A sodium ion battery positive electrode sheet, sodium ion battery and application

Abstract

The present application provides a sodium ion battery positive electrode sheet, a sodium ion battery and an application. The sodium ion battery positive electrode sheet includes an active material and an over-discharge protection agent, wherein the over-discharge protection agent includes a chemical formula of M a Ti b O c Compounds, wherein M includes one or more of Li, Na, and K, a+4b=2c, 0≤a, 0<b, 0<c. The sodium ion positive electrode sheet is suitable for a battery system that has been treated with sodium supplementation. When the battery is over-discharged, the over-discharge protection agent can effectively protect the positive electrode active material, thereby improving the stability of the positive electrode active material and ensuring that the battery has good cycle stability.

Description

Technical Field

[0001] The present application relates to the field of sodium ion batteries, and in particular to a sodium ion battery positive electrode sheet, a sodium ion battery and applications. Background Art

[0002] Lithium-ion batteries have a wide range of applications in the field of energy storage. However, lithium-ion batteries face the problem of uneven distribution and increasing shortage of lithium resources, which limits the application of lithium-ion batteries. Sodium has similar chemical properties to lithium, and its reserves are far more abundant than lithium, its distribution is more extensive, and its acquisition cost is low. It is expected to become a highly promising next-generation energy storage system.

[0003] Sodium-ion batteries have a certain amount of irreversible capacity loss during the first charging process, and generally sodium-ion batteries need to be supplemented with sodium to make up for the irreversible capacity loss in the first cycle. However, after the battery is supplemented with sodium, the sodium ions in the battery system are in a surplus state. Once the battery becomes abnormal and over-discharge occurs, the positive electrode active material will collapse due to excessive embedding of sodium ions, and the battery capacity will decrease. Therefore, it is necessary to provide a new sodium-ion battery positive electrode to reduce the harm of over-discharge of sodium-ion batteries after sodium supplementation and ensure that the battery has good cycle performance. Summary of the invention

[0004] In view of this, the present application provides a sodium ion battery positive electrode plate, which is suitable for a battery system that has been treated with sodium supplementation. When the battery is over-discharged, the over-discharge protection agent in the sodium ion battery positive electrode plate can effectively protect the positive electrode active material, thereby improving the stability of the positive electrode active material and ensuring that the battery has good cycle stability.

[0005] In a first aspect, the present application provides a positive electrode sheet for a sodium ion battery, comprising a current collector and a positive electrode material layer disposed on the surface of the current collector, wherein the positive electrode material layer comprises a blended active material and an over-discharge protective agent;

[0006] Or, the sodium ion battery positive electrode plate comprises a current collector, an active material layer and an over-discharge protection layer, wherein the over-discharge protection layer is arranged on a side surface of the active material layer close to the current collector and / or a side surface away from the current collector; the active material layer comprises an active material, and the over-discharge protection layer comprises an over-discharge protection agent;

[0007] The over discharge protection agent comprises a chemical formula of M a Ti b O c A compound wherein M includes one or more of Li, Na, and K, a+4b=2c, a≥0, b>0, and c>0.

[0008] After the sodium ion battery is treated with sodium supplementation, the sodium ions in the battery system are in a surplus state. When the battery is over-discharged, too many sodium ions are embedded in the active material, which will destroy the structure of the active material and cause the battery performance to decline. a Ti b O c The compound can store sodium ions at low potential. When the battery is over-discharged and the battery voltage is lower than the normal discharge voltage, the over-discharge protection agent can store excess sodium ions, thereby reducing the damage to the active material caused by excessive sodium ion embedding. When the battery is recharged, the sodium ions in the active material can be released again and participate in the electrode reaction as active ions. When the sodium ion battery positive electrode is used in the battery, the battery can have good cycle stability.

[0009] Optional, 0≤a≤5, 0<b≤7, 0<c<14.

[0010] Optionally, the over-discharge protection agent includes Li 4 Ti 5 O 12 , K 4 Ti 5 O 12 、Na 4 Ti 5 O 12 or TiO 2 One or more of .

[0011] Optionally, the average particle size of the over-discharge protection agent is 1 μm to 10 μm.

[0012] Optionally, the mass ratio of the over-discharge protection agent to the active material is 1:(150-1000).

[0013] Optionally, the mass ratio of the over-discharge protection agent to the active material is 1:(200-1000).

[0014] Optionally, the over-discharge protection agent also includes a a Ti b O c A carbon coating on the surface of the compound.

[0015] Optionally, in the over-discharge protection agent, the mass percentage of the carbon coating layer is 0.1% to 5%.

[0016] Optionally, the mass percentage of the over-discharge protection agent in the positive electrode material layer is 0.1% to 1%.

[0017] Optionally, the active material includes one or more of sodium ion layered oxides, polyanionic compounds and Prussian blue compounds.

[0018] Optionally, the sodium ion battery positive electrode plate further includes a binder and / or a conductive agent.

[0019] In a second aspect, the present application provides a sodium ion battery, comprising a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode comprises the positive electrode sheet of the sodium ion battery as described in the first aspect;

[0020] Or the sodium ion battery comprises a positive electrode, a negative electrode and a solid electrolyte or a semi-solid electrolyte located between the positive electrode and the negative electrode, and the positive electrode comprises the sodium ion battery positive electrode plate as described in the first aspect.

[0021] In a third aspect, the present application provides a vehicle, comprising the sodium ion battery as described in the second aspect. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 A schematic diagram of the structure of a sodium ion battery provided in one embodiment of the present application;

[0023] Figure 2 A schematic diagram of the structure of a positive electrode sheet of a sodium ion battery provided in one embodiment of the present application;

[0024] Figure 3 A schematic diagram of the structure of a positive electrode sheet of a sodium ion battery provided in one embodiment of the present application;

[0025] Figure 4 A schematic diagram of the structure of a positive electrode plate for a sodium ion battery provided in one embodiment of the present application. DETAILED DESCRIPTION

[0026] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0027] See also Figure 1 , Figure 1A schematic diagram of the structure of a sodium ion battery provided in one embodiment of the present application. The sodium ion battery includes a positive electrode 10, a negative electrode 20, a separator 30, and an electrolyte 40. When the sodium ion battery is charged, sodium ions are released from the positive electrode 10, and are deposited on the negative electrode 20 after passing through the electrolyte 40; when the sodium ion battery is discharged, the sodium ions are released from the negative electrode 20, and are embedded in the positive electrode 10 after passing through the electrolyte 40. For sodium ion batteries that have been treated with sodium supplementation, there are a certain amount of excess sodium ions in the battery. Within the normal charge and discharge range of the battery, the battery can operate normally. However, once the battery becomes abnormal and causes over-discharge, the active material in the positive electrode will collapse due to excessive embedding of sodium ions, resulting in battery failure. In response to the above problems, the present application provides a new sodium ion battery positive electrode plate, which includes an active material and an over-discharge protection agent, and the over-discharge protection agent includes a chemical formula of M a Ti b O c A compound wherein M includes one or more of Li, Na, and K, a+4b=2c, 0≤a, 0<b, 0<c. In some embodiments, 0≤a≤5, 0<b≤7, 0<c<14. In some embodiments, a may be, for example, 4, b may be, for example, 5, and c may be, for example, 12. In some embodiments, a may be, for example, 0, b may be, for example, 1, and c may be, for example, 2.

[0028] In the present application, the over-discharge protection agent has the function of storing sodium ions. Specifically, the chemical formula is M a Ti b O c The compound has a lower sodium storage potential. In the normal charge and discharge range of the sodium ion battery (1.5V to 4V), the material does not react and does not affect the normal operation of the battery. When the battery is over-discharged due to loss of control, the over-discharge protector can store excess sodium ions, inhibit excessive embedding of sodium ions into the positive electrode active material, protect the positive electrode active material, and improve the battery's cycle performance. In some embodiments of the present application, the sodium storage potential of the over-discharge protector is 0.5V to 1.3V, that is, when the battery is over-discharged and the voltage is between 0.5V and 1.3V, the over-discharge protector can store sodium ions before the positive electrode active material, thereby reducing the damage to the structure of the positive electrode active material caused by excessive embedding of sodium ions.

[0029] In some embodiments of the present application, the average particle size of the over-discharge protective agent is 1 μm to 10 μm. The average particle size of the over-discharge protective agent can be, but is not limited to, 1 μm, 2 μm, 4 μm, 6 μm, 8 μm or 10 μm. In some embodiments, the average particle size of the over-discharge protective agent is 3 μm to 5 μm. Controlling the particle size of the over-discharge protective agent is conducive to the over-discharge protective agent being in full contact with the positive electrode material, thereby achieving more effective protection, and the over-discharge protective agent can also be in full contact with the conductive agent, thereby accelerating the reaction rate of the over-discharge protective agent, and ensuring that the over-discharge protective agent fully stores excess sodium ions when the battery is over-discharged.

[0030] In some embodiments of the present application, the over-discharge protection agent also includes a a Ti b O c The carbon coating layer on the surface of the over-discharge protective agent has a mass percentage of 0.1% to 5% in the over-discharge protective agent. The mass percentage of the carbon coating layer in the over-discharge protective agent can be, but is not limited to, 0.1%, 0.3%, 0.5%, 1%, 3%, 4% or 5%. In some embodiments, the mass percentage of the carbon coating layer in the over-discharge protective agent is 1% to 5%. The carbon coating layer on the surface of the over-discharge protective agent can improve the conductivity of the over-discharge protective agent, reduce the electrochemical impedance, increase the storage rate of the over-discharge protective agent for sodium ions when the battery is over-discharged, and reduce the damage of the battery over-discharge to the positive electrode active material. In some embodiments of the present application, the carbon coating layer and the chemical formula M a Ti b O c The mass ratio of the compounds is 1:(20~300).

[0031] In some embodiments of the present application, the mass ratio of the over-discharge protection agent to the active material in the positive electrode plate is 1:(150-1000). The mass ratio of the over-discharge protection agent to the active material can be, but is not limited to, 1:150, 1:200, 1:300, 1:400, 1:500, 1:600, 1:700, 1:800 or 1:1000. Controlling the mass ratio of the over-discharge protection agent to the active material within the above range can ensure that the positive electrode plate of the sodium ion battery has a higher energy density, and the over-discharge protection agent can effectively protect the positive active material when the battery is over-discharged.

[0032] The sodium ion battery positive electrode sheet provided in this application does not specifically limit the type of positive electrode active material, and those skilled in the art can choose according to actual needs. In some embodiments of this application, the active material includes one or more of a sodium ion layered oxide, a polyanionic compound, and a Prussian blue compound. In some embodiments, the active material includes a sodium transition metal oxide, and the chemical formula of the sodium ion layered oxide is Na x M'O 2, wherein M' is selected from one or more of Ni, Co, Mn, Fe, Cu, Mg, Ti, Al, Li, and Zn, and 0 < x ≤ 1. In some embodiments, the polyanionic compound includes NaFePO 4 , Na 3 V 2 (PO 4 ) 3 , NaM” 2 PO 4 F and Na 3 (VO y ) 2 (PO 4 ) 2 F 3-2y or one or more of them, wherein M” is selected from one or more of V, Fe, Mn, and Ni, and 0 ≤ y ≤ 1. In some embodiments, the Prussian blue compound includes Na z M”'M””(CN) 6 , wherein M”' and M”” are selected from one or more of Ni, Cu, Fe, Mn, Co, and Zn, and 0 < z ≤ 2.

[0033] Please refer to Figure 2 , Figure 2 is a schematic structural diagram of a positive electrode plate of a sodium-ion battery provided by an embodiment of the present application. The positive electrode plate 100 of the sodium-ion battery includes a current collector 101 and a positive electrode material layer 102 provided on the surface of the current collector. The positive electrode material layer includes a blended active material and an over-discharge protection agent. Among them, the active material and the over-discharge protection agent are a physically blended system. It should be noted that in the positive electrode material layer of the present application, the over-discharge protection agent is not attached to the surface of the active material in a coating form. The over-discharge protection agent is mixed with the active material in a single dispersed state to form a physically blended system.

[0034] In some embodiments of the present application, the positive electrode plate of the sodium-ion battery includes a current collector, an active material layer, and an over-discharge protection layer. The over-discharge protection layer is provided on one surface of the active material layer. The active material layer includes an active material, and the over-discharge protection layer includes an over-discharge protection agent. Please refer to Figure 3 , Figure 3 is a schematic structural diagram of a positive electrode plate of a sodium-ion battery provided by an embodiment of the present application. The positive electrode plate 100 of the sodium-ion battery includes a current collector 101, an active material layer 103, and an over-discharge protection layer 104 arranged in sequence. Please refer to Figure 4 , Figure 4 is a schematic structural diagram of a positive electrode plate of a sodium-ion battery provided by an embodiment of the present application. The positive electrode plate 100 of the sodium-ion battery includes a current collector 101, an over-discharge protection layer 104, and an active material layer 103 arranged in sequence.

[0035] In some embodiments of the present application, the active material layer and the positive electrode material layer also include a conductive agent and a binder, and the conductive agent and the binder can be conventional choices in the field of batteries. For example, the binder can be selected from polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethyl cellulose (CMC) and sodium alginate. One or more of the conductive agent can be selected from carbon fiber, carbon nanotubes, acetylene black, carbon black and graphene.

[0036] The present application also provides a method for preparing a positive electrode sheet of a sodium ion battery. In some embodiments, the method for preparing a positive electrode sheet of a sodium ion battery comprises: mixing an active material, an over-discharge protection agent, a conductive agent, a binder, and a solvent to form a positive electrode slurry, coating and drying the positive electrode slurry to form a positive electrode material layer on the surface of a current collector to obtain a positive electrode sheet of a sodium ion battery, wherein the over-discharge protection agent comprises a material having a chemical formula of M a Ti b O c Compound, wherein M includes one or more of Li, Na, and K, a+4b=2c, 0≤a, 0<b, 0<c. In some embodiments of the present application, the mass percentage of the over-discharge protection agent in the positive electrode slurry is 0.1% to 1%. The mass percentage of the over-discharge protection agent in the positive electrode slurry can be, but is not limited to, 0.1%, 0.3%, 0.5%, 0.8% or 1%. In some embodiments, the mass percentage of the over-discharge protection agent in the positive electrode slurry is 0.1% to 0.8%.

[0037] In some embodiments, a method for preparing a positive electrode sheet for a sodium ion battery includes: mixing an active material, a conductive agent, a binder, and a solvent to form a positive electrode slurry, coating and drying the positive electrode slurry to form an active material layer on the surface of a current collector, and coating an over-discharge protection agent on the surface of the active material layer to form an over-discharge protection layer, thereby obtaining a positive electrode sheet for a sodium ion battery;

[0038] In some embodiments, the preparation method of the positive electrode sheet of a sodium ion battery includes: coating an over-discharge protection agent on the surface of a current collector to form an over-discharge protection layer, mixing an active material, a conductive agent, a binder and a solvent to form a positive electrode slurry, coating the positive electrode slurry on the surface of the over-discharge protection layer to form an active material layer, and obtaining a positive electrode sheet for a sodium ion battery.

[0039] The present application also provides a sodium ion battery, which includes a positive electrode, a negative electrode, an electrolyte, and a separator located between the positive electrode and the negative electrode, or the sodium ion battery includes a positive electrode, a negative electrode, and a solid electrolyte or a semi-solid electrolyte located between the positive electrode and the negative electrode; wherein the positive electrode includes the sodium ion battery positive electrode plate provided in the present application.

[0040] In the present application, the negative electrode of the sodium ion battery can be any negative electrode known in the art. In the embodiment of the present application, the negative electrode active material may include one or more of carbon materials, silicon materials, alloy materials, overplated metal oxides, overplated metal sulfides, phosphorus-based materials and titanate materials, wherein the carbon material includes one or more of graphite, hard carbon, soft carbon, and graphene; the silicon material includes one or more of silicon, silicon carbon, silicon oxygen, and silicon metal compounds. In some embodiments of the present application, the current collector of the negative electrode is copper foil, and the negative electrode active material includes one or more of natural graphite, artificial graphite, hard carbon, soft carbon, silicon, silicon oxide, and silicon-carbon composite materials; the binder includes one or more of polyacrylic acid (PAA), polyvinylidene fluoride (PVDF), carboxymethyl cellulose (CMC) and styrene butadiene latex (SBR); the conductive agent includes one or more of acetylene black, Ketjen black, Super-P, carbon nanotubes, carbon nanofibers, activated carbon and graphene. In the present application, the preparation method of the negative electrode can adopt any method known in the art.

[0041] In the present application, the separator of the sodium ion battery can be any separator known to those skilled in the art, for example, the separator can be one or more of polyolefin microporous membrane, polyethylene terephthalate, polyethylene felt, glass fiber felt or ultrafine glass fiber paper.

[0042] In the present application, the electrolyte of the sodium ion battery includes a solution of an electrolyte sodium salt in a non-aqueous solvent. In the embodiment of the present application, the electrolyte sodium salt includes NaPF 6 、NaClO 4 、NaBCl 4 、NaSO 3 CF 3 and Na(CH 3 )C 6 H 4 SO 3 In some embodiments of the present application, the non-aqueous solvent includes one or more of ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC) and diethyl carbonate (DEC). In some embodiments of the present application, the concentration of the electrolyte sodium salt in the electrolyte is 0.1mol / L-15mol / L. In some embodiments of the present application, the concentration of the electrolyte sodium salt is 1mol / L-10mol / L.

[0043] In the embodiments of the present application, the battery can be prepared by using either a lamination process or a winding process. In some embodiments of the present application, the battery is prepared by using a lamination process.

[0044] The sodium ion battery provided in the present application has a higher first coulombic efficiency and a longer cycle life due to the use of the sodium ion battery positive electrode sheet of the present application.

[0045] The technical solution of the present application is further described below with reference to a number of embodiments.

[0046] Example 1

[0047] A method for preparing a sodium ion battery, comprising:

[0048] 1) Preparation of positive electrode

[0049] 900g of positive electrode active material (NaNi 0.4 Fe 0.2 Mn 0.4 O 2 Materials), 50g acetylene black, 45g binder (PVDF), 5g over-discharge protection agent (Li 4 Ti 5 O 12 ) was added into 2000g of solvent nitrogen methyl pyrrolidone (NMP), and stirred in a vacuum mixer to form a stable and uniform positive electrode slurry. The particle size of the over-discharge protection agent was 4μm.

[0050] The positive electrode slurry is evenly and intermittently coated on both sides of the aluminum foil (aluminum foil size: width 160mm, thickness 12μm) using a slit coating device, dried at 393K, and pressed by a roller press to obtain the positive electrode sheet. The positive electrode sheet is cut into a rectangular sheet with a size of 48mm*56mm, and the ear is spot welded in the width direction.

[0051] 2) Preparation of negative electrode sheet

[0052] Weigh 910g of hard carbon, 50g of sodium supplement (inert sodium wire), 30g of binder (PVDF), 5g of acetylene black, and 5g of conductive carbon (HV) and add them to 2000g of solvent nitrogen methyl pyrrolidone (NMP), stir in a vacuum mixer to form a stable and uniform negative electrode slurry. Use a slit coating device to evenly and intermittently coat the negative electrode slurry on both sides of the aluminum foil (copper foil size: width 160mm, thickness 8μm), place it at 393K to dry, and obtain the negative electrode sheet after roller pressing. Cut the negative electrode sheet into a 49mm*57mm rectangular sheet, and spot weld the pole ear in the width direction.

[0053] 3) Preparation of sodium ion batteries

[0054] The positive electrode sheets, negative electrode sheets and separators are alternately stacked together to prepare the battery by lamination, wherein the positive and negative electrode sheets are alternately separated by separators to obtain dry cells. The dry cells are placed in an aluminum-plastic film outer package and injected with 1 mol / L sodium hexafluorophosphate electrolyte (the solvent is a 1:1 EC:DEC mixed solution containing 5% by mass of the electrolyte additive fluoroethylene carbonate (FEC)). After vacuum sealing, the battery is placed at 60°C for 48 hours, pressurized at 60°C, repackaged, exhausted, and divided into different volumes to obtain a sodium ion battery.

[0055] Example 2

[0056] The difference between Example 2 and Example 1 is that the composition of the positive electrode sheet is different. The preparation of the positive electrode sheet in Example 2 includes:

[0057] 900g of positive electrode active material (NaNi 0.4 Fe 0.2 Mn 0.4 O 2 Materials), 50g acetylene black, 45g binder (PVDF), 5g over-discharge protection agent (K 4 Ti 5 O 12 ) is added into 2000 g of solvent nitrogen methyl pyrrolidone (NMP), and stirred in a vacuum mixer to form a stable and uniform positive electrode slurry, wherein the particle size of the over-discharge protection agent is 4 μm.

[0058] The slurry was coated in the same manner as in Example 1 to obtain a positive electrode sheet, and the negative electrode sheet and a sodium ion battery were prepared in the same manner as in Example 1.

[0059] Example 3

[0060] The difference between Example 3 and Example 1 is that the composition of the positive electrode sheet is different. The preparation of the positive electrode sheet in Example 3 includes:

[0061] 900g of positive electrode active material (NaNi 0.4 Fe 0.2 Mn 0.4 O 2 Materials), 50g acetylene black, 45g binder (PVDF), 5g over-discharge protection agent (Na 4 Ti 5 O 12 ) is added into 2000 g of solvent nitrogen methyl pyrrolidone (NMP), and stirred in a vacuum mixer to form a stable and uniform positive electrode slurry, wherein the particle size of the over-discharge protection agent is 4 μm.

[0062] The slurry was coated in the same manner as in Example 1 to obtain a positive electrode sheet, and the negative electrode sheet and a sodium ion battery were prepared in the same manner as in Example 1.

[0063] Example 4

[0064] The difference between Example 4 and Example 1 is that the composition of the positive electrode sheet is different. The preparation of the positive electrode sheet in Example 4 includes:

[0065] 900g of positive electrode active material (NaNi 0.4 Fe 0.2 Mn 0.4 O 2 Materials), 50g acetylene black, 45g binder (PVDF), 5g over-discharge protection agent (TiO 2 ) was added into 2000g of solvent nitrogen methyl pyrrolidone (NMP), and stirred in a vacuum mixer to form a stable and uniform positive electrode slurry. The particle size of the over-discharge protection agent was 4μm.

[0066] The slurry was coated in the same manner as in Example 1 to obtain a positive electrode sheet, and the negative electrode sheet and a sodium ion battery were prepared in the same manner as in Example 1.

[0067] Example 5

[0068] The difference between Example 5 and Example 1 is that the composition of the positive electrode sheet is different. The preparation of the positive electrode sheet in Example 5 includes:

[0069] 904.5 g of positive electrode active material (NaNi 0.4 Fe 0.2 Mn 0.4 O 2 Materials), 50g acetylene black, 45g binder (PVDF), 0.5g over-discharge protection agent (Li 4 Ti 5 O 12 ) was added into 2000g of solvent nitrogen methyl pyrrolidone (NMP), and stirred in a vacuum mixer to form a stable and uniform positive electrode slurry. The particle size of the over-discharge protection agent was 4μm.

[0070] The slurry was coated in the same manner as in Example 1 to obtain a positive electrode sheet, and the negative electrode sheet and a sodium ion battery were prepared in the same manner as in Example 1.

[0071] Example 6

[0072] The difference between Example 6 and Example 1 is that the composition of the positive electrode sheet is different. The preparation of the positive electrode sheet in Example 6 includes:

[0073] 895g of positive electrode active material (NaNi 0.4 Fe0.2 Mn 0.4 O 2 Materials), 50g acetylene black, 45g binder (PVDF), 10g over-discharge protection agent (Li 4 Ti 5 O 12 ) was added into 2000g of solvent nitrogen methyl pyrrolidone (NMP), and stirred in a vacuum mixer to form a stable and uniform positive electrode slurry. The particle size of the over-discharge protection agent was 4μm.

[0074] The slurry was coated in the same manner as in Example 1 to obtain a positive electrode sheet, and the negative electrode sheet and a sodium ion battery were prepared in the same manner as in Example 1.

[0075] Example 7

[0076] The difference between Example 7 and Example 1 is that the composition of the positive electrode sheet is different. The preparation of the positive electrode sheet in Example 7 includes:

[0077] 900g of positive electrode active material (NaNi 0.4 Fe 0.2 Mn 0.4 O 2 Materials), 50g acetylene black, 45g binder (PVDF), 5g over-discharge protection agent (Li 4 Ti 5 O 12 ) is added into 2000 g of solvent nitrogen methyl pyrrolidone (NMP), and stirred in a vacuum mixer to form a stable and uniform positive electrode slurry, wherein the particle size of the over-discharge protection agent is 20 μm.

[0078] The slurry was coated in the same manner as in Example 1 to obtain a positive electrode sheet, and the negative electrode sheet and a sodium ion battery were prepared in the same manner as in Example 1.

[0079] Example 8

[0080] The difference between Example 8 and Example 1 is that the composition of the positive electrode plate is different. The preparation of the positive electrode plate in Example 8 includes:

[0081] 900g of positive electrode active material (NaNi 0.4 Fe 0.2 Mn 0.4 O 2 Materials), 50g acetylene black, 45g binder (PVDF), 5g over-discharge protection agent (Li 4 Ti 5 O 12 / C) was added into 2000g of solvent nitrogen methyl pyrrolidone (NMP), and stirred in a vacuum mixer to form a stable and uniform positive electrode slurry, wherein the over-discharge protection agent Li4 Ti 5 O 12 The surface of the carbon has a carbon coating layer, and the preparation method of the carbon coating layer comprises: in an atmosphere of acetylene: nitrogen volume ratio of 1:1, Li 4 Ti 5 O 12 The compound is carbon-coated by chemical vapor deposition (CVD) for 1.5 hours to obtain an over-discharge protection agent. The mass percentage of the carbon coating layer in the over-discharge protection agent is 3%, and the particle size of the over-discharge protection agent is 5 μm.

[0082] The slurry was coated in the same manner as in Example 1 to obtain a positive electrode sheet, and the negative electrode sheet and a sodium ion battery were prepared in the same manner as in Example 1.

[0083] Example 9

[0084] The difference between Example 9 and Example 1 is that the composition of the positive electrode sheet is different. The preparation of the positive electrode sheet in Example 9 includes:

[0085] 900g of positive electrode active material (NaNi 0.4 Fe 0.2 Mn 0.4 O 2 Materials), 50g acetylene black, 45g binder (PVDF), 5g over-discharge protection agent (Li 4 Ti 5 O 12 / C) is added to 2000g of solvent nitrogen methyl pyrrolidone (NMP), and stirred in a vacuum mixer to form a stable and uniform positive electrode slurry, wherein the surface of the over-discharge protection agent has a carbon coating layer, and the preparation method of the carbon coating layer comprises: in an atmosphere with an acetylene: nitrogen volume ratio of 1:1, Li 4 Ti 5 O 12 The compound is carbon-coated by chemical vapor deposition (CVD) for 5 hours to obtain an over-discharge protection agent. The mass percentage of the carbon coating layer in the over-discharge protection agent is 14%, and the particle size of the over-discharge protection agent is 6 μm.

[0086] The slurry was coated in the same manner as in Example 1 to obtain a positive electrode sheet, and the negative electrode sheet and a sodium ion battery were prepared in the same manner as in Example 1.

[0087] Example 10

[0088] The difference between Example 10 and Example 1 is that the positive electrode sheet has a different composition. The preparation of the positive electrode sheet in Example 10 includes:

[0089] 900g of positive electrode active material (Na 3V 2 (PO 4 ) 3 Materials), 50g acetylene black, 45g binder (PVDF), 5g over-discharge protection agent (Li 4 Ti 5 O 12 ) is added into 2000 g of solvent nitrogen methyl pyrrolidone (NMP), and stirred in a vacuum mixer to form a stable and uniform positive electrode slurry, wherein the particle size of the over-discharge protection agent is 4 μm.

[0090] The slurry was coated in the same manner as in Example 1 to obtain a positive electrode sheet, and the negative electrode sheet and a sodium ion battery were prepared in the same manner as in Example 1.

[0091] Embodiment 11

[0092] The difference between Example 11 and Example 1 is that the structure of the positive electrode plate is different. The preparation of the positive electrode plate in Example 11 includes:

[0093] 900g of positive electrode active material (NaNi 0.4 Fe 0.2 Mn 0.4 O 2 50g of acetylene black, 50g of binder (PVDF) were added to 2000g of solvent nitrogen methyl pyrrolidone (NMP), stirred in a vacuum mixer to form a stable and uniform positive electrode slurry, and the positive electrode slurry was evenly and intermittently coated on both sides of aluminum foil (aluminum foil size: width 160mm, thickness 12μm) by a slit coating device, dried at 393K, and pressed by a roller press to obtain an active material layer, and 5g of over-discharge protection agent (Li 4 Ti 5 O 12 ) is dispersed in 200g of solvent nitrogen methyl pyrrolidone (NMP) to obtain a mixed solution, the mixed solution is coated on the surface of the active material layer, and dried at 393K to form an over-discharge protection layer to obtain a positive electrode sheet, and the positive electrode sheet is cut into a rectangular sheet with a size of 48mm*56mm, and the ear is spot welded in the width direction.

[0094] The negative electrode sheet and the sodium ion battery were prepared in the same manner as in Example 1.

[0095] Comparative Example 1

[0096] A method for preparing a sodium ion battery, comprising:

[0097] 1) Preparation of positive electrode

[0098] 900g of positive electrode active material (NaNi 0.4 Fe 0.2 Mn0.4 O 2 Materials), 50 g of acetylene black, and 50 g of a binder (PVDF) were added to 2000 g of a solvent, nitrogen methyl pyrrolidone (NMP), and stirred in a vacuum mixer to form a stable and uniform positive electrode slurry.

[0099] The positive electrode slurry is evenly and intermittently coated on both sides of the aluminum foil (aluminum foil size: width 160mm, thickness 12μm) using a slit coating device, dried at 393K, and pressed by a roller press to obtain the positive electrode sheet. The positive electrode sheet is cut into a rectangular sheet with a size of 48mm*56mm, and the ear is spot welded in the width direction.

[0100] The negative electrode sheet and the sodium ion battery were prepared in the same manner as in Example 1.

[0101] Effect Example

[0102] In order to verify the performance of the sodium ion battery positive electrode plate prepared in the present application, the present application also provides an effect embodiment.

[0103] The electrochemical performance test of the sodium ion battery of each embodiment and comparative example was carried out, specifically including:

[0104] 1) The first efficiency test was performed on the batteries of each embodiment and comparative example. The specific test conditions were as follows: 5 batteries prepared in each embodiment and comparative example were taken, and the batteries were subjected to a charge and discharge cycle test at 0.1C at a temperature of 25±1°C using a LAND CT 2001C secondary battery performance testing device. The test steps were as follows: standing for 10 min; charging at 0.1C constant current to 4.0 V; standing for 10 min; discharging at constant current to 2.0 V, and recording the first discharge capacity and first charge capacity of the battery. The first efficiency (%) = first charge capacity / first discharge capacity × 100%.

[0105] The battery of each embodiment and comparative example was tested for cycle performance. The test conditions were as follows: 5 batteries prepared in each embodiment and comparative example were taken, and the battery was subjected to charge and discharge cycle test at 0.2C at a temperature of 25±1°C using a LAND CT 2001C secondary battery performance tester. The test steps were as follows: 10 minutes of standby; 0.2C constant current charging to 4.0V, constant voltage charging to 0.05C cut-off; 10 minutes of standby; constant current discharge to 0V, which was 1 cycle. Repeat this step. When the battery capacity is lower than 80% of the initial discharge capacity during the cycle, the cycle is terminated. The number of cycles is the cycle life of the battery. The average value of each group (i.e., 5 batteries in each embodiment or comparative example) was taken, and the capacity retention rate and energy retention rate of the battery under the corresponding number of cycles were taken. The test results of the sodium ion batteries of each embodiment and comparative example are shown in Table 1.

[0106] Table 1 Electrochemical performance parameters of sodium ion batteries of Examples 1-11 and Comparative Example 1

[0107] Experimental Group Cycle times First efficiency (%) Example 1 580 103.9％ Example 2 500 102.8％ Example 3 520 103.1％ Example 4 510 102.7％ Example 5 450 102.5％ Example 6 560 102.1％ Example 7 530 102.2％ Example 8 590 103.2％ Example 9 585 103.3％ Example 10 583 103.1％ Embodiment 11 586 103.5％ Comparative Example 1 430 102.3％

[0108] As can be seen from Table 1, in the battery of Comparative Example 1, after the battery is supplemented with sodium, the surplus sodium ions in the battery are embedded in the active material when the battery is over-discharged, so that the structure of the active material is destroyed and the battery cycle life is reduced. However, the battery in the embodiment of the present application has a longer cycle life because it uses a positive electrode plate containing an over-discharge protection agent. Compared with the battery of Comparative Example 1 without adding an over-discharge protection agent, under the condition of over-discharge, the battery cycle performance is improved by about 34.8%. For each embodiment, in the battery of embodiment 5, the amount of over-discharge protective agent added is low, its protective effect on the battery is relatively limited, and the number of battery cycles is low; in the battery of embodiment 6, the over-discharge protective agent is added in excess, which can achieve full protection of the battery, but the energy density of the battery will also decrease; in the battery of embodiment 7, the particle size of the over-discharge protective agent is large, its reaction rate is relatively low, and the protective effect is slightly reduced; in the battery of embodiment 8, the over-discharge protective agent contains a carbon coating layer, which effectively improves the conductivity of the over-discharge protective agent and improves the battery cycle performance; in the battery of embodiment 9, the carbon content in the over-discharge protective agent is too high, which reduces the sodium storage capacity of the over-discharge protective agent, and the battery cycle performance is reduced compared with that of embodiment 8; the battery of embodiment 10 uses different positive electrode active materials, and the battery still has good cycle performance, indicating that the over-discharge protective agent of the present invention is suitable for different positive electrode active materials; in the battery of embodiment 11, the over-discharge protective agent is coated on the surface of the active material layer in a layered structure. From the experimental results, the over-discharge protective agent under this structure can also achieve protection of the positive electrode active material, so that the battery has a longer service life.

[0109] The above is a preferred embodiment of the present application, but it should not be understood as limiting the scope of the present application. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principles of the present application, and these improvements and modifications are also considered to be within the scope of protection of the present application.

Claims

1. A sodium ion battery positive electrode plate, characterized in that: It includes a current collector and a positive electrode material layer arranged on the surface of the current collector, wherein the positive electrode material layer includes a blended active material and an over-discharge protective agent; Or, the sodium ion battery positive electrode plate comprises a current collector, an active material layer and an over-discharge protection layer, wherein the over-discharge protection layer is arranged on a side surface of the active material layer close to the current collector and / or a side surface away from the current collector; the active material layer comprises an active material, and the over-discharge protection layer comprises an over-discharge protection agent; The over discharge protection agent comprises a chemical formula of M a Ti b O c A compound, wherein M includes one or more of Na and K, a+4b=2c, a>0, b>0, c>0; the mass ratio of the over-discharge protection agent to the active material is 1:(150~1000); the average particle size of the over-discharge protection agent is 1μm~10μm.

2. The sodium ion battery positive electrode sheet according to claim 1, characterized in that: The mass ratio of the over-discharge protection agent to the active material is 1:(200-1000).

3. The sodium ion battery positive electrode sheet according to claim 1, characterized in that: The over discharge protection agent also includes a coating on the chemical formula M a Ti b O c A carbon coating on the surface of the compound.

4. The sodium ion battery positive electrode sheet according to claim 3, characterized in that: In the over-discharge protection agent, the mass percentage of the carbon coating layer is 0.1% to 5%.

5. The sodium ion battery positive electrode sheet according to claim 1, characterized in that: The mass percentage of the over-discharge protection agent in the positive electrode material layer is 0.1% to 1%.

6. The sodium ion battery positive electrode sheet according to any one of claims 1 to 5, characterized in that: The active material comprises one or more of sodium ion layered oxides, polyanionic compounds and Prussian blue compounds.

7. A sodium ion battery, characterized in that: It comprises a positive electrode, a negative electrode, a separator and an electrolyte, wherein the positive electrode comprises the positive electrode sheet of a sodium ion battery according to any one of claims 1 to 6; Or the sodium ion battery comprises a positive electrode, a negative electrode and a solid electrolyte or a semi-solid electrolyte located between the positive electrode and the negative electrode, and the positive electrode comprises the positive electrode plate of the sodium ion battery according to any one of claims 1 to 6.

8. A vehicle, characterized in that: The vehicle includes the sodium ion battery of claim 7.

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