Composite negative electrode active material, preparation method, negative electrode and battery

Abstract

The invention relates to the technical field of lithium ion battery production, in particular to a composite negative electrode active material, a preparation method, a negative electrode and a battery. The composite negative electrode active material is characterized in that the composite negative electrode active material is of a core-shell structure, the core comprises lithium titanate, the shell comprises Li1 + xAlx-aMaTi2-x-yNy (PO4) 3, M is one of trivalent metal elements La and Ga, N is one of tetravalent metal elements Zr and Si, x is greater than or equal to 0.3 and less than or equal to 0.5, a is greater than or equal to 0.01 and less than or equal to 0.1, and b is greater than or equal to 0.01 and less than or equal to 0.1. The Li1 + xAlx-aMaTi2-x-yNy (PO4) 3 coating layer coats the surfaces of the lithium titanate particles to form a core-shell structure, so that the contact between the composite negative electrode active material and a solid electrolyte can be effectively improved, the lithium ion transmission efficiency in the negative electrode is improved, and the rate capability and the energy density of the battery are effectively improved.

Description

Technical Field

[0001] This application relates to the field of lithium-ion battery production technology, and in particular to a composite negative electrode active material, preparation method, negative electrode and battery. Background Technology

[0002] Lithium titanate materials have low volume expansion, high lithium-ion insertion / extraction potential, and excellent cycle stability, making them suitable as negative electrode active materials in power batteries, energy storage batteries, and other fields to improve battery safety and cycle performance. However, when used in all-solid-state batteries, they have poor interfacial compatibility with solid electrolytes, resulting in a large lithium-ion transport impedance at the interface. This hinders lithium-ion transport, significantly reducing the battery's rate performance and cycle performance. Existing modification methods, such as carbon coating, have limited effect on improving lithium-ion transport and easily introduce electronic conductivity, leading to additional side reactions.

[0003] Therefore, a technical solution is urgently needed to solve the above problems. Summary of the Invention

[0004] To address the aforementioned issues, this application discloses a composite negative electrode active material, a preparation method, a negative electrode, and a battery, which can effectively improve interfacial compatibility with solid electrolytes, improve lithium-ion transport between the negative electrode and the solid electrolyte membrane, thereby improving the rate performance of the battery and increasing its energy density.

[0005] The technical solution of this application is implemented as follows:

[0006] The first aspect of this application discloses a composite negative electrode active material, which has a core-shell structure, wherein the core includes lithium titanate and the shell includes Li... 1+x Al x-a M a Ti 2-x-y Ny(PO4)3, where M is one of the trivalent metal elements La and Ga, and N is one of the tetravalent metal elements Zr and Si, 0.3≤x≤0.5, 0.01≤a≤0.1, 0.01≤b≤0.1.

[0007] In one embodiment, the shell thickness is 2nm to 20nm.

[0008] In one embodiment, the shell accounts for 1% to 5% of the mass of the composite negative electrode active material.

[0009] In one embodiment, the particle size D50 of the lithium titanate particles is 0.5 to 1 μm.

[0010] In one embodiment, lithium titanate is a secondary spherical particle.

[0011] The second aspect of this application discloses a method for preparing a composite negative electrode active material as described in the first aspect, comprising the following steps:

[0012] S1. Disperse lithium titanate particles in a solvent to form a suspension;

[0013] S2. Add lithium source, aluminum source, titanium source and phosphorus source to the suspension to prepare the first intermediate product, and evaporate and dry the first intermediate product to obtain the second intermediate product in dry powder form.

[0014] S3. The second intermediate product is subjected to heat treatment to obtain a composite negative electrode active material.

[0015] In one embodiment, in step S2, lithium source, aluminum source, titanium source and phosphorus source are dissolved in a solvent to form a precursor sol, and the precursor sol is added to the suspension.

[0016] In one embodiment, at least one of the following conditions is met:

[0017] 1) The heat treatment temperature is 400℃~800℃;

[0018] 2) The heat treatment time is 3 hours to 10 hours;

[0019] 3) Heat treatment is carried out in air or oxygen.

[0020] The third aspect of this application discloses a negative electrode, comprising a composite negative electrode active material as described in the first aspect and / or a composite negative electrode active material prepared by the preparation method described in the second aspect.

[0021] The fourth aspect of this application discloses a battery including a positive electrode, a separator and / or a solid electrolyte membrane, and a negative electrode as described in the third aspect.

[0022] The beneficial technical effects of this application are as follows:

[0023] This application involves coating the surface of lithium titanate particles with Li 1+x Al x-a M a Ti 2-x-y The Ny(PO4)3 coating layer forms a core-shell structure, which can effectively improve the contact between the composite negative electrode active material and the solid electrolyte, and enhance the lithium-ion transport efficiency in the negative electrode, thereby effectively improving the rate performance and energy density of the battery. Detailed Implementation

[0024] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0025] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The terms “comprising” or “including” and similar terms used herein mean that an element or object preceding the word encompasses the elements or objects listed following the word and their equivalents, without excluding other elements or objects. The terms “and / or” or “and / or” as used herein include any and all combinations of one or more of the associated listed items.

[0026] The following describes some preferred embodiments of this application. It should be noted that the following description is for illustrative purposes only and is not intended to limit the scope of protection of this application. The steps involved in this application may be performed precisely in sequence, or various steps may be processed in reverse order or simultaneously. Furthermore, other operations may be added to these processes, or one or more steps may be removed from these processes.

[0027] Lithium titanate (Li4Ti5O) 12 Lithium titanate (LTO) is considered a highly promising anode material for lithium-ion batteries due to its low volume expansion (volume change rate of only 0.2%), high lithium-ion insertion / extraction potential (~1.55V vs Li+ / Li), and excellent cycle stability. It has attracted significant attention, especially in power batteries and energy storage batteries where safety and long cycle life are critical requirements. However, in practical applications, lithium titanate still faces several bottlenecks that need to be addressed. When used in liquid batteries, it is prone to side reactions with the electrolyte, generating gases such as CO2 and H2, causing battery swelling and reduced safety performance. When used in all-solid-state batteries, it exhibits poor interfacial compatibility with the solid electrolyte, resulting in significant lithium-ion transport impedance at the interface. This hinders lithium-ion transport, leading to a substantial decrease in rate performance and cycle performance. Existing modification methods, such as carbon coating, have limited effectiveness in improving lithium-ion transport and can introduce electronic conductivity, causing additional side reactions.

[0028] To address the above problems, this application proposes a technical solution.

[0029] The first aspect of this application discloses a composite negative electrode active material, which has a core-shell structure, wherein the core includes lithium titanate and the shell includes Li... 1+x Al x-a M a Ti 2-x-y Ny(PO4)3, where M is one of the trivalent metal elements La and Ga, and N is one of the tetravalent metal elements Zr and Si, 0.3≤x≤0.5, 0.01≤a≤0.1, 0.01≤b≤0.1.

[0030] This application involves coating the surface of lithium titanate particles with Li 1+x Al x-a M a Ti 2-x-y The Ny(PO4)3 coating layer forms a core-shell structure, which can effectively improve the contact between the composite negative electrode active material and the solid electrolyte, and enhance the lithium-ion transport efficiency in the negative electrode, thereby effectively improving the rate performance and energy density of the battery.

[0031] At the same time, it can effectively isolate lithium titanate from the electrolyte solution, preventing side reactions from occurring.

[0032] In some embodiments, the shell includes Li 1.3 Al 0.3 Ti 1.7 (PO4)3, Li 1.4 Al 0.4 Ti 1.6 (PO4)3, Li 1.3 Al 0.27 Ga 0.03 Ti 1.7 (PO4)3, Li 1.4 Al 0.4 Zr 0.1 Ti 1.5 At least one of (PO4)3.

[0033] In some embodiments, the shell thickness is 2nm to 20nm. For example, the shell thickness can be selected as 2nm, 3nm, 5nm, 7nm, 10nm, 12nm, 15nm, 16nm, 18nm, 20nm, etc. It is understood that the shell thickness is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0034] If the shell thickness is too small, it is not easy to form a continuous coating on the surface of lithium titanate. If the shell thickness is too large, the lithium ion transport path becomes longer, which is not conducive to lithium ion transport. In addition, the mass ratio increases, and the energy density of the battery decreases.

[0035] When the shell thickness is within the above range, a continuous and complete coating can be formed on the surface of lithium titanate, while also ensuring good lithium-ion transport. 1+x Al x-a M a Ti 2-x-y Ny(PO4)3 itself has good lithium-ion transport capabilities, which can effectively improve the lithium-ion transport efficiency in the negative electrode.

[0036] In some embodiments, the shell mass percentage in the composite negative electrode active material is 1% to 5%. Exemplarily, the shell mass percentage can be selected as 1%, 1.5%, 2%, 2.5%, 3%, 3.5%, 4%, 4.5%, or 5%, etc. It is understood that the shell mass percentage is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0037] If the mass of the casing is too small, it cannot form a complete coating on the surface of lithium titanate; if the mass of the casing is too large, it will cause a decrease in the energy density of the battery.

[0038] In some embodiments, the particle size D50 of lithium titanate is 0.5 μm to 5 μm. Exemplarily, the particle size D50 of lithium titanate can be selected as 0.5 μm, 1 μm, 2 μm, 3 μm, 4 μm, or 5 μm, etc. It is understood that the particle size D50 of lithium titanate is not limited to the listed values, and other unlisted values ​​within the range are also applicable. Preferably, it is 0.1 μm to 1 μm.

[0039] Lithium titanate has a moderate particle size and suitable specific surface area, which is conducive to the adsorption and dispersion of the coating precursor, and to the formation of a continuous, uniform and complete coating layer. It can also effectively prevent the agglomeration of lithium titanate particles during the preparation process, and is conducive to the formation of a uniform and continuous coating layer on the surface of each lithium titanate particle.

[0040] In some embodiments, lithium titanate is in the form of secondary spherical particles. Specifically, lithium titanate is composed of spherical secondary particles formed by the close packing of primary particles with a particle size of 50–300 nm. Micron-sized secondary spheres are less prone to agglomeration, making it easier to achieve uniform encapsulation of each secondary sphere by the precursor gel.

[0041] The second aspect of this application discloses a method for preparing a composite negative electrode active material as described in the first aspect, comprising the following steps:

[0042] S1. Disperse lithium titanate particles in a solvent to form a suspension;

[0043] S2. Add lithium source, aluminum source, titanium source and phosphorus source to the suspension to prepare the first intermediate product, and evaporate and dry the first intermediate product to obtain the second intermediate product in dry powder form.

[0044] S3. The second intermediate product is subjected to heat treatment to obtain a composite negative electrode active material.

[0045] In some embodiments, in step S1, the solvent is one of ethanol, deionized water, or a mixture of ethanol and deionized water.

[0046] In some embodiments, in step S1, the mass percentage of lithium titanate particles in the suspension is 0.1 g / ml to 0.5 g / ml. Exemplarily, the mass percentage of lithium titanate particles is 0.1 g / ml, 0.2 g / ml, 0.3 g / ml, 0.4 g / ml, 0.5 g / ml, etc. It is understood that the mass percentage of lithium titanate particles is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0047] In some embodiments, in step S2, the lithium source, aluminum source, titanium source and phosphorus source are dissolved in a second solvent to form a precursor sol, and the precursor sol is added to the suspension.

[0048] In some embodiments, the lithium source includes at least one of lithium nitrate, lithium carbonate, and lithium acetate.

[0049] In some embodiments, the aluminum source includes at least one of aluminum nitrate, aluminum oxide, aluminum hydroxide, and aluminum carbonate.

[0050] In some embodiments, the titanium source includes at least one of tetraethoxytitanium, tetrabutyl titanate, and titanium nitrate.

[0051] In some embodiments, the phosphorus source includes at least one of triethyl phosphate, ammonium dihydrogen phosphate, diammonium hydrogen phosphate, and lithium phosphate.

[0052] In some embodiments, the second solvent includes ethanol.

[0053] In some embodiments, in step S2, the precursor sol is slowly added dropwise to the lithium titanate suspension while continuously stirring.

[0054] In some embodiments, the evaporation temperature in step S2 is 60°C to 100°C. Exemplarily, the evaporation temperature can be selected from 60°C, 65°C, 70°C, 75°C, 80°C, 85°C, 90°C, or 100°C, etc. It is understood that the evaporation temperature is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0055] In some embodiments, the heat treatment temperature in step S3 is 400°C to 800°C. Exemplarily, the heat treatment temperature can be selected from 400°C, 450°C, 500°C, 550°C, 600°C, 650°C, 700°C, 750°C, or 800°C, etc. It is understood that the heat treatment temperature is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0056] In some embodiments, the heat treatment time is 3 to 10 hours. For example, the heat treatment time can be selected as 3 hours, 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours, or 10 hours. It is understood that the heat treatment time is not limited to the listed values, and other unlisted values ​​within the range are also applicable.

[0057] Heat treatment allows the precursor to crystallize and form a shell structure. By controlling the temperature and time of the heat treatment, the uniformity and integrity of the shell coating can be effectively improved, which is beneficial for forming a continuous, uniform, and complete coating on the surface of lithium titanate.

[0058] In some implementations, the heat treatment is carried out in air or oxygen.

[0059] The third aspect of this application discloses a negative electrode, comprising a composite negative electrode active material as described in the first aspect and / or a composite negative electrode active material prepared by the preparation method described in the second aspect.

[0060] In some embodiments, the negative electrode includes a negative electrode current collector and a negative electrode layer disposed on at least one side surface of the negative electrode current collector, the negative electrode layer including the aforementioned composite negative electrode active material.

[0061] In some embodiments, the composite negative electrode active material accounts for 50% to 97% of the mass of the negative electrode layer.

[0062] In some embodiments, the negative current collector may be a metal foil, metal mesh or wire mesh, or mesh metal containing copper or any other suitable conductive material known to those skilled in the art.

[0063] In some embodiments, the negative electrode layer also includes a negative electrode binder.

[0064] In some embodiments, the negative electrode binder may be selected from at least one or a combination of several of polytetrafluoroethylene (PTFE), sodium carboxymethyl cellulose (CMC), styrene-butadiene rubber (SBR), polyvinylidene fluoride (PVDF), nitrile rubber (NBR), styrene-ethylene-butene-styrene copolymer (SEBS), styrene-butadiene-styrene copolymer (SBS), lithium polyacrylate (LiPAA), sodium polyacrylate (NaPAA), sodium alginate, and lithium alginate.

[0065] In some embodiments, the negative electrode binder accounts for 0.1% to 20% of the mass of the negative electrode layer.

[0066] In some embodiments, the negative electrode layer also includes a negative electrode conductive agent.

[0067] In some embodiments, the negative electrode conductive agent may include one or more of carbon-based materials, powdered nickel or other metal particles, or conductive polymers. Exemplarily, the carbon-based material may be carbon black, graphite, SuperP, acetylene black (such as KETCHENTM black or DENKATM black), carbon fiber, nanotubes, graphene, etc. The conductive polymer may be polyaniline, polythiophene, polyacetylene, polypyrrole, poly(3,4-ethylenedioxythiophene)polysulfonated styrene, etc.

[0068] In some embodiments, the mass percentage of the negative electrode conductive agent in the negative electrode layer is 0.1% to 20%.

[0069] In some implementations, the negative electrode layer also includes a fast ion conductor for constructing an efficient lithium-ion transport channel within the negative electrode layer.

[0070] In some embodiments, the fast ion conductor includes one or a mixture of several of the following: oxide solid electrolyte, sulfide solid electrolyte, halide solid electrolyte, and lithium salt.

[0071] In some embodiments, the oxide solid electrolyte may comprise one or more garnet ceramics, LISICON-type oxides, NASICON-type oxides, and perovskite-type ceramics. For example, one or more garnet ceramics may be selected from the group consisting of: Li 6.5 La 24 Zr 1.75 Te 0.25 O 12 、Li7La 24 Zr2O 12 Li 6.2 Ga 0.24 La 2.95 Rb 0.05 Zr2O 12 Li 6.85 La 2.9 Ca 0.1 Zr 1.75 Nb 0.25 O 12 Li 6.25 Al 0.25 La 24 Zr2O 12 Li 6.75 La 24 Zr 1.75 Nb 0.25 O 12Li 6.75 La 24 Zr 1.75 Nb 0.25 O 12 And combinations thereof. One or more LISICON-type oxides may be selected from the group consisting of: Li 14 Zn(GeO4)4, Li 24+x (P 1-x Si x O4 (where 0 < x < 1), Li 24+x Ge x V 1-x O4 (where 0 < x < 1) and combinations thereof. One or more NASICON-type oxides can be produced from LiMM′(PO4). 24 Defined where M and M′ are independently selected from Al, Ge, Ti, Sn, Hf, Zr, and La. For example: in some variants, one or more NASICON-type oxides may be selected from the group consisting of: Li 1+x Al x Ge 2-x (PO4) 24 (LAGP) (where 0 ≤ x ≤ 2), Li 1+x Al x Ti 2-x (PO4) 24 (LATP) (where 0 ≤ x ≤ 2), Li 1+x Y x Zr2-x(PO4)24(LYZP) (where 0≤x≤2), Li 1.24 Al 0.24 Ti 1.7 (PO4) 24 LiTi2(PO4) 24 LiGeTi(PO4) 24 LiGe2(PO4) 24 LiHf2(PO4) 24 And combinations thereof. One or more perovskite ceramics may be selected from the group consisting of: Li 24.24 La 0.524 TiO 24 LiSr 1.65 Zr 1.24 Ta 1.7 O9、Li 2x-y Sr 1-x Ta y Zr 1-y O 24 (where x = 0.75y and 0.60 < y < 0.75), Li 24 / 8 Sr 7 / 16Nb 24 / 4 Zr 1 / 4 O 24 Li 24x La (2 / 24-x) TiO 24 (where 0 < x < 0.25) and combinations thereof. In one variant, one or more oxide-based materials may have a value greater than or equal to about 10. -5 S / cm to less than or equal to approximately 10 -1 Ionic conductivity in S / cm.

[0072] In some embodiments, the sulfide solid electrolyte may include one or more sulfide-based materials selected from the group consisting of: Li2S-P2S5, Li2S-P2S5-MS x (where M is Si, Ge, and Sn and 0 ≤ x ≤ 2), Li 24.4 Si 0.4 P 0.6 S4, Li 10 GeP2S 11.7 O 0.24 Li 9.6 P 24 S 12 Li7P 24 S 11 Li9P 24 S9O 24 Li 10.245 Si 1.245 P 1.65 S 12 Li 9.81 Sn 0.81 P 2.19 S 12 Li 10 (Si 0.5 Ge 0.5 P2S 12 Li (Ge 0.5 Sn 0.5 P2S 12 Li 10 GeP2S 12 (LGPS), Li6PS5X (where X is Cl, Br, or I), Li7P2S8I, Li 10.245 Ge 1.245 P 1.65 S 12 Li 24.25 Ge 0.25 P 0.75 S4, Li 10 SnP2S 12 Li 10 SiP2S 12Li 9.54 Si 1.74 P 1.44 S 11.7 Cl 0.24 (1-x)P₂S₅-xLi₂S (where 0.5 ≤ x ≤ 0.7) and combinations thereof. In one variant, one or more sulfide-based materials may have a content greater than or equal to about 10 -7 Ionic conductivity from S / cm to less than or equal to about 1 S / cm.

[0073] In some embodiments, the halide solid electrolyte includes Li a M b X c N d M includes one or more of the basic metal elements, such as Zr, Hf, In, Sc, Y, La, Ce, Pr, Nb, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. M also includes doped metal elements, used in conjunction with the aforementioned basic metal elements, such as one or more of Nb, Ta, Al, La, Mg, Ca, Ba, and Ag. X includes one or more of F, Cl, Br, and I. N includes one or more of O and S, and satisfies a + mb = c + nd, where m and n are the weighted valences of M and N, respectively, and 1 ≤ a ≤ 4.

[0074] In some embodiments, the halide solid electrolyte particles can be Li₂ZrCl₆, Li₂ZrCl₅F, or Li₂ZrCl₆. 5.5 O 0.25 At least one of Li3InCl6, Li3YCl6, Li2HfCl6, LiInBr4, Li3InBr6, Li3LaI6, Li3LuCl6, and Li3ErCl6.

[0075] In some embodiments, the lithium salt includes LiNbO3 and Li4Ti5O. 12 At least one of Li2TiO3, LiAlO2, LiTaO3, LiMoO3, Li2RuO3 or Li2WO4.

[0076] In some preferred embodiments, the negative electrode layer includes at least an oxide solid electrolyte Li1+xAlxTi2-x-yMy(PO4)3.

[0077] In some embodiments, the negative electrode layer can be prepared by wet or dry methods. The dry process involves uniformly mixing the negative electrode active particles, negative electrode conductive agent, and negative electrode binder, then subjecting the mixture to fibrillation treatment. Under the fibrillation effect of the negative electrode binder, a self-supporting film is formed, and finally, it is rolled onto the surface of the negative electrode current collector. The wet process involves adding a solvent (such as NMP) to the negative electrode active particles, negative electrode conductive agent, and negative electrode binder to form a slurry. The slurry is then coated onto the surface of the negative electrode current collector using a coating machine, and after drying, a negative electrode sheet is formed.

[0078] Understandably, when using a dry method to prepare the negative electrode layer, the negative electrode binder needs to include a fiberizable binder. The fiberizable binder transforms from particulate to fibrous under high shear force, thereby achieving the bonding of the composite negative electrode active material, negative electrode conductive agent, and solid electrolyte.

[0079] In some embodiments, the fiberizable binder includes one or more of polytetrafluoroethylene, polyvinylidene fluoride, polyvinylidene fluoride hexafluoropropylene, polypropylene, polyethylene, and polyimide.

[0080] In some embodiments, to further enhance the adhesion ability of the negative electrode binder to the negative electrode, the negative electrode binder may further include at least one of the following: polyvinyl alcohol, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0081] The fourth aspect of this application discloses a battery including a positive electrode, a separator and / or a solid electrolyte membrane, and a negative electrode as described in the third aspect.

[0082] In some embodiments, the positive electrode includes a positive current collector and a positive electrode layer disposed on the positive current collector.

[0083] In some preferred embodiments, the positive electrode layer is disposed on both sides of the positive electrode current collector.

[0084] In some embodiments, the positive electrode layer includes a positive electrode active material, which includes a compound that can reversibly insert and deintercalate lithium ions.

[0085] In some embodiments, the positive electrode active material comprises one or more transition metal cations, such as manganese (Mn), nickel (Ni), cobalt (Co), chromium (Cr), iron (Fe), vanadium (V), and combinations thereof.

[0086] In some embodiments, the positive electrode active material is one of layered oxides, spinel, and polyanionic materials. For example, layered oxides (e.g., rock salt layered oxides) comprise one or more lithium-based positive electrode active materials selected from: LiCoO2 (LCO), LiNi x Mn y Co 1-x-y O2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNi 1-x-y Co x Al y O2 (where 0 ≤ x ≤ 1 and 0 ≤ y ≤ 1), LiNi x Mn 1-x O2 (where 0 ≤ x ≤ 1), and Li 1+x MO2 (where M is one of Mn, Ni, Co, and Al and 0 ≤ x ≤ 1). Spinel contains one or more lithium-based cathode active materials selected from the following: LiMn2O4 (LMO) and LiNi. x Mn 1.5 O4. The olivine type contains one or more lithium-based positive electrode active materials, LiMPO4 (where M is at least one of Fe, Ni, Co, and Mn). The polyanionic cation contains, for example, phosphates such as LiV2(PO4). 24 And / or silicates such as LiFeSiO4.

[0087] In some embodiments, the mass of the positive electrode active material accounts for 60% to 95% of the mass of the positive electrode layer.

[0088] In some embodiments, the positive electrode layer includes a binder. The binder improves the bonding between the positive electrode active material particles and also improves the bonding between the positive electrode layer and the positive electrode current collector.

[0089] In some embodiments, non-limiting examples of adhesives include polyvinyl alcohol,

[0090] Hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, polyvinyl fluoride, polymers containing ethylene oxide, polyvinylpyrrolidone, polyurethane, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, styrene-butadiene rubber, acrylated styrene-butadiene rubber, epoxy resin, nylon, etc.

[0091] In some embodiments, the binder accounts for 0.1% to 20% of the mass of the positive electrode layer.

[0092] In some embodiments, the positive electrode layer includes a conductive agent, thereby imparting conductivity to the electrode. The conductive agent may include any conductive material, as long as it does not cause a chemical change. Non-limiting examples of conductive materials include carbon-based materials (e.g., natural graphite, synthetic graphite, carbon black, acetylene black, Ketjen black, carbon fiber, etc.), metal-based materials (e.g., metal powders, metal fibers, etc., including, for example, copper, nickel, aluminum, silver, etc.), conductive polymers (e.g., polyphenylene derivatives), and mixtures thereof.

[0093] In some embodiments, the conductive agent accounts for 0.1% to 20% of the mass of the positive electrode layer.

[0094] In some embodiments, the positive electrode layer provided in this application further includes a fast ion conductor to improve the ionic conductivity of the positive electrode layer. This application does not limit the type of fast ion conductor, which can be an oxide solid electrolyte, a sulfide solid electrolyte, a halide solid electrolyte, a lithium salt, etc.

[0095] In some embodiments, the mass of the fast ion conductor accounts for 1% to 20% of the mass of the positive electrode layer; preferably 5% to 20%.

[0096] In some embodiments, the positive current collector includes a metallic material that can conduct electrons; for example, the positive current collector includes at least one of Al, Ni, tin, copper, and stainless steel.

[0097] In some embodiments, the surface of the aluminum foil can be anodized to form a nanoscale aluminum oxide layer to enhance its corrosion resistance and interfacial adhesion with the cathode material.

[0098] In some implementations, the aluminum alloy foil may contain trace amounts of titanium (Ti) or (Si) to enhance mechanical strength and high-temperature stability.

[0099] In some embodiments, the aluminum foil may also be carbon-coated aluminum foil.

[0100] In this application, the battery can be a liquid lithium battery, a semi-solid lithium battery, or an all-solid lithium battery.

[0101] In some embodiments, the solid electrolyte membrane includes inorganic solid electrolytes and / or polymer solid electrolytes.

[0102] Inorganic solid electrolytes include oxide solid electrolytes, sulfide solid electrolytes, and halide solid electrolytes.

[0103] In some embodiments, the separator separates the negative and positive electrodes and provides a path for lithium ions to move. Any separator can be used without particular limitation, as long as it is a commonly used separator. A separator with excellent electrolyte moisture content and low resistance to ion movement in the electrolyte is preferred. Porous polymer membranes can be used, such as porous polymer membranes made from polyolefin polymers such as ethylene homopolymers, propylene homopolymers, ethylene / butene copolymers, ethylene / hexene copolymers, and ethylene / methacrylate copolymers, or laminated structures having two or more layers. Typical porous nonwoven fabrics can also be used, such as nonwoven fabrics formed from high-melting-point glass fibers, polyethylene terephthalate fibers, etc. Furthermore, coated separators containing ceramic components or polymer materials can be used to ensure heat resistance or mechanical strength, and can be selectively used in single-layer or multi-layer structures.

[0104] In some embodiments, the battery is a liquid lithium battery or a semi-solid lithium battery, and the battery also includes an electrolyte, which includes a solvent, an electrolyte salt, and electrolyte additives.

[0105] In some embodiments, the solvent includes a non-aqueous organic solvent.

[0106] In some embodiments, the non-aqueous organic solvent includes one or more of carbonate solvents, carboxylic acid ester solvents, and aromatic hydrocarbon solvents.

[0107] In some embodiments, the carbonate solvent includes halocarbonates and / or non-halocarbonates.

[0108] In some embodiments, the halogenated carbonate includes one or more of fluoroethylene carbonate, difluoropropylene carbonate, trifluoroethyl methyl carbonate, trifluoromethyl ethylene carbonate, 4-trifluoromethyl ethylene carbonate, chloroethylene carbonate, di(2,2,2-trifluoroethyl) carbonate, or 1,1,1,3,3,3-hexafluoroisopropyl acrylate.

[0109] In some embodiments, the non-halogenated carbonate includes one or more of ethylene carbonate, propylene carbonate, diethyl carbonate, dimethyl carbonate, or ethyl methyl carbonate.

[0110] In some embodiments, the carboxylic acid ester solvent includes halocarboxylic acid esters and / or non-halocarboxylic acid esters.

[0111] In some embodiments, the halocarboxylic acid ester includes one or more of propyl fluorobutyrate, propyl fluoroacetate, ethyl fluoroacetate, isopropyl fluoroacetate, butyl fluoropropionate, isopropyl fluoropropionate, ethyl fluorobutyrate, methyl fluoropropionate, ethyl fluoropropionate, or propyl fluoropropionate.

[0112] In some embodiments, the non-halogenated carboxylic acid esters include one or more of ethyl acetate, methyl acetate, propyl butyrate, propyl acetate, isopropyl acetate, butyl propionate, isopropyl propionate, ethyl butyrate, methyl propionate, ethyl propionate, or propyl propionate.

[0113] In some embodiments, the aromatic hydrocarbon solvent includes halogenated aromatic hydrocarbons and / or non-halogenated aromatic hydrocarbons.

[0114] In some embodiments, the halogenated aromatic hydrocarbon includes one or more of monofluorobenzene, difluorobenzene, 1,3,5-trifluorobenzene, trifluorotoluene, 2-fluorotoluene, or 2,4-dichlorotrifluorotoluene.

[0115] In some embodiments, the electrolyte salt includes one or more of lithium hexafluorophosphate (LiPF6), lithium hexafluoroarsenate (LiAsF6), lithium perchlorate (LiClO4), lithium bisfluorosulfonylimide (LiFSI), lithium tetrafluoroborate (LiBF4), and lithium bistrifluoromethanesulfonylimide (LiTFSI).

[0116] In some embodiments, the electrolyte salt is present in the electrolyte at a mass percentage of 0.5% to 20%, including but not limited to 0.5%, 1%, 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12%, 13%, 14%, 15%, 16%, 17%, 18%, 19%, and 20%.

[0117] In some embodiments, the electrolyte additive includes one or more of sulfonyl lactones, cyclic sulfates, phosphates, and borates.

[0118] In some embodiments, the electrolyte additive constitutes 0.1% to 5% by mass in the electrolyte, including but not limited to 0.1%, 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, and 5.0%.

[0119] In some embodiments, the sulfonyl lactone compound is selected from one or more of 1,3-propanesulfonyl lactone, 1,4-butanesulfonyl lactone, and propenyl-1,3-sulfonyl lactone.

[0120] In some embodiments, the cyclic sulfate compound is selected from one or more of vinyl sulfate, 4-methylvinyl sulfate, and propylene sulfate.

[0121] In some embodiments, the phosphate ester compound is selected from at least one of saturated phosphate ester compounds and unsaturated phosphate ester compounds. The saturated phosphate ester compounds include tris(trimethylsilane) phosphate; the unsaturated phosphate ester compounds include at least one of triallyl phosphate, triallyl phosphite, and hydroxyethyl methacrylate phosphate.

[0122] In some embodiments, the borate ester compound is selected from one or more of tris(trimethylsilane)borate and tris(triethylsilane)borate.

[0123] The fifth aspect of this application discloses an electrical device including a battery as described in the fourth aspect.

[0124] The electrical device used in this application is not particularly limited and can be any electrical device known in the prior art. For example, the electrical device may include, but is not limited to, laptops, pen input computers, mobile computers, e-book players, portable telephones, portable fax machines, portable copiers, portable printers, stereo headphones, video recorders, LCD TVs, portable cleaners, portable CD players, mini CDs, transceivers, electronic notebooks, calculators, memory cards, portable recorders, radios, backup power supplies, motors, automobiles, motorcycles, electric bicycles, bicycles, lighting fixtures, toys, game consoles, clocks, power tools, flashlights, cameras, household large-capacity batteries, and lithium-ion capacitors.

[0125] To better understand the above-mentioned objectives, features, and advantages of this application, the solutions of this application will be further described below through embodiments and comparative examples. Obviously, the embodiments in this specification are only one embodiment of this application, and not all embodiments.

[0126] Example 1:

[0127] This embodiment provides a composite negative electrode active material, which has a core-shell structure, with the core comprising lithium titanate Li4Ti5O. 12 The shell includes Li 1.3 Al 0.3 Ti 1.7 (PO4)3. Lithium titanate consists of secondary spherical particles with a particle size D50 = 0.75 μm.

[0128] The shell thickness is 7.5 nm. In the composite negative electrode active material, the shell accounts for 3% of the total mass. The preparation method of the above composite negative electrode active material includes the following steps:

[0129] S1. Disperse lithium titanate particles in anhydrous ethanol, mechanically stir and sonicate to form a uniform suspension; the mass percentage of lithium titanate particles in the suspension is 0.2 g / ml.

[0130] S2. The lithium source (lithium nitrate), aluminum source (aluminum nitrate), titanium source (tetrabutyl titanate), and phosphorus source (triethyl phosphate) are mixed according to the following formula: 1.3 Al 0.3 Ti 1.7 (PO4)3 was dissolved in anhydrous ethanol in a stoichiometric ratio to form a transparent sol. The precursor sol was slowly added dropwise to a lithium titanate suspension under continuous stirring to prepare an intermediate product. The solvent was evaporated at 80°C to obtain a dry powder.

[0131] S3. The intermediate product is subjected to heat treatment to obtain a composite negative electrode active material. The heat treatment is carried out in an air atmosphere, the heat treatment temperature is 600℃, the heat treatment time is 4h, and the heat treatment method is calcination.

[0132] Among them, Li 1.3 Al 0.3 Ti 1.7 (PO4)3 accounts for 3% of the mass of the composite negative electrode active material.

[0133] Preparation of the negative electrode:

[0134] The above composite negative electrode active material and solid electrolyte powder (Li7La3Zr2O) were used. 12 The conductive agent Super-P and the binder PTFE are mixed in a mass ratio of 80:15:4.6:0.4 and then pressed to form a negative electrode sheet.

[0135] Preparation of solid electrolyte membranes:

[0136] Solid electrolyte powder (Li7La3Zr2O) 12 The electrolyte is mixed with PVDF binder at a mass ratio of 99.5:0.5 and then pressed to form a solid electrolyte membrane.

[0137] Preparation of the positive electrode:

[0138] The positive electrode active material LiMn2O4 and the solid electrolyte powder Li7La3Zr2O were used. 12 Conductive agent Super-P and binder PTFE are mixed in a mass ratio of 80:15:4.6:0.4 and then pressed to form a positive electrode sheet.

[0139] Fabrication of all-solid-state batteries:

[0140] The negative electrode, solid electrolyte membrane, and positive electrode are stacked in sequence and hot-pressed at a high temperature of 80°C and a high pressure of 500MPa to form an all-solid-state battery.

[0141] Example 2:

[0142] Referring to Example 1, the only difference from Example 1 is that the mass ratio of the shell in the composite negative electrode active material is 0.5%, and the thickness of the shell layer is 1 nm.

[0143] Example 3:

[0144] Referring to Example 1, the only difference from Example 1 is that the mass ratio of the shell in the composite negative electrode active material is 1%, and the thickness of the shell layer is 3.5 nm.

[0145] Example 4:

[0146] Referring to Example 1, the only difference from Example 1 is that in the composite negative electrode active material, the mass ratio of the shell is 5%, and the thickness of the shell layer is 15 nm.

[0147] Example 5:

[0148] Referring to Example 1, the only difference from Example 1 is that in the composite negative electrode active material, the mass ratio of the shell is 8%, and the thickness of the shell layer is 25 nm.

[0149] Example 6:

[0150] Referring to Example 1, the only difference from Example 1 is that the shell in the composite negative electrode active material includes Li 1.3 Al 0.27 Ga 0.03 Ti 1.7 (PO4)3.

[0151] Comparative Example 1:

[0152] Referring to Example 1, the only difference from Example 1 is that lithium titanate is used instead of the composite negative electrode active material.

[0153] Comparative Example 2

[0154] Referring to Example 1, the only difference from Example 1 is that the shell of the composite negative electrode active material includes carbon. The composite negative electrode active material is lithium carbonate particles coated with a carbon layer.

[0155] Performance testing

[0156] The performance of the composite negative electrode active materials and the prepared batteries of the above embodiments and comparative examples was tested.

[0157] 1) Coating thickness test

[0158] The composite negative electrode active material powder was ultrasonically dispersed in ethanol, then dropped onto an ultrathin carbon film copper grid, dried, and the sample was observed using a high-resolution transmission electron microscope. The average value was taken from ten different positions.

[0159] 2) Discharge capacity test

[0160] The prepared battery was discharged at a constant current of 1C until the discharge cutoff voltage of 1.8V, and the discharge capacity of the battery was recorded.

[0161] 3) Cyclic performance test

[0162] 1. Place the battery in an ambient temperature of 25±2℃, charge it at 1C until the charging cutoff voltage is 3V and the cutoff current is 0.05C, and let it stand for 1 hour;

[0163] 2. Under ambient temperature of 25±2℃, discharge at a constant current of 1C until the discharge cutoff voltage is 1.8V, and let stand for 1 hour;

[0164] 3. Repeat steps 1 and 2 for 200 cycles and calculate the capacity retention rate; Cyclic capacity retention rate = Discharge capacity on the 200th cycle / Discharge capacity on the first cycle × 100%.

[0165] 4) Ratio Performance Test

[0166] Discharge the fully charged battery at a constant current of 1C until the discharge cutoff voltage of 1.8V, and record the discharge capacity C0 of the battery.

[0167] Discharge the fully charged battery at a constant current of 5C until the discharge cutoff voltage of 1.8V, and record the discharge capacity C1 of the battery.

[0168] Rate performance (5C capacity retention rate) = C1 / C0 * 100%.

[0169] 5) Energy density test:

[0170] 1. Weigh the battery and measure its mass m;

[0171] 2. Charge at 1C until the charging termination voltage is 3V, with a cutoff current of 0.05C, and let stand for 1 hour; discharge at 1C constant current until the lower limit voltage is 1.8V, and let stand for 1 hour; record the battery's discharge capacity Q and average discharge voltage V. Energy density = (Q + V) / m.

[0172] The results are shown in the table below:

[0173]

[0174] As shown in the table above, compared to Comparative Example 1, Examples 1-6 showed better results in coating Li on the surface of lithium titanate. 1+x Al x-a M a Ti 2-x-yThe Ny(PO4)3 layers form a core-shell structure, which can effectively improve the contact between the composite negative electrode active material and the solid electrolyte, and enhance the lithium-ion transport efficiency within the negative electrode. This can effectively improve the battery's capacity performance, cycle performance, and rate performance, thereby increasing the battery's energy density.

[0175] Compared to Comparative Example 2, Example 1 exhibits superior electrochemical performance, possibly because the use of Li compared to a carbon coating layer... 1+x Al x-a M a Ti 2-x-y The Ny(PO4)3 layer can effectively improve the lithium-ion transport effect without causing side reactions.

[0176] It should be noted that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A composite negative electrode active material, characterized in that, The composite negative electrode active material has a core-shell structure, the core comprising lithium titanate, and the shell comprising Li. 1+x Al x-a M a Ti 2-x-y Ny(PO4)3, where M is one of the trivalent metal elements La and Ga, and N is one of the tetravalent metal elements Zr and Si, 0.3≤x≤0.5, 0.01≤a≤0.1, 0.01≤b≤0.

1.

2. The composite negative electrode active material as described in claim 1, characterized in that, The shell thickness is 2nm to 20nm.

3. The composite negative electrode active material as described in claim 1, characterized in that, In the composite negative electrode active material, the shell accounts for 1% to 5% of the total mass.

4. The composite negative electrode active material as described in claim 1, characterized in that, The particle size D50 of the lithium titanate particles is 0.5 to 1 μm.

5. The composite negative electrode active material as described in claim 1, characterized in that, The lithium titanate is in the form of secondary spherical particles.

6. The method for preparing the composite negative electrode active material as described in claim 1, characterized in that, Includes the following steps: S1. Disperse lithium titanate particles in a solvent to form a suspension; S2. Add lithium source, aluminum source, titanium source and phosphorus source to the suspension to prepare a first intermediate product, and perform evaporation and drying treatment on the first intermediate product to obtain a dry powdered second intermediate product. S3. The second intermediate product is subjected to heat treatment to obtain a composite negative electrode active material.

7. The preparation method according to claim 6, characterized in that, In step S2, lithium source, aluminum source, titanium source and phosphorus source are dissolved in solvent to form precursor sol, and the precursor sol is added to the suspension.

8. The preparation method according to claim 6, characterized in that, At least one of the following conditions must be met: 1) The temperature of the heat treatment is 400℃~800℃; 2) The heat treatment time is 3h to 10h; 3) The heat treatment is carried out in air or oxygen.

9. Negative electrode, characterized in that, It includes the composite negative electrode active material as described in any one of claims 1 to 5 and / or the composite negative electrode active material prepared by the preparation method as described in any one of claims 6 to 8.

10. A battery, characterized in that, It includes a positive electrode, a separator and / or a solid electrolyte membrane, and a negative electrode as described in claim 9.

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