Positive electrode active material and preparation method therefor, positive electrode sheet and battery

Abstract

Provided in the present invention are a positive electrode active material and a preparation method therefor, a positive electrode sheet and a battery. The positive electrode active material sequentially comprises, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer and a carbon material, wherein the core comprises manganese ions having a valence state of not less than tetravalent; the intermediate layer comprises trivalent manganese ions and tetravalent manganese ions, and in the intermediate layer, the concentration of the trivalent manganese ions decreases gradually in a direction from a region adjacent to the outer shell layer toward a region adjacent to the core; and the outer shell layer comprises a fast ion conductor. The positive electrode active material provided in the present invention can have an improved interface stability and inhibit the dissolution of manganese, while ensuring the diffusion rate of lithium ions, thus enabling a battery to have an excellent rate performance, cycling performance, storage stability, etc.

Description

A positive electrode active material and its preparation method, positive electrode sheet, and battery

[0001] This application claims priority to Chinese Patent Application No. 202411920099.7, filed on December 24, 2024, entitled "A positive electrode active material and its preparation method, positive electrode sheet, battery", the entire contents of which are incorporated herein by reference. Technical Field

[0002] This invention relates to the field of battery technology, and in particular to a positive electrode active material and its preparation method, a positive electrode sheet, and a battery. Background Technology

[0003] Lithium-ion batteries have become the preferred power source for mobile electronic devices and electric vehicles due to their high energy density, long lifespan, and good environmental stability. Among lithium-ion battery cathode materials, lithium nickel manganese oxide has become one of the most popular high-energy-density lithium-ion batteries in recent years due to its advantages such as high voltage platform, high specific energy, and low watt-hour cost.

[0004] However, under high voltage, the unstable interface of lithium nickel manganese oxide cathode material and manganese dissolution are the main problems hindering its commercialization. Specifically, during the charging process, highly oxidized Ni4+ and commercial carbonate-based electrolytes are unstable under the electrochemical window, resulting in the formation of a solid electrolyte interphase (SEI) film on the surface of the anode material, which increases the anode impedance. In addition, due to the high surface activity of lithium nickel manganese oxide active material, side reactions occur with fluorine-containing electrolytes, which easily cause trivalent manganese to undergo disproportionation reaction to generate divalent manganese. As the voltage increases during charging, manganese dissolution increases, the manganese content deposited on the anode increases, until the active material is depleted, ultimately leading to rapid battery degradation and failure.

[0005] To address the issues of unstable interface stability and manganese dissolution in lithium nickel manganese oxide cathode materials, researchers have attempted to reduce interfacial reactions and manganese dissolution by coating the surface of the lithium nickel manganese oxide cathode material with a layer of aluminum oxide or titanium oxide. While these methods can improve the interfacial stability and inhibit manganese dissolution to some extent, the low chemical activity of the coating agent leads to slower lithium-ion diffusion and deteriorated rate performance. Summary of the Invention

[0006] This invention provides a positive electrode active material, which, from the center to the surface, sequentially comprises a core, an intermediate layer, an outer shell layer, and a carbon material. The intermediate layer, due to the presence of trivalent manganese, can improve the overall electronic conductivity of the positive electrode active material. The presence of the outer shell layer and the carbon material can further improve the ionic conductivity and electronic conductivity, which is beneficial to the rapid lithium insertion / extraction behavior and prevents the electrolyte from directly contacting the intermediate layer, thereby improving the interfacial stability of the positive electrode active material and inhibiting the dissolution of manganese.

[0007] The present invention also provides a method for preparing the above-mentioned positive electrode active material, which can obtain the above-mentioned positive electrode active material and is simple to operate.

[0008] The present invention also provides a positive electrode sheet comprising the above-mentioned positive electrode active material, which is beneficial to ensuring the overall rate performance, cycle performance and storage effect of the battery.

[0009] The present invention also provides a battery comprising the above-mentioned positive electrode, which has excellent rate performance, cycle performance, storage stability, etc.

[0010] In detail, in a first aspect, the present invention provides a positive electrode active material, which, in a direction from the center to the surface, sequentially comprises a core, an intermediate layer, an outer shell layer, and a carbon material. The core comprises manganese ions with a valence state not lower than +4, the intermediate layer comprises +3 and +4 manganese ions, and the concentration of +3 manganese ions in the intermediate layer decreases from the adjacent outer shell layer to the adjacent core. The outer shell layer comprises a fast ion conductor.

[0011] Furthermore, the total thickness of the core, intermediate layer, and outer shell is m, and the thickness of the intermediate layer is n, where 0.002 ≤ n / m ≤ 0.1;

[0012] And / or, in the positive electrode active material, the mass concentration of trivalent manganese ions is 0.5-50 g / L.

[0013] Furthermore, the thickness of the core is 3-20 μm;

[0014] And / or, the thickness of the intermediate layer is 0.05-0.3 μm;

[0015] And / or, the thickness of the outer shell layer is 0.08-0.5 μm;

[0016] And / or, the carbon material includes at least one of carbon nanotubes, Ketjen black, porous carbon particles, carbon black, activated carbon fiber, and carbon nanotube onion.

[0017] Furthermore, the core and the intermediate layer comprise an ordered lithium nickel manganese oxide material.

[0018] Furthermore, the core and / or the intermediate layer also include disordered lithium nickel manganese oxide.

[0019] Furthermore, the content of the disordered lithium nickel manganese oxide is 1-10%.

[0020] Furthermore, the chemical composition of the core includes: Li a1 Ni 0.5+b1 Mn 1.5+c1 Od1 ;

[0021] Wherein, 0.95≤a1≤1.25, -0.2≤b1≤0.2, -0.2≤c1≤0.2, 3.8≤d1≤4.2;

[0022] The chemical composition of the intermediate layer includes: Li a2 Ni 0.5+b2 Mn 1.5+c2 O d2 ;

[0023] Wherein, 0.95≤a2≤1.25, -0.2≤b2≤0.2, -0.15≤c2≤0.25, 3.7≤d2≤4.1, and c2≥c1, d2≤d1;

[0024] And / or, the fast ion conductor includes at least one of lithium aluminum titanium phosphate, lithium phosphate, lithium borate, lithium titanate, lithium zirconate, lithium zirconium phosphate, lithium lanthanum titanate, lithium lanthanum zirconate, and lithium aluminum germanium phosphate.

[0025] Furthermore, the positive electrode active material is a single crystal material, and the particle size of the positive electrode active material is 3μm to 10μm; or, the positive electrode active material is a polycrystalline material, and the particle size of the positive electrode active material is 8μm to 20μm.

[0026] In a second aspect, the present invention provides a method for preparing a positive electrode active material as described in the first aspect, comprising the following steps:

[0027] A positive electrode active material precursor with an order degree of ≥95% is mixed with a solution containing fast ion conductors, and then separated after stirring. The resulting solid is sintered once at 500℃~950℃ to obtain a first-sintered product.

[0028] The calcined product is mixed with a carbon source, and the resulting mixture is subjected to secondary sintering at 100℃~600℃ to obtain the positive electrode active material.

[0029] The chemical composition of the positive electrode active material precursor includes: Li a Ni 0.5+b Mn 1.5+c O d ;

[0030] Wherein, 0.95≤a≤1.25, -0.2≤b≤0.2, -0.2≤c≤0.2, 3.8≤d≤4.2; the carbon source accounts for 0.3-3.5% of the mass percentage of the calcined product.

[0031] Furthermore, the specific surface area of ​​the carbon source is 800-1600 m². 2 / g, with a porosity of 70-95%;

[0032] And / or, the secondary sintering is carried out in a protective atmosphere.

[0033] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a current collector and a positive electrode active material layer coated on at least one surface of the current collector, the positive electrode active material layer comprising the positive electrode active material described in the first aspect.

[0034] Fourthly, the present invention provides a battery comprising a negative electrode and a positive electrode as described in the third aspect.

[0035] The positive electrode active material provided by this invention can improve the interfacial stability of the positive electrode active material and inhibit manganese dissolution while ensuring the lithium-ion diffusion rate. This results in excellent rate performance, cycle performance, and storage stability of the battery. Specifically, while the presence of trivalent manganese on the surface of traditional positive electrode active materials can improve the electronic conductivity and increase the specific capacity to some extent, trivalent manganese is prone to disproportionation reactions, and the resulting divalent manganese has high solubility in the electrolyte. These factors can lead to manganese dissolution and loss, thus affecting the cycle life of the battery. In contrast, this invention sets trivalent and tetravalent manganese ions in the intermediate layer outside the core, and then sets an outer shell layer including fast ion conductors outside the intermediate layer. The concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core, which can prevent the electrolyte from directly contacting the intermediate layer, thereby effectively avoiding the dissolution and loss of manganese. Furthermore, the outer shell layer can also work synergistically with carbon materials to improve the ion conduction channels, thereby further promoting the rapid insertion and extraction of lithium ions during charging and discharging. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the accompanying drawings used in the description of the embodiments of the present invention or related technologies are briefly introduced below. Obviously, the drawings described below are merely some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 is a schematic diagram of the structure of a positive electrode active material according to a specific embodiment of the present invention;

[0038] Figure 2 is a microscopic morphology diagram of the positive electrode active material in Example 1 of the present invention;

[0039] Figure 3 is the XRD pattern of the positive electrode active material of Example 1 of the present invention;

[0040] Figure 4 shows the XRD pattern of the positive electrode active material of Example 9 of the present invention;

[0041] Figure 5 shows the microstructure of the positive electrode active material of Comparative Example 1 of the present invention.

[0042] Figure 6 shows the charge-discharge curves of the batteries assembled with the positive electrode active materials of Example 1 and Comparative Example 1 of the present invention. Detailed Implementation

[0043] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0044] In a first aspect, the present invention provides a positive electrode active material, as shown in FIG1. ​​The positive electrode active material comprises, in sequence from the center to the surface, a core 01, an intermediate layer 02, an outer shell layer 03 and a carbon material 04. The core comprises manganese ions with a valence state not lower than tetravalent. The intermediate layer comprises trivalent manganese ions and tetravalent manganese ions. In the intermediate layer, the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. The outer shell layer comprises a fast ion conductor.

[0045] In this invention, by setting a core, intermediate layer, outer shell layer, and carbon material, the interfacial stability of the positive electrode active material and the suppression of manganese dissolution can be improved while ensuring the lithium-ion diffusion rate. This results in excellent rate performance, cycle performance, and storage stability of the battery. The main reasons include the presence of trivalent manganese; the electronic conductivity of disordered nickel-manganese is 2-3 orders of magnitude higher than that of ordered nickel-manganese, which can increase the specific capacity to some extent. However, trivalent manganese is prone to disproportionation reaction (2Mn). 3+ →Mn 2+ +Mn 4+The generated divalent manganese dissolves in the electrolyte and reacts with lithium ions in the SEI film formed on the negative electrode, occupying part of the lithium ion channels. This further leads to a rapid capacity decay during the cycling of lithium nickel manganese oxide, affecting the battery's lifespan. This invention discovers that by setting tetravalent manganese ions in the core, trivalent and tetravalent manganese ions in the intermediate layer, and then setting an outer shell layer including fast ion conductors outside the intermediate layer, and by making the concentration of trivalent manganese ions decrease from the adjacent outer shell layer to the adjacent core, on the one hand, adding an appropriate amount of trivalent manganese on the nickel-manganese surface can increase the 4V platform, reduce powder resistance, and provide a faster transport channel for lithium ions; on the other hand, it prevents direct contact between the electrolyte and the intermediate layer, inhibits the occurrence of disproportionation reaction near the surface of the active material and the decomposition of the electrolyte, and does not affect manganese ions in the bulk phase, maintaining the structural stability of spinel nickel-manganese, thereby effectively avoiding the dissolution and loss of manganese; the outer shell layer can also work synergistically with carbon materials to improve the ion conduction and electron conduction channels, thereby further promoting the rapid insertion and extraction of lithium ions during charging and discharging, improving rate performance. In addition, carbon materials with a certain specific surface area and porosity can also adsorb manganese ions in the electrolyte, effectively inhibiting the dissolution of manganese, thereby improving cycle storage performance.

[0046] It is understood that the carbon material is located on at least a portion of the surface of the outer shell layer. As for the morphology of the carbon material, the present invention does not make any particular limitation. In some embodiments, the carbon material is carbon particles and / or carbon nanotubes.

[0047] The concentration of trivalent manganese ions decreases from the vicinity of the outer shell to the vicinity of the core, and can be tested using the following methods:

[0048] The coated sample was etched with 1 mol / L nitric acid solution for 20–60 min. The specific etching depth was the thickness of the intermediate layer measured by transmission electron microscopy. Materials with different etching depths were characterized by X-ray photoelectron spectroscopy (XPS) to quantitatively determine the content of trivalent manganese.

[0049] In one specific embodiment, the total thickness of the core, intermediate layer, and outer shell is m, and the thickness of the intermediate layer is n, wherein 0.002 ≤ n / m ≤ 0.1;

[0050] And / or, in the positive electrode active material, the mass concentration of trivalent manganese ions is 0.5-50 g / L.

[0051] The above implementation method, by controlling the appropriate proportion of trivalent manganese in the intermediate layer, can reduce the occurrence of disproportionation reaction while improving conductivity. In addition, the outer shell layer is slightly thicker than the intermediate layer, which can effectively block the direct contact between the electrolyte and the surface and reduce unnecessary side reactions.

[0052] The testing method for m is as follows: First, anhydrous ethanol is used to disperse the positive electrode active material powder sample. Then, field emission transmission electron microscopy (Talos F200X, Thermo Fisher Scientific, USA) is used to characterize the thickness of the positive electrode active material. The accelerating voltage for the test is 60 kV. The testing method for n includes: first, acid etching is used to etch different thicknesses of the positive electrode active material. Then, X-ray photoelectron spectroscopy (XPS) is used to test the signal of trivalent manganese until the signal disappears. The thickness corresponding to this point is the thickness n of the intermediate layer.

[0053] In the above-mentioned positive electrode active material, the mass concentration of trivalent manganese ions can be understood as the average mass concentration of trivalent manganese ions in the positive electrode active material. The positive electrode active material can be directly characterized by X-ray photoelectron spectroscopy (XPS) to quantitatively determine the content of trivalent manganese.

[0054] To further improve the interfacial stability of the positive electrode active material, in one specific embodiment, the thickness of the core is 3-20 μm;

[0055] And / or, the thickness of the intermediate layer is 0.05-0.3 μm;

[0056] And / or, the thickness of the outer shell layer is 0.08-0.5 μm.

[0057] In one specific embodiment, the carbon material includes at least one of carbon nanotubes, Ketjen black, porous carbon particles, carbon black, activated carbon fiber, and carbon nanotube onion.

[0058] The carbon materials mentioned above can not only improve the conductivity of the positive electrode active material surface, but also adsorb Mn dissolved in the electrolyte. 2+ This reduces manganese deposition at the negative electrode, thereby further stabilizing the positive electrode active material.

[0059] In one specific embodiment, the specific surface area of ​​the positive electrode active material is 1-3 m². 2 / g; porosity 1-10%.

[0060] The positive electrode active material with the above specific surface area can provide more active sites, which helps to improve the electrochemical reaction rate and thus improve the rate performance of the battery. Meanwhile, appropriate porosity provides channels for lithium-ion transport, reduces diffusion resistance, and promotes electrolyte penetration, thereby improving the reaction rate.

[0061] In some embodiments, the specific surface area and pore volume of the positive electrode active material sample can be directly measured using a specific surface area-pore size analyzer (Best 3H-2000BET-A). The porosity is equal to the pore volume divided by the total volume of the sample.

[0062] In some embodiments, the outer surface of the outer shell layer is relatively smooth, which is within any 1 μm.2 The height difference within the area is no greater than 0.1 μm.

[0063] The smooth outer shell layer can further reduce the direct contact between the electrolyte and the positive electrode material, thereby reducing the incidence of side reactions, which helps to further improve the cycle life of the battery.

[0064] In one specific embodiment, the core and intermediate layer comprise an ordered lithium nickel manganese oxide material.

[0065] The positive electrode active material described above has a wide 4V plateau, which reduces the average voltage of the battery, thereby further increasing the cycle stability of the battery.

[0066] Ordered lithium nickel manganese oxide typically has a cubic spinel structure with space group P4332, where lithium ions occupy octahedral sites. Disordered lithium nickel manganese oxide has space group Fd3m and also has a cubic spinel structure, but the nickel and manganese ions are randomly distributed in the lattice. Ordered lithium nickel manganese oxide usually has a higher energy density because of its higher voltage plateau, while disordered lithium nickel manganese oxide is more conducive to lithium ion diffusion and transport, thus having better rate performance. However, the completely disordered lithium nickel manganese oxide structure contains too much rock salt phase, which can easily cause battery capacity decay. Therefore, in order to further balance the rate and cycle stability of the battery, in one specific embodiment, the core and / or intermediate layer also includes disordered lithium nickel manganese oxide.

[0067] In one specific embodiment, the content of disordered lithium nickel manganese oxide is 1-10% based on the total mass of ordered lithium nickel manganese oxide material and disordered lithium nickel manganese oxide material.

[0068] In some embodiments, the content of disordered lithium nickel manganese oxide can be calculated using XDR refinement images.

[0069] In one specific embodiment, the chemical composition of the core includes: Li a1 Ni 0.5+b1 Mn 1.5+c1 O d1 ;

[0070] Wherein, 0.95≤a1≤1.25, -0.2≤b1≤0.2, -0.2≤c1≤0.2, 3.8≤d1≤4.2;

[0071] The chemical composition of the intermediate layer includes: Li a2 Ni 0.5+b2 Mn 1.5+c2 O d2 ;

[0072] Wherein, 0.95≤a2≤1.25, -0.2≤b2≤0.2, -0.15≤c2≤0.25, 3.7≤d2≤4.1, and c2≥c1, d2≤d1;

[0073] And / or, fast ion conductors include at least one of lithium aluminum titanium phosphate (LATP), lithium phosphate (LPO), lithium borate (LBO), lithium titanate (LTO), lithium zirconate (LZO), lithium zirconium phosphate (LZPO), lithium lanthanum titanate (LLTO), lithium lanthanum zirconate (LLZO), and lithium aluminum germanium phosphate (LAGP).

[0074] The fast ion conductors mentioned above can significantly improve the lithium-ion conduction rate of the positive electrode active material, which helps to improve the rate performance of the battery, enabling the battery to charge and discharge quickly at high current densities.

[0075] In some embodiments, the element content and chemical composition of the intermediate layer and the core can be tested by a method including the following process: first, acid etching is used to etch different thicknesses of the positive electrode active material, and then X-ray photoelectron spectroscopy (XPS) is used to test the signal of trivalent manganese. If a trivalent manganese signal is present, the corresponding layer is the intermediate layer. The lithium, nickel, trivalent manganese, and tetravalent manganese content of this layer can be measured using XPS, and the chemical composition of the intermediate layer can be determined by balancing. The content of a certain element in the core = the total content of the corresponding element - the content of the corresponding element in the intermediate layer - the content of the corresponding element in the outer shell layer. The content of the corresponding element in the outer shell layer is tested with reference to the content of the corresponding element in the intermediate layer, and the total content of the corresponding element can be directly tested using ICP.

[0076] In one specific embodiment, the positive electrode active material is a single crystal material, and the particle size of the positive electrode active material is 3μm to 10μm; or, the positive electrode active material is a polycrystalline material, and the particle size of the positive electrode active material is 8μm to 20μm.

[0077] Among them, the single-crystal positive electrode active material is easier to synthesize, has stronger processability, is less likely to come into contact with electrolyte, and has better stability, while the polycrystalline positive electrode active material has higher strength and better stability.

[0078] In a second aspect, the present invention provides a method for preparing a positive electrode active material as described in the first aspect, comprising the following steps:

[0079] A positive electrode active material precursor with an order degree of ≥95% is mixed with a solution containing fast ion conductors, stirred and then separated. The resulting solid is sintered at 500℃~950℃ to obtain a first-sintered product.

[0080] The product from the first calcination is mixed with a carbon source, and the resulting mixture is sintered a second time at 100℃~600℃ to obtain the positive electrode active material.

[0081] The chemical composition of the positive electrode active material precursor includes: Li a Ni 0.5+b Mn 1.5+c O d ;

[0082] Wherein, 0.95≤a≤1.25, -0.2≤b≤0.2, -0.2≤c≤0.2, 3.8≤d≤4.2, 0≤m≤0.1, 0≤n≤0.1; the carbon source accounts for 0.3-3.5% of the mass percentage of the first-burn product.

[0083] The above preparation method involves first mixing the positive electrode active material precursor with a solution containing fast ion conductors, followed by a first sintering. This allows the fast ion conductors to uniformly coat the surface of the positive electrode active material precursor, forming a dense outer shell layer. During the second sintering after mixing the first sintering product with a carbon source, carbothermic reduction occurs, causing the portion of the positive electrode active material precursor adjacent to the outer shell layer to be reconstructed, forming an intermediate layer. The mass ratio of the first sintering product to the carbon source and the temperature parameters of the second sintering affect the thickness of the intermediate layer, the concentration ratio of trivalent manganese ions, and the proportion of disordered positive electrode active material, thereby affecting the lithium ion diffusion channels, interface stability, and manganese leaching inhibition effect of the positive electrode active material.

[0084] The aforementioned positive electrode active material precursor and core have the same chemical composition. Those skilled in the art can select a positive electrode active material precursor with a specific chemical composition as needed. Regarding its source, this invention does not impose any particular limitation; those skilled in the art can directly purchase it commercially or prepare it using existing methods. In some embodiments, the positive electrode active material precursor is prepared by a method including the following process:

[0085] The order degree of the above-mentioned positive electrode active material precursor ≥95% means that the 4V plateau of the positive electrode active material precursor is ≤5%.

[0086] The nickel-manganese hydroxide precursor was mixed with a lithium source and sintered in an oxygen-containing atmosphere at 700–1150 °C for 2–20 h. Then, it was annealed at a rate of 0.1–5 °C / min to 400–700 °C and held for 1–18 h to obtain the positive electrode active material precursor.

[0087] The aforementioned nickel-manganese hydroxide precursor is a hydroxide containing Ni and Mn elements, and its chemical formula can be Ni. 0.5+x Mn 1.5+y (OH)z, -0.2≤x≤0.2, -0.2≤y≤0.2, 3.5≤z≤5.5, x+y=2.

[0088] The lithium source mentioned above is a lithium-containing substance, such as at least one selected from lithium carbonate, lithium hydroxide, lithium fluoride, lithium chloride, lithium acetate, lithium oxalate, and lithium citrate. Preferably, it is at least one selected from lithium carbonate and lithium hydroxide.

[0089] The aforementioned carbon sources include, but are not limited to, at least one of: Ketjen black (KB), carbon nanotubes (CNTs), porous carbon, carbon black, activated carbon fiber, and carbon nanotubes. Preferably, it includes at least one of Ketjen black, carbon nanotubes, and porous carbon.

[0090] The protective atmosphere includes at least one of nitrogen, argon, and helium. Preferably, it is at least one of nitrogen and argon.

[0091] The gas flow rate of the protective atmosphere is not particularly limited in this invention. In some embodiments, the gas flow rate is 1-50 mL / min, preferably 1-30 mL / min.

[0092] Furthermore, the time for the first and second sintering can be determined according to the extent of the reaction, and the present invention does not impose any particular limitation on this. In order to ensure that each system reacts fully, in some embodiments, the time for the first sintering is 2 to 15 hours, preferably 4 to 10 hours, and the temperature for the first sintering is preferably 700 to 900°C; the time for the second sintering is 1 to 10 hours, preferably 2 to 6 hours, and the temperature for the second sintering is preferably 300 to 500°C.

[0093] Furthermore, the specific surface area of ​​the carbon source is 800-1600 m². 2 / g, with a porosity of 70-95%.

[0094] The carbon sources mentioned above have high specific surface area and high porosity. After coating the calcined products, the adhesion of Mn to the positive electrode active material can be further improved. 2+ Adsorption effect.

[0095] To ensure sufficient carbothermic reduction, in some embodiments, secondary sintering is carried out in a protective atmosphere.

[0096] Thirdly, the present invention provides a positive electrode sheet, the positive electrode sheet comprising a current collector and a positive electrode active material layer coated on at least one surface of the current collector, the positive electrode active material layer comprising the positive electrode active material of the first aspect.

[0097] In some embodiments, the positive electrode active material layer comprises, by weight percentage: 93–98 wt% positive electrode active material, 2–5 wt% conductive agent, 2–5 wt% binder, and 0–1 wt% dispersant. This system possesses a more complete electronic conductive network and stronger adhesion between particles and between particles and the current collector, which contributes to performance at low temperatures and the stability of the system during long-term cycling.

[0098] For example, the conductive agent may be selected from at least one of natural graphite, artificial graphite, carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene; the binder may be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate; and the dispersant may be selected from at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium dodecyl sulfate.

[0099] Fourthly, the present invention provides a battery comprising a negative electrode and a positive electrode as described in the third aspect.

[0100] For example, the negative electrode sheet includes a negative electrode active material layer, which includes a negative electrode active material, a conductive agent, a binder, and optionally a dispersant; wherein, the negative electrode active material includes at least one of graphite, tin-based materials (such as SnO2), lithium titanate, black phosphorus, and tin sulfide (SnS); the conductive agent may be selected from at least one of carbon black, acetylene black, Ketjen black, carbon fiber, carbon nanotubes, metal powder, and graphene; the binder may be selected from at least one of carboxymethyl cellulose, styrene-butadiene rubber, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, ethylene oxide-containing polymers, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polyamide-imide, polyvinyl alcohol, and sodium polyacrylate; the dispersant may be selected from at least one of sodium carboxymethyl cellulose, triethylhexyl phosphate, and sodium dodecyl sulfate.

[0101] The battery described above also includes a separator; the present invention does not impose any particular limitation on the separator, and any known porous structure separator with electrochemical and chemical stability can be selected, such as at least one of glass fiber, non-woven fabric, polyethylene, polypropylene, or polyvinylidene fluoride. The separator can be single-layer or multi-layer.

[0102] The battery described above also includes an electrolyte, which comprises an organic solvent and an electrolyte salt. The organic solvent acts as a medium for transporting ions in the electrochemical reaction, and organic solvents known in the art for use in battery electrolytes can be employed.

[0103] Exemplarily, the organic solvent may be at least one selected from ethylene carbonate (EC), propylene carbonate (PC), dimethyl carbonate (DMC), diethyl carbonate (DEC), methyl ethyl carbonate (EMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butenyl carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), 1,4-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), methyl ethyl sulfone (EMS), and diethyl sulfone (ESE). In specific embodiments, two or more of the above-mentioned organic solvents may be selected.

[0104] The electrolyte salt serves as the ion source and can be any electrolyte salt known in the art for use in battery electrolytes. Exemplarily, the electrolyte salt can be lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium hexafluoroantimonyate (LiSbF6), lithium difluorophosphate (LiPF2O2), lithium 4,5-dicyano-2-trifluoromethylimidazolium (LiDTI), lithium dioxoborate (LiBOB), lithium (malonate-oxalate)borate (LiMOB), lithium (difluoromalonate-oxalate)borate (LiDFMOB), lithium tri(oxalate)phosphate (LiTOP), lithium tri(difluoromalonate)phosphate (LiTDFMP), lithium tetrafluorooxalate phosphate (LiTFOP), lithium nitrate (LiNO3), lithium fluoride (LiF), or LiN(SO2R). F )2 or LiN(SO2F)(SO2R F At least one of ), wherein R F =C n F 2n+1 n is between 2 and 10 and is an integer.

[0105] The battery of the present invention can be manufactured according to conventional methods in the art. For example, the positive electrode, separator and negative electrode can be stacked in sequence and assembled into a cell by winding or stacking process. After packaging and baking, electrolyte is injected and then the battery is manufactured by hot pressing and other processes.

[0106] The technical solution of the present invention will be further illustrated below with reference to specific embodiments. All parts, percentages and ratios recorded in the following embodiments are based on weight. All reagents used in the embodiments are commercially available or synthesized by conventional methods and can be used directly without further processing. The instruments used in the embodiments are also commercially available.

[0107] Example 1

[0108] This example provides a positive electrode active material comprising, in sequence from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material; the core has a chemical composition of Li. 1.03 Ni 0.495 Mn 1.495 O4, the chemical composition of the intermediate layer is Li 1.03 Ni 0.495 Mn 1.517 O 3.9 The outer shell is made of lithium aluminum titanium phosphate (LATP), the carbon material is Ketjen black (KB), the manganese ions in the core are tetravalent, the middle layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell to the adjacent core.

[0109] In the positive electrode active material, the mass concentration of trivalent manganese ions is 22.5 g / L, the core thickness is 5.4 μm, the intermediate layer thickness is 0.1 μm, the outer shell thickness is 0.2 μm, the carbon material size is 0.2 μm, and the specific surface area of ​​the positive electrode active material is 1.52 m². 2 / g; porosity 6.5%, the core and intermediate layer include ordered lithium nickel manganese oxide material and disordered lithium nickel manganese oxide material, the content of ordered lithium nickel manganese oxide is 95% and the content of disordered lithium nickel manganese oxide is 5%.

[0110] Its preparation method includes the following steps:

[0111] S1: Preparation of raw lithium nickel manganese oxide (P-LNMO) samples

[0112] Take 1000g of precursor Ni 0.5 Mn 1.5 (OH)4 was designed to be mixed with Li2CO3 at a Li:(Ni+Mn) molar ratio of 1.03:2 for 60 min at a speed of 900 rpm / min. The mixture was then placed in a box furnace and held at 1050℃ for 8 h, then cooled to 550℃ at a speed of 0.5℃ / min and held for 10 h. After natural cooling, it was crushed and sieved to obtain P-LNMO with an order degree ≥95%.

[0113] S2: Fast ion conductor coating

[0114] 0.037 mol LiNO3, 0.01 mol Al(NO3)3·9H2O, and 0.079 mol H3PO4 were weighed and dispersed in ethanol, and an appropriate amount of CH3COOH was added and stirred thoroughly to obtain solution A. 0.042 mol Ti(C4H9O)4 was weighed and dissolved in ethanol and stirred thoroughly to obtain mixed solution B. P-LNMO was mixed with solution A and stirred continuously. Solution B was then added uniformly at a constant flow rate to form a gel. After drying in an oven at 100℃ for 12 h, the gel was placed in a box furnace and kept at 800℃ for 8 h. After natural cooling, the gel was crushed and sieved to obtain LNMO coated with LATP (one-calcination product: LNMO·0.026LATP).

[0115] S3: Carbon coating

[0116] Weigh out 1000g LNMO·0.026LATP and 1wt% KB (specific surface area of ​​1200m²). 2 The mixture (LNMO·0.83C·0.026LATP) was mixed at 900 rpm / min for 60 min in a high-speed mixer. The mixture was then kept at 400℃ for 4 h in a tube furnace filled with nitrogen at a flow rate of 10 mL / min. After natural cooling, the mixture was crushed and sieved to obtain the positive electrode active material (LNMO·0.83C·0.026LATP). Its SEM and XRD patterns are shown in Figures 2 and 3, respectively.

[0117] The positive electrode active material was etched with 1 mol / L nitric acid solution at different depths of 10 nm, 50 nm, and 90 nm. The materials with different etching depths were characterized by X-ray photoelectron spectroscopy (XPS) to quantitatively determine the manganese content. The results showed that the concentration of trivalent manganese ions at 10 nm adjacent to the outer shell was 26.4 g / L, at 50 nm adjacent to the outer shell was 16.5 g / L, and at 90 nm adjacent to the outer shell was 5.46 g / L.

[0118] Example 2

[0119] This example provides a positive electrode active material comprising, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material in sequence; the manganese ions in the core are tetravalent, the intermediate layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. Other differences from Example 1 are shown in Table 1.

[0120] The preparation method differs from Example 1 in that, in step S2, 0.055 mol LiNO3, 0.01 mol Al(NO3)3·9H2O, and 0.079 mol H3PO4 are weighed and dispersed in ethanol, and an appropriate amount of CH3COOH is added and stirred thoroughly to obtain solution A; 0.063 mol Ti(C4H9O)4 is weighed and dissolved in ethanol and stirred thoroughly to obtain mixed solution B. P-LNMO is mixed with solution A and stirred continuously, and then solution B is added uniformly at a constant flow rate to form a gel. After drying in an oven at 100℃ for 12 h, it is placed in a box furnace and kept at 800℃ for 8 h. After natural cooling, it is crushed and sieved to obtain LNMO coated with LATP (LNMO·0.052LATP). After carbon coating, the positive electrode active material (LNMO·0.83C·0.052LATP) is obtained.

[0121] Example 3

[0122] This example provides a positive electrode active material comprising, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material in sequence; the manganese ions in the core are tetravalent, the intermediate layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. Other differences from Example 1 are shown in Table 1.

[0123] The preparation method differs from that in Example 1 in that, in step S2, 0.055 mol LiNO3, 0.016 mol Al(NO3)3·9H2O, and 0.118 mol H3PO4 are weighed and dispersed in ethanol, and an appropriate amount of CH3COOH is added and stirred thoroughly to obtain solution A; 0.063 mol Ti(C4H9O)4 is weighed and dissolved in ethanol and stirred thoroughly to obtain mixed solution B. P-LNMO is mixed with solution A and stirred continuously, and then solution B is added uniformly at a constant flow rate. After drying in an oven at 100℃ for 12 hours, it is placed in a box furnace and kept at 800℃ for 8 hours. After natural cooling, it is crushed and sieved, and after carbon coating, the positive electrode active material (LNMO·0.83C·0.039LATP) is obtained.

[0124] Example 4

[0125] This example provides a positive electrode active material comprising, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material in sequence; the manganese ions in the core are tetravalent, the intermediate layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. Other differences from Example 1 are shown in Table 1.

[0126] The preparation method differs from that in Example 1 in that, in step S2, 0.086 mol of NH4H2PO4 and 0.259 mol of LiOH are weighed and dissolved in deionized water to obtain solution A and solution B. P-LNMO is mixed with solution A and stirred continuously, and then solution B is added at a constant flow rate. After drying in an oven at 100°C for 12 hours, the mixture is placed in a box furnace and kept at 800°C for 8 hours. After natural cooling, it is crushed and sieved, and after carbon coating, the positive electrode active material (LNMO·0.83C·0.086LPO) is obtained.

[0127] Example 5

[0128] This example provides a positive electrode active material comprising, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material in sequence; the manganese ions in the core are tetravalent, the intermediate layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. Other differences from Example 1 are shown in Table 1.

[0129] The preparation method differs from that in Example 1 in that, in step S2, 0.216 mol of NH4H2PO4 and 0.648 mol of LiOH are weighed and dissolved in deionized water to obtain solution A and solution B. P-LNMO is mixed with solution A and stirred continuously, and then solution B is added at a constant flow rate. After drying in an oven at 100°C for 12 hours, the mixture is placed in a box furnace and kept at 800°C for 8 hours. After natural cooling, it is crushed and sieved, and after carbon coating, the positive electrode active material (LNMO·0.83C·0.216LPO) is obtained.

[0130] Example 6

[0131] This example provides a positive electrode active material comprising, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material in sequence; the manganese ions in the core are tetravalent, the intermediate layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. Other differences from Example 1 are shown in Table 1.

[0132] The preparation method differs from that in Example 1 in that, in step S2, 0.126 mol H3BO3 and 0.188 mol Li2CO3 are weighed and dissolved in deionized water to obtain solution A and solution B. P-LNMO is mixed with solution A and stirred continuously, and then solution B is added at a constant flow rate. After drying in an oven at 100°C for 12 hours, the mixture is placed in a box furnace and kept at 800°C for 8 hours. After natural cooling, it is crushed and sieved, and after carbon coating, the positive electrode active material (LNMO·0.83C·0.126LBO) is obtained.

[0133] Example 7

[0134] This example provides a positive electrode active material comprising, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material in sequence; the manganese ions in the core are tetravalent, the intermediate layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. Other differences from Example 1 are shown in Table 1.

[0135] The preparation method differs from that in Example 1 in that, in step S3, 1000g of LNMO·0.026LATP and 3wt%KB are weighed and mixed at 900rpm / min for 60min in a high-speed mixer. The mixture is then kept at 400℃ for 4h in a tube furnace filled with nitrogen at a nitrogen flow rate of 10mL / min. After natural cooling, it is crushed and sieved. After carbon coating, the positive electrode active material (LNMO·2.5C·0.026LATP) is obtained.

[0136] Example 8

[0137] This example provides a positive electrode active material comprising, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material in sequence; the manganese ions in the core are tetravalent, the intermediate layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. Other differences from Example 1 are shown in Table 1.

[0138] The preparation method differs from that in Example 1 in that, in step S3, 1000g of LNMO·0.026LATP and 2wt% CNT (with a specific surface area of ​​850m²) are weighed. 2 The mixture (LNMO·1.67C·0.026LATP) was mixed at 900 rpm / min for 60 min in a high-speed mixer. The mixture was then kept at 400℃ for 4 h in a tube furnace filled with nitrogen at a flow rate of 10 mL / min. After natural cooling, the mixture was crushed and sieved. After carbon coating, the positive electrode active material (LNMO·1.67C·0.026LATP) was obtained.

[0139] Example 9

[0140] This example provides a positive electrode active material comprising, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material in sequence; the manganese ions in the core are tetravalent, the intermediate layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. Other differences from Example 1 are shown in Table 1.

[0141] The preparation method differs from that in Example 1 in that, in step S3, 1000g of LNMO·0.026LATP and 0.5wt% porous carbon (with a specific surface area of ​​1450m²) are weighed.2 The mixture (LNMO·0.42C·0.026LATP) was mixed at 900 rpm / min for 60 min in a high-speed mixer. The mixture was then kept at 400℃ for 4 h in a tube furnace filled with nitrogen at a flow rate of 15 mL / min. After natural cooling, the mixture was crushed and sieved. After carbon coating, the positive electrode active material (LNMO·0.42C·0.026LATP) was obtained, and its XRD pattern is shown in Figure 4.

[0142] Example 10

[0143] This example provides a positive electrode active material comprising, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material in sequence; the manganese ions in the core are tetravalent, the intermediate layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. Other differences from Example 1 are shown in Table 1.

[0144] The preparation method differs from that in Example 1 in that, in step S3, 1000g of LNMO·0.026LATP and 1wt%KB are weighed and mixed at 900rpm / min for 60min in a high-speed mixer. The mixture is then kept at 300℃ for 4h in a tube furnace filled with nitrogen at a nitrogen flow rate of 10mL / min. After natural cooling, it is crushed and sieved. After carbon coating, the positive electrode active material (LNMO·0.83C·0.026LATP) is obtained.

[0145] Example 11

[0146] This example provides a positive electrode active material comprising, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material in sequence; the manganese ions in the core are tetravalent, the intermediate layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. Other differences from Example 1 are shown in Table 1.

[0147] The preparation method differs from that in Example 1 in that, in step S3, 1000g of LNMO·0.026LATP and 1wt%KB are weighed and mixed at 900rpm / min for 60min in a high-speed mixer. The mixture is then kept at 500℃ for 4h in a tube furnace filled with nitrogen at a nitrogen flow rate of 10mL / min. After natural cooling, it is crushed and sieved. After carbon coating, the positive electrode active material (LNMO·0.83C·0.026LATP) is obtained.

[0148] Example 12

[0149] This example provides a positive electrode active material comprising, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material in sequence; the manganese ions in the core are tetravalent, the intermediate layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. Other differences from Example 1 are shown in Table 1.

[0150] The preparation method differs from that in Example 1 in that, in step S3, 1000g of LNMO·0.026LATP and 1wt%KB are weighed and mixed at 900rpm / min for 60min in a high-speed mixer. The mixture is then kept at 400℃ for 2h in a tube furnace filled with nitrogen at a nitrogen flow rate of 10mL / min. After natural cooling, it is crushed and sieved. After carbon coating, the positive electrode active material (LNMO·0.83C·0.026LATP) is obtained.

[0151] Example 13

[0152] This example provides a positive electrode active material comprising, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material in sequence; the manganese ions in the core are tetravalent, the intermediate layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. Other differences from Example 1 are shown in Table 1.

[0153] The preparation method differs from that in Example 1 in that, in step S3, 1000g of LNMO·0.026LATP and 1wt%KB are weighed and mixed at 900rpm / min for 60min in a high-speed mixer. The mixture is then kept at 400℃ for 6h in a tube furnace filled with nitrogen at a nitrogen flow rate of 10mL / min. After natural cooling, it is crushed and sieved. After carbon coating, the positive electrode active material (LNMO·0.83C·0.026LATP) is obtained.

[0154] Example 14

[0155] This example provides a positive electrode active material comprising, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material in sequence; the manganese ions in the core are tetravalent, the intermediate layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. Other differences from Example 1 are shown in Table 1.

[0156] The preparation method differs from that in Example 1 in that, in step S1, 1000g of precursor Ni is taken. 0.5 Mn 1.5(OH)4, designed according to a Li:(Ni+Mn) molar ratio of 1:2, was mixed with Li2CO3 at a speed of 900 rpm / min for 60 min. The mixture was then placed in a box furnace and held at 700℃ for 10 h, then cooled to 550℃ at a speed of 0.5℃ / min and held for 10 h. After natural cooling, it was crushed and sieved to obtain P-LNMO. This P-LNMO was then coated with LATP and carbon to obtain the positive electrode active material (LNMO·0.83C·0.026LATP).

[0157] Example 15

[0158] This example provides a positive electrode active material comprising, in a direction from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material in sequence; the manganese ions in the core are tetravalent, the intermediate layer includes trivalent and tetravalent manganese ions, and the concentration of trivalent manganese ions decreases from the adjacent outer shell layer to the adjacent core. Other differences from Example 1 are shown in Table 1.

[0159] The preparation method differs from that in Example 1 in that, in step S1, 1000g of precursor Ni is taken. 0.5 Mn 1.5 (OH)4 was mixed with Li2CO3 at a molar ratio of Li:(Ni+Mn) = 1:2 for 60 min at 900 rpm / min. The mixture was then placed in a box furnace and held at 850 °C for 6 h, then cooled to 550 °C at 0.5 °C / min and held for 10 h. After natural cooling, the mixture was crushed and sieved to obtain P-LNMO. After LATP and carbon coating, the positive electrode active material (LNMO·0.83C·0.026LATP) was obtained.

[0160] Example 16

[0161] This example provides a positive electrode active material, which differs from Example 1 in that it is shown in Table 1.

[0162] Its preparation method includes the following steps:

[0163] S1: Preparation of raw lithium nickel manganese oxide (P-LNMO) samples

[0164] Take 1000g of precursor Ni 0.5 Mn 1.5 (OH)4 was designed to be mixed with Li2CO3 according to a Li:(Ni+Mn) molar ratio of 1.03:2 at a speed of 900 rpm / min for 60 min. The mixture was then placed in a box furnace and held at 1050℃ for 8 h, then cooled to 550℃ at a speed of 0.5℃ / min and held for 10 h. After natural cooling, it was crushed and sieved to obtain P-LNMO.

[0165] S2: Fast ion conductor coating

[0166] 0.037 mol LiNO3, 0.01 mol Al(NO3)3·9H2O, and 0.079 mol H3PO4 were weighed and dispersed in ethanol, and an appropriate amount of CH3COOH was added and stirred thoroughly to obtain solution A. 0.042 mol Ti(C4H9O)4 was weighed and dissolved in ethanol and stirred thoroughly to obtain mixed solution B. P-LNMO was mixed with solution A and stirred continuously. Then, solution B was added uniformly at a constant flow rate to form a gel. After drying in an oven at 100℃ for 12 h, the gel was placed in a box furnace and kept at 500℃ for 8 h. After natural cooling, the gel was crushed and sieved to obtain LNMO coated with LATP (LNMO·0.026LATP).

[0167] S3: Carbon coating

[0168] Weigh 1000g LNMO·0.026LATP and 1wt%KB and mix them in a high-speed mixer at 900rpm / min for 60min. The mixture is then kept at 400℃ for 4h in a tube furnace filled with nitrogen at a nitrogen flow rate of 10mL / min. After natural cooling, the mixture is crushed and sieved to obtain the positive electrode active material.

[0169] Example 17

[0170] This example provides a positive electrode active material, which differs from Example 1 in that it is shown in Table 1.

[0171] Its preparation method includes the following steps:

[0172] S1: Preparation of raw lithium nickel manganese oxide (P-LNMO) samples

[0173] Take 1000g of precursor Ni 0.5 Mn 1.5 (OH)4 was designed to be mixed with Li2CO3 according to a Li:(Ni+Mn) molar ratio of 1.03:2 at a speed of 900 rpm / min for 60 min. The mixture was then placed in a box furnace and held at 1050℃ for 8 h, then cooled to 550℃ at a speed of 0.5℃ / min and held for 10 h. After natural cooling, it was crushed and sieved to obtain P-LNMO.

[0174] S2: Fast ion conductor coating

[0175] 0.037 mol LiNO3, 0.01 mol Al(NO3)3·9H2O, and 0.079 mol H3PO4 were weighed and dispersed in ethanol, and an appropriate amount of CH3COOH was added and stirred thoroughly to obtain solution A. 0.042 mol Ti(C4H9O)4 was weighed and dissolved in ethanol and stirred thoroughly to obtain mixed solution B. P-LNMO was mixed with solution A and stirred continuously. Then, solution B was added uniformly at a constant flow rate to form a gel. After drying in an oven at 100℃ for 12 h, the gel was placed in a box furnace and kept at 800℃ for 8 h. After natural cooling, the gel was crushed and sieved to obtain LNMO coated with LATP (LNMO·0.026LATP).

[0176] S3: Carbon coating

[0177] Weigh 1000g LNMO·0.026LATP and 1wt%KB and mix them in a high-speed mixer at 900rpm / min for 60min. The mixture is then kept at 200℃ for 4h in a tube furnace filled with nitrogen at a nitrogen flow rate of 10mL / min. After natural cooling, the mixture is crushed and sieved to obtain the positive electrode active material.

[0178] Example 18

[0179] This example provides a positive electrode active material, which differs from Example 1 in that it is shown in Table 1.

[0180] Its preparation method includes the following steps:

[0181] S1: Preparation of raw lithium nickel manganese oxide (P-LNMO) samples

[0182] Take 1000g of precursor Ni 0.5 Mn 1.5 (OH)4 was designed to be mixed with Li2CO3 according to a Li:(Ni+Mn) molar ratio of 1.03:2 at a speed of 900 rpm / min for 60 min. The mixture was then placed in a box furnace and held at 1050℃ for 8 h, then cooled to 550℃ at a speed of 0.5℃ / min and held for 10 h. After natural cooling, it was crushed and sieved to obtain P-LNMO.

[0183] S2: Fast ion conductor coating

[0184] 0.037 mol LiNO3, 0.01 mol Al(NO3)3·9H2O, and 0.079 mol H3PO4 were weighed and dispersed in ethanol, and an appropriate amount of CH3COOH was added and stirred thoroughly to obtain solution A. 0.042 mol Ti(C4H9O)4 was weighed and dissolved in ethanol and stirred thoroughly to obtain mixed solution B. P-LNMO was mixed with solution A and stirred continuously. Then, solution B was added uniformly at a constant flow rate to form a gel. After drying in an oven at 100℃ for 12 h, the gel was placed in a box furnace and kept at 800℃ for 8 h. After natural cooling, the gel was crushed and sieved to obtain LNMO coated with LATP (LNMO·0.026LATP).

[0185] S3: Carbon coating

[0186] Weigh out 1000g LNMO·0.026LATP and 1wt% graphite (specific surface area 2.8m²). 2 The mixture (g, porosity 25%) was mixed at 900 rpm / min for 60 min in a high-speed mixer. The mixture was then kept at 400℃ for 4 h in a tube furnace filled with nitrogen at a flow rate of 10 mL / min. After natural cooling, the mixture was crushed and sieved to obtain the positive electrode active material.

[0187] Example 19

[0188] This example provides a positive electrode active material, which differs from Example 1 in that it is shown in Table 1.

[0189] Its preparation method includes the following steps:

[0190] S1: Preparation of raw lithium nickel manganese oxide (P-LNMO) samples

[0191] Take 1000g of precursor Ni 0.5 Mn 1.5 (OH)4 was designed to be mixed with Li2CO3 according to a Li:(Ni+Mn) molar ratio of 1.03:2 at a speed of 900 rpm / min for 60 min. The mixture was then placed in a box furnace and held at 1050℃ for 8 h, then cooled to 550℃ at a speed of 0.5℃ / min and held for 10 h. After natural cooling, it was crushed and sieved to obtain P-LNMO.

[0192] S2: Fast ion conductor coating

[0193] 0.037 mol LiNO3, 0.01 mol Al(NO3)3·9H2O, and 0.079 mol H3PO4 were weighed and dispersed in ethanol, and an appropriate amount of CH3COOH was added and stirred thoroughly to obtain solution A. 0.042 mol Ti(C4H9O)4 was weighed and dissolved in ethanol and stirred thoroughly to obtain mixed solution B. P-LNMO was mixed with solution A and stirred continuously. Then, solution B was added uniformly at a constant flow rate to form a gel. After drying in an oven at 100℃ for 12 h, the gel was placed in a box furnace and kept at 800℃ for 8 h. After natural cooling, the gel was crushed and sieved to obtain LNMO coated with LATP (LNMO·0.026LATP).

[0194] S3: Carbon coating

[0195] Weigh 1000g LNMO·0.026LATP and 1wt%KB and mix them in a high-speed mixer at 900rpm / min for 60min. The mixture is then kept at 400℃ for 4h in a sealed tube furnace. After natural cooling, it is crushed and sieved to obtain the positive electrode active material.

[0196] Comparative Example 1

[0197] This example provides a positive electrode active material whose chemical composition is consistent with that of Example 1.

[0198] Its preparation method includes the following steps:

[0199] Take 1000g of precursor Ni 0.5 Mn 1.5 (OH)4 was designed to be mixed with Li2CO3 according to a Li:(Ni+Mn) molar ratio of 1.03:2 at a speed of 900 rpm / min for 60 min. The mixture was then placed in a box furnace and held at 1050℃ for 8 h, then cooled to 550℃ at a speed of 0.5℃ / min and held for 10 h. After natural cooling, it was crushed and sieved to obtain the bare LNMO sample (P-LNMO), and its SEM image is shown in Figure 5.

[0200] Comparative Example 2

[0201] This example provides a positive electrode active material; the difference from Example 1 is shown in Table 1.

[0202] Its preparation method includes the following steps:

[0203] S1: Preparation of raw lithium nickel manganese oxide (P-LNMO) samples

[0204] Take 1000g of precursor Ni 0.5 Mn 1.5(OH)4 was designed to be mixed with Li2CO3 according to a Li:(Ni+Mn) molar ratio of 1.03:2 at a speed of 900 rpm / min for 60 min. The mixture was then placed in a box furnace and held at 1050℃ for 8 h, then cooled to 550℃ at a speed of 0.5℃ / min and held for 10 h. After natural cooling, it was crushed and sieved to obtain P-LNMO.

[0205] S2: Fast ion conductor coating

[0206] 0.037 mol LiNO3, 0.01 mol Al(NO3)3·9H2O, and 0.079 mol H3PO4 were weighed and dispersed in ethanol, and an appropriate amount of CH3COOH was added and stirred thoroughly to obtain solution A. 0.042 mol Ti(C4H9O)4 was weighed and dissolved in ethanol and stirred thoroughly to obtain mixed solution B. P-LNMO was mixed with solution A and stirred continuously. Then, solution B was added uniformly at a constant flow rate to form a gel. After drying in an oven at 100℃ for 12 h, the gel was placed in a box furnace and kept at 800℃ for 8 h. After natural cooling, the gel was crushed and sieved to obtain LNMO coated with LATP (LNMO·0.026LATP).

[0207] Comparative Example 3

[0208] This example provides a positive electrode active material; the specific differences from Example 1 are shown in Table 1.

[0209] Its preparation method includes the following steps:

[0210] S1: Preparation of raw lithium nickel manganese oxide (P-LNMO) samples

[0211] Take 1000g of precursor Ni 0.5 Mn 1.5 (OH)4 was designed to be mixed with Li2CO3 according to a Li:(Ni+Mn) molar ratio of 1.03:2 at a speed of 900 rpm / min for 60 min. The mixture was then placed in a box furnace and held at 1050℃ for 8 h, then cooled to 550℃ at a speed of 0.5℃ / min and held for 10 h. After natural cooling, it was crushed and sieved to obtain P-LNMO.

[0212] S2: Carbon coating

[0213] Weigh 1000g of P-LNMO and 1wt%KB and mix them in a high-speed mixer at 900rpm / min for 60min. The mixture is then kept at 400℃ for 4h in a tube furnace filled with nitrogen at a nitrogen flow rate of 10mL / min. After natural cooling, the mixture is crushed and sieved to obtain the positive electrode active material.

[0214] Comparative Example 4

[0215] This example provides a positive electrode active material, which differs from Example 1 in that it is shown in Table 1.

[0216] Its preparation method includes the following steps:

[0217] S1: Preparation of raw lithium nickel manganese oxide (P-LNMO) samples

[0218] Take 1000g of precursor Ni 0.5 Mn 1.5 (OH)4 was mixed with Li2CO3 at a molar ratio of Li:(Ni+Mn) = 1:2 for 60 min at 900 rpm / min. The mixture was then placed in a box furnace and held at 700℃ for 10 h, then cooled to 550℃ at 0.5℃ / min and held for 10 h. After natural cooling, the mixture was crushed and sieved to obtain P-LNMO.

[0219] S2: Alumina coating

[0220] P-LNMO and 1% Al2O3 (based on 100% of the active cathode P-LNMO) are mixed evenly and placed in a box furnace. The mixture is kept at 800℃ for 8 hours. After natural cooling, it is crushed and sieved to obtain alumina-coated LNMO cathode material.

[0221] S3: Carbon coating

[0222] Weigh 1000g LNMO·0.026LATP and 1wt%KB and mix them in a high-speed mixer at 900rpm / min for 60min. The mixture is then kept at 400℃ for 4h in a tube furnace filled with nitrogen at a nitrogen flow rate of 10mL / min. After natural cooling, the mixture is crushed and sieved to obtain the positive electrode active material.

[0223] Table 1

[0224] Summary: As shown in Figures 2 and 5, the surface of the uncoated sample in Comparative Example 1 is smooth, while the surface of the coated sample in Example 1 has many particles, confirming that LATP and KB have been successfully coated. As shown in Figure 3, the XRD diffraction peaks of Example 1 are very sharp, indicating a well-crystallized ordered structure. However, there are small diffraction peaks at 37.6°, 43.7°, and 63.5°, which correspond to the rock salt phase in disordered LNMO. Therefore, carbothermic reduction under an inert atmosphere can reduce tetravalent manganese to trivalent manganese, forming a structure with an ordered core and a disordered middle layer. The increase in trivalent manganese improves the electronic conductivity of the material surface. As shown in Figure 4, the XRD diffraction peaks of Example 9 are also very sharp, indicating a well-crystallized ordered structure. No diffraction peaks were observed at 37.6°, 43.7°, and 63.5°, which indicates that no disordered phase was formed on its surface. Therefore, a wide 4V plateau ordered structure can also be formed by carbothermal reduction under an inert atmosphere. The widening of the 4V plateau will reduce the average voltage and increase the cycle stability.

[0225] Application Example 1

[0226] The above-mentioned positive electrode active materials are used to prepare positive electrode sheets, including the following steps:

[0227] By weight, 80% of the positive electrode active material, 10% of the conductive carbon black, and 10% of the polyvinylidene fluoride were uniformly dispersed in N-methylpyrrolidone solvent. The prepared positive electrode slurry was uniformly coated onto aluminum foil with a scraper, then dried in an 80°C forced-air drying oven for 6 hours, and then cold-pressed into sheets to form positive electrode sheets.

[0228] Application Example 2

[0229] A battery is prepared using the positive electrode sheets from Application Example 1, comprising the following steps:

[0230] (1) Button cell battery: The above positive electrode and lithium negative electrode were used to assemble CR2505 button cells in a dry glove box filled with high-purity argon gas. Celgard2500 was used as the separator, a mixture of dimethyl carbonate, diethyl carbonate and ethyl carbonate with a volume ratio of 1:1:1 was used as the solvent, and 1 mol / L LiPF6 solution was used as the electrolyte. The assembled button cell battery was subjected to 100 charge-discharge cycles.

[0231] (2) Soft-pack battery: By weight, 80wt% artificial graphite, 15wt% hard carbon, 2wt% carbon black, 2wt% polyacrylic acid and 1wt% sodium carboxymethyl cellulose are added to the mixing tank and evenly dispersed in deionized water to prepare a negative electrode slurry. The negative electrode slurry is evenly coated onto copper foil. After the electrode is baked and rolled, a negative electrode sheet is obtained. The graphite negative electrode sheet, the above positive electrode sheet, electrolyte and separator are used to assemble a 0.6Ah capacity battery cell and packaged with aluminum-plastic film.

[0232] Performance testing

[0233] The following performance characteristics of the test application battery are shown in Table 2:

[0234] 1. Button cell battery cycle test: The button cell battery assembled with lithium nickel manganese oxide positive electrode and lithium foil negative electrode was subjected to constant current + constant voltage charge and discharge test. The nominal capacity is 140mAh / g, and the voltage window is 3.4~4.85V (vs. Li+ / Li). The specific test steps are as follows: 2 cycles of 0.1C charge and discharge, 1 cycle of 0.33C charge and discharge, 1 cycle of 1C charge and discharge, and 100 cycles of 1C charge and 2C discharge. The cycle retention rate is the percentage of the 2C discharge capacity of the 100th cycle to the 2C discharge capacity of the 1st cycle. The 4V plateau percentage is the ratio of the specific capacity of the first discharge to 4.4V to the total specific capacity of the first discharge.

[0235] 2. Manganese leaching: The coin cell after cycling was disassembled, and the manganese content of the obtained negative electrode was tested by ICP.

[0236] 3. Full-electric cycle test: The lithium nickel manganese oxide positive electrode material and the graphite negative electrode are combined to form a soft-pack full battery. Under the conditions of 25℃ and 45℃, the battery is charged at a constant current of 1C to 4.85V. Then, it is charged at a constant voltage of 4.85V to the current equal to 0.05C. After that, it is left to stand for 5 minutes, and then discharged at a constant current of 1C to 3.4V. This cycle test is repeated until the capacity decays to 80%, and the number of cycles is recorded.

[0237] 4. 28-day capacity retention: After the pouch battery is formed, the air bag is removed and it is sealed. The initial capacity after formation is tested. After charging to the upper limit voltage of 4.85V and storing for 28 days, the remaining capacity of the battery is tested. The ratio of the remaining battery capacity to the initial capacity is the 28-day storage capacity retention rate.

[0238] 5. High-temperature storage gas generation performance: The positive active material was coated into a positive electrode sheet according to the method in the coin cell capacity test to prepare a positive soft pack battery. The soft pack battery before storage was placed in water and the initial volume V0 of the soft pack battery was tested by the water displacement method. The temperature was controlled at 70℃. After storage for 28 days, the volume V1 of the soft pack battery was tested again by the water displacement method. The volume change (V1-V0) / V0 was calculated to obtain the gas generation performance during high-temperature storage.

[0239] Figure 6 shows the charge-discharge curves of the batteries assembled with the positive electrode active materials of Example 1 and Comparative Example 1 of the present invention.

[0240] Table 2:

[0241] As shown in Table 2, compared to the comparative example, the positive electrode active material of the embodiment, from the center to the surface, sequentially includes a core, an intermediate layer, a shell layer, and carbon material. The core includes manganese ions with a valence state of not less than +4, the intermediate layer includes +3 and +4 manganese ions, and the concentration of +3 manganese ions in the intermediate layer decreases from the vicinity of the shell layer to the vicinity of the core; the shell layer includes a fast ion conductor. This can improve the interfacial stability of the positive electrode active material and suppress manganese dissolution while ensuring the lithium ion diffusion rate, thereby giving the battery excellent rate performance, cycle performance, and storage stability.

[0242] Furthermore, by comparing Example 16 with Examples 1-15, it can be seen that the modification effect of coating LATP at 500℃ is not as good as that at 800℃. This is because the binding force between LATP and LNMO surface is higher at high temperature, and some LATP can diffuse into the bulk phase, thereby enhancing the stability of the material surface and bulk structure.

[0243] By comparing Example 17 with Examples 1-15, it can be seen that when carbon-coated materials are coated at 200℃, LNMO has a shorter 4V platform and more manganese is dissolved, indicating that the carbothermic reduction at low temperature is insufficient and cannot form the specific structure of an ordered core + disordered middle layer and a wide 4V platform.

[0244] By comparing Example 18 with Examples 1-6, it can be seen that the positive electrode or energy material of Examples 1-6, which is composite coated with different fast ion conductors and carbon materials with high specific surface area and high porosity, has excellent overall rate performance, room temperature and high temperature cycling performance, good storage effect and less gas production. In contrast, the carbon material of Example 18 has a relatively low specific surface area and porosity, resulting in a higher amount of manganese leaching.

[0245] By comparing Example 19 with Examples 1-15, it can be seen that the carbon material coating in Example 19 under non-aeration conditions resulted in a shorter 4V plateau and greater manganese dissolution in the battery, indicating that the carbothermic reduction reaction of carbon material coating under non-aeration conditions was insufficient.

[0246] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A positive electrode active material, characterized by, The positive electrode active material comprises, in sequence from the center to the surface, a core, an intermediate layer, an outer shell layer, and a carbon material. The core includes manganese ions with a valence state of not less than +4. The intermediate layer includes +3 and +4 manganese ions, and the concentration of +3 manganese ions in the intermediate layer decreases from the adjacent outer shell layer to the adjacent core. The outer shell layer includes a fast ion conductor.

2. The positive electrode active material according to claim 1, characterized by The total thickness of the core, intermediate layer and outer shell is m, and the thickness of the intermediate layer is n, where 0.002≤n / m≤0.1; And / or, in the positive electrode active material, the mass concentration of trivalent manganese ions is 0.5-50 g / L.

3. The positive electrode active material according to claim 1 or 2, characterized in that, The thickness of the core is 3-20 μm; And / or, the thickness of the intermediate layer is 0.05-0.3 μm; And / or, the thickness of the outer shell layer is 0.08-0.5 μm; And / or, the carbon material includes at least one of carbon nanotubes, Ketjen black, porous carbon particles, carbon black, activated carbon fiber, and carbon nanotube onion.

4. The positive electrode active material according to any one of claims 1-3, characterized in that, The core and the intermediate layer comprise an ordered lithium nickel manganese oxide material.

5. The positive electrode active material according to claim 4, characterized by The core and / or the intermediate layer further include disordered lithium nickel manganese oxide; Preferably, the content of the disordered lithium nickel manganese oxide is 1-10%.

6. The positive electrode active material according to any one of claims 1 to 5, characterized by The chemical composition of the inner core includes: Li a1 Ni 0.5+b1 Mn 1.5+c1 O d1 ; Wherein, 0.95≤a1≤1.25, -0.2≤b1≤0.2, -0.2≤c1≤0.2, 3.8≤d1≤4.2; The chemical composition of the intermediate layer includes: Li a2 Ni 0.5+b2 Mn 1.5+c2 O d2 ; Wherein, 0.95≤a2≤1.25, -0.2≤b2≤0.2, -0.15≤c2≤0.25, 3.7≤d2≤4.1, and c2≥c1, d2≤d1; And / or, the fast ion conductor includes at least one of lithium aluminum titanium phosphate, lithium phosphate, lithium borate, lithium titanate, lithium zirconate, lithium zirconium phosphate, lithium lanthanum titanate, lithium lanthanum zirconate, and lithium aluminum germanium phosphate.

7. The positive electrode active material according to claim 6, characterized by The positive electrode active material is a single crystal material with a particle size of 3 μm to 10 μm; or, the positive electrode active material is a polycrystalline material with a particle size of 8 μm to 20 μm.

8. A method for preparing the positive electrode active material according to any one of claims 1-7, characterized in that, Includes the following steps: A positive electrode active material precursor with an order degree of ≥95% is mixed with a solution containing fast ion conductors, stirred and then separated. The resulting solid is sintered at 500℃~950℃ to obtain a first-sintered product. The calcined product is mixed with a carbon source, and the resulting mixture is subjected to secondary sintering at 100℃~600℃ to obtain the positive electrode active material. The chemical composition of the positive electrode active material precursor includes: Li a Ni 0.5+b Mn 1.5+c O d ; Wherein, 0.95≤a≤1.25, -0.2≤b≤0.2, -0.2≤c≤0.2, 3.8≤d≤4.2; the carbon source accounts for 0.3-3.5% of the mass percentage of the calcined product.

9. The preparation method according to claim 8, characterized in that, The specific surface area of the carbon source is 800-1600 m 2 / g, and the porosity is 70-95%. And / or, the secondary sintering is carried out in a protective atmosphere.

10. A positive electrode sheet comprising a current collector and a positive electrode active material layer coated on at least one surface of the current collector, characterized by, The positive electrode active material layer includes the positive electrode active material according to any one of claims 1-7, or the positive electrode active material prepared by the preparation method of the positive electrode active material according to claim 8 or 9.

11. A battery comprising a negative electrode and a positive electrode as described in claim 10.

Images