E4.

[0094] Example 5

[0095] The method for preparing the electrode in this example is carried out with reference to Example 1. The difference from Example 1 is that the depth of the groove is 80% of the electrode thickness; the obtained electrode product is denoted as E5.

[0096] Example 6

[0097] The method for preparing the electrode in this example is carried out with reference to Example 1. The difference from Example 1 is that the depth of the groove is 90% of the electrode thickness; the obtained electrode product is denoted as E6.

[0098] Example 7

[0099] The method for preparing the electrode in this example is carried out with reference to Example 1. The difference from Example 1 is that the groove pitch is 400 μm; the obtained electrode product is denoted as E7.

[0100] Example 8

[0101] The method for preparing the electrode in this example is carried out with reference to Example 1. The difference from Example 1 is that the groove spacing is 100 μm; the obtained electrode product is denoted as E8.

[0102] Example 9

[0103] The method for preparing the electrode in this example is carried out with reference to Example 1. The difference from Example 1 is that the groove spacing is 50 μm; the obtained electrode product is denoted as E9.

[0104] Example 10

[0105] The method for preparing the electrode in this example is carried out with reference to Example 1. The difference from Example 1 is that the grooves only exist on the carbonized film and the groove depth is 5 μm; the obtained electrode product is denoted as E10.

[0106] Comparative Example 1

[0107] The current collector used in this comparative example for preparing the electrode is aluminum foil, and the preparation method includes the following steps:

[0108] (1) Add lithium iron manganese phosphate cathode material, conductive agent, binder, dispersant and solvent NMP to the mixing tank, and stir evenly to obtain the cathode slurry;

[0109] (2) Coat the above-mentioned cathode slurry on the surface of the current collector, and design the single-sided surface density of this electrode to be 220 g / m 2 , with a thickness of 110 μm, to obtain a green body;

[0110] (3) Bake the above-mentioned green body at 150 °C for 5 hours, and take out the product after cooling to obtain the dried electrode sheet;

[0111] (4) Roll press the dried electrode sheet to obtain the electrode product, denoted as D1.

[0112] Comparative Example 2

[0113] The current collector used in this comparative example for preparing the electrode is aluminum foil, and the preparation method includes the following steps:

[0114] (1) Add lithium iron manganese phosphate cathode material, conductive agent, binder, dispersant and solvent NMP to the mixing tank, and stir evenly to obtain the cathode slurry;

[0115] (2) Coat the above-mentioned cathode slurry on the surface of the current collector, and design the single-sided surface density of this electrode to be 220 g / m 2 , with a thickness of 110 μm, to obtain a green body;

[0116] (3) Send the above-mentioned green body into the oven for baking, control the baking temperature and time to obtain a semi-solid coating, and the solid content of the semi-solid coating is 55%;

[0117] (4) An array of groove structures is formed on the semi-solid coating by using array suction treatment, and then it is sent to an oven for secondary baking to obtain a dried electrode sheet; wherein, the width of the groove is 200 μm, the groove spacing is 200 μm, and the depth of the groove is 50% of the electrode thickness;

[0118] (5) The dried electrode sheet is roll-pressed to obtain an electrode product, denoted as D2.

[0119] Performance test

[0120] The electrodes provided in Examples 1-10 and Comparative Examples 1-2 are used as the positive electrode, and are assembled with a separator, a graphite negative electrode, etc. into a full cell for electrochemical performance testing. Charge and discharge tests at different rates are carried out at 0 °C and 25 °C respectively, and the test results are shown in Table 1.

[0121] Table 1

[0122]

[0123]

[0124] From the data results of Comparative Example 1 and Comparative Example 2, it can be seen that the grooves opened on the electrode optimize the ion transport of the electrode; from the data results of Examples 1-10, it can be seen that the electrodes obtained by using the organic polymer film with groove structure in the present invention for pore formation form a uniform and efficient mass transfer channel. From the data results of Example 1 and Comparative Example 2, it can be seen that the carbon-coated structure formed by carbonization of the organic polymer film significantly improves the rate performance compared with the positive electrode without a special carbonized layer, and further improves the conductivity of the positive electrode.

[0125] From the data results of Example 1 and Example 2, it can be seen that reducing the width of the groove increases the effective area for lithium ion diffusion, which is beneficial to mass transfer in the electrode thickness direction. Therefore, the rate performance at different temperatures is slightly better. However, when the groove width is continuously reduced while keeping the spacing the same (i.e., Example 3), although the proportion of active material is increased, the transport channel becomes narrower, but like the unimproved electrode, the electrolyte infiltration is poor, the ion transport is blocked, and at high rates, the ion transport is not ideal, which in turn affects the discharge capacity.

[0126] By comparing the data in Example 1 and Example 4, it can be found that although reducing the groove depth increases the proportion of the positive electrode material, it will reduce the contact area of the electrolyte. In the case of high current, the capacity decay is more serious. As the depth increases (i.e., Example 5), the increased transport channel area makes the capacity at high rates slightly higher than that in Example 4, but the loss of the positive electrode material aggravates the capacity decay at smaller currents.

[0127] The rate capacity of Example 7 is lower than that of Example 1. This is because the groove width remains unchanged, and the groove spacing is too large, which reduces the number of channels and the longitudinal transmission area, affecting the high-rate ion transmission. The reduction of the groove spacing (i.e., Example 8) will also lead to a reduction in the mass of active materials, so the low-rate performance is significantly reduced.

[0128] From the data results of Examples 1 and 6, it can be seen that the excessive groove depth in Example 6 will lead to a significant reduction in the proportion of active material mass, so its discharge capacity at different rates is lower than that of Example 1. Similar to Example 6, the small groove spacing in Example 9 makes it difficult for the electrolyte to infiltrate, affecting the discharge capacity.

[0129] According to Example 8, due to the increased loss of positive electrode material, the rate performance at both temperatures is affected.

[0130] To sum up, compared with Example 1, a groove that is too deep or a groove that is too small will make it difficult for the electrolyte to fully infiltrate, resulting in serious capacity attenuation; a groove that is too large in width (the groove spacing remains unchanged) or a groove that is too small in width (the groove width remains unchanged) will lead to loss of active substances and a decrease in low-rate performance; a groove spacing that is too large (the groove width remains unchanged) will reduce the effective contact area between the electrode material and the electrolyte, affecting high-rate ion transmission.

[0131] The preferred embodiments of the present invention are described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the technical concept of the present invention, a variety of simple modifications can be made to the technical solution of the present invention, and these simple modifications all belong to the protection scope of the present invention.

[0132] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not further describe various possible combinations.

[0133] In addition, various embodiments of the present invention may be arbitrarily combined, and as long as they do not violate the concept of the present invention, they should also be regarded as the contents disclosed by the present invention.

Claims

1. An electrode, characterized in that, The electrode includes a current collector and a carbonized film. The carbonized film has a plurality of grooves arranged at intervals on the surface parallel to the current collector. The electrode further includes a cured electrode paste layer disposed between the carbonized film and the current collector.

2. The electrode according to claim 1, wherein, The edge of the carbonized film is bonded to the current collector.

3. The electrode according to claim 1, wherein, A recess is provided on the cured electrode paste layer, and the recess of the cured electrode paste layer matches the groove of the carbonized film; alternatively, no recess is provided on the cured electrode paste layer.

4. The electrode according to claim 1, wherein, The grooves are arranged in an array; and / or The shape of the groove is a sawtooth wave shape, a square wave shape, a trapezoidal wave shape or an arc wave shape; and / or The width of the groove is 50-200 μm, and the spacing between two adjacent grooves is 100-500 μm; and / or The depth of the groove is 20-80% of the thickness of the cured electrode paste layer.

5. The electrode according to any one of claims 1-4, wherein, The thickness of the carbonized film is 2-10 μm; the width of the contact surface between the carbonized film and the current collector ≤ 1 mm.

6. The electrode according to claim 1, wherein, The thickness of the current collector is 6-17 μm; the current collector is selected from at least one of copper foil and aluminum foil.

7. The electrode according to claim 1 or 6, wherein, The thickness of the solidified electrode material layer is 100 - 200 μm, preferably 110 - 160 μm; the single-sided areal density of the electrode is 200 - 260 g / m 2 , preferably 220 - 240 g / m 2 .

8. The electrode according to claim 1 or 6, wherein, An outwardly convex arc surface is formed between adjacent grooves of the electrode.

9. The electrode according to claim 1 or 6, wherein, The active material in the solidified electrode material layer is a lithium iron manganese phosphate cathode material; the chemical formula of the lithium iron manganese phosphate cathode material is LiMn x Fe 1-x PO4, where 0.5 ≤ x ≤ 0.

9.

10. A method for preparing an electrode, characterized in that, The method includes the following steps: Bond an organic polymer film on the surface of the current collector to form a cavity between the surface of the current collector and the organic polymer film; wherein, the organic polymer film has a plurality of grooves arranged at intervals on the surface parallel to the current collector; Inject electrode paste into the cavity to obtain a green body; Perform heat treatment on the green body so that the electrode paste cures to obtain a cured electrode paste layer, and the organic polymer film carbonizes to form a carbonized film.

11. The preparation method according to claim 10, wherein, The grooves are arranged in an array; and / or The shape of the groove is a sawtooth wave shape, a square wave shape, a trapezoidal wave shape or an arc wave shape; and / or The width of the groove is 50-200 μm, and the spacing between two adjacent grooves is 100-500 μm; and / or The depth of the groove is 20-80% of the thickness of the cured electrode paste layer.

12. The preparation method according to claim 10 or 11, wherein The organic polymer film is polyvinyl alcohol with a molecular weight of 25,000-35,000; wherein, the heat distortion temperature of the polyvinyl alcohol is 75-100 °C, preferably 87-92 °C; the carbonization temperature is 200-250 °C, preferably 200-220 °C; The thickness of the organic polymer film is 2-10 μm; the width of the contact surface between the organic polymer film and the current collector ≤ 1 mm.

13. The preparation method according to claim 10, wherein, The thickness of the current collector is 6-17 μm; the current collector is selected from at least one of copper foil and aluminum foil.

14. The preparation method according to claim 10 or 13, wherein, The thickness of the solidified electrode material layer is 100 - 200 μm, preferably 110 - 160 μm; the single-sided surface density of the electrode is 200 - 260 g / m 2 , preferably 220 - 240 g / m 2 .

15. The preparation method according to claim 10, wherein, An outwardly convex arc surface is formed between adjacent grooves of the electrode.

16. The preparation method according to claim 10 or 15, wherein The electrode paste includes a positive electrode paste or a negative electrode paste; the active material in the positive electrode paste is a lithium manganese iron phosphate positive electrode material; wherein, the chemical formula of the lithium manganese iron phosphate positive electrode material is LiMn x Fe 1-x PO4, where 0.5 ≤ x ≤ 0.

9.

17. A lithium-ion battery, characterized in that, The lithium-ion battery includes the electrode according to any one of claims 1-9 or the electrode prepared by the method according to any one of claims 10-16.

18. An electrical device, characterized in that, The electrical device includes the lithium-ion battery according to claim 17.

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