CN112289982B - Positive electrode material, preparation method thereof and solid-state lithium battery - Google Patents
Positive electrode material, preparation method thereof and solid-state lithium battery Download PDFInfo
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Abstract
The invention provides a positive electrode material, a preparation method thereof and a solid-state lithium battery. The positive electrode material has a coating layer with excellent properties, and the coating layer has higher electronic conductivity and ionic conductivity, so that an electronic conductive path and an ionic transmission path can be simultaneously constructed by the coated positive electrode material, and the battery performance is favorably improved.
Description
Technical Field
The invention relates to the field of lithium ion battery anode materials, in particular to an anode material, a preparation method thereof and a solid-state lithium battery.
Background
The traditional lithium ion battery adopts organic liquid as electrolyte to transmit lithium ions, but the problems of liquid leakage, gas expansion and the like are easy to occur, and even the battery is caused to be fired and exploded in severe cases, so that the battery has potential safety hazards. The all-solid-state lithium battery adopts the all-solid-state electrolyte to replace a diaphragm and electrolyte in the traditional battery to transmit lithium ions, so that the all-solid-state lithium battery is safer compared with organic electrolyte.
In the existing all-solid-state lithium battery based on inorganic solid electrolyte, a side reaction between a high-voltage positive electrode material and a solid electrolyte material exists, so that the capacity of the battery is rapidly reduced. Therefore, it is necessary to perform surface coating treatment on the positive electrode material, and the coating material generally used is an oxide, a lithium-containing transition metal oxide, or the like, such as LiNbO 3 、LiTaO 3 、Li 4 Ti 5 O 12 、Al 2 O 3 And the like. Wherein, liNbO is used 3 The coated cathode material is most widely applied, and the surface coating can reduce the occurrence of side reactions between the cathode material and the solid electrolyte which is not resistant to oxidation, thereby improving the overall performance of the battery. However, these coating materials have low ionic conductivity and low electron conductivity, and thus, although side reactions between the positive electrode material and the solid electrolyte are suppressed to some extent, the formation of electron paths of the positive electrode material is also hindered. Therefore, it is necessary to improve the overall coating of the positive electrode material by adding a conductive agent after the post-coatingThe electron conductivity, however, the addition of the conductive agent hinders the formation of ion channels in the positive electrode material to some extent, and the performance of the battery as a whole still cannot be improved.
Disclosure of Invention
The invention provides a positive electrode material, a preparation method thereof and a solid-state lithium battery, aiming at solving the technical problem that the positive electrode material with a coating layer in the prior art has lower electronic conductivity and ionic conductivity.
In order to achieve the above object, in a first aspect, the present invention provides a positive electrode material including a positive electrode active material and a coating layer coated on a surface of the positive electrode active material, the coating layer including a transition metal sulfide and a transition metal oxide, the transition metal oxide being generated in situ from a portion of the transition metal sulfide.
Compared with the prior art in which a transition metal sulfide or a transition metal oxide is singly coated, the coating layer of the positive electrode material provided by the invention simultaneously contains the transition metal sulfide and the transition metal oxide, wherein the transition metal sulfide has better electronic conductivity, and the transition metal oxide has good ionic conductivity, so that the positive electrode material provided by the invention simultaneously has electronic conductivity and ionic conductivity, and an electronic conduction path and an ionic conduction path can be simultaneously constructed in a battery in the battery cycle, and the two paths are indispensable in the battery cycle, so that the battery is more stable in the cycle, the phenomenon of rapid capacity attenuation cannot occur, and the improvement of the battery performance is facilitated. If the transition metal sulfide and the transition metal oxide are simply mixed and then coated, due to the difference in morphology between the two materials, for example, the transition metal disulfide is in a flaky morphology, the transition metal oxide is in a granular morphology, and the flaky sulfide is more advantageous in coating, when the transition metal disulfide and the flaky sulfide are mixed and coated, the flaky sulfide with electronic conductivity can cover the surface of the positive electrode material in a large area, so that the coating of the oxide with ionic conductivity is greatly hindered, the coating effect is not good, and the transmission of electrons and ions in the battery is influenced due to the mutual interference between an electronic conduction path and an ionic conduction path. Therefore, the transition metal oxide in the coating layer of the positive electrode material provided by the invention is generated in situ on the basis of the transition metal sulfide, namely, part of the transition metal sulfide in the coating layer is directly converted into the transition metal oxide, so that the consistency of the shapes of the transition metal sulfide and the transition metal oxide can be ensured, a good coating effect is achieved, an electronic conducting path and an ionic conducting path built in the battery cannot interfere with each other, the cycle performance of the battery is greatly improved, and the ionic conducting path and the electronic conducting path can be simultaneously built in the battery cycle by the positive electrode material.
In a second aspect, the invention provides a preparation method of the above cathode material, comprising the following steps:
(1) Mixing the positive active substance with transition metal sulfide, and reacting at 100-300 ℃;
(2) And (2) sintering the reactant obtained in the step (1) in an inert atmosphere to obtain the anode material coated by the transition metal sulfide and the transition metal oxide together.
The transition metal sulfide and the transition metal oxide jointly coated positive electrode material can be prepared by the method, and the transition metal oxide is generated in situ on the transition metal sulfide, namely the transition metal oxide is obtained by directly converting part of the transition metal sulfide in the coating layer, so that the obtained coating layer has high ionic conductivity and electronic conductivity at the same time, and the prepared positive electrode material can simultaneously construct an ionic conduction path and an electronic conduction path, thereby being beneficial to improving the cycle performance of the battery. Moreover, the transition metal oxide generated in situ does not damage the appearance of the transition metal sulfide, but keeps consistent with the transition metal sulfide, so that a better coating effect can be achieved, and the purposes of isolating the positive active material from the solid electrolyte and avoiding side reactions between the positive active material and the solid electrolyte are achieved.
In a third aspect, the invention provides a solid-state lithium battery, which comprises the above positive electrode material or the positive electrode material prepared by the above preparation method.
In the solid-state lithium battery, the surface of the anode material is simultaneously coated with transition metal sulfide and transition metal oxide, and the coating material has high ionic conductivity and electronic conductivity, so that the anode material can simultaneously construct an ionic conduction path and an electronic conduction path, thereby being beneficial to improving the cycle performance of the battery; in addition, the existence of the coating layer can isolate the contact between the positive electrode active material and the solid electrolyte, and avoid the occurrence of side reaction between the positive electrode active material and the solid electrolyte to influence the performance of the battery.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects solved by the present invention more apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.
In a first aspect, the present invention provides a positive electrode material, including a positive electrode active material and a coating layer coated on the surface of the positive electrode active material, wherein the coating layer includes a transition metal sulfide and a transition metal oxide, and the transition metal oxide is generated in situ from a part of the transition metal sulfide.
The transition metal oxide refers to an oxide corresponding to a transition metal in the transition metal sulfide, that is, the transition metal in the transition metal sulfide and the transition metal in the transition metal oxide are the same metal. In addition, because the transition metal oxide is generated in situ by part of the transition metal sulfide, namely the transition metal sulfide in the coating is partially converted into the transition metal oxide, the transition metal sulfide can provide an electronic path, the transition metal oxide can provide an ionic path, and the transition metal oxide is generated in situ, namely the ionic path is formed on the electronic path.
Furthermore, the transition metal sulfide is of a nanoscale lamellar structure, the diameter of the transition metal sulfide is 5nm-500nm, and the thickness of the transition metal sulfide is 1nm-50nm.
Generally, the adopted coating material is granular, so that the dosage of the coating material needs to be increased when the coating material is required to be coated more uniformly on the positive electrode active substance, the thickness of the coating layer is increased when the dosage of the coating material is increased, the coating effect is poor, and the energy density of the coated positive electrode material is reduced. If the coating material is flaky, a smaller amount of coating material can be adopted to achieve a better coating effect, namely, the coating is more uniform, the thickness of the coating layer is thinner, the volume energy density of the coated anode material can be improved, and the normal performance of the capacity of the anode material is ensured.
The transition metal sulfide with the nanoscale sheet structure is adopted for coating the positive electrode active substance, the transition metal oxide is generated in situ on the basis of the transition metal sulfide, namely, is obtained by converting part of the transition metal sulfide, so that the sheet structure can still be maintained, and the coating material with the sheet structure is coated, so that the coating layer is large in area and complete, the positive electrode active substance can be effectively coated, the contact between the positive electrode active substance and the solid electrolyte is reduced to the greatest extent, and the occurrence of side reaction between the positive electrode active substance and the solid electrolyte is effectively avoided. The transition metal sulfide with the structure is selected for coating, so that the using amount of the transition metal sulfide can be reduced, the thickness of a coating layer is reduced, and the volume energy density of the anode material is improved; on the other hand, the flaky shape enables the coating to be easier to realize and the coating to be more complete.
Further, the transition metal sulfide is selected from MS x (wherein M1 is at least one of Ti, V, nb, ta, W, cr, fe, ni, cu, mo and transition metal, x is more than or equal to 1 and less than or equal to 2.5), and the transition metal oxide is selected from MO y Wherein M is at least one of Ti, V, nb, ta, W, cr, fe, ni, cu, mo and transition metal, and y is more than or equal to 1 and less than or equal to 3.
Further, the transition metal sulfide is a transition metal disulfide.
The transition metal disulfide has a laminated structure, is stable in structure and cannot be oxidized by the anode material.
Further, the mass ratio of the transition metal sulfide in the coating layer is 1-90%.
Further preferably, the transition metal sulfide accounts for 5 to 20% by mass of the coating layer.
Because the electronic conductivity of the transition metal sulfide is extremely high, the battery cycle requirement can be met only by a small amount of transition metal sulfide in the coating layer, and therefore the transition metal oxide in the coating layer has a higher proportion.
Further, the mass ratio of the coating layer in the positive electrode material is 0.01-10%.
The coating amount is less, the occupation ratio of the positive active substance is high, and the energy density of the positive material can be improved.
Further, the thickness of the coating layer is 1-500nm.
The thickness of the coating layer is thinner, so that the positive active material cannot be completely coated, and the side reaction between the positive active material and the solid electrolyte cannot be avoided due to incomplete coating; on the other hand, when the thickness of the coating layer is large, the volumetric energy density of the positive electrode material is reduced, and the large thickness of the coating layer affects the performance of the capacity of the positive electrode material.
Further, the positive electrode active material is selected from LiCoO 2 、LiNiO 2 、LiCo x1 Ni 1-x1 O 2 （0≤x1≤1）、LiCo x2 Ni 1-x2-y1 Al y1 O 2 （0≤x2≤1，0≤y1≤1）、LiMn 2 O 4 、LiFe x3 Mn y2 M z1 O 4 (wherein M1 is at least one of Al, mg, ga, cr, co, ni, cu, zn and Mo, wherein x3 is more than or equal to 0 and less than or equal to 1,0 and less than or equal to y2 is more than or equal to 1,0 and less than or equal to z1, and x3+ y2+ z1= 1), li 1＋x4 L 1－y3－z2 M2 y3 N z2 O 2 (wherein L, M, N is at least one of Li, co, mn, ni, fe, al, mg, ga, ti, cr, cu, zn, mo, F, I, S, B, wherein-0.1. Ltoreq. X4. Ltoreq. 0.2,0. Ltoreq. Y3. Ltoreq. 1,0. Ltoreq. Z2. Ltoreq. 1,0. Ltoreq. Y3+ z 2. Ltoreq.1), liFePO 4 、Li 3 V 2 (PO 4 ) 3 、Li 3 V 3 (PO 4 ) 3 、LiVPO 4 F、Li 2 CuO 2 、Li 5 FeO 4 One or more of them.
In a second aspect, the invention provides a preparation method of the above cathode material, including the following steps:
(1) Dispersing transition metal sulfide into a mixed solution of water and ethanol, adding a positive active substance, uniformly mixing, sealing in a reaction kettle, and carrying out a solvothermal process at 100-300 ℃;
(2) And (2) sintering the reactant obtained in the step (1) in an inert atmosphere to obtain the anode material coated by the transition metal sulfide and the transition metal oxide together.
Further, the concentration of the transition metal sulfide in the step (1) is 0.1-10mg/mL.
Further, the sintering temperature in the step (2) is 300-800 ℃.
Sintering treatment can make the coating layer and the positive active material combined more tightly.
In a third aspect, the invention provides a solid-state lithium battery, which includes the above-mentioned positive electrode material or the positive electrode material prepared by the above-mentioned preparation method.
Further, the solid electrolyte adopted by the solid lithium battery is one or more of garnet type solid electrolyte, NASICON type solid electrolyte, LISICON type solid electrolyte, perovskite type solid electrolyte and sulfur type solid electrolyte.
Further, the garnet-type solid electrolyte is Li 7-3x+y-z A x La 3-y B y Zr 2-z C z O 12 Wherein A is selected from one or more of Ga and Al; b is selected from Ca,One or more of Sr, ba and Ce; c is selected from one or more of Ta, nb, ge, sc, W, zr, hf, sn and Sb, x is more than or equal to 0 and less than or equal to 0.3, and y is more than or equal to 0 and less than or equal to 2.
Further, the NASICON type solid electrolyte is selected from LiM 2 (PO 4 ) 3 LiM containing doping element 2 (PO 4 ) 3 Wherein M is one or more selected from Ti, zr, ge, sn and Pb, and the doping elements are one or more selected from Mg, ca, sr, ba, sc, al, ga, in, nb, ta and V.
Further, the LISICON-type solid electrolyte is Li 14 A(BO 4 ) 4 Wherein A is selected from one or more of Zn, zr, cr and Sn, and B is selected from one or more of Ge, si, S and P.
Further, the chemical formula of the perovskite type solid electrolyte is A x B y TiO 3 、A x B y Ta 2 O 6 、A x B y Nb 2 O 6 、A h M k D n Ti w O 3 Wherein x +3y =2, h +2k +5n +4w =6,0 < x < 2,0 < y < 2/3,h, k, n, w are all greater than 0; a is at least one of Li and Na elements, B is at least one of La, ce, pr, Y, sc, nd, sm, eu and Gd elements, M is at least one of Sr, ca, ba, ir and Pt elements, and D is at least one of Nb and Ta elements.
Further, the sulfur-based solid electrolyte is selected from crystalline Li x M y P z S w (M is one or more of Si, ge and Sn, wherein x +4y +5z =2w, y is more than or equal to 0 and less than or equal to 1.5) and glassy Li 2 S-P 2 S 5 (including Li) 7 P 3 S 11 、70Li 2 S-30P 2 S 5 Etc.) glass-ceramic state Li 2 S-P 2 S 5 Li containing doping element 2 S-P 2 S 5 Wherein the doping element is one or more of F, cl, br, I, B, O, N, se, zn, al and Si.
Further, the particle diameter of the solid electrolyte is preferably in the range of 1nm to 5 μm.
The negative electrode active material used in the solid-state lithium battery is a negative electrode active material capable of intercalating and deintercalating lithium, which is commonly used by those skilled in the art, and may be selected from one or more of carbon materials, tin alloys, silicon, tin, and germanium, and metallic lithium, lithium-indium alloys, and the like may be used. The carbon material may be non-graphitized carbon, graphite, or carbon obtained by high-temperature oxidation of polyacetylene polymer material, or one or more of pyrolytic carbon, coke, organic polymer sinter, and activated carbon.
Further, the preparation method of the solid-state lithium battery is also a commonly used process method in the field, and specifically comprises the following steps:
coating the selected positive electrode material layer (C) on the positive electrode current collector, then coating a solid electrolyte layer (E) on the surface of the positive electrode material layer, and laminating the negative electrode active material layer (A) coated on the negative electrode current collector and the CE layer together to form the solid lithium battery (CEA).
The positive electrode material layer comprises a positive electrode active substance which is compositely coated by transition metal sulfide and transition metal oxide, a conductive agent, a binder and the like, and can be prepared by the existing preparation method:
coating slurry containing a positive active substance compositely coated by a transition metal sulfide and a transition metal oxide, an electrode adhesive and a solvent on a positive current collector, drying, forming a positive material layer on the positive current collector, and then performing rolling treatment at 0-5 MPa to obtain a positive material layer (C). Wherein, the binder is a cathode binder commonly used in the field, and can be one or more of fluorine-containing resin and polyolefin compound, such as polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE) and Styrene Butadiene Rubber (SBR). The conductive agent is a positive conductive agent commonly used in the field, and can be acetylene black, carbon nanotubes, carbon fibers, carbon black and the like. The content of the binder is 0.01 to 10wt%, preferably 0.02 to 5wt%, based on the weight of the positive electrode material; the content of the conductive agent is 0.1 to 20wt%, preferably 1 to 10wt%. Wherein, the solvent can be one or more selected from N-methylpyrrolidone (NMP), water, ethanol and acetone, and the dosage of the solvent is generally 50-400wt%.
Wherein the solid electrolyte layer (E) contains a solid electrolyte and a binder. The solid electrolyte layer (E) is produced by a coating method:
and (3) coating the slurry containing the solid electrolyte, the adhesive and the solvent on the surface of the positive electrode material layer (C), drying and rolling to form the CE. Wherein, the binder is selected from one or more of polythiophene, polypyrrole, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polystyrene, polyacrylamide, ethylene-propylene-diene copolymer resin, styrene butadiene rubber, polybutadiene, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyester resin, acrylic resin, phenolic resin, epoxy resin, polyvinyl alcohol, carboxypropyl cellulose, ethyl cellulose, polyethylene oxide, sodium carboxymethyl cellulose (CMC) and styrene butadiene latex (SBR), and the solvent is selected from one or more of water, acetone, N-methyl pyrrolidone, dimethyl sulfoxide, N-dimethyl formamide and ethanol.
Among them, the components of the anode active material layer (a) are commonly used in the art, and include an anode active material and a binder. The adopted negative electrode active material is various negative electrode active materials which can insert and remove lithium and are commonly used in the field; the binder is various negative electrode binders commonly used in the art, and may be, for example, one or more selected from polythiophene, polypyrrole, polytetrafluoroethylene, polyvinylidene fluoride, polyethylene, polypropylene, polystyrene, polyacrylamide, ethylene-propylene-diene copolymer resin, styrene butadiene rubber, polybutadiene, fluororubber, polyethylene oxide, polyvinylpyrrolidone, polyester resin, acrylic resin, phenol resin, epoxy resin, polyvinyl alcohol, carboxypropyl cellulose, ethyl cellulose, sodium carboxymethylcellulose (CMC), and styrene butadiene latex (SBR). Preferably, the binder is contained in the anode active material layer (a) in an amount of 0.01 to 10wt% based on the weight of the anode active material. The negative active material layer (A) is obtained by mixing a negative active material, a binder and the like in a solvent according to a certain proportion, uniformly stirring to obtain required negative slurry, then coating the slurry on a negative current collector, and drying and tabletting to obtain the negative active material layer (A). When lithium or lithium-indium alloy is used for the negative electrode, a metallic lithium ribbon or a lithium-indium alloy ribbon can be directly used.
And finally, pressing the A and the CE together to form CEA, thus obtaining the solid lithium battery, wherein the pressing mode is preferably isostatic pressing.
The present invention is further illustrated by the following specific examples, which are provided only for illustrating and explaining the present invention and are not intended to limit the present invention.
Example 1
（1）TiS 2 Synthesis of nanoplatelets
First, 36ml oleylamine was added to a 250ml three necked round bottom flask, followed by aeration with argon for 30 minutes to remove air. Subsequently, 4ml of TiCl are injected under argon 4 Heating to 300 deg.C at a heating rate of 5 deg.C/min, and injecting 7ml CS via syringe 2 . After a short 1min reaction, the heat was removed and cooled to room temperature. Washing the obtained solid mixture with butanol, acetone, methanol and ethanol in sequence, centrifuging, and drying in a vacuum drying oven at 60 deg.C for 2 hr to obtain nanometer TiS 2 A sheet.
(2) Preparation of cathode material
2g of LiCoO 2 (particle size about 5 μm) was added with 20mg of TiS dispersed therein 2 (diameter about 10nm, thickness about 2 nm) in a mixed solvent of water and ethanol (35 ml of ethanol, 5ml of water, tiS) 2 Concentration of 0.5 mg/ml), stirred and mixed evenly, and then added into a 50ml closed reaction kettle for sealing. Heating to 110 ℃, reacting for 3h, then cooling to room temperature, taking out, drying and sintering at 500 ℃ for 3h under inert atmosphere to obtain TiS 2 /TiO 2 Coated LiCoO 2 Wherein the thickness of the coating layer is about 10nm, and TiS is in the coating layer 2 Is about 10% by mass.
(3) Production of Positive electrode Material layer (C)
LiCoO coated with 8.8 g via a transition metal disulfide/oxide composite 2 Positive electrode Material (88%), 0.5g solid electrolyte Li 7 P 3 S 11 (5%), 0.3 g binder PVDF (3%), 0.2 g acetylene black (2%), 0.2 g conductive agent carbon fiber (2%) were added to 15 g solvent NMP (azomethylpyrrolidone), and then stirred in a vacuum stirrer to form stable and uniform positive electrode slurry. The positive electrode slurry was uniformly coated intermittently on both sides of an aluminum foil (aluminum foil size: width 160 mm, thickness 16 μm), and then 393K was dried, and was pressed into sheets by a roll press to obtain C.
(4) Fabrication of positive electrode material layer and solid electrolyte layer (CE)
In a glove box, 6 g of Li 7 P 3 S 11 The mixture is put into a toluene solution of 12 g, wherein the toluene solution contains 0.3 g butadiene rubber binder, and then the mixture is heated and stirred to form a stable and uniform solution. The solution was continuously coated on the C obtained in step (3), then dried at a temperature of 333K, and cut to CE with dimensions of 485 mm (long) × 46 mm (wide).
(5) Production of negative electrode active Material layer (A)
8.9 g negative active material artificial graphite (89%), 0.5g solid electrolyte Li 7 P 3 S 11 (5%), 0.3 g binder CMC (3%) and 0.3 g binder SBR (3%) were added to 12 g xylene, which was then stirred in a vacuum mixer to form a stable uniform anode slurry. The slurry was uniformly coated on both sides of a copper foil (copper foil size: 160 mm width, 16 μm thickness) intermittently, then dried at 393K temperature, sheeted by a roll press, and cut into negative electrode active material layers (a) having size 480 mm (length) × 45 mm (width).
(6) Preparation of CEA
And (3) in a glove box, aligning the CE obtained in the step (4) and the A obtained in the step (5) after cutting, placing the CE and the A in a hot press, performing 453K hot pressing on 1h, vacuumizing and sealing by using an aluminum plastic film, and taking out a sample.
And pressing the pressed sample in an isostatic press under the condition of 200MPa for 300 s to obtain the solid lithium battery of the embodiment.
Example 2
The same procedure as in example 1 was used to prepare a coated positive electrode material and a solid lithium battery of this example, except that:
in step (1), tiS is prepared 2 /TiO 2 Composite coated LiCoO 2 In the process, tiS is used 2 Is 2mg/ml, the thickness of the obtained coating layer is about 40nm 2 Is about 4%.
Example 3
The same procedure as in example 1 was used to prepare a coated positive electrode material and a solid-state lithium battery of the present example, except that:
in step (1), tiS is prepared 2 /TiO 2 Composite coated LiCoO 2 In the process, the coating process time in the reaction kettle is shortened to 1h, and finally TiS in the coating layer is obtained 2 Is about 40% by mass.
Comparative example 1
A solid lithium battery of this comparative example was prepared by the same procedure as in example 1, except that:
the positive electrode material used was uncoated LiCoO 2 And then assembling the solid lithium battery directly using the positive active material.
Comparative example 2
A solid lithium battery of this comparative example was prepared by the same procedure as in example 1, except that:
the positive electrode material used is TiO 2 Coated LiCoO 2 And the coating thickness is 10nm, and the solid lithium battery is used as a positive electrode active material to be assembled.
Comparative example 3
A solid lithium battery of this comparative example was prepared by the same procedure as in example 1, except that:
the positive electrode material used is not TiS 2 Coated LiCoO 2 The coating thickness was 10nm, and the all solid-state lithium battery was assembled as a positive electrode active material.
Comparative example 4
A solid lithium battery of this comparative example was prepared by the same procedure as in example 1, except that:
the positive electrode material used was not TiS generated in situ by the method of example 1 2 /TiO 2 Composite coated LiCoO 2 Instead of using TiS 2 With TiO 2 LiCoO coated as a coating material after simple mixing 2 The coating thickness was 10nm, and the assembly of the all-solid lithium battery was performed as a positive electrode active material.
Comparative example 5
A lithium battery of this comparative example was prepared by the same procedure as in example 1, except that:
the positive electrode material used is LiNbO 3 Coated LiCoO 2 The coating thickness was 10nm, and then the assembly of the all solid-state lithium battery was performed directly using the positive electrode active material.
Battery performance testing
The solid-state lithium batteries CEA1-CEA8 obtained in examples 1-3 and comparative examples 1-5 were subjected to a battery cycle performance test by the following method:
20 batteries prepared in each example and each comparative example were subjected to a charge-discharge cycle test at 0.1C on a LAND CT 2001C secondary battery performance testing apparatus under the condition of 298. + -. 1K. The method comprises the following steps: standing for 10 min; constant current charging is carried out until 4.2V is cut off; standing for 10 min; constant current discharge to 1.5V, i.e. 1 cycle. Repeating the steps, when the battery capacity is lower than 80% of the first discharge capacity in the circulation process, the circulation is terminated, the circulation times are the circulation service life of the battery, each group is averaged, and the parameters and the data of the average first discharge capacity of the battery are shown in the following table.
TABLE 1
As can be seen from the test results obtained in table 1, when the surface of the positive active material is coated, the first discharge specific capacity and the cycle life of the solid-state lithium battery can be improved, as compared with the positive active material (comparative example 1) in which the surface coating is not performed; compared with the method that the surface is singly coated with the transition metal sulfide or the transition metal oxide (comparative example 2 and comparative example 3), the positive electrode material simultaneously coated with the transition metal sulfide and the transition metal oxide can exert more capacity and has better cycle performance; compared with a simple mixture of a transition metal sulfide and a transition metal oxide coated on the surface, the transition metal oxide in the coating layer is generated in situ on the basis of the transition metal sulfide, and the coating layer is generated originally, so that the mutual interference of the two materials can be better avoided, a better ion passage and an electron passage can be respectively constructed, higher capacity can be exerted, and the assembled solid-state lithium battery has higher first-time discharge specific capacity and cycle life; since the coating layer has only an ion conductive coating material, capacity expression and cyclability are inferior to those of the positive electrode material in which the transition metal sulfide and the transition metal oxide are simultaneously coated in the examples, compared with the coating with the lithium-containing transition metal oxide.
Claims (11)
1. A positive electrode material is characterized by comprising a positive electrode active substance and a coating layer coated on the surface of the positive electrode active substance, wherein the coating layer comprises a transition metal sulfide and a transition metal oxide, and the transition metal oxide is generated in situ from part of the transition metal sulfide;
the transition metal sulfide is of a nanoscale sheet structure;
the diameter of the transition metal sulfide is 5nm-500nm, and the thickness of the transition metal sulfide is 1nm-50nm.
2. The positive electrode material according to claim 1, wherein the transition metal sulfide is selected from the group consisting of MS x ，MS x In the formula, M is at least one of Ti, V, nb, ta, W, cr, fe, ni, cu and Mo, and x is more than or equal to 1 and less than or equal to 2.5; the transition metal oxide is selected from MO y ，MO y In the formula, M is at least one of Ti, V, nb, ta, W, cr, fe, ni, cu and Mo, and y is more than or equal to 1 and less than or equal to 3.
3. The positive electrode material according to claim 1 or 2, wherein the transition metal sulfide is a transition metal disulfide.
4. The positive electrode material according to claim 1, wherein the transition metal sulfide is present in the coating layer in a proportion of 1 to 90% by mass.
5. The positive electrode material according to claim 1, wherein the mass ratio of the coating layer in the positive electrode material is 0.01 to 10%.
6. The positive electrode material according to claim 1, wherein the thickness of the clad layer is 1 to 500nm.
7. The positive electrode material according to claim 1, wherein the positive electrode active material is selected from LiCoO 2 、LiNiO 2 、LiCo x1 Ni 1-x1 O 2 、LiCo x2 Ni 1-x2-y1 Al y1 O 2 、LiMn 2 O 4 、LiFe x3 Mn y2 M z1 O 4 、Li 1+x4 L 1－y3－ z2 M2 y3 N z2 O 2 ，LiFePO 4 、Li 3 V 2 (PO 4 ) 3 、Li 3 V 3 (PO 4 ) 3 、LiVPO 4 F、Li 2 CuO 2 、Li 5 FeO 4 One or more of the components (A) and (B),
wherein x1 is more than or equal to 0 and less than or equal to 1,0 and less than or equal to 1,0 and less than or equal to y1 and less than or equal to 1;
LiFe x3 Mn y2 M z1 O 4 wherein M is at least one of Al, mg, ga, cr, co, ni, cu, zn and Mo, x3 is more than or equal to 0 and is more than or equal to 1,0 and is more than or equal to y2 is more than or equal to 1,0 and is more than or equal to z and is less than or equal to 1, and x3+ y2+ z1=1;
Li 1+x4 L 1－y3－z2 M2 y3 N z2 O 2 in L, M, N is at least one of Li, co, mn, ni, fe, al, mg, ga, ti, cr, cu, zn, mo, F, I, S and B, -0.1-4≤0.2，0≤y3≤1，0≤z2≤1，0≤y3+z2≤1。
8. A method for producing the positive electrode material according to claim 1, comprising the steps of:
(1) Dispersing transition metal sulfide into a mixed solution of water and ethanol, adding a positive active substance, uniformly mixing, sealing in a reaction kettle, and carrying out a solvothermal process at 100-300 ℃;
(2) And (2) sintering the reactant obtained in the step (1) in an inert atmosphere to obtain the anode material coated by the transition metal sulfide and the transition metal oxide together.
9. The method according to claim 8, wherein the concentration of the transition metal sulfide in the step (1) is 0.1 to 10mg/mL.
10. The production method according to claim 8, wherein the sintering temperature in the step (2) is 300 to 800 ℃.
11. A solid lithium battery comprising the positive electrode material according to any one of claims 1 to 7 or the positive electrode material produced by the production method according to any one of claims 8 to 10.
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