Positive plate, battery and electric equipment

Abstract

The invention provides a positive plate, a battery and electric equipment. The positive plate comprises a current collector and a positive active material layer arranged on at least one side of the current collector, the positive active material layer comprises a first positive active material and a second positive active material, and the first positive active material comprises a polyanion material; the second positive electrode active material comprises a sodium-containing oxide material and / or a Prussian material; in the positive electrode active material layer, the mass ratio of the first positive electrode active material and the second positive electrode active material on the side close to the current collector is smaller than the mass ratio of the first positive electrode active material and the second positive electrode active material on the side far away from the current collector. The positive plate provided by the embodiment of the invention can simultaneously have relatively good energy density and cycle capacity retention ratio.

Description

Technical Field

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

[0002] Sodium-ion batteries are currently the most common power batteries. Existing technologies are mostly based on the development stage of positive electrode materials, combining multiple positive electrode materials to improve overall performance, but this improvement is limited and cannot meet usage needs. Summary of the Invention

[0003] The technical problem to be solved by the present application is to provide a positive electrode sheet, a battery and an electrical device, so that the battery can have both good energy density and cycle capacity retention rate.

[0004] In order to solve the above problems, the present application discloses a positive electrode sheet, characterized in that the positive electrode sheet includes a current collector and a positive electrode active material layer provided on at least one side of the current collector, the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material, the first positive electrode active material includes a polyanion material; the second positive electrode active material includes a sodium oxide-containing material and / or a Prussian material;

[0005] In the positive electrode active material layer, a mass ratio of the first positive electrode active material to the second positive electrode active material on a side close to the current collector is smaller than a mass ratio of the first positive electrode active material to the second positive electrode active material on a side far from the current collector.

[0006] Optionally, in the positive electrode active material layer, the mass ratio of the first positive electrode active material to the second positive electrode active material is (40-65):(35-60).

[0007] Optionally, the positive electrode active material layer comprises at least:

[0008] a first positive electrode active material layer, the first positive electrode active material layer being disposed on at least one side of the current collector, the first positive electrode active material layer comprising the first positive electrode active material and the second positive electrode active material;

[0009] a second positive electrode active material layer, the second positive electrode active material layer being disposed on a side of the first positive electrode active material layer away from the current collector, the second positive electrode active material layer comprising the first positive electrode active material and the second positive electrode active material;

[0010] The mass ratio of the first positive electrode active material to the second positive electrode active material in the first positive electrode active material layer is smaller than the mass ratio of the first positive electrode active material to the second positive electrode active material in the second positive electrode active material layer.

[0011] Optionally, in the first positive electrode active material layer, the mass proportion of the first positive electrode active material is less than the mass proportion of the second positive electrode active material; and / or, in the second positive electrode active material layer, the mass proportion of the first positive electrode active material is greater than the mass proportion of the second positive electrode active material

[0012] Optionally, it is characterized in that the polyanion material includes at least one of sodium ferric phosphate pyrophosphate, sodium vanadium fluorophosphate, sodium ferric phosphate and sodium ferric pyrophosphate.

[0013] Optionally, the sodium oxide-containing material includes at least one of sodium nickel iron manganate, sodium nickel manganate, sodium manganese iron, and sodium copper iron manganate.

[0014] Optionally, in the first positive electrode active material layer, the mass proportion of the first positive electrode active material is 20% to 50%; the mass proportion of the second positive electrode active material is 50% to 80%; and / or, in the second positive electrode active material layer, the mass proportion of the first positive electrode active material is 60% to 80%, and the mass proportion of the second positive electrode active material is 20% to 40%.

[0015] Optionally, the current collector includes two conductive layers and a non-conductive layer disposed between the two conductive layers.

[0016] Optionally, the conductive layer includes at least one of aluminum foil, nickel foil, and stainless steel foil; and the non-conductive layer includes non-conductive resin.

[0017] An embodiment of the present application further provides a battery, which includes the positive electrode sheet as described in the embodiment of the present application or a positive electrode sheet prepared using the method for preparing the positive electrode sheet as described in the embodiment of the present application.

[0018] Optionally, the battery includes a negative electrode sheet, and the negative electrode sheet includes a negative electrode active material; the negative electrode active material includes at least one of a hard carbon material, a soft carbon material, and a silicon-based material.

[0019] Optionally, the negative electrode sheet includes a conductive agent and / or a binder.

[0020] The present application also provides an electrical device, which includes the battery described in the embodiments of the present application.

[0021] Compared with the prior art, this application has the following advantages:

[0022] The positive electrode sheet provided in the embodiments of the present application includes a current collector and a positive electrode active material layer disposed on at least one side of the current collector. The positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material, wherein the first positive electrode active material includes a polyanion material; the second positive electrode active material includes a sodium oxide-containing material and / or a Prussian material; the mass ratio of the first positive electrode active material to the second positive electrode active material on the side closer to the current collector is less than the mass ratio of the first positive electrode active material to the second positive electrode active material on the side farther from the current collector. As a result, the positive electrode sheet provided in the embodiments of the present application can contain more of the second positive electrode active material on the side closer to the current collector, providing a higher specific capacity, thereby enabling the overall positive electrode sheet to have better capacity and energy density. At the same time, the side farther from the current collector can contain more of the first positive electrode active material, resulting in better stability and cycle capacity retention. As a result, a battery fabricated using the positive electrode sheet provided in the embodiments of the present application can simultaneously have good energy density and cycle capacity retention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 This is a schematic structural diagram of a positive electrode sheet provided in an embodiment of the present application;

[0024] FIG2( a ) is a schematic diagram of the puncture test of Comparative Example 1 provided in the present application;

[0025] FIG2( b ) is a schematic diagram of the puncture test of Example 1 provided in the present application;

[0026] FIG2( c ) is a schematic diagram of the puncture test of Example 2 provided in the present application.

[0027] Among them, 101 is a current collector; 102 is a first positive electrode active material layer; 103 is a second positive electrode active material layer. DETAILED DESCRIPTION

[0028] In order to make the above-mentioned purposes, features and advantages of the present application more obvious and easy to understand, the present application is further described in detail below with reference to the accompanying drawings and specific implementation methods.

[0029] The present application discloses a positive electrode sheet, comprising a current collector and a positive electrode active material layer disposed on at least one side of the current collector, wherein the positive electrode active material layer comprises a first positive electrode active material and a second positive electrode active material, wherein the first positive electrode active material comprises a polyanion material; and the second positive electrode active material comprises a sodium oxide-containing material and / or a Prussian material.

[0030] In the positive electrode active material layer, the mass ratio of the first positive electrode active material to the second positive electrode active material on the side close to the current collector is smaller than the mass ratio of the first positive electrode active material to the second positive electrode active material on the side far from the current collector.

[0031] Specifically, the positive electrode sheet may be provided with a current collector. The current collector is generally used to collect and conduct current, and may be attached to the positive electrode active material layer, thereby conducting the current generated by the positive electrode active material layer to an external circuit.

[0032] In the embodiment of the present application, the positive electrode active material layer may generally include a positive electrode active material, which may be used to store and release charges, thereby generating current.

[0033] The positive electrode active material may be of various types. The positive electrode active material may include a first positive electrode active material and a second positive electrode active material. The first positive electrode active material may include a polyanion material; the second positive electrode active material may include a sodium oxide material and / or a Prussian material.

[0034] Polyanionic materials typically possess high thermal and chemical stability, maintaining structural integrity even under high temperatures or harsh environments. They also exhibit low reactivity, making them less susceptible to thermal runaway during charge and discharge, resulting in increased safety. Furthermore, polyanionic materials typically exhibit good cycling stability, resulting in a long cycle life.

[0035] A sodium oxide material may refer to an oxide material containing sodium. Optionally, in addition to sodium, it may also contain at least one metal element. Sodium oxide materials generally have higher reactivity and specific capacity, making them more likely to participate in electrochemical reactions in a battery.

[0036] Prussian materials can refer to transition metal cyanide anions (M'(CN)6 m- ) and transition metal cations (M n+ ) in aqueous solution to obtain a material that can generally have a three-dimensional open framework structure with a large number of vacancies in the lattice, which is suitable for alkali metal ions (such as Na + , K + ) embedding and extraction, with good reactivity and gram capacity.

[0037] Among them, gram capacity can refer to the amount of charge that a battery electrode material can store per unit mass, which can usually be expressed in milliampere hours per gram (mAh / g).

[0038] Specifically, for positive electrode active materials, their theoretical gram capacity can be the capacity that can be provided when the active substances (such as lithium ions, sodium ions, etc.) in the positive electrode active materials fully participate in the electrochemical reaction, which can usually be expressed as:

[0039] C 理论 =nF / 3.6M

[0040] Among them, C 理论 is the theoretical gram capacity, n is the number of electrons gained or lost during the electrochemical reaction, F is the Faraday constant, the Faraday constant value is 96500 C / mol, and M is the molecular weight of the positive electrode active material.

[0041] The actual capacity of the positive electrode active material may refer to the capacity that the positive electrode active material can actually provide under certain discharge conditions, which is equal to the integral of the discharge current and the discharge time.

[0042] Reactivity refers to the ability of a positive electrode active material to participate in electrochemical reactions during the charge and discharge process. This is often correlated with the properties of the positive electrode active material itself. The faster the positive electrode active material's electrochemical reaction rate, the higher its reactivity.

[0043] Gram capacity and reactivity can be important indicators for measuring the energy storage capacity of battery electrode materials. When the gram capacity of the positive electrode active material is higher, it can have better energy storage capacity and energy density. However, when the positive electrode active material has a higher gram capacity, it may also have a higher reactivity, which may be more likely to produce side reactions, resulting in difficulty in maintaining good cycle performance and low capacity retention. For example, some positive electrode active materials may have lower reactivity, so that it is less likely to have side reactions or gas production, and can have better cycle performance and higher safety, but its gram capacity may be relatively low.

[0044] Therefore, in the embodiments of the present application, a positive electrode active material layer can be provided on at least one side of the current collector. Part of the positive electrode active material layer can be close to the current collector, while part of the positive electrode active material layer can be far away from the current collector. The mass ratio of the first positive electrode active material to the second positive electrode active material on the side close to the current collector is less than the mass ratio of the first positive electrode active material to the second positive electrode active material on the side far away from the current collector.

[0045] For the side of the positive electrode active material layer close to the current collector, since the positive electrode active material is close to the current collector and far away from the electrolyte, it is less likely for the positive electrode active material to produce side reactions with the electrolyte, affecting the cycle life. In the case of thermal runaway, it is also less likely to react violently with the electrolyte to cause serious phenomena such as fire and explosion. Therefore, the side close to the current collector can contain a higher content of the second positive electrode active material than the side far from the current collector, while the content of the first positive electrode active material, whose gram capacity is lower than that of the second positive electrode active material, can be relatively small, so as to increase the gram capacity of the overall composite positive electrode material.

[0046] As for the side of the positive electrode active material layer away from the current collector, since the positive electrode active material layer is now away from the current collector and closer to the electrolyte, the positive electrode active material can be relatively more likely to produce side reactions with the electrolyte, affecting the cycle life. In the event of thermal runaway, it is also more likely to react violently with the electrolyte and cause serious phenomena such as fire and explosion. Therefore, the side away from the current collector can contain a higher content of the first positive electrode active material than the side close to the current collector, while the content of the second positive electrode active material, which is less stable than the first positive electrode active material, can be relatively less, so as to reduce side reactions, improve cycle capacity retention, and avoid serious phenomena such as fire and explosion.

[0047] Therefore, by making the mass ratio of the first positive electrode active material and the second positive electrode active material close to the current collector smaller than the mass ratio of the first positive electrode active material and the second positive electrode active material on the side away from the current collector, the safety performance of the positive electrode sheet can be effectively improved while maintaining a good capacity and energy density as a whole.

[0048] In one embodiment of the present application, in the positive electrode active material layer, the mass ratio of the first positive electrode active material to the second positive electrode active material is (40-65):(35-60).

[0049] When the overall mass ratio of the first positive electrode active material to the second positive electrode active material in the positive electrode sheet is in the range of (40-65):(35-60), the positive electrode sheet as a whole can achieve good energy density and cycle capacity retention. At the same time, there will be no situation where the battery is prone to fire and explosion due to an excessive amount of the second positive electrode active material, or the battery energy density is too low due to an excessive amount of the first positive electrode active material.

[0050] In one embodiment of the present application, the positive electrode active material layer includes at least:

[0051] a first positive electrode active material layer, the first positive electrode active material layer being disposed on at least one side of the current collector, the first positive electrode active material layer comprising a first positive electrode active material and a second positive electrode active material;

[0052] a second positive electrode active material layer, the second positive electrode active material layer being disposed on a side of the first positive electrode active material layer away from the current collector, the second positive electrode active material layer comprising a first positive electrode active material and a second positive electrode active material;

[0053] The mass ratio of the first positive electrode active material to the second positive electrode active material in the first positive electrode active material layer is smaller than the mass ratio of the first positive electrode active material to the second positive electrode active material in the second positive electrode active material layer.

[0054] Specifically, the positive electrode active material layer may include at least two layers. The positive electrode active material layer may include at least a first positive electrode active material layer and a second active material layer. The first positive electrode active material layer may be closer to the current collector and may include both the first positive electrode active material and the second positive electrode active material. The second positive electrode active material layer may be disposed on the side of the first positive electrode active material layer away from the current collector, further away from the current collector than the first positive electrode active material layer and closer to the electrolyte. The second positive electrode active material layer may include both the first positive electrode active material and the second positive electrode active material.

[0055] The mass ratio of the first positive electrode active material to the second positive electrode active material in the first positive electrode active material layer is less than the mass ratio of the first positive electrode active material to the second positive electrode active material in the second positive electrode active material layer. Since the first positive electrode active material layer is close to the current collector and away from the electrolyte, the positive electrode active material is less likely to produce side reactions with the electrolyte, thereby affecting the cycle life. In the event of thermal runaway, it is also less likely to violently react with the electrolyte to cause serious phenomena such as fire and explosion. Therefore, it can contain a higher content of the second positive electrode active material than the second positive electrode active material layer, and the content of the first positive electrode active material, which has a lower gram capacity than the second positive electrode active material, can be relatively small, thereby increasing the overall gram capacity of the composite positive electrode material.

[0056] The second positive electrode active material layer, located farther from the current collector and closer to the electrolyte, is more susceptible to side reactions with the electrolyte, impacting cycle life. In the event of thermal runaway, it is also more likely to violently react with the electrolyte, resulting in serious consequences such as fire and explosion. The second positive electrode active material layer contains a higher concentration of the first positive electrode active material than the first positive electrode active material layer. The second positive electrode active material, which is less stable than the first positive electrode active material, can be contained in a relatively lower concentration, thereby reducing side reactions, improving cycle capacity retention, and avoiding serious consequences such as fire and explosion.

[0057] As a specific example of this application, Figure 1It is a schematic structural diagram of a positive electrode sheet in an embodiment of the present application. Among them, a first positive electrode active material layer 102 and a second positive electrode active material layer 103 are provided on the current collector 101. In the first positive electrode active material layer 102, the mass proportion of the first positive electrode active material is less than the mass proportion of the second positive electrode active material; and / or, in the second positive electrode active material layer 103, the mass proportion of the first positive electrode active material is greater than the mass proportion of the second positive electrode active material. As a result, the first positive electrode active material layer 102 close to the current collector 101 can have a higher gram capacity, and the second positive electrode active material layer 103 away from the current collector 101 can have higher stability, reduce side reactions with the electrolyte, and improve cycle life. Thereby, the overall positive electrode sheet can maintain a good capacity and energy density, and have a good cycle capacity retention rate.

[0058] In one embodiment of the present application, in the first positive electrode active material layer, the mass proportion of the first positive electrode active material is less than the mass proportion of the second positive electrode active material; and / or, in the second positive electrode active material layer, the mass proportion of the first positive electrode active material is greater than the mass proportion of the second positive electrode active material.

[0059] Specifically, when the positive electrode active material layer is located away from the current collector and closer to the electrolyte, the positive electrode active material is more likely to react with the electrolyte, affecting the cycle life. In the event of thermal runaway, it is also more likely to react violently with the electrolyte, causing serious phenomena such as fire and explosion. Therefore, in the second positive electrode active material layer, the mass proportion of the first positive electrode active material is less than the mass proportion of the second positive electrode active material, providing higher safety performance.

[0060] In the case where the positive electrode active material layer is closer to the current collector, the positive electrode active material layer is closer to the current collector and farther away from the electrolyte. The positive electrode active material is farther away from the electrolyte, so it is less likely to produce side reactions with the electrolyte, affecting the cycle life, and it is also less likely to cause thermal runaway. At this time, in the first positive electrode active material layer, the mass proportion of the first positive electrode active material is less than the mass proportion of the second positive electrode active material. The positive electrode active material layer close to the current collector can contain a relatively higher content of the second positive electrode active material, and the content of the first positive electrode active material with a gram capacity lower than that of the second positive electrode active material can be relatively small, so as to increase the overall gram capacity of the composite positive electrode material.

[0061] In the embodiment of the present application, the battery may be a sodium ion battery, which is a new type of rechargeable battery. Its working principle is similar to that of a lithium ion battery, but it uses sodium ions (Na +) as a charge carrier. Due to the abundance of sodium in the Earth's crust and its low cost, sodium-ion batteries are considered a potential alternative to lithium-ion batteries, particularly in areas such as large-scale energy storage and electric vehicles. However, sodium-ion batteries still present certain safety risks. Under extreme conditions such as overcharging, over-discharging, and short-circuiting, sodium-ion batteries may experience thermal runaway, causing the battery to overheat or catch fire or explode, resulting in insufficient safety.

[0062] In one embodiment of the present application, the first positive electrode active material includes a polyanion material.

[0063] Specifically, the first positive electrode active material may include a material with low reactivity, which may include a polyanion material. Specifically, the polyanion material may be a material having a polyanion group. It may include phosphates, sulfates, fluorophosphates, silicates, etc. containing sodium. For example, sodium ferric pyrophosphate (NFPP, Na4Fe3(PO4)2P2O7), sodium vanadium fluorophosphate (NVFP, Na 3.5 V 1.5 Fe 0.5 (PO4)3), at least one of sodium ferric phosphate (NaFePO4) and sodium ferric pyrophosphate (Na4Fe2(P2O7)2), which is not limited in this application.

[0064] Among them, sodium ferric pyrophosphate (NFPP) and sodium vanadium fluorophosphate (NVFP) have good thermal stability and chemical stability and are not prone to thermal runaway. Sodium ferric pyrophosphate and / or sodium vanadium fluorophosphate can be used as the first positive electrode active material.

[0065] In one embodiment of the present application, the second positive electrode active material includes a sodium oxide material and / or a Prussian material.

[0066] Specifically, the second positive electrode active material may include an active material with a higher gram capacity and lower stability, which may include a sodium oxide material and / or a Prussian material. The sodium oxide material may be an oxide material containing sodium and other metal ions, such as sodium nickel iron manganese oxide (NFM, NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2), sodium nickel manganate (NaNi 0.5 Mn 0.5 O2), sodium manganese ferrite (NaFe 0.55 Mn 0.45 O2), copper iron sodium manganate (Na 0.9 Cu 0.22 Fe 0.3 Mn 0.48 O2), etc., this application does not impose any restrictions on this.

[0067] Alternatively, the sodium oxide-containing material may include tunnel-type oxides and layered oxides. Tunnel-type oxides generally refer to materials containing tunnels within their structure. Layered oxides may be materials formed by alternating layers of transition metal oxides and sodium ion layers.

[0068] When the sodium ion content is high, it can usually form a layered oxide. In the case of a high sodium ion content, the positive electrode active material can usually have a higher gram capacity. Therefore, layered oxides with higher gram capacity such as sodium nickel iron manganese oxide (NFM) can be used as the second positive electrode active material. Sodium nickel iron manganese oxide can also have the characteristics of high compaction and high voltage platform, which can provide higher energy density for the positive electrode sheet.

[0069] Prussian materials may include, for example, Prussian blue or Prussian white, and this application does not limit this. Prussian materials may have a three-dimensional framework structure. Prussian materials are formed by transition metal ions (such as iron, cobalt, nickel, etc.) and cyanide ligands. This structure is similar to a cubic lattice, with a large number of gaps and channels, and sodium ions can be embedded and de-embedded in these gaps and channels. As a result, it can have a higher specific surface area, provide abundant energy storage sites, and increase the capacity and energy density of the material.

[0070] In one embodiment of the present application, in the first positive electrode active material layer, the first positive electrode active material accounts for 20% to 50% by mass, for example, 20%, 25%, 30%, 35%, 40%, 45%, 50%, etc. The second positive electrode active material accounts for 50% to 80% by mass, for example, 50%, 55%, 60%, 65%, 70%, 75%, 80%, etc. At this mass ratio, the second positive electrode active material can provide a higher gram capacity, thereby increasing the overall capacity and energy density of the first positive electrode active material layer.

[0071] In the second positive electrode active material layer, the first positive electrode active material accounts for 60% to 80% by mass, for example, 60%, 65%, 70%, 75%, 80%, etc. The second positive electrode active material accounts for 20% to 40% by mass, for example, 20%, 25%, 30%, 35%, 40%, etc. At this mass ratio, the first positive electrode active material can provide higher stability for the second positive electrode active material layer, preventing thermal runaway of the battery, without significantly reducing the overall capacity and energy density of the second positive electrode active material layer.

[0072] In one embodiment of the present application, the current collector includes two conductive layers and a non-conductive layer disposed between the conductive layers.

[0073] Specifically, to further improve the safety of the positive electrode sheet, a non-conductive layer can be further provided in the current collector. This allows the current collector to form a structure comprising two conductive layers and a non-conductive layer disposed between the conductive layers. By providing a non-conductive layer, in the event of a puncture of the sodium-ion battery, the non-conductive layer can mitigate abnormal phenomena caused by short circuits, thereby improving safety. Furthermore, the non-conductive layer can also, to a certain extent, reduce the contact between the positive electrode active material layer near the current collector and the external environment, further improving the safety of the sodium-ion battery.

[0074] In one embodiment of the present application, the conductive layer includes at least one of aluminum foil, nickel foil, and stainless steel foil; and the non-conductive layer includes non-conductive resin.

[0075] Specifically, the conductive layer can be made of at least one of a conductive metal foil, such as aluminum foil, nickel foil, and stainless steel foil. The non-conductive layer can be made of a non-conductive, lightweight, non-conductive resin, such as PP (polypropylene) and PET (polyethylene terephthalate), which is not limited in this application.

[0076] In one embodiment of the present application, the positive electrode active material layer further includes a conductive agent and / or a binder.

[0077] The conductive agent may be a material that improves the conductivity of the positive electrode active material layer, such as carbon black, carbon nanotubes, graphene, etc., and this application does not impose any restrictions on this.

[0078] The binder can be a material that improves the bonding performance between the positive electrode active material layers and between the positive electrode active material layer and the current collector, such as carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), etc., and this application does not impose any restrictions on this.

[0079] The present invention also provides a method for preparing a positive electrode sheet, the method comprising:

[0080] A first positive electrode active material layer slurry and a second positive electrode active material layer slurry are prepared; the first positive electrode active material layer slurry is disposed on the current collector to form a first positive electrode active material layer; the second positive electrode active material layer slurry is disposed on a side of the first positive electrode active material layer away from the current collector to form a second positive electrode active material layer, thereby obtaining a positive electrode sheet.

[0081] Specifically, the first positive electrode active material and the second positive electrode active material can be mixed in at least two proportions and then added to a positive electrode material solvent to obtain a first positive electrode active material layer slurry and a second positive electrode active material layer slurry for forming different positive electrode active material layers. The positive electrode material solvent can be N-methylpyrrolidone (NMP), ethanol, acetone, water, etc., and this application does not limit this.

[0082] The first positive electrode active material includes a polyanion material; the second positive electrode active material includes a sodium oxide material and / or a Prussian material.

[0083] Optionally, a dispersant may be added to the slurry to facilitate uniform dispersion of the first positive electrode active material and the second positive electrode active material. The dispersant may be, for example, carboxymethyl cellulose (CMC), sodium lauryl sulfate (SDS), polyvinyl alcohol (PVA), etc., and this application does not impose any restrictions thereon.

[0084] Afterwards, different positive electrode coating slurries can be applied layer by layer on the surface of the current collector. As an example of the present application, the first positive electrode active material layer slurry is first placed on the current collector, and the positive electrode coating slurry forms the first positive electrode active material layer after rolling, die-cutting, and baking. Thereafter, the second positive electrode active material layer slurry is placed on the side of the first positive electrode active material layer away from the current collector, and the positive electrode coating slurry forms the second positive electrode active material layer after rolling, die-cutting, and baking to obtain a positive electrode sheet. The first positive electrode active material layer and the second positive electrode active material layer can also be provided at the same time, and the present application does not limit this.

[0085] Among them, in the first positive electrode active material layer, the mass proportion of the first positive electrode active material is smaller than the mass proportion of the second positive electrode active material; in the second positive electrode active material layer, the mass proportion of the first positive electrode active material is greater than the mass proportion of the second positive electrode active material.

[0086] For the positive electrode active material layer close to the current collector, since it is close to the current collector and far away from the electrolyte, the positive electrode active material is less likely to produce side reactions with the electrolyte, affecting the cycle life. In the event of thermal runaway, it is also less likely to react violently with the electrolyte to cause serious phenomena such as fire and explosion. Therefore, the positive electrode active material layer close to the current collector can contain a relatively higher content of the second positive electrode active material, while the content of the first positive electrode active material, which has a lower gram capacity than the second positive electrode active material, can be relatively low, so as to increase the gram capacity of the entire positive electrode sheet.

[0087] As for the positive electrode active material layer away from the current collector, since it is closer to the electrolyte and farther away from the current collector, the positive electrode active material is relatively more likely to produce side reactions with the electrolyte, affecting the cycle life. In the event of thermal runaway, it is also more likely to react violently with the electrolyte, resulting in serious phenomena such as fire and explosion. Therefore, the positive electrode active material layer away from the current collector can contain a relatively higher content of the first positive electrode active material, while the content of the second positive electrode active material, which is less stable than the first positive electrode active material, can be relatively low, to increase side reactions, improve cycle life, and avoid serious phenomena such as fire and explosion.

[0088] Therefore, in the first positive electrode active material layer, the mass proportion of the first positive electrode active material is smaller than the mass proportion of the second positive electrode active material; in the second positive electrode active material layer, the mass proportion of the first positive electrode active material is greater than the mass proportion of the second positive electrode active material, thereby maintaining the overall good capacity and energy density of the positive electrode sheet while effectively improving the safety performance of the positive electrode sheet.

[0089] An embodiment of the present application further provides a battery, which includes a negative electrode material and a positive electrode sheet as in the embodiment of the present application or a positive electrode sheet prepared using the method for preparing the positive electrode sheet as in the embodiment of the present application.

[0090] The negative electrode material includes a negative electrode active material; the negative electrode active material includes at least one of a hard carbon material, a soft carbon material, and a silicon-based material.

[0091] Among them, hard carbon materials can be generally composed of amorphous carbon with a high degree of graphitization. Carbon materials can be generally composed of amorphous carbon with a low degree of graphitization. Both can have a porous structure containing a large number of micropores and mesopores, providing abundant energy storage sites. This can result in a high theoretical capacity, making it easy to obtain sodium-ion batteries with high energy density.

[0092] Silicon-based materials can be composed of silicon and its compounds, such as silicon nanowires, silicon nanoparticles, silicon-carbon composites, etc., which can provide energy storage sites through nanostructures.

[0093] The negative electrode material includes at least one of a conductive agent, a binder, and a dispersant.

[0094] The conductive agent may be a material that improves the conductivity of the negative electrode active material layer, such as carbon black, carbon nanotubes, graphene, etc., and this application does not impose any restrictions on this.

[0095] The binder can be a material that improves the bonding performance between the negative electrode active material layer and the current collector, such as carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), etc., which is not limited in this application.

[0096] The dispersant may be a material that uniformly disperses the various materials in the auxiliary negative electrode active material layer, such as carboxymethyl cellulose (CMC), sodium dodecyl sulfate (SDS), polyvinyl alcohol (PVA), etc., and this application does not impose any limitation on this.

[0097] The batteries of the present application may include battery cells, battery modules, and battery packs. In some embodiments, battery cells may be assembled into a battery module, which may contain one or more battery cells, with the specific number selected by those skilled in the art based on the application and capacity of the battery module. In some embodiments, battery modules may also be assembled into a battery pack, which may contain one or more battery modules, with the specific number selected by those skilled in the art based on the application and capacity of the battery pack.

[0098] The present application also provides an electrical device comprising a battery as described in the present application. Specifically, the electrical device may include, but is not limited to, an electric vehicle, a battery-powered vehicle, a mobile phone, a tablet, a laptop computer, an electric toy, a ship, a spacecraft, and the like. The electric toy may include fixed or mobile electric toys, such as game consoles, electric car toys, electric ship toys, and electric airplane toys, and the spacecraft may include airplanes, rockets, space shuttles, and spacecraft, among others.

[0099] In order to enable those skilled in the art to better understand the present application, the preparation method of the composite battery cell of the present application is described below through multiple specific examples.

[0100] Example 1

[0101] The slurry formula of the first positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 50:50:2:3, and the solid content is 58%.

[0102] The slurry formula of the second positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 80:20:2:3, and the solid content is 58%.

[0103] 1) using polyvinylidene fluoride as a binder and N-methylpyrrolidone as a solvent, uniformly dispersing the binder in the solvent to form a transparent colloidal first solution;

[0104] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the transparent colloidal solution and uniformly dispersing the conductive agent to obtain a second solution;

[0105] 3) Sodium ferric pyrophosphate is used as the first positive electrode active material, and sodium nickel iron manganese oxide is used as the second positive electrode active material. The first positive electrode active material and the second positive electrode active material are added to the second solution in batches to obtain a positive electrode coating slurry.

[0106] 4) The first positive electrode active material layer slurry is coated on the composite aluminum foil current collector, and then rolled, die-cut, and baked to form the first positive electrode active material layer. The second positive electrode active material layer slurry is then coated on the first positive electrode active material layer, and then rolled, die-cut, and baked to form the second positive electrode active material layer to obtain a positive electrode sheet. The total coating area density of the positive electrode sheet is 440g / m 2 The coating amount of the first positive electrode active material layer slurry is the same as that of the second positive electrode active material layer slurry. The composite aluminum foil current collector consists of two aluminum foil layers and a PP / PET composite layer disposed between the aluminum foil layers.

[0107] In the positive electrode sheet, the mass ratio of the first positive electrode active material to the second positive electrode active material is 65:35.

[0108] Preparation of negative electrode materials

[0109] The negative electrode material slurry formula: the mass ratio of negative electrode active material: conductive agent: dispersant: binder is 94.5:1:1.5:3, and the solid content is 48%.

[0110] 1) using sodium carboxymethyl cellulose as a dispersant and water as a solvent, uniformly dispersing the dispersant in the solvent to form a third solution;

[0111] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the third solution and uniformly dispersing the conductive agent to obtain a fourth solution;

[0112] 3) Using hard carbon as the negative electrode active material, the negative electrode active material is added to the fourth solution in batches and dispersed evenly to obtain a fifth solution;

[0113] 4) using styrene-butadiene latex as a binder, adding the binder to the fifth solution and dispersing it evenly to obtain a negative electrode material slurry;

[0114] 5) Apply the negative electrode slurry to the negative electrode current collector with a coating density of 175 g / m 2 , and the negative electrode material is obtained after rolling, die cutting and baking.

[0115] The positive electrode sheet, negative electrode material, and separator are assembled to obtain a composite battery cell. Subsequently, the composite battery cell undergoes welding, shelling, baking, liquid injection (sodium hexafluorophosphate electrolyte), formation, and capacity separation to obtain a sodium ion battery.

[0116] Example 2

[0117] Preparation of positive electrode

[0118] The slurry formula of the first positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 45:55:2:3, and the solid content is 58%.

[0119] The slurry formula of the second positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 75:25:2:3, and the solid content is 58%.

[0120] 1) using polyvinylidene fluoride as a binder and N-methylpyrrolidone as a solvent, uniformly dispersing the binder in the solvent to form a transparent colloidal first solution;

[0121] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the transparent colloidal solution and uniformly dispersing the conductive agent to obtain a second solution;

[0122] 3) Sodium ferric pyrophosphate is used as the first positive electrode active material, and sodium nickel iron manganese oxide is used as the second positive electrode active material. The first positive electrode active material and the second positive electrode active material are added to the second solution in batches to obtain a positive electrode coating slurry.

[0123] 4) The first positive electrode active material layer slurry is coated on the composite aluminum foil current collector, and then rolled, die-cut, and baked to form the first positive electrode active material layer. The second positive electrode active material layer slurry is then coated on the first positive electrode active material layer, and then rolled, die-cut, and baked to form the second positive electrode active material layer to obtain a positive electrode sheet. The total coating area density of the positive electrode sheet is 440g / m 2 The coating amount of the first positive electrode active material layer slurry is the same as that of the second positive electrode active material layer slurry. The composite aluminum foil current collector consists of two aluminum foil layers and a PP / PET composite layer disposed between the aluminum foil layers.

[0124] In the positive electrode sheet, the mass ratio of the first positive electrode active material to the second positive electrode active material is 60:40.

[0125] Preparation of negative electrode materials

[0126] The negative electrode material slurry formula: the mass ratio of negative electrode active material: conductive agent: dispersant: binder is 94.5:1:1.5:3, and the solid content is 48%.

[0127] 1) using sodium carboxymethyl cellulose as a dispersant and water as a solvent, uniformly dispersing the dispersant in the solvent to form a third solution;

[0128] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the third solution and uniformly dispersing the conductive agent to obtain a fourth solution;

[0129] 3) Using hard carbon as the negative electrode active material, the negative electrode active material is added to the fourth solution in batches and dispersed evenly to obtain a fifth solution;

[0130] 4) using styrene-butadiene latex as a binder, adding the binder to the fifth solution and dispersing it evenly to obtain a negative electrode material slurry;

[0131] 5) Apply the negative electrode slurry to the negative electrode current collector with a coating density of 175 g / m 2 , and the negative electrode material is obtained after rolling, die cutting and baking.

[0132] The positive electrode sheet, negative electrode material, and separator are assembled to obtain a composite battery cell. Subsequently, the composite battery cell undergoes welding, shelling, baking, liquid injection (sodium hexafluorophosphate electrolyte), formation, and capacity separation to obtain a sodium ion battery.

[0133] Example 3

[0134] Preparation of positive electrode

[0135] The slurry formula of the first positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 40:60:2:3, and the solid content is 58%.

[0136] The slurry formula of the second positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 70:30:2:3, and the solid content is 58%.

[0137] 1) using polyvinylidene fluoride as a binder and N-methylpyrrolidone as a solvent, uniformly dispersing the binder in the solvent to form a transparent colloidal first solution;

[0138] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the transparent colloidal solution and uniformly dispersing the conductive agent to obtain a second solution;

[0139] 3) Sodium ferric pyrophosphate is used as the first positive electrode active material, and sodium nickel iron manganese oxide is used as the second positive electrode active material. The first positive electrode active material and the second positive electrode active material are added to the second solution in batches to obtain a positive electrode coating slurry.

[0140] 4) The first positive electrode active material layer slurry is coated on the composite aluminum foil current collector, and then rolled, die-cut, and baked to form the first positive electrode active material layer. The second positive electrode active material layer slurry is then coated on the first positive electrode active material layer, and then rolled, die-cut, and baked to form the second positive electrode active material layer to obtain a positive electrode sheet. The total coating area density of the positive electrode sheet is 440g / m 2 The coating amount of the first positive electrode active material layer slurry is the same as that of the second positive electrode active material layer slurry. The composite aluminum foil current collector consists of two aluminum foil layers and a PP / PET composite layer disposed between the aluminum foil layers.

[0141] In the positive electrode sheet, the mass ratio of the first positive electrode active material to the second positive electrode active material is 55:45.

[0142] Preparation of negative electrode materials

[0143] The negative electrode material slurry formula: the mass ratio of negative electrode active material: conductive agent: dispersant: binder is 94.5:1:1.5:3, and the solid content is 48%.

[0144] 1) using sodium carboxymethyl cellulose as a dispersant and water as a solvent, uniformly dispersing the dispersant in the solvent to form a third solution;

[0145] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the third solution and uniformly dispersing the conductive agent to obtain a fourth solution;

[0146] 3) Using hard carbon as the negative electrode active material, the negative electrode active material is added to the fourth solution in batches and dispersed evenly to obtain a fifth solution;

[0147] 4) using styrene-butadiene latex as a binder, adding the binder to the fifth solution and dispersing it evenly to obtain a negative electrode material slurry;

[0148] 5) Apply the negative electrode slurry to the negative electrode current collector with a coating density of 175 g / m 2 , and the negative electrode material is obtained after rolling, die cutting and baking.

[0149] The positive electrode sheet, negative electrode material, and separator are assembled to obtain a composite battery cell. Subsequently, the composite battery cell undergoes welding, shelling, baking, liquid injection (sodium hexafluorophosphate electrolyte), formation, and capacity separation to obtain a sodium ion battery.

[0150] Example 4

[0151] Preparation of positive electrode

[0152] The slurry formula of the first positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 35:65:2:3, and the solid content is 58%.

[0153] The slurry formula of the second positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 65:35:2:3, and the solid content is 58%.

[0154] 1) using polyvinylidene fluoride as a binder and N-methylpyrrolidone as a solvent, uniformly dispersing the binder in the solvent to form a transparent colloidal first solution;

[0155] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the transparent colloidal solution and uniformly dispersing the conductive agent to obtain a second solution;

[0156] 3) Sodium ferric pyrophosphate is used as the first positive electrode active material, and sodium nickel iron manganese oxide is used as the second positive electrode active material. The first positive electrode active material and the second positive electrode active material are added to the second solution in batches to obtain a positive electrode coating slurry.

[0157] 4) The first positive electrode active material layer slurry is coated on the composite aluminum foil current collector, and then rolled, die-cut, and baked to form the first positive electrode active material layer. The second positive electrode active material layer slurry is then coated on the first positive electrode active material layer, and then rolled, die-cut, and baked to form the second positive electrode active material layer to obtain a positive electrode sheet. The total coating area density of the positive electrode sheet is 440g / m 2 The coating amount of the first positive electrode active material layer slurry is the same as that of the second positive electrode active material layer slurry. The composite aluminum foil current collector consists of two aluminum foil layers and a PP / PET composite layer disposed between the aluminum foil layers.

[0158] In the positive electrode sheet, the mass ratio of the first positive electrode active material to the second positive electrode active material is 50:50.

[0159] Preparation of negative electrode materials

[0160] The negative electrode material slurry formula: the mass ratio of negative electrode active material: conductive agent: dispersant: binder is 94.5:1:1.5:3, and the solid content is 48%.

[0161] 1) using sodium carboxymethyl cellulose as a dispersant and water as a solvent, uniformly dispersing the dispersant in the solvent to form a third solution;

[0162] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the third solution and uniformly dispersing the conductive agent to obtain a fourth solution;

[0163] 3) Using hard carbon as the negative electrode active material, the negative electrode active material is added to the fourth solution in batches and dispersed evenly to obtain a fifth solution;

[0164] 4) using styrene-butadiene latex as a binder, adding the binder to the fifth solution and dispersing it evenly to obtain a negative electrode material slurry;

[0165] 5) Apply the negative electrode slurry to the negative electrode current collector with a coating density of 175 g / m 2 , and the negative electrode material is obtained after rolling, die cutting and baking.

[0166] The positive electrode sheet, negative electrode material, and separator are assembled to obtain a composite battery cell. Subsequently, the composite battery cell undergoes welding, shelling, baking, liquid injection (sodium hexafluorophosphate electrolyte), formation, and capacity separation to obtain a sodium ion battery.

[0167] Example 5

[0168] Preparation of positive electrode

[0169] The slurry formula of the first positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 30:70:2:3, and the solid content is 58%.

[0170] The slurry formula of the second positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 60:40:2:3, and the solid content is 58%.

[0171] 1) using polyvinylidene fluoride as a binder and N-methylpyrrolidone as a solvent, uniformly dispersing the binder in the solvent to form a transparent colloidal first solution;

[0172] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the transparent colloidal solution and uniformly dispersing the conductive agent to obtain a second solution;

[0173] 3) Sodium ferric pyrophosphate is used as the first positive electrode active material, and sodium nickel iron manganese oxide is used as the second positive electrode active material. The first positive electrode active material and the second positive electrode active material are added to the second solution in batches to obtain a positive electrode coating slurry.

[0174] 4) The first positive electrode active material layer slurry is coated on the composite aluminum foil current collector, and then rolled, die-cut, and baked to form the first positive electrode active material layer. The second positive electrode active material layer slurry is then coated on the first positive electrode active material layer, and then rolled, die-cut, and baked to form the second positive electrode active material layer to obtain a positive electrode sheet. The total coating area density of the positive electrode sheet is 440g / m 2 The coating amount of the first positive electrode active material layer slurry is the same as that of the second positive electrode active material layer slurry. The composite aluminum foil current collector consists of two aluminum foil layers and a PP / PET composite layer disposed between the aluminum foil layers.

[0175] In the positive electrode sheet, the mass ratio of the first positive electrode active material to the second positive electrode active material is 45:55.

[0176] Preparation of negative electrode materials

[0177] The negative electrode material slurry formula: the mass ratio of negative electrode active material: conductive agent: dispersant: binder is 94.5:1:1.5:3, and the solid content is 48%.

[0178] 1) using sodium carboxymethyl cellulose as a dispersant and water as a solvent, uniformly dispersing the dispersant in the solvent to form a third solution;

[0179] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the third solution and uniformly dispersing the conductive agent to obtain a fourth solution;

[0180] 3) Using hard carbon as the negative electrode active material, the negative electrode active material is added to the fourth solution in batches and dispersed evenly to obtain a fifth solution;

[0181] 4) using styrene-butadiene latex as a binder, adding the binder to the fifth solution and dispersing it evenly to obtain a negative electrode material slurry;

[0182] 5) Apply the negative electrode slurry to the negative electrode current collector with a coating density of 175 g / m 2 , and the negative electrode material is obtained after rolling, die cutting and baking.

[0183] The positive electrode sheet, negative electrode material, and separator are assembled to obtain a composite battery cell. Subsequently, the composite battery cell undergoes welding, shelling, baking, liquid injection (sodium hexafluorophosphate electrolyte), formation, and capacity separation to obtain a sodium ion battery.

[0184] Example 6

[0185] Preparation of positive electrode

[0186] The slurry formula of the first positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 20:80:2:3, and the solid content is 58%.

[0187] The slurry formula of the second positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 60:40:2:3, and the solid content is 58%.

[0188] 1) using polyvinylidene fluoride as a binder and N-methylpyrrolidone as a solvent, uniformly dispersing the binder in the solvent to form a transparent colloidal first solution;

[0189] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the transparent colloidal solution and uniformly dispersing the conductive agent to obtain a second solution;

[0190] 3) Sodium ferric pyrophosphate is used as the first positive electrode active material, and sodium nickel iron manganese oxide is used as the second positive electrode active material. The first positive electrode active material and the second positive electrode active material are added to the second solution in batches to obtain a positive electrode coating slurry.

[0191] 4) The first positive electrode active material layer slurry is coated on the composite aluminum foil current collector, and then rolled, die-cut, and baked to form the first positive electrode active material layer. The second positive electrode active material layer slurry is then coated on the first positive electrode active material layer, and then rolled, die-cut, and baked to form the second positive electrode active material layer to obtain a positive electrode sheet. The total coating area density of the positive electrode sheet is 440g / m 2The coating amount of the first positive electrode active material layer slurry is the same as that of the second positive electrode active material layer slurry. The composite aluminum foil current collector consists of two aluminum foil layers and a PP / PET composite layer disposed between the aluminum foil layers.

[0192] In the positive electrode sheet, the mass ratio of the first positive electrode active material to the second positive electrode active material is 40:60.

[0193] Preparation of negative electrode materials

[0194] The negative electrode material slurry formula: the mass ratio of negative electrode active material: conductive agent: dispersant: binder is 94.5:1:1.5:3, and the solid content is 48%.

[0195] 1) using sodium carboxymethyl cellulose as a dispersant and water as a solvent, uniformly dispersing the dispersant in the solvent to form a third solution;

[0196] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the third solution and uniformly dispersing the conductive agent to obtain a fourth solution;

[0197] 3) Using hard carbon as the negative electrode active material, the negative electrode active material is added to the fourth solution in batches and dispersed evenly to obtain a fifth solution;

[0198] 4) using styrene-butadiene latex as a binder, adding the binder to the fifth solution and dispersing it evenly to obtain a negative electrode material slurry;

[0199] 5) Apply the negative electrode slurry to the negative electrode current collector with a coating density of 175 g / m 2 , and the negative electrode material is obtained after rolling, die cutting and baking.

[0200] The positive electrode sheet, negative electrode material, and separator are assembled to obtain a composite battery cell. Subsequently, the composite battery cell undergoes welding, shelling, baking, liquid injection (sodium hexafluorophosphate electrolyte), formation, and capacity separation to obtain a sodium ion battery.

[0201] Example 7

[0202] Preparation of positive electrode

[0203] The slurry formula of the first positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 50:50:2:3, and the solid content is 58%.

[0204] The slurry formula of the second positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 80:20:2:3, and the solid content is 58%.

[0205] 1) using polyvinylidene fluoride as a binder and N-methylpyrrolidone as a solvent, uniformly dispersing the binder in the solvent to form a transparent colloidal first solution;

[0206] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the transparent colloidal solution and uniformly dispersing the conductive agent to obtain a second solution;

[0207] 3) Sodium ferric pyrophosphate is used as the first positive electrode active material, and sodium nickel iron manganese oxide is used as the second positive electrode active material. The first positive electrode active material and the second positive electrode active material are added to the second solution in batches to obtain a positive electrode coating slurry.

[0208] 4) The first positive electrode active material layer slurry is coated on the aluminum foil current collector, and then rolled, die-cut, and baked to form the first positive electrode active material layer. The second positive electrode active material layer slurry is then coated on the first positive electrode active material layer, and then rolled, die-cut, and baked to form the second positive electrode active material layer to obtain a positive electrode sheet. The total coating area density of the positive electrode sheet is 440g / m 2 The coating amount of the first positive electrode active material layer slurry is the same as that of the second positive electrode active material layer slurry.

[0209] In the positive electrode sheet, the mass ratio of the first positive electrode active material to the second positive electrode active material is 65:35.

[0210] Preparation of negative electrode materials

[0211] The negative electrode material slurry formula: the mass ratio of negative electrode active material: conductive agent: dispersant: binder is 94.5:1:1.5:3, and the solid content is 48%.

[0212] 1) using sodium carboxymethyl cellulose as a dispersant and water as a solvent, uniformly dispersing the dispersant in the solvent to form a third solution;

[0213] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the third solution and uniformly dispersing the conductive agent to obtain a fourth solution;

[0214] 3) Using hard carbon as the negative electrode active material, the negative electrode active material is added to the fourth solution in batches and dispersed evenly to obtain a fifth solution;

[0215] 4) using styrene-butadiene latex as a binder, adding the binder to the fifth solution and dispersing it evenly to obtain a negative electrode material slurry;

[0216] 5) Apply the negative electrode slurry to the negative electrode current collector with a coating density of 175 g / m 2 , and the negative electrode material is obtained after rolling, die cutting and baking.

[0217] The positive electrode sheet, negative electrode material, and separator are assembled to obtain a composite battery cell. Subsequently, the composite battery cell undergoes welding, shelling, baking, liquid injection (sodium hexafluorophosphate electrolyte), formation, and capacity separation to obtain a sodium ion battery.

[0218] Comparative Example 1

[0219] Preparation of positive electrode

[0220] The slurry formula of the first positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 60:40:2:3, and the solid content is 58%.

[0221] The slurry formula of the second positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 10:90:2:3, and the solid content is 58%.

[0222] 1) using polyvinylidene fluoride as a binder and N-methylpyrrolidone as a solvent, uniformly dispersing the binder in the solvent to form a transparent colloidal first solution;

[0223] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the transparent colloidal solution and uniformly dispersing the conductive agent to obtain a second solution;

[0224] 3) Sodium ferric pyrophosphate is used as the first positive electrode active material, and sodium nickel iron manganese oxide is used as the second positive electrode active material. The first positive electrode active material and the second positive electrode active material are added to the second solution in batches to obtain a positive electrode coating slurry.

[0225] 4) The first positive electrode active material layer slurry is coated on the composite aluminum foil current collector, and then rolled, die-cut, and baked to form the first positive electrode active material layer. The second positive electrode active material layer slurry is then coated on the first positive electrode active material layer, and then rolled, die-cut, and baked to form the second positive electrode active material layer to obtain a positive electrode sheet. The total coating area density of the positive electrode sheet is 440g / m 2 The coating amount of the first positive electrode active material layer slurry is the same as that of the second positive electrode active material layer slurry. The composite aluminum foil current collector consists of two aluminum foil layers and a PP / PET composite layer disposed between the aluminum foil layers.

[0226] Preparation of negative electrode materials

[0227] The negative electrode material slurry formula: the mass ratio of negative electrode active material: conductive agent: dispersant: binder is 94.5:1:1.5:3, and the solid content is 48%.

[0228] 1) using sodium carboxymethyl cellulose as a dispersant and water as a solvent, uniformly dispersing the dispersant in the solvent to form a third solution;

[0229] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the third solution and uniformly dispersing the conductive agent to obtain a fourth solution;

[0230] 3) Using hard carbon as the negative electrode active material, the negative electrode active material is added to the fourth solution in batches and dispersed evenly to obtain a fifth solution;

[0231] 4) using styrene-butadiene latex as a binder, adding the binder to the fifth solution and dispersing it evenly to obtain a negative electrode material slurry;

[0232] 5) Apply the negative electrode slurry to the negative electrode current collector with a coating density of 175 g / m 2 , and the negative electrode material is obtained after rolling, die cutting and baking.

[0233] The positive electrode sheet, negative electrode material, and separator are assembled to obtain a composite battery cell. Subsequently, the composite battery cell undergoes welding, shelling, baking, liquid injection (sodium hexafluorophosphate electrolyte), formation, and capacity separation to obtain a sodium ion battery.

[0234] Comparative Example 2

[0235] Preparation of positive electrode

[0236] The slurry formula of the first positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 80:20:2:3, and the solid content is 58%.

[0237] The slurry formula of the second positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 50:50:2:3, and the solid content is 58%.

[0238] 1) using polyvinylidene fluoride as a binder and N-methylpyrrolidone as a solvent, uniformly dispersing the binder in the solvent to form a transparent colloidal first solution;

[0239] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the transparent colloidal solution and uniformly dispersing the conductive agent to obtain a second solution;

[0240] 3) Sodium ferric pyrophosphate is used as the first positive electrode active material, and sodium nickel iron manganese oxide is used as the second positive electrode active material. The first positive electrode active material and the second positive electrode active material are added to the second solution in batches to obtain a positive electrode coating slurry.

[0241] 4) The first positive electrode active material layer slurry is coated on the composite aluminum foil current collector, and then rolled, die-cut, and baked to form the first positive electrode active material layer. The second positive electrode active material layer slurry is then coated on the first positive electrode active material layer, and then rolled, die-cut, and baked to form the second positive electrode active material layer to obtain a positive electrode sheet. The total coating area density of the positive electrode sheet is 440g / m2 The coating amount of the first positive electrode active material layer slurry is the same as that of the second positive electrode active material layer slurry. The composite aluminum foil current collector consists of two aluminum foil layers and a PP / PET composite layer disposed between the aluminum foil layers.

[0242] Preparation of negative electrode materials

[0243] The negative electrode material slurry formula: the mass ratio of negative electrode active material: conductive agent: dispersant: binder is 94.5:1:1.5:3, and the solid content is 48%.

[0244] 1) using sodium carboxymethyl cellulose as a dispersant and water as a solvent, uniformly dispersing the dispersant in the solvent to form a third solution;

[0245] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the third solution and uniformly dispersing the conductive agent to obtain a fourth solution;

[0246] 3) Using hard carbon as the negative electrode active material, the negative electrode active material is added to the fourth solution in batches and dispersed evenly to obtain a fifth solution;

[0247] 4) using styrene-butadiene latex as a binder, adding the binder to the fifth solution and dispersing it evenly to obtain a negative electrode material slurry;

[0248] 5) Apply the negative electrode slurry to the negative electrode current collector with a coating density of 175 g / m 2 , and the negative electrode material is obtained after rolling, die cutting and baking.

[0249] The positive electrode sheet, negative electrode material, and separator are assembled to obtain a composite battery cell. Subsequently, the composite battery cell undergoes welding, shelling, baking, liquid injection (sodium hexafluorophosphate electrolyte), formation, and capacity separation to obtain a sodium ion battery.

[0250] Comparative Example 3

[0251] Preparation of positive electrode

[0252] The slurry formula of the first positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 80:20:2:3, and the solid content is 58%.

[0253] The slurry formula of the second positive electrode active material layer is as follows: the mass ratio of the first positive electrode active material: the second positive electrode active material: the conductive agent: the binder is 50:50:2:3, and the solid content is 58%.

[0254] 1) using polyvinylidene fluoride as a binder and N-methylpyrrolidone as a solvent, uniformly dispersing the binder in the solvent to form a transparent colloidal first solution;

[0255] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the transparent colloidal solution and uniformly dispersing the conductive agent to obtain a second solution;

[0256] 3) Sodium ferric pyrophosphate is used as the first positive electrode active material, and sodium nickel iron manganese oxide is used as the second positive electrode active material. The first positive electrode active material and the second positive electrode active material are added to the second solution in batches to obtain a positive electrode coating slurry.

[0257] 4) The first positive electrode active material layer slurry is coated on the aluminum foil current collector, and then rolled, die-cut, and baked to form the first positive electrode active material layer. The second positive electrode active material layer slurry is then coated on the first positive electrode active material layer, and then rolled, die-cut, and baked to form the second positive electrode active material layer to obtain a positive electrode sheet. The total coating area density of the positive electrode sheet is 440g / m 2 The coating amount of the first positive electrode active material layer slurry is the same as that of the second positive electrode active material layer slurry. The composite aluminum foil current collector consists of two aluminum foil layers and a PP / PET composite layer disposed between the aluminum foil layers.

[0258] Preparation of negative electrode materials

[0259] The negative electrode material slurry formula: the mass ratio of negative electrode active material: conductive agent: dispersant: binder is 94.5:1:1.5:3, and the solid content is 48%.

[0260] 1) using sodium carboxymethyl cellulose as a dispersant and water as a solvent, uniformly dispersing the dispersant in the solvent to form a third solution;

[0261] 2) using conductive carbon black as a conductive agent, adding the conductive agent to the third solution and uniformly dispersing the conductive agent to obtain a fourth solution;

[0262] 3) Using hard carbon as the negative electrode active material, the negative electrode active material is added to the fourth solution in batches and dispersed evenly to obtain a fifth solution;

[0263] 4) using styrene-butadiene latex as a binder, adding the binder to the fifth solution and dispersing it evenly to obtain a negative electrode material slurry;

[0264] 5) Apply the negative electrode slurry to the negative electrode current collector with a coating density of 175 g / m 2 , and the negative electrode material is obtained after rolling, die cutting and baking.

[0265] The positive electrode sheet, negative electrode material, and separator are assembled to obtain a composite battery cell. Subsequently, the composite battery cell undergoes welding, shelling, baking, liquid injection (sodium hexafluorophosphate electrolyte), formation, and capacity separation to obtain a sodium ion battery.

[0266] The sodium ion batteries prepared in Example 1, Example 2, and Comparative Example 1 were subjected to a steel needle penetration test to test the safety of the sodium ion batteries. The results are shown in Figures 2(a), 2(b), and 2(c).

[0267] It can be seen that Figure 2(a) is the puncture test result of Example 1. In Example 1, the mass ratio of sodium nickel iron manganese oxide with higher gram capacity in the positive electrode layer is higher. The mass ratio of sodium ferric pyrophosphate to sodium nickel iron manganese oxide in the first positive electrode active material layer is greater than the mass ratio of sodium ferric pyrophosphate to sodium nickel iron manganese oxide in the second positive electrode active material layer. Although a composite current collector is used, it cannot pass the puncture test and catches fire after being pierced by a steel needle.

[0268] Figure 2(b) is the puncture test result of Example 1. The mass proportion of sodium nickel iron manganese oxide with higher gram capacity in Example 1 in the positive electrode layer is lower than that in Comparative Example 1. The mass ratio of sodium ferric pyrophosphate to sodium nickel iron manganese oxide in the first positive electrode active material layer is less than the mass ratio of sodium ferric pyrophosphate to sodium nickel iron manganese oxide in the second positive electrode active material layer. The current collector is set with a composite aluminum foil, which can pass the puncture test without fire or explosion.

[0269] Figure 2(c) is the puncture test result of Example 2. The mass proportion of sodium nickel iron manganese oxide with higher gram capacity in Example 2 in the positive electrode layer is higher than that in Example 1. The current collector is set with a composite aluminum foil. The mass proportion of sodium nickel iron manganese oxide in the positive electrode layer close to the current collector is larger, while the mass proportion of sodium nickel iron manganese oxide in the positive electrode layer far from the current collector is smaller, and the mass proportion of sodium ferric pyrophosphate is larger. It can pass the puncture test while maintaining a higher capacity without fire or explosion.

[0270] Test method:

[0271] Battery energy density: Charge the battery to 3.6V at 1 / 3C constant current at 25°C, let it rest for 30 minutes, then discharge it to 2.0V at 1C constant current. This measurement is the average of the three charge values. Energy density / battery mass = energy density (Wh / Kg).

[0272] Cycle capacity retention rate: 1) 25℃ cycle capacity test: Charge to 3.6V at 1 / 3C constant current at 25℃, let stand for 30 minutes, then discharge to 2.0V at 1C constant current. The number of cycles is 300. The cycle capacity retention rate is calculated by dividing the capacity after 300 cycles C300 by the initial capacity C0.

[0273] Table 1 Battery energy density and cycle capacity retention test results

[0274]

[0275]

[0276] It can be seen that the energy density of the batteries of Examples 1 to 7 is not less than that of Comparative Examples 2 to 3. Examples 1 to 7 can maintain a good energy density, and at the same time, the battery cycle capacity retention rate is better than that of Comparative Examples 2 to 3. This shows that the method provided by the embodiments of the present invention in which the positive electrode sheet can contain more second positive electrode active material on the side close to the current collector and more first positive electrode active material on the side away from the current collector can make the battery have both good energy density and cycle capacity retention rate.

[0277] Comparing Example 1 with Example 7, it can be seen that Example 1, by providing a composite aluminum foil current collector, protects the positive electrode sheet from external environmental influences, thereby slightly improving its cycle capacity retention. Furthermore, the composite aluminum foil current collector further improves the safety of the positive electrode sheet, with Example 1 safely passing the needle penetration test, while Example 7 failed.

[0278] By comparing Example 1 with Comparative Example 2, it can be seen that Example 1 of the present application can effectively improve the battery cycle energy retention rate by arranging that the side close to the current collector can contain more second positive electrode active material, and the side away from the current collector can contain more first positive electrode active material, while the content of the first positive electrode active material and the second positive electrode active material in the positive electrode sheet is the same as that in Comparative Example 2.

[0279] Furthermore, it can be seen from Comparative Example 1 that when more second positive electrode active materials are provided in the positive electrode sheet, although the energy density is improved to a certain extent, since the second positive electrode active material with higher reaction activity is closer to the current collector, the cycle capacity retention rate is worse than that of the embodiment and cannot pass the needle puncture test.

[0280] It can be seen from Examples 1 to 6 that the positive electrode sheet provided in the embodiments of the present application can contain more second positive electrode active material on the side close to the current collector, and can contain more first positive electrode active material on the side away from the current collector. When the content of the second positive electrode active material with higher reaction activity in the positive electrode sheet is increased, since the second positive electrode active material can be relatively close to the current collector and away from the electrolyte, the safety of the battery can be improved to a certain extent, and the battery can pass the pinhole test while maintaining good energy density and cycle capacity retention rate.

[0281] The above is a detailed introduction to a positive electrode sheet and its preparation method, battery and electrical equipment provided by the present application. Specific examples are used in this article to illustrate the principles and implementation methods of the present application. The description of the above embodiments is only used to help understand the method of the present application and its core idea; at the same time, for general technical personnel in this field, based on the ideas of the present application, there will be changes in the specific implementation methods and application scope. In summary, the content of this specification should not be understood as a limitation on the present application.

Claims

1. A positive electrode sheet, characterized in that: The positive electrode sheet includes a current collector and a positive electrode active material layer disposed on at least one side of the current collector, wherein the positive electrode active material layer includes a first positive electrode active material and a second positive electrode active material, wherein the first positive electrode active material includes a polyanion material; and the second positive electrode active material includes a sodium oxide-containing material and / or a Prussian material. In the positive electrode active material layer, a mass ratio of the first positive electrode active material to the second positive electrode active material on a side close to the current collector is smaller than a mass ratio of the first positive electrode active material to the second positive electrode active material on a side far from the current collector.

2. The positive electrode sheet according to claim 1, characterized in that In the positive electrode active material layer, the mass ratio of the first positive electrode active material to the second positive electrode active material is (40-65):(35-60).

3. The positive electrode sheet according to claim 1, characterized in that The positive electrode active material layer comprises at least: a first positive electrode active material layer, the first positive electrode active material layer being disposed on at least one side of the current collector, the first positive electrode active material layer comprising the first positive electrode active material and the second positive electrode active material; a second positive electrode active material layer, the second positive electrode active material layer being disposed on a side of the first positive electrode active material layer away from the current collector, the second positive electrode active material layer comprising the first positive electrode active material and the second positive electrode active material; The mass ratio of the first positive electrode active material to the second positive electrode active material in the first positive electrode active material layer is smaller than the mass ratio of the first positive electrode active material to the second positive electrode active material in the second positive electrode active material layer.

4. The positive electrode sheet according to claim 3, characterized in that In the first positive electrode active material layer, the mass proportion of the first positive electrode active material is less than the mass proportion of the second positive electrode active material; and / or, in the second positive electrode active material layer, the mass proportion of the first positive electrode active material is greater than the mass proportion of the second positive electrode active material.

5. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The polyanion material includes at least one of sodium ferric phosphate, sodium vanadium fluorophosphate, sodium ferric phosphate and sodium ferric pyrophosphate.

6. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The sodium oxide material includes at least one of sodium nickel iron manganate, sodium nickel manganate, sodium manganese iron, and sodium copper iron manganate.

7. The positive electrode sheet according to claim 3 or 4, characterized in that: In the first positive electrode active material layer, the mass proportion of the first positive electrode active material is 20% to 50%; the mass proportion of the second positive electrode active material is 50% to 80%; and / or, in the second positive electrode active material layer, the mass proportion of the first positive electrode active material is 60% to 80%, and the mass proportion of the second positive electrode active material is 20% to 40%.

8. The positive electrode sheet according to any one of claims 1 to 4, characterized in that: The current collector includes two conductive layers and a non-conductive layer arranged between the two conductive layers.

9. The positive electrode sheet according to claim 8, characterized in that: The conductive layer includes at least one of aluminum foil, nickel foil, and stainless steel foil; and the non-conductive layer includes non-conductive resin.

10. A battery, characterized in that: The battery comprises the positive electrode sheet according to any one of claims 1 to 9.

11. The battery according to claim 10, characterized in that The battery includes a negative electrode sheet, and the negative electrode sheet includes a negative electrode active material; the negative electrode active material includes at least one of a hard carbon material, a soft carbon material, and a silicon-based material.

12. The battery according to claim 11, characterized in that The negative electrode sheet includes a conductive agent and / or a binder.

13. An electrical device, characterized in that: The electrical device comprises the battery according to any one of claims 10 to 12.

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