Positive electrode sheet, and preparation method therefor and use thereof

Abstract

The present invention belongs to the technical field of lithium battery energy storage. Provided are a positive electrode sheet, and a preparation method therefor and the use thereof. In the positive electrode sheet, besides a conventional current collector and a conventional active material layer, a lithium-supplementing layer and an isolating layer are further introduced among the structures thereof according to a specific sequence; therefore, lithium can be effectively supplemented and a stable SEI layer can be formed after a product, an electrolyte and a negative electrode sheet are assembled into a lithium battery energy storage device, active materials can be prevented from reacting with a lithium-supplementing agent or a lithium-supplementing product thereof in the lithium-supplementing layer, and the electrochemical performance of the product is good. A construction method for the positive electrode sheet is simple, and industrial large-scale production can be achieved.

Description

A positive electrode sheet and its preparation method and application Technical Field

[0001] The present invention relates to the field of lithium battery energy storage technology, and in particular to a positive electrode plate and a preparation method and application thereof. Background Art

[0002] Lithium-ion battery energy storage devices typically require lithium replenishment because a solid electrolyte interface (SEI) film forms at the negative electrode interface during the initial charge-discharge cycle, deactivating some of the active lithium and causing irreversible capacity loss. The most common lithium replenishment process involves adding a lithium-containing compound to the active material layer during the fabrication of the device's positive electrode. This compound replenishes a certain amount of lithium ions during the device's charge-discharge process.

[0003] However, lithium-containing compounds have poor air stability and are easily deteriorated by reaction when exposed to air and contact with moisture and carbon dioxide in the air. They may even directly affect the active substances in the positive electrode. Ultimately, not only will the expected lithium replenishment effect fail to be achieved, but the electrochemical performance of lithium-ion energy storage devices may even be significantly reduced.

[0004] Summary of the Invention

[0005] Based on the defects of the existing technology, the purpose of the present invention is to provide a positive electrode plate. In addition to the conventional current collector and active material layer, this product also introduces a lithium replenishment layer and an isolation layer between the structures in a specific order. This not only enables the product to effectively replenish lithium and form a stable SEI layer after being assembled into a lithium battery energy storage device with an electrolyte and a negative electrode plate, but also prevents the active material from reacting with the lithium replenishment agent or its lithium replenishment product in the lithium replenishment layer, resulting in excellent electrochemical performance of the product.

[0006] In order to achieve the above object, the technical solution adopted by the present invention is:

[0007] A positive electrode sheet, comprising a current collector, an active material layer, a separator and a positive electrode lithium replenishing layer which are sequentially arranged and stacked;

[0008] The isolation layer includes at least one of a conductive agent, a solid electrolyte, and a polyanion phosphate;

[0009] The positive electrode lithium replenishing layer contains a lithium-containing compound and a reducing agent.

[0010] In existing processes, in order to replenish lithium in the positive electrode, a lithium replenisher is often added to the active material layer. However, this method has been verified to be unsatisfactory. This is because although the lithium replenisher can effectively provide additional lithium ions to the active material layer, the active material will still come into direct contact with the electrolyte and quickly produce a SEI film. Therefore, the lithium ion conduction efficiency of the final lithium battery energy storage device is still constrained by the formation of the SEI film. At the same time, the lithium replenisher itself will also react with the electrolyte and even the active material. In particular, some products such as oxygen produced may cause oxidation of the active material. Ultimately, not only will it fail to achieve effective lithium replenishment, but it may even cause the capacity and cycle performance of the lithium battery energy storage device to rapidly decay. Therefore, in the technical solution of the present invention, the positive electrode sheet adopts a structural distribution of current collector-active material layer-isolation layer-positive electrode lithium replenishment layer. When applied to lithium battery energy storage devices, the active material layer and the positive electrode lithium replenishment layer realize electronic conduction under the action of the current collector. During the charging process, the active material in the active material layer and the lithium-containing compound in the positive electrode lithium replenishment layer are both delithiated, thereby realizing lithium replenishment. At this time, the positive electrode lithium replenishment layer will produce a certain amount of residual substances, which cooperate with the isolation layer to prevent the active material layer from direct contact with the electrolyte. Therefore, the SEI film on the positive electrode surface is more stable. The lithium battery energy storage device has better cycle stability; on the other hand, the isolation layer located between the active material layer and the positive electrode lithium replenishment layer contains at least one of a conductive agent, a solid electrolyte, and a polyanionic phosphate, which significantly improves the ion / electron conduction efficiency of the positive electrode sheet. Most importantly, the isolation layer can effectively prevent direct contact between the active material layer and the positive electrode lithium replenishment layer. The lithium-containing compound and the reducing agent in the positive electrode lithium replenishment layer will not react with the active material. At the same time, it can also prevent the reaction products generated by the positive electrode lithium replenishment layer during lithium replenishment from reacting with the active material. On this basis, the reducing agent in the positive electrode lithium replenishment layer can fully reduce the potential of the lithium-containing compound during the lithium replenishment process, thereby further improving its lithium replenishment performance, without having to worry about excessive reaction affecting the original lithium insertion and extraction efficiency of the active material layer.

[0011] Preferably, the active material layer includes a positive electrode active material, and the positive electrode active material is a doped or undoped material, including at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, a ternary positive electrode material, lithium nickel manganese oxide, and a lithium-rich material.

[0012] The positive electrode sheet described in the present invention is applicable to all types of existing common active material positive electrode systems. The main reason is that the technical solution of the present invention not only separates the lithium replenishing component and the active material in the form of different layers, but also provides an isolation layer between the two layers. Regardless of the lithium deintercalation rate of the active material, it will not affect the lithium replenishment efficiency of the positive electrode lithium replenishment layer.

[0013] More preferably, the active material layer further contains a conductive agent and a binder.

[0014] Preferably, the conductive agent is at least one of conductive carbon black, carbon nanotubes, graphene, and carbon nanofibers; the solid electrolyte is at least one of an oxide solid electrolyte, a chloride solid electrolyte, and a polymer solid electrolyte; the polyanion phosphate is lithium iron phosphate (LiFePO4), lithium manganese phosphate (LiMnPO4), lithium manganese iron phosphate (LiMn x Fe 1-x PO4, wherein 0<x<1), at least one of lithium vanadium phosphate (Li3V2(PO4)3), lithium cobalt phosphate (LiCoPO4), and lithium nickel phosphate (LiNiPO4).

[0015] More preferably, the isolation layer comprises a conductive agent and a solid electrolyte;

[0016] More preferably, the conductive agent is carbon nanotubes, and the solid electrolyte is LATP (lithium aluminum titanium phosphate with sodium ion conductor (NaSICON) structure) solid electrolyte;

[0017] More preferably, the isolation layer comprises carbon nanotubes and LATP solid electrolyte, and the mass ratio of the carbon nanotubes and LATP solid electrolyte is (1:9) to (4:6).

[0018] The inventors discovered that during the lithium replenishment and circulation process of the positive electrode sheet, the conductive agent, solid electrolyte and polyanion phosphate in the isolation layer can effectively improve the lithium ion / electron conduction rate of the positive electrode sheet when used alone. When the types of conductive agent and solid electrolyte are different, the charge and discharge capacity and cycle stability of the product when used in lithium battery energy storage devices are also different. When carbon nanotubes are selected as the conductive agent and LATP solid electrolyte is selected as the solid electrolyte, the electrochemical performance of the positive electrode sheet is better, especially when the two are combined and compounded in the above-mentioned preferred ratio, the product can exhibit optimal electrochemical activity.

[0019] Preferably, the solid electrolyte comprises a coated solid electrolyte.

[0020] It should be noted that when the conductive agent and the solid electrolyte in the isolation layer of the present invention are mixed and used, the two can be a powder mixed structure or exist in the form of a combined layer, that is, the conductive agent in the isolation layer can exist in a layered form or a powdered form, and the solid electrolyte can be combined with the surface of the conductive agent in a layered form or in a powdered form. The same applies to the case where the positions of the two are interchanged. Those skilled in the art should be aware that this combination form is actually related to the conventional original form of the two, and the difference in the above combination form does not affect the final performance of the product.

[0021] Preferably, the isolation layer further comprises an adhesive.

[0022] Preferably, the lithium-containing compound is Li aM b O c , wherein a=1-12, M is at least one of Ni, Cu, Mo, V, Ru, Mn, Si, Nb, Ti, Fe, Ta, Re, Co, W, Zr, Bi, Sn, and Ce, b=0-2, and c=0-11;

[0023] More preferably, the lithium-containing compound is LiO2, Li2O, Li2O2, Li2NiO2, Li2CuO2, Li2MoO3, Li2VO3, Li2RuO3, Li2MnO3, Li2SiO3, Li2Si2O5, Li3VO4, Li3NbO4, Li3RuO4, Li3PO4, Li4SiO4, Li4TiO4, Li5FeO4, Li5NbO5, Li5TaO5, Li5ReO6, Li6CoO4, Li6MnO4, Li6NiO4, Li6WO6, Li6Zr2O7, Li7NbO6, Li7VO6, Li7BiO6, Li7TaO6, Li8ZrO6, Li8SnO6, Li8SiO6, Li8CeO6, Li8MoO6, Li8MnO6, Li8Nb2O9, Li 12 Nb2O 11 At least one of .

[0024] Preferably, the reducing agent is at least one of a boride, a sulfide, a phosphide, and a reducing element;

[0025] More preferably, the boride is at least one of cobalt boride, molybdenum boride, calcium boride, aluminum boride, magnesium boride, titanium boride, zirconium boride, silicon boride, and lanthanum boride; the sulfide is at least one of sodium sulfide, iron sulfide, cobalt sulfide, molybdenum sulfide, tungsten sulfide, titanium sulfide, magnesium sulfide, calcium sulfide, copper sulfide, lanthanum sulfide, zinc sulfide, tin sulfide, nickel sulfide, and silicon sulfide; the phosphide is at least one of iron phosphide, boron phosphide, nickel phosphide, sodium phosphide, and zinc phosphide; and the reducing element is at least one of elemental sulfur, elemental phosphorus, elemental boron, elemental silicon, elemental aluminum, elemental germanium, elemental arsenic, elemental iodine, elemental vanadium, elemental manganese, elemental iron, elemental cobalt, elemental nickel, and elemental tin.

[0026] Preferably, the positive electrode lithium replenishing layer further contains a conductive agent and a binder.

[0027] Preferably, the positive electrode active material is a ternary positive electrode material and / or a lithium nickel manganese oxide positive electrode material; and the positive electrode lithium replenishing layer contains Li4SiO4 and elemental sulfur.

[0028] Preferably, the positive electrode lithium replenishing layer may further include a phosphate positive electrode material or an electrolyte.

[0029] More preferably, the positive electrode lithium replenishing layer includes the following components in parts by weight: 80 to 96 parts of a lithium-containing compound and a conductive agent, 2 to 10 parts of a conductive agent, and 2 to 10 parts of a binder.

[0030] It should be noted that, except for the isolation layer defined in the present invention, the conductive agents involved in the remaining layers are not particularly limited. Those skilled in the art can choose the type of self-made or commercially available conductive agent according to actual conditions, including but not limited to acetylene black, carbon black, carbon fiber, carbon nanotubes, Ketjen black, etc.; the binders used in the layers can also be selected according to actual conditions. Self-made or commercially available types include but are not limited to polyvinyl pyrrolidone, polyvinylidene fluoride, polyethylene oxide, polytetrafluoroethylene, carboxymethyl cellulose, copolymers of styrene and butadiene, etc.

[0031] Preferably, in the positive electrode sheet, the thickness of the active material layer is 20 to 300 μm, the thickness of the isolation layer is 0.5 to 20 μm, and the thickness of the positive electrode lithium replenishing layer is 1 to 50 μm.

[0032] According to actual needs, those skilled in the art can set structural layers of different thicknesses in the positive electrode sheet for lithium battery energy storage devices with different positive electrode active materials and electrolyte systems.

[0033] Preferably, the current collector is aluminum foil.

[0034] Another object of the present invention is to provide a method for preparing the positive electrode sheet, comprising the following steps:

[0035] constructing an active material layer on the current collector;

[0036] constructing an isolation layer on the active material layer;

[0037] A positive electrode lithium replenishing layer is constructed on the isolation layer.

[0038] Preferably, the active material layer is constructed on the current collector by coating, dipping, spraying, composite film and / or dry electrode rolling, pressing and / or bonding.

[0039] Preferably, the isolation layer is constructed on the active material layer by coating, dipping, spraying, composite film and / or dry electrode rolling, pressing and / or bonding.

[0040] Preferably, the positive electrode lithium replenishing layer is constructed on the isolation layer by coating, dipping, spraying, composite film and / or dry electrode rolling, pressing and / or bonding.

[0041] Another object of the present invention is to provide a secondary battery comprising the positive electrode sheet, a separator and a negative electrode sheet according to the present invention.

[0042] When the positive electrode plate of the present invention is used in a secondary battery, the active lithium content in the product is effectively replenished. At the same time, the active material in the positive electrode plate will not be affected by the lithium replenishing material. After the first charge and discharge, not only can a stable SEI film be formed, but the energy density of the secondary battery is also effectively improved due to the lithium replenishing effect. The secondary battery has the characteristics of high specific capacity, high rate performance and high cycle stability.

[0043] It should be noted that the negative electrode sheet and the separator in the secondary battery can be made of conventional materials in the art; the secondary battery can be prepared by conventional methods in the art.

[0044] Another object of the present invention is to provide an electrical device comprising the secondary battery of the present invention, wherein the secondary battery serves as a power supply for the electrical device.

[0045] The present invention provides a positive electrode sheet that, in addition to the conventional current collector and active material layer, incorporates a lithium replenishment layer and a separator layer in a specific order between the structures. This not only enables the product to effectively replenish lithium and form a stable SEI layer after being assembled with an electrolyte and a negative electrode sheet into a lithium-ion energy storage device, but also prevents the active material from reacting with the lithium replenishment agent or its lithium replenishment product in the lithium replenishment layer, resulting in excellent electrochemical performance. The positive electrode sheet construction method is simple and can be produced on an industrial scale. DETAILED DESCRIPTION

[0046] In order to better illustrate the purpose, technical solutions and advantages of the present invention, the present invention will be further described below in conjunction with specific embodiments and comparative examples. Its purpose is to understand the content of the present invention in detail, rather than to limit the present invention. All other embodiments obtained by those of ordinary skill in the art without making creative work premise all fall within the protection scope of the present invention. The experimental reagents and instruments involved in the implementation of the present invention are all conventional common reagents and instruments unless otherwise specified.

[0047] The carbon nanotubes described in each embodiment and comparative example are LB120-50 produced by Tiannai Technology;

[0048] The graphene is a product produced by Xianfeng Nano;

[0049] The carbon fiber is a product produced by Kulude Company;

[0050] The solid electrolyte LLZO is produced by Ganfeng Lithium;

[0051] The solid electrolyte LATP is a product produced by Ganfeng Lithium;

[0052] The solid electrolyte PEO is a product produced by Inokite;

[0053] The remaining raw materials and auxiliary agents not mentioned are all commercially available products, and the raw materials and auxiliary agents used in the parallel experiments of the embodiments and comparative examples are all of the same kind.

[0054] Examples 1 to 24

[0055] An embodiment of the positive electrode sheet and the preparation method thereof according to the present invention comprises the following steps:

[0056] (1) An active material layer constructed on a 12 μm aluminum foil, wherein the active material layer is prepared by weighing a commercially available positive electrode active material, a conductive agent, conductive carbon black SuperP, and a binder, PVDF, in a mass ratio of 95:2:3, then adding NMP to prepare a slurry, coating the slurry on the aluminum foil, and then drying the slurry to obtain the active material layer;

[0057] (2) An isolation layer constructed on the surface of the active material layer, wherein the isolation layer is prepared by weighing a conductive agent or a solid electrolyte and a binder PVDF in a mass ratio of 85:15, then adding a solvent NMP to prepare a slurry, coating the slurry on the active material layer, and then drying to obtain an isolation layer; or weighing a conductive agent, a solid electrolyte, and a binder PVDF in a mass ratio of 90:10, then adding a solvent NMP to prepare a slurry, coating the slurry on the active material layer, and then drying to obtain an isolation layer;

[0058] (3) A positive electrode lithium replenishing layer is constructed on the surface of the isolation layer. The preparation method of the positive electrode lithium replenishing layer is as follows: a reducing agent and a lithium-containing compound, a conductive agent SP, and a binder PVDF are weighed in a mass ratio of 80:15:15, and then added to NMP to prepare a slurry, which is coated on the isolation layer and then dried to obtain the positive electrode lithium replenishing layer.

[0059] The ratio and composition of each raw material are shown in Table 1.

[0060] Table 1

[0061] Comparative Example 1

[0062] A positive electrode sheet and a method for preparing the same. The method for preparing the positive electrode sheet described in this embodiment comprises the following steps:

[0063] (1) A positive electrode lithium replenishing layer constructed on a 12 μm aluminum foil, wherein the positive electrode lithium replenishing layer is prepared by weighing a reducing agent and a lithium-containing compound, a conductive agent SP, and a binder PVDF in a mass ratio of 80:15:15, then adding the mixture to a solvent NMP to prepare a slurry, coating the mixture on the aluminum foil, and then drying the mixture to obtain the positive electrode lithium replenishing layer;

[0064] (2) an isolation layer constructed on the surface of the positive electrode lithium replenishing layer, wherein the isolation layer is prepared by weighing a conductive agent and a binder PVDF in a mass ratio of 85:15, then adding a solvent NMP to prepare a slurry, coating the slurry on the positive electrode lithium replenishing layer, and then drying to obtain the isolation layer;

[0065] (3) An active material layer is constructed on the surface of the isolation layer. The preparation method of the active material layer is as follows: a commercially available positive electrode active material, a conductive agent conductive carbon black superP, and a binder PVDF are weighed in a mass ratio of 95:2:3, and then a solvent NMP is added to prepare a slurry, which is coated on the isolation layer and then dried to obtain the active material layer.

[0066] The thickness of each layer is the same as that of the corresponding layer in Example 1. The difference from Example 1 is basically only that the order of constructing the structural layers of the positive electrode sheet is different.

[0067] Comparative Example 2

[0068] A positive electrode sheet and a method for preparing the same. The method for preparing the positive electrode sheet described in this embodiment comprises the following steps:

[0069] (1) An active material layer was constructed on a 12 μm aluminum foil. The preparation method of the active material layer was as follows: a commercially available positive electrode active material, a conductive agent, conductive carbon black superP, and a binder PVDF were weighed in a mass ratio of 95:2:3, and then a solvent NMP was added to prepare a slurry, which was coated on the aluminum foil and then dried to obtain an active material layer.

[0070] (2) A positive electrode lithium replenishing layer constructed on the surface of the active material layer, wherein the positive electrode lithium replenishing layer is prepared by weighing a reducing agent and a lithium-containing compound, a conductive agent SP, and a binder PVDF in a mass ratio of 80:15:15, then adding the mixture to a solvent NMP to prepare a slurry, coating the mixture on the active material layer, and then drying the mixture to obtain the positive electrode lithium replenishing layer;

[0071] (3) Constructing an isolation layer on the surface of the positive electrode lithium replenishing layer. The preparation method of the isolation layer is as follows: weighing the conductive agent and the binder PVDF according to a mass ratio of 85:15, then adding the solvent NMP to prepare a slurry, coating it on the positive electrode lithium replenishing layer, and then drying to obtain the isolation layer.

[0072] The thickness of each layer is the same as that of the corresponding layer in Example 1. The difference from Example 1 is basically only that the order of constructing the structural layers of the positive electrode sheet is different.

[0073] Effect Example 1

[0074] In order to verify the use effect of the positive electrode sheet of the present invention, the positive electrode sheets prepared in each embodiment and comparative example were used to prepare lithium-ion batteries. The specific method is as follows:

[0075] Commercial graphite, conductive carbon black, and PVDF binder were mixed in a 93:2:5 ratio to form a slurry, which was then coated to prepare a negative electrode sheet. Coin cells were assembled in a glove box using this negative electrode sheet, the positive electrode sheets from each example and comparative example, and a 1M LiPF6 electrolyte dissolved in EC / DMC (1:1, volume ratio) (purchased from BASF Electrolytes GmbH, Germany). After each coin cell was left to rest for 24 hours, the following test method was used to test the LNMO, ternary, lithium cobalt oxide, and lithium nickel oxide cathode materials, respectively, based on the type of cathode material used. The initial charge-discharge cycle was performed at a rate of 0.05C, with the theoretical specific capacity of LNMO calculated as 146.7 mAh / g, and an operating voltage of 3.0-4.85 V. The cycle was then increased to 0.2C for 100 cycles. The charge and discharge capacities of the initial charge-discharge cycle were calculated, as well as the discharge capacity after 100 cycles. The theoretical specific capacity of the ternary battery is calculated to be 210 mAh / g. The operating voltage is 2.75-4.3 V. The first charge and discharge cycle is carried out at a rate of 0.05C. The rate is then increased to 0.2C and the cycle is repeated 100 times. The charge and discharge capacity of the first charge and discharge cycle is calculated, and the discharge capacity after 100 cycles is calculated. The theoretical specific capacity of lithium cobalt oxide is calculated to be 200 mAh / g. The operating voltage is 3-4.45 V. The first charge and discharge cycle is carried out at a rate of 0.05C. The rate is then increased to 0.2C and the cycle is repeated 100 times. The charge and discharge capacity of the first charge and discharge cycle is calculated, and the discharge capacity after 100 cycles is calculated. The theoretical specific capacity of lithium nickel oxide is calculated to be 220 mAh / g. The operating voltage is 2.75-4.3 V. The first charge and discharge cycle is carried out at a rate of 0.05C. The rate is then increased to 0.2C and the cycle is repeated 100 times. The charge and discharge capacity of the first charge and discharge cycle is calculated, and the discharge capacity after 100 cycles is calculated.

[0076] At the same time, in order to facilitate the comparison of the functionality of each structural layer in the product, the semi-finished products prepared in steps (1) and / or (2) of Examples 1 to 8 and Comparative Examples 1 and 2 were also tested as positive electrode sheets and named as Step (1) and Step (2), respectively (for example, Step (1) in Example 1 only obtained a positive electrode sheet containing a current collector and an active material layer, and the semi-finished product was applied to the same test and named Example 1-(1)).

[0077] The results are shown in Table 2.

[0078] Table 2

[0079] It can be seen from the performance of each positive electrode sheet in Table 2 that, under the conditions of different thicknesses, different active material layers, isolation layers and positive electrode lithium replenishing layer compositions, the positive electrode sheets of each embodiment of the present invention have significantly improved first efficiency and cycle stability compared with the single current collector-active material layer positive electrode sheet or the current collector-active material layer-isolation layer positive electrode sheet, indicating that in the positive electrode sheet, the positive electrode lithium replenishing layer can effectively replenish lithium, and under the joint action of the isolation layer and the positive electrode lithium replenishing layer, the product has a high content of reversible lithium ion insertion and deintercalation, which can achieve long-term positive and negative electrode conduction. Among them, when the isolation layer is composed of a composite of a conductive agent and a solid electrolyte, the performance improvement effect is higher than that of products with a single conductive agent or a solid electrolyte as a component. When the types of conductive agents and solid electrolytes are selected differently, the electrochemical properties of the positive electrode sheet are also different. According to the product performance of Examples 8 to 19, it can be seen that when the conductive agent is carbon nanotubes, the discharge capacity of the product can still reach 195.6 mAh / g after 100 cycles when used alone. When combined with a solid electrolyte, the electrochemical performance of the product is further improved, and when combined with LATP solid electrolytes, the discharge capacity can reach a higher 205.2 mAh / g after 100 cycles, which is much higher than the effect of carbon nanotubes and other solid electrolytes when combined as an isolation layer. However, if the mass ratio of the two is not in the range of (1:9) to (4:6), the optimal performance improvement may not be achieved. As shown in the products of Examples 23 and 24, their performance is not much different from that of Examples 9 and 15 in which the conductive agent or solid electrolyte is used alone. In addition, Examples 25 to 30 show that polyanion phosphates such as lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate can also achieve the same effect as an isolation layer.

[0080] In contrast, the product of Comparative Example 1, constructed with a structure of current collector-positive electrode lithium replenishment layer-barrier layer-active material layer, exhibited poor electrochemical performance despite also having a lithium replenishment layer and a barrier layer. Clearly, this two-layer structure did not effectively inhibit direct contact between the active material layer and the electrolyte. The product's performance was even comparable to that of the positive electrode sheet obtained in step (1) of Example 1, which consisted of only a current collector and an active material layer. Similarly, the positive electrode sheet obtained in Comparative Example 2, which employed an inappropriate configuration, also lacked ideal lithium replenishment performance.

[0081] Furthermore, in order to study the functionality of the isolation layer in the positive electrode sheet of the present invention separately, reference products 1 to 7 were prepared according to a similar method as described in Examples 1 to 7. The only difference between these reference products and the products of Examples 1 to 7 is that after constructing the active material layer to the current collector in the preparation method, the isolation layer is not further constructed on the active material layer, but the positive electrode lithium replenishing layer is directly constructed on the active material layer. The rest of the parameters and process methods are the same as those of the corresponding embodiments. Similarly, reference product 8 was prepared according to a similar method as described in Comparative Example 1. The only difference between this reference product and the product of Comparative Example 1 is that in the preparation method, after constructing the positive electrode lithium replenishing layer on the current collector, the active material layer is further constructed. The rest of the parameters and process methods are the same as those of Comparative Example 1. According to Example 26, the lithium iron phosphate in the isolation layer is directly added to the ternary active material, without setting an isolation layer, and then the positive electrode lithium replenishing layer is constructed on the surface of the active material to prepare reference product 26.

[0082] The same test was performed on reference samples 1 to 8, and the results are shown in Table 3.

[0083] Table 3

[0084] From the comparison of Table 3 and Table 2, it can be seen that the isolation layer of the present invention does not just function as a conventional conductive agent in the positive electrode sheet. Taking the test results of Example 1 and Reference Sample 1 as an example, it can be seen that in the absence of an isolation layer, the positive electrode lithium replenishing layer has a very limited effect on the lithium replenishment of the overall button battery. Both the initial capacity and the retained capacity after 100 cycles are close to those of the positive electrode sheet with only a current collector and an active material layer. After the isolation layer is included, the performance of the product is significantly improved, while Reference Sample 8 also shows performance degradation compared to the product of Comparative Example 1, indicating that the isolation layer of the present invention also effectively inhibits the contact between the positive electrode lithium replenishing layer and its reactants and the active material layer, avoiding mutual side reactions between the two structural layers. Compared with Example 26, Reference Sample 26 shows that the performance of the product is also significantly improved after the isolation layer containing lithium iron phosphate is included. Lithium iron phosphate is not used as an active material as an isolation layer.

[0085] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit the scope of protection of the present invention. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that the technical solutions of the present invention may be modified or replaced by equivalents without departing from the essence and scope of the technical solutions of the present invention.

Claims

1. A positive electrode sheet, characterized in that: It includes a current collector, an active material layer, a separation layer and a positive electrode lithium supplement layer which are sequentially arranged and stacked; The isolation layer includes at least one of a conductive agent, a solid electrolyte, and a polyanion phosphate; The positive electrode lithium replenishing layer contains a lithium-containing compound and a reducing agent.

2. The positive electrode sheet according to claim 1, characterized in that: The active material layer includes a positive electrode active material, which is a doped or undoped material, including at least one of lithium cobalt oxide, lithium nickel oxide, lithium manganese oxide, a ternary positive electrode material, lithium nickel manganese oxide, and a lithium-rich material.

3. The positive electrode sheet according to claim 2, characterized in that: The conductive agent is at least one of conductive carbon black, carbon nanotubes, graphene, and carbon nanofibers; the solid electrolyte is at least one of an oxide solid electrolyte, a chloride solid electrolyte, and a polymer solid electrolyte; and the polyanion phosphate is at least one of lithium iron phosphate, lithium manganese phosphate, lithium manganese iron phosphate, lithium vanadium phosphate, lithium cobalt phosphate, and lithium nickel phosphate.

4. The positive electrode sheet according to claim 3, characterized in that: The isolation layer includes a conductive agent and a solid electrolyte.

5. The positive electrode sheet according to claim 3, characterized in that: The solid electrolyte includes a coated solid electrolyte.

6. The positive electrode sheet according to claim 4, characterized in that: The isolation layer includes carbon nanotubes and LATP solid electrolyte, and the mass ratio of the carbon nanotubes and LATP solid electrolyte is (1:9) to (4:6).

7. The positive electrode sheet according to claim 6, characterized in that: The isolation layer includes carbon nanotubes and LATP solid electrolyte, and the mass ratio of the two is 2:8; the positive electrode active material is a ternary positive electrode material and / or a lithium nickel manganese oxide positive electrode material; the positive electrode lithium supplement layer contains Li4SiO4 and elemental sulfur.

8. The positive electrode sheet according to claim 1, characterized in that: The lithium-containing compound is Li a M b O c , wherein a=1-12, M is at least one of Ni, Cu, Mo, V, Ru, Mn, Si, Nb, Ti, Fe, Ta, Re, Co, W, Zr, Bi, Sn, and Ce, b=0-2, and c=0-11; and the reducing agent is at least one of a boride, a sulfide, a phosphide, and a reducing element.

9. The positive electrode sheet according to claim 1, characterized in that: In the positive electrode sheet, the thickness of the active material layer is 20 to 300 μm, the thickness of the isolation layer is 0.5 to 20 μm, and the thickness of the positive electrode lithium supplement layer is 1 to 50 μm.

10. The method for preparing a positive electrode sheet according to any one of claims 1 to 9, characterized in that: The following steps are involved: constructing an active material layer on the current collector; constructing an isolation layer on the active material layer; A positive electrode lithium replenishing layer is constructed on the isolation layer.

11. A secondary battery, characterized in that: It comprises the positive electrode sheet, separator and negative electrode sheet as described in any one of claims 1 to 9.

12. An electrical device, characterized in that: It comprises the secondary battery as claimed in claim 11, and the secondary battery is used as a power supply for the electrical device.

Images