Positive electrode material and preparation method therefor, positive electrode sheet, and sodium ion battery

Abstract

A positive electrode material and a preparation method therefor, a positive electrode sheet, and a sodium ion battery. The positive electrode material comprises a layered oxide serving as a core and an MOF material coating layer coating the surface of the layered oxide. The MOF material comprises a first metal and an organic ligand, and the organic ligand is selected from one or more of compounds having a structure represented by formula (1) below.

Description

A positive electrode material, a preparation method thereof, a positive electrode sheet and a sodium ion battery

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] The present disclosure claims priority to Chinese Patent Application No. 202410883456.0, filed on July 3, 2024, the contents of which are incorporated herein in their entirety as part of the present disclosure. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of sodium ion batteries, in particular, to a positive electrode material, a preparation method thereof, a positive electrode sheet and a sodium ion battery. BACKGROUND

[0004] Among the three positive electrode materials of sodium ion batteries, layered oxides have the highest energy density, and the synthesis process is simple, the production line is compatible with lithium batteries, and the development is relatively mature. However, due to the structural characteristics of layered oxides, the interface stability is poor, and active oxygen is easily produced, which leads to the decline of the cycle performance. The common method is to perform coating treatment on the surface of the layered oxide to reduce the material interface and inhibit the occurrence of side reactions. However, the uniformity of the commonly used dry coating method is limited, and only point or island coating can be achieved, which cannot completely inhibit the generation of active oxygen, thereby negatively affecting the cycle stability of the battery. SUMMARY

[0005] The purpose of the present disclosure is to provide a positive electrode material, a preparation method thereof, a positive electrode sheet and a sodium ion battery, which has a uniform MOF material coating layer on the surface of the layered oxide, can inhibit the generation of active oxygen and also can absorb the generated active oxygen, and effectively improves the cycle stability of the battery.

[0006] To achieve the above purpose, the first aspect of the present disclosure provides a positive electrode material, comprising a layered oxide as a core and a MOF material coating layer coated on the surface of the layered oxide; the MOF material coating layer comprises a first metal coordination compound, and the organic ligand of the first metal coordination compound comprises a compound having the structure shown in the following formula (1):

[0007] wherein R1-R6 are the same or different, and each is independently selected from one of hydrogen, an alkyl group with 1-10 carbon atoms, an alkenyl group with 1-10 carbon atoms and an alkynyl group with 1-10 carbon atoms.

[0008] In some embodiments, the first metal element in the first metal coordination compound is selected from one or more of Cu, Fe, Mn, Ca, Ni, Co, Cr, Zn, Ti, V, Zr, Mg, Al, Li and Nb.

[0009] The organic ligand in the first metal coordination compound comprises a first organic ligand selected from one or more of isophthalic acid, orthophthalic acid, terephthalic acid, trimesic acid, 1,2,4-benzene tricarboxylic acid and 1,3,5-benzene tricarboxylic acid; and a second organic ligand comprising a compound having a structure shown in the following formula (1), wherein R1-R6 are the same or different, and each is independently selected from one of hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, ethenyl, propenyl, allyl, alkenyl, butadienyl, ethynyl, propynyl and butynyl;

[0010] The layered oxide comprises a compound having a composition shown in the following formula (2):

[0011] Na x TmO2formula (2); wherein Tm is a second metal element, Tm is selected from one or more of Cu, Fe, Mn, Ca, Ni, Co, Cr, Zn, Ti, V, Zr, Mg, Al, Li and Nb; the structure of the layered oxide is selected from one or more of P2 type, O3 type, P3 type and tunnel type, 0 < x ≤ 1.

[0012] In some embodiments, the content of the layered oxide is 58-99.9% by weight, and the content of the MOF material coating layer is 0.1-42% by weight, based on the total weight of the positive electrode material; preferably, the content of the layered oxide is 86.0-99.9% by weight, and the content of the MOF material coating layer is 0.1-14.0% by weight.

[0013] The content of the first metal element is 5-50% by weight, the content of the first organic ligand is 15-60% by weight, and the content of the second organic ligand is 15-60% by weight, based on the total weight of the MOF material coating layer; preferably, the content of the first metal is 10-40% by weight, the content of the first organic ligand is 20-50% by weight, and the content of the second organic ligand is 20-50% by weight.

[0014] In some embodiments, the particle size of the positive electrode material is 2.1-23 μm; the particle size of the layered oxide is 2-20 μm; and the thickness of the MOF material coating layer is 0.1-4 μm, preferably 0.1-3 μm.

[0015] The second aspect of the present disclosure provides a method for preparing a positive electrode material, comprising the following steps:

[0016] The layered oxide, the first metal source and the organic ligand are contacted and reacted in a solvent; wherein the organic ligand comprises a compound having a structure shown in the following formula (1):

[0017] wherein R1-R6 are the same or different, and each is independently selected from one of hydrogen, an alkyl group having 1-10 carbon atoms, an alkenyl group having 1-10 carbon atoms, and an alkynyl group having 1-10 carbon atoms.

[0018] In some embodiments, the first metal source is selected from one or more of a nitrate salt, a sulfate salt, a halide salt, and a phosphate salt of a first metal element; the first metal element is selected from one or more of Cu, Fe, Mn, Ca, Ni, Co, Cr, Zn, Ti, V, Zr, Mg, Al, Li, and Nb.

[0019] The layered oxide has a composition represented by the following formula (2):

[0020] Na x TmO2 formula (2); wherein Tm is a second metal element, Tm is selected from one or more of Cu, Fe, Mn, Ca, Ni, Co, Cr, Zn, Ti, V, Zr, Mg, Al, Li, and Nb; the structure of the layered oxide is selected from one or more of P2 type, O3 type, P3 type, and tunnel type, 0 < x ≤ 1; the particle size of the layered oxide is 2-20 μm.

[0021] The organic ligand includes a first organic ligand and a second organic ligand, the first organic ligand is selected from one or more of isophthalic acid, phthalic acid, terephthalic acid, trimesic acid, 1,2,4-benzene tricarboxylic acid, and 1,3,5-benzene tricarboxylic acid; the second organic ligand has the structure represented by the above formula (1), wherein R1-R6 are the same or different, and each is independently selected from one of hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, ethenyl, propenyl, allyl, alkenyl, butadienyl, ethynyl, propynyl, and butynyl.

[0022] The solvent is selected from one or more of acetonitrile, ethanol, ethylene glycol, methanol, propanol, tetrahydrofuran, and N,N-dimethylformamide.

[0023] In some embodiments, the weight ratio of the layered oxide: the first metal source: the first organic ligand: the second organic ligand is 1000: 0.05-70: 0.15-84: 0.15-84; preferably 1000: 1-48: 2-60: 2-60.

[0024] In some embodiments, the conditions of the contact reaction include: in a solvent thermal reaction kettle, the reaction temperature is 100-300°C, and the reaction time is 5-36 h.

[0025] The third aspect of the present disclosure provides a positive electrode material prepared by the method according to the second aspect of the present disclosure.

[0026] The fourth aspect of the present disclosure provides a positive electrode sheet of a sodium ion battery, which comprises the positive electrode material according to the first aspect or the third aspect of the present disclosure.

[0027] The fifth aspect of the present disclosure provides a sodium ion battery, which comprises the positive electrode sheet according to the fourth aspect of the present disclosure.

[0028] By the above technical solution, the present disclosure provides a positive electrode material and a preparation method thereof, a positive electrode sheet and a sodium ion battery. The positive electrode material provided by the present disclosure comprises a layered oxide as a core and a MOF material coating layer coated on the surface of the layered oxide. The MOF material coating layer has a dual effect: on the one hand, the MOF material coating layer can achieve uniform coating effect, and can effectively inhibit the active oxygen in the lattice of the positive electrode active material (layered oxide) from escaping and other side reactions from occurring; on the other hand, the first metal coordination compound in the MOF material comprises a compound (such as triethylenediamine and its derivatives) having a structure shown in formula (1) as an organic ligand, which can absorb active oxygen generated by other ways (such as side reactions caused by residual alkali decomposition and sodium salt hydrolysis), and can further inhibit the occurrence of side reactions. The positive electrode material provided by the present disclosure can effectively improve the cycle stability of the sodium ion battery and prolong the service life in the application of the sodium ion battery.

[0029] Other features and advantages of the present disclosure will be described in detail in the subsequent specific embodiments section. DETAILED DESCRIPTION

[0030] The specific embodiments of the present disclosure are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present disclosure, and are not used to limit the present disclosure.

[0031] The first aspect of the present disclosure provides a positive electrode material, which comprises a layered oxide as a core and a MOF material coating layer coated on the surface of the layered oxide; the MOF material coating layer comprises a first metal coordination compound, and an organic ligand of the first metal coordination compound comprises a compound having a structure shown in formula (1):

[0032] wherein R1-R6 are the same or different, and each is independently selected from hydrogen, an alkyl group with 1-10 carbon atoms, an alkenyl group with 1-10 carbon atoms, or an alkyne group with 1-10 carbon atoms.

[0033] The present disclosure provides a positive electrode material, comprising a layered oxide as a core and a MOF material coating layer coated on the surface of the layered oxide, the MOF material coating layer having a dual effect: on the one hand, the MOF material coating layer can achieve uniform coating effect, and can effectively inhibit the occurrence of active oxygen release and other side reactions in the lattice of the positive electrode active material (layered oxide); on the other hand, the first metal coordination compound in the MOF material comprises a compound (such as triethylenediamine and its derivatives) having the structure shown in formula (1) as an organic ligand, which can absorb active oxygen generated by other pathways (such as side reactions caused by residual alkali decomposition and sodium salt hydrolysis), and can further inhibit the occurrence of side reactions. The positive electrode material provided by the present disclosure can effectively improve the cycle stability of the battery and prolong the service life in the application of sodium ion battery.

[0034] In a specific embodiment, the first metal element in the first metal coordination compound is selected from one or more of Cu, Fe, Mn, Ca, Ni, Co, Cr, Zn, Ti, V, Zr, Mg, Al, Li and Nb; in a preferred embodiment, the first metal element in the first metal coordination compound is selected from one or more of Cu, Zn, Zr, Ca, Mn, Ni, Fe, Al, Ti, Nb and Co.

[0035] In an embodiment, the organic ligand comprises a first organic ligand and a second organic ligand, the first organic ligand being selected from one or more of isophthalic acid, phthalic acid, terephthalic acid, trimesic acid, 1,2,4-benzene tricarboxylic acid and 1,3,5-benzene tricarboxylic acid; the second organic ligand comprising a compound having the structure shown in formula (1) above. The present disclosure uses a combination of the first organic ligand and the second organic ligand, wherein the first organic ligand helps to form the MOF framework.

[0036] In a preferred embodiment, in formula (1), R1-R6 are the same or different, and each is independently selected from one of hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, ethenyl, propenyl, allyl, aldenyl, butadienyl, ethynyl and propynyl. The second organic ligand represented by formula (1) having the group types of R1-R6 in this embodiment can form a MOF organic coating layer with more excellent effect.

[0037] In a specific embodiment, the layered oxide comprises a compound having the following formula (2) composition:

[0038] Na xTmO2 Formula (2); wherein Tm is a second metal element, Tm is selected from one or more of Cu, Fe, Mn, Ca, Ni, Co, Cr, Zn, Ti, V, Zr, Mg, Al, Li and Nb; in one preferred embodiment, Tm is selected from one or more of Cu, Fe, Mn, Ca, Ni, Co, Zn, Ti, Zr, Mg, Al, Li and Nb; the structure of the layered oxide is selected from one or more of P2 type, O3 type, P3 type and tunnel type, 0 < x < 1; in one preferred embodiment, 0.7 < x < 1. In the present disclosure, one or more than one metal Tm can exist in the same layered oxide. The positive electrode material having the composition shown in Formula (2) in the present embodiment can have more excellent effects in battery applications.

[0039] In one embodiment, the content of the layered oxide is 58-99.9% by weight, and the content of the MOF material coating layer is 0.1-42% by weight, based on the total weight of the positive electrode material; in one preferred embodiment, the content of the layered oxide is 86-99.9% by weight, and the content of the metal organic framework coating layer is 0.1-14% by weight; in one more preferred embodiment, the content of the layered oxide is 88-99% by weight, and the content of the metal organic framework coating layer is 1-12% by weight. When the content of the active material (layered oxide) and the MOF coating layer in the positive electrode material of the present disclosure is within the content range of the present embodiment, especially within the preferred content range, the positive electrode material can have more excellent effects of inhibiting the generation of side reactions, inhibiting gas generation and absorbing active oxygen, and is more helpful to improve the cycle stability and service life of the battery.

[0040] In one embodiment, the content of the first metal element is 5-50% by weight, the content of the first organic ligand is 15-60% by weight, and the content of the second organic ligand is 15-60% by weight, based on the total weight of the MOF material coating layer; in one preferred embodiment, the content of the first metal is 10-40% by weight, the content of the first organic ligand is 20-50% by weight, and the content of the second organic ligand is 20-50% by weight. When the component content of the MOF material coating layer in the positive electrode material provided by the present disclosure is within the content range of the present embodiment, especially within the optimized range, the positive electrode material has better effects of inhibiting the generation of active oxygen, reducing the occurrence of side reactions of the positive electrode material and absorbing active oxygen, and is more helpful to improve the cycle stability of the battery.

[0041] In an embodiment, the particle size of the positive electrode material is 2-23 μm, preferably 4.2-11 μm; the particle size of the layered oxide is 2-20 μm, preferably 4-10 μm; and the thickness of the metal organic framework coating layer is 0.1-4 μm, preferably 0.1-3 μm, more preferably 0.2-1 μm. The positive electrode material provided by the present disclosure has a suitable particle size and coating layer thickness, which is beneficial to exert excellent effects in the positive electrode application.

[0042] The second aspect of the present disclosure provides a method for preparing a positive electrode material, comprising the following steps:

[0043] The layered oxide, the first metal source and the organic ligand are contacted and reacted in a solvent to grow a metal organic framework material in situ to form a metal organic framework coating layer on the surface of the layered oxide; wherein the organic ligand comprises a compound having a structure shown in the following formula (1):

[0044] wherein R1-R6 are the same or different, and each is independently selected from hydrogen, an alkyl group having 1-10 carbon atoms, an alkenyl group having 1-10 carbon atoms, or an alkynyl group having 1-10 carbon atoms.

[0045] The present disclosure provides a method for preparing a positive electrode material, which adopts a wet coating process to grow a uniform metal organic framework (MOF) coating layer in situ on the surface of the active material layered oxide. The MOF coating layer can effectively inhibit the generation of active oxygen and other side reactions in the crystal lattice. The MOF coating layer is prepared by using diethylene triamine (DABCO) and its derivatives shown in formula (1) as ligands, which can also absorb the active oxygen generated in the reaction, achieving the dual effect of the MOF coating layer. The method can also control the product structure (such as the thickness of the coating layer) of the positive electrode material by adjusting the conditions of the preparation process. After growing the MOF coating layer, the method does not require further heat treatment, which ensures that the organic ligand can remain on the surface of the layered oxide.

[0046] In a specific embodiment, the first metal source is selected from one or more of the nitrate, sulfate, halide and phosphate of a first metal element; the first metal element is selected from one or more of Cu, Fe, Mn, Ca, Ni, Co, Cr, Zn, Ti, V, Zr, Mg, Al, Li and Nb; in a preferred embodiment, the first metal element is selected from one or more of Cu, Zn, Zr, Ca, Mn, Ni, Fe, Al, Ti, Nb and Co; and in a more preferred embodiment, the first metal source is selected from one or more of the nitrate, halide, sulfide, phosphate or other organic acid salt of the above transition metal.

[0047] In one embodiment, the layered oxide has a composition represented by the following formula (2):

[0048] Na x TmO2formula (2); wherein Tm is a second metal element, and Tm is selected from one or more of Cu, Fe, Mn, Ca, Ni, Co, Cr, Zn, Ti, V, Zr, Mg, Al, Li and Nb, and in one preferred embodiment, Tm is selected from one or more of Cu, Fe, Mn, Ca, Ni, Co, Zn, Ti, Zr, Mg, Al, Li and Nb; the structure of the layered oxide is selected from one or more of P2 type, O3 type, P3 type and tunnel type, and 0 < x ≤ 1; preferably, 0.6 ≤ x ≤ 1. The particle size of the layered oxide is 2-20 μm, and preferably 5-10 μm. The layered oxide provided in this embodiment can obtain a positive electrode material with better performance.

[0049] In one embodiment, the organic ligand comprises a first organic ligand and a second organic ligand, the first organic ligand is selected from one or more of isophthalic acid, phthalic acid, terephthalic acid, trimesic acid, 1,2,4-benzene tricarboxylic acid and 1,3,5-benzene tricarboxylic acid; and the second organic ligand has the structure represented by the above formula (1); wherein R1-R6 are the same or different, and each is independently selected from one of hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, vinyl, propenyl, allyl, alkenyl, butadienyl, ethynyl, propargyl and butynyl.

[0050] In one embodiment, the solvent is a solvent that does not react with the layered oxide Na x TmO2, i.e. a solvent that does not react with Na x TmO2; and the XRD spectrum of the layered oxide dispersed in the solvent does not change; in one preferred embodiment, the solvent is selected from one or more of acetonitrile, ethanol, ethylene glycol, methanol, propanol, tetrahydrofuran and N,N-dimethylformamide.

[0051] In one embodiment, the weight ratio of the layered oxide: the first metal source: the first organic ligand: the second organic ligand is 1000: 0.05-70: 0.15-84: 0.15-84; and in one preferred embodiment, the weight ratio of the layered oxide: the first metal source: the first organic ligand: the second organic ligand is 1000: 1-48: 2-60: 2-60. According to the optimized raw material ratio provided in this embodiment, and in particular the preferred raw material ratio, the prepared positive electrode material can have more excellent performance, and thus is conducive to improving the cycle stability of the sodium ion battery. In one embodiment, the amount of the solvent is 2-200 mL, and preferably 10-100 mL, relative to 1 g of the layered oxide. The amount of the solvent can be adjusted according to experimental conditions.

[0052] In one specific embodiment, the method comprises:

[0053] mixing the layered oxide and the solvent to obtain a suspension;

[0054] adding the first metal source and the organic ligand into the suspension to obtain a reaction mixture;

[0055] subjecting the reaction mixture to a solvothermal reaction to in-situ grow the metal-organic framework material on the surface of the layered oxide and form a metal-organic framework coating layer;

[0056] subjecting the solvothermal reaction product to centrifugation and drying.

[0057] In one embodiment, the conditions of the contact reaction include: in the solvothermal reaction kettle, the reaction temperature is 100-300℃, the reaction time is 5-36h, and the reaction pressure is autogenous pressure.

[0058] In a preferred embodiment, in the solvothermal reaction kettle, the reaction temperature is 100-200℃, the reaction time is 8-18h, and the reaction pressure is autogenous pressure. The preferred solvothermal reaction conditions provided in this embodiment can achieve a more excellent effect of in-situ generating the MOF coating layer.

[0059] The third aspect of the present disclosure provides a positive electrode material prepared by the method according to the second aspect of the present disclosure.

[0060] The fourth aspect of the present disclosure provides a positive electrode sheet of a sodium ion battery, which comprises the positive electrode material according to the first aspect or the third aspect of the present disclosure.

[0061] In one specific embodiment, the positive electrode sheet is prepared by a method comprising the following steps: coating a positive electrode slurry on a current collector, and then performing baking and drying; wherein the positive electrode slurry comprises the positive electrode material, optionally a binder, optionally a conductive agent, and a solvent.

[0062] In a preferred embodiment, based on the total weight of the positive electrode slurry, the content of the positive electrode material is 50-100wt%, the content of the binder is 0-50wt%, and the content of the conductive agent is 0-50wt%; the amount of the solvent can be adjusted according to experimental requirements. The positive electrode sheet prepared according to the component content ratio of the positive electrode slurry provided in this embodiment can have more excellent performance.

[0063] In the present disclosure, the binder, the conductive agent, and the solvent can be conventional reagents in the art.

[0064] In one specific embodiment, the binder is selected from one or more of fluorine-based resin such as polyvinylidene fluoride, polyaniline, polypyrrole, styrene-butadiene copolymer, and acrylic copolymer; the conductive agent is selected from one or more of carbon black, acetylene black, graphene, carbon nanotube, conductive graphite, and graphite-based conductive agent; and the solvent is selected from one or more of N-methylpyrrolidone and acetone.

[0065] The fifth aspect of the present disclosure provides a sodium-ion battery, which comprises the positive electrode sheet of the fourth aspect of the present disclosure.

[0066] The sodium-ion battery provided by the present disclosure can be assembled in a conventional manner in the art. The negative electrode material of the sodium-ion battery can be a hard carbon negative electrode, a soft carbon negative electrode, a silicon-based negative electrode, a sodium metal negative electrode, a transition metal sulfide negative electrode, or a phosphide negative electrode. The electrolyte can be an ester-based electrolyte or an ether-based electrolyte.

[0067] The present disclosure is further described in detail below by way of examples. The raw materials used in the examples can be obtained by commercial channels.

[0068] The component content of the positive electrode material and the component content of the coating layer in the present disclosure are obtained by calculating the designed stoichiometry.

[0069] The particle size of the positive electrode material and the thickness of the coating layer are measured from the micro-morphology diagram obtained by a scanning electron microscope.

[0070] Example 1

[0071] 1 g of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2(O3-type structure, the second metal element includes Ni, Fe, and Mn) is dispersed in 60 ml of N,N-dimethylformamide and stirred and ultrasonicated to obtain a suspension. 22 mg of Cu(NO3)2(first metal source), 30 mg of terephthalic acid (PTA, first organic ligand), and 30 mg of triethylene diamine (DABCO, second organic ligand) are added to the above suspension, which is stirred for 30 min and then ultrasonicated for 30 min, wherein the weight ratio of the layered oxide: first metal source: first organic ligand: second organic ligand is 1000:22:30:30, and the amount of solvent is 60 mL relative to 1 g of the layered oxide. Subsequently, the suspension is transferred to a solvent thermal kettle of tetrafluoroethylene, and the solvent thermal kettle is placed in a muffle furnace for solvent thermal reaction, with a reaction temperature of 150°C and a reaction time of 12 h. After the reaction is completed, the suspension is centrifuged and washed with anhydrous ethanol, and then dried in a vacuum drying oven at 100°C to obtain NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@Cu-DABCO / PTA.

[0072] The prepared NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@Cu-DABCO / PTA as a positive active material, a binder polyvinylidene fluoride (PVDF) and a conductive agent CNT (CNT concentration 15 wt%) were added into N-methyl pyrrolidone to make a slurry, based on the total weight of the slurry, the content of the positive active material was 85 wt%, the content of the binder was 7.5 wt%, and the content of the conductive agent was 7.5 wt%; the positive electrode slurry was uniformly coated on an aluminum foil, followed by 110°C baking and drying, and after cooling, a positive electrode sheet was prepared. The prepared positive electrode sheet was matched with a hard carbon negative electrode, a conventional carbonate electrolyte was used as the electrolyte, and a full cell was assembled.

[0073] Example 2

[0074] The prepared NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2(O3 type structure, the second metal element includes Ni, Fe and Mn) was dispersed in 60 ml of N,N-dimethylformamide and stirred and ultrasonicated to obtain a suspension. 22 mg of Cu(NO3)2(first metal source), 20 mg of trimesic acid (BTC, first organic ligand), and 30 mg of triethylene diamine (DABCO, second organic ligand) were added to the above suspension, stirred for 30 min, and then ultrasonicated for 30 min, wherein the weight ratio of the layered oxide: first metal source: first organic ligand: second organic ligand was 1000:22:20:30, and the amount of solvent was 60 mL relative to 1 g of the layered oxide. Subsequently, the suspension was transferred to a teflon solvent kettle, and the solvent kettle was placed in a muffle furnace for solvent thermal reaction, the reaction temperature was 150°C, and the reaction time was 12 h. After the reaction was completed, the suspension was centrifuged and washed with anhydrous ethanol, and then dried in a 100°C vacuum drying oven, to obtain NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@Cu-DABCO / BTC.

[0075] The prepared NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3O2@Cu-DABCO / BTC as the positive active material, binder polyvinylidene fluoride (PVDF) and conductive agent CNT-15% were added into N-methyl pyrrolidone to make slurry, based on the total weight of the slurry, the content of the positive active material was 85 wt%, the content of the binder was 7.5 wt%, and the content of the conductive agent was 7.5 wt%; the positive electrode slurry was uniformly coated on an aluminum foil, followed by baking and drying at 110°C, and the positive electrode sheet was prepared after cooling. The prepared positive electrode sheet was matched with a hard carbon negative electrode, a conventional carbonate electrolyte was used as the electrolyte, and a full battery was assembled.

[0076] Example 3

[0077] 1 g of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2(O3 type structure, the second metal element includes Ni, Fe and Mn) was dispersed in 60 ml of N,N-dimethylformamide and stirred and ultrasonicated to obtain a suspension. 22 mg of Zn(NO3)2(first metal source), 30 mg of terephthalic acid (PTA, first organic ligand), and 30 mg of triethylene diamine (DABCO, second organic ligand) were added to the above suspension, stirred for 30 min, and then ultrasonicated for 30 min, wherein the weight ratio of the layered oxide: first metal source: first organic ligand: second organic ligand was 1000:22:30:30, and the amount of solvent was 60 mL relative to 1 g of the layered oxide. Subsequently, the suspension was transferred to a solvent thermal kettle of tetrafluoroethylene, and the solvent thermal kettle was placed in a muffle furnace for solvent thermal reaction, the reaction temperature was 150°C, and the reaction time was 12 h. After the reaction was completed, the suspension was centrifuged and washed with anhydrous ethanol, and then dried in a vacuum drying oven at 100°C, to obtain NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@Zn-DABCO / PTA.

[0078] The prepared NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@Zn-DABCO / PTA as the positive active material, binder polyvinylidene fluoride (PVDF) and conductive agent CNT-15% were added into N-methyl pyrrolidone to make slurry, based on the total weight of the slurry, the content of the positive active material was 85 wt%, the content of the binder was 7.5 wt%, and the content of the conductive agent was 7.5 wt%; the positive electrode slurry was uniformly coated on an aluminum foil, followed by baking and drying at 110°C, and the positive electrode sheet was prepared after cooling. The prepared positive electrode sheet was matched with a hard carbon negative electrode, a conventional carbonate electrolyte was used as the electrolyte, and a full battery was assembled.

[0079] Example 4

[0080] This example was prepared according to the method of Example 1, except that the raw materials were added in a ratio of 1000: 0.05: 0.15: 0.15 by weight of layered oxide: first metal source: first organic ligand: second organic ligand, and the rest of the process was the same as Example 1.

[0081] Example 5

[0082] This example was prepared according to the method of Example 1, except that the raw materials were added in a ratio of 1000: 70: 84: 84 by weight of layered oxide: first metal source: first organic ligand: second organic ligand, and the rest of the process was the same as Example 1.

[0083] Example 6

[0084] This example was prepared according to the method of Example 1, except that the raw materials were added in a ratio of 1000: 220: 300: 300 by weight of layered oxide: first metal source: first organic ligand: second organic ligand, and the rest of the process was the same as Example 1.

[0085] Example 7

[0086] This example was prepared according to the method of Example 1, except that the second organic ligand triethylenediamine (DABCO) was replaced with 2-methyl-1,4-diazidobicyclo[2.2.2]octane (i.e., in the compound structure shown in formula (1), R1 is methyl, and R2-R6 are hydrogen), and the rest of the process was the same as Example 1.

[0087] Example 8

[0088] This example was prepared according to the method of Example 1, except that the raw materials were added in a ratio of 1000: 2: 19: 19 by weight of layered oxide: first metal source: first organic ligand: second organic ligand, and the rest of the process was the same as Example 1.

[0089] Comparative Example 1

[0090] Ni 1 / 3 Fe 1 / 3 Mn 1 / 3O2 as the positive active material, binder polyvinylidene fluoride (PVDF) and conductive agent CNT-15% were added into N-methyl pyrrolidone to make slurry, based on the total weight of the slurry, the content of the positive active material was 85% by weight, the content of the binder was 7.5% by weight, and the content of the conductive agent was 7.5% by weight; the positive electrode slurry was uniformly coated on an aluminum foil, followed by baking and drying at 110°C, and the positive electrode sheet was prepared after cooling. The prepared positive electrode sheet was matched with a hard carbon negative electrode to assemble a full battery.

[0091] Comparative Example 2

[0092] The present comparative example refers to the preparation method in Example 1, and the difference from Example 1 is that no second organic ligand DABCO is added, including the following steps:

[0093] 1 g of NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2 was dispersed in 60 ml of N,N-dimethylformamide and stirred and ultrasonicated to obtain a suspension. 22 mg of Cu(NO3)2 and 60 mg of benzene-1,3,5-tricarboxylic acid (BTC) were added to the suspension and stirred for 30 min and then ultrasonicated for 30 min. Then the suspension was transferred to a teflon solvent kettle, and the solvent kettle was placed in a muffle furnace for solvothermal reaction, the reaction temperature was 150°C, and the reaction time was 12 h. After the reaction was completed, the suspension was centrifuged and washed with anhydrous ethanol, and then dried in a vacuum drying oven at 100°C, to obtain NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@Cu-BTC.

[0094] The prepared NaNi 1 / 3 Fe 1 / 3 Mn 1 / 3 O2@Cu-BTC was used as the positive active material, binder polyvinylidene fluoride (PVDF) and conductive agent CNT-15% were added into N-methyl pyrrolidone to make slurry, based on the total weight of the slurry, the content of the positive active material was 85% by weight, the content of the binder was 7.5% by weight, and the content of the conductive agent was 7.5% by weight; the positive electrode slurry was uniformly coated on an aluminum foil, followed by baking and drying at 110°C, and the positive electrode sheet was prepared after cooling. The prepared positive electrode sheet was matched with a hard carbon negative electrode to assemble a full battery.

[0095] In order to achieve better coordination effect of the MOF material and better coating effect of the MOF material coating layer, in the above examples, some raw materials are added in excess, specifically: in the layered oxide, the first metal source, the first organic ligand and the second organic ligand for forming the positive electrode material, the first metal source, the first organic ligand and the second organic ligand are added in excess; in the first metal source, the first organic ligand and the second organic ligand for forming the MOF material, the first organic ligand and the second organic ligand are added in excess based on the complete conversion of the first metal element in the first metal source into the MOF material; the actual component content of the positive electrode material and the MOF coating layer prepared in the examples is listed in Table 1.

[0096] The component content and structure parameters of the positive electrode material prepared in the above examples and comparative examples are listed in Table 1 below.

[0097] Table 1

[0098] In Table 1, the data marked with “*” indicates that the total weight of the positive electrode material is taken as the basis, and the data marked with “**” indicates that the total weight of the MOF material coating layer is taken as the basis.

[0099] Test Example

[0100] The soft pack battery assembled from the above examples and comparative examples is subjected to charge-discharge cycle test, including normal temperature cycle.

[0101] Normal temperature cycle: the full battery is clamped with a clamp and installed on a test instrument, and placed in a 25±2℃ environment, with a cycle rate of 1C and a voltage window of 2.0-4.1V. The capacity retention rate during 500 cycles is recorded, and the battery volume during the whole cycle is measured by the drainage method. After 500 cycles, the gas in the battery is taken out with a syringe, and the gas composition is determined by gas chromatography-mass spectrometer. The test results are listed in Table 2 below.

[0102] Table 2

[0103] According to the data in Tables 1-2 above, it can be seen that:

[0104] The coating layer of the positive electrode material prepared in Examples 1-8 introduces Tm-DABCO coating, the coating in Comparative Example 1 is not performed, and Comparative Example 2 is coated with Tm-BTC but does not introduce DABCO or its derivatives.

[0105] From the aspect of the thickness of the coating layer, Example 6 was overcoated, and the thickness of the coating layer reached 3.57 μm; the thicknesses of the coating layers in Examples 1-5 and 7-8 were within the optimized thickness range (0.1-3 μm) provided in the present disclosure, and compared with the positive electrode material in Example 6, the positive electrode material in Examples 1-5 and 7-8 could obtain higher initial charge capacity, initial discharge capacity and initial efficiency; this was because the large impedance caused by the over-thick coating layer in Example 6 hindered the capacity from being exerted; in addition, the coating layer (Examples 1-3 and 7) synthesized by using the preferred ratio had a thickness of about 0.4 μm, and the thickness of the coating layer was good in consistency.

[0106] Compared with Comparative Example 1 without coating, Comparative Example 2 with Tm-BTC coating had higher capacity retention rate and better cycle stability, and the gas volume was significantly reduced, which indicated that the coating layer inhibited the side reaction in the battery cell, improved the material stability during the cycle process, and reduced the gas production while improving the cycle life. In the gas species in Comparative Example 2, the proportion of oxidative CO2 was significantly reduced, which indicated that the introduced coating layer acted on the positive electrode and had the effect of reducing the side reaction at the interface of the positive electrode material.

[0107] On the basis of Comparative Example 2, Examples 1-8 introduced DABCO or its derivative as the ligand of the MOF coating layer, which could further improve the capacity retention rate of the battery cell and reduce the volume of the gas produced, and further reduce the proportion of the oxidative gas CO2. This indicated that DABCO and its derivatives had an additional inhibitory effect on the side reaction of the battery cell, and this effect originated from the reaction between DABCO and its derivatives and active oxygen. DABCO and its derivatives could effectively absorb and combine the active oxygen generated by the positive electrode material, thereby avoiding the side reaction with the electrolyte.

[0108] Further, Examples 1-5, 7-8 were compared with Example 6. In Example 6, the coating layer was too thick, and the content of the MOF coating layer in the positive electrode material was high, which could also reduce the interface side reaction of the positive electrode material and reduce the volume of the gas, and the effect was comparable to that of other examples (Examples 1-5, 7-8), which indicated that the over-thick coating layer could not bring additional inhibitory effect. In terms of the cycle stability of the battery, the introduction of the over-thick coating layer could not comprehensively improve the performance of the battery.

[0109] Comparing examples 1-3 and 7 with example 4, the content of the MOF material coating layer in examples 1-3 and 7 is within the preferred content range provided by the present disclosure, and the content of the MOF material coating layer in example 4 is lower, compared with the positive electrode material of example 4, the positive electrode material prepared in examples 1-3 and 7 has higher initial efficiency, and lower gas production volume and CO2 content in the produced gas after 500 cycles; comparing examples 1-3 and 7 with example 5, the content of the MOF material coating layer in examples 1-3 and 7 is within the preferred content range provided by the present disclosure, and the content of the MOF material coating layer in example 5 is higher, compared with the positive electrode material of example 5, the positive electrode material prepared in examples 1-3 and 7 has higher battery specific capacity and initial efficiency; it is illustrated that the comprehensive performance of the positive electrode material with preferred component content in examples 1-3 and 7 of the present disclosure is better.

[0110] Comparing examples 1-3 and 7 with example 8, the component content of the MOF coating layer in examples 1-3 and 7 is within the preferred range, and the battery performance of the positive electrode material prepared in examples 1-3 and 7 is comparable to that of example 8, but the positive electrode material of examples 1-3 and 7 has higher 500 cycle capacity retention rate and lower gas production volume and CO2 content in the produced gas.

[0111] The above describes the preferred embodiments of the present disclosure in detail, but the present disclosure is not limited to the specific details in the above embodiments, and various simple modifications can be made to the technical solutions of the present disclosure within the technical concept of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.

[0112] In addition, it should be noted that each specific technical feature described in the above specific embodiments can be combined in any appropriate manner without contradiction. In order to avoid unnecessary repetition, various possible combinations are not described again in the present disclosure.

[0113] In addition, various different embodiments of the present disclosure can also be combined in any appropriate manner, as long as they do not deviate from the idea of the present disclosure, and they should also be considered as disclosed by the present disclosure.

Claims

1. A positive electrode material, characterized by, The positive electrode material comprises a core of a layered oxide and a MOF material coating layer coated on the surface of the layered oxide; the MOF material coating layer comprises a first metal complex compound, and the organic ligand of the first metal complex compound comprises a compound having a structure shown in the following formula (1): wherein R1-R6 are the same or different, and each is independently selected from one of hydrogen, an alkyl group with a carbon atom number of 1-10, an alkenyl group with a carbon atom number of 1-10, or an alkynyl group with a carbon atom number of 1-10.

2. The positive electrode material of claim 1, wherein, The first metal element in the first metal complex compound is selected from one or more of Cu, Fe, Mn, Ca, Ni, Co, Cr, Zn, Ti, V, Zr, Mg, Al, Li, and Nb; The organic ligand in the first metal complex compound comprises a first organic ligand and a second organic ligand, the first organic ligand is selected from one or more of isophthalic acid, phthalic acid, terephthalic acid, trimesic acid, 1,2,4-benzene tricarboxylic acid, and 1,3,5-benzene tricarboxylic acid; and the second organic ligand comprises a compound having a structure shown in the above formula (1), wherein R1-R6 are the same or different, and each is independently selected from one of hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, ethenyl, propenyl, allyl, alkenyl, butadienyl, ethynyl, propargyl, and butynyl; The layered oxide comprises a compound having a composition shown in the following formula (2): Na x TmO2formula (2); wherein Tm is a second metal element, Tm is selected from one or more of Cu, Fe, Mn, Ca, Ni, Co, Cr, Zn, Ti, V, Zr, Mg, Al, Li and Nb; the structure of the layered oxide is selected from one or more of P2-type, O3-type, P3-type and tunnel-type, 0 < x < 1.

3. The positive electrode material according to claim 2, characterized in that, The content of the layered oxide is 58-99.9% by weight, and the content of the MOF material coating layer is 0.1-42% by weight, based on the total weight of the positive electrode material; The content of the first metal element is 5-50% by weight, the content of the first organic ligand is 15-60% by weight, and the content of the second organic ligand is 15-60% by weight, based on the total weight of the MOF material coating layer.

4. The positive electrode material according to any one of claims 1 to 3, characterized by The particle size of the positive electrode material is 2.1-23 μm, the particle size of the layered oxide is 2-20 μm, and the thickness of the MOF material coating layer is 0.1-4 μm.

5. The positive electrode material according to any one of claims 1 to 4, characterized by, The thickness of the MOF material coating layer is 0.1-3 μm.

6. A method of producing a positive electrode material, characterized by, The method comprises the following steps: The layered oxide, a first metal source, and an organic ligand are contacted and reacted in a solvent; wherein the organic ligand comprises a compound having a structure shown in the following formula (1): wherein R1-R6 are the same or different, and each is independently selected from one of hydrogen, an alkyl group with a carbon atom number of 1-10, an alkenyl group with a carbon atom number of 1-10, and an alkynyl group with a carbon atom number of 1-10.

7. The method of claim 6, wherein, The first metal source is selected from one or more of a nitrate salt, a sulfate salt, a halide salt, and a phosphate salt of a first metal element; and the first metal element is selected from one or more of Cu, Fe, Mn, Ca, Ni, Co, Cr, Zn, Ti, V, Zr, Mg, Al, Li, and Nb; The layered oxide has a composition shown in the following formula (2): ​ Na x Tm02formula (2); wherein Tm is a second metal element, Tm is selected from one or more of Cu, Fe, Mn, Ca, Ni, Co, Cr, Zn, Ti, V, Zr, Mg, Al, Li and Nb; the structure of the layered oxide is selected from one or more of P2-type, O3-type, P3-type and tunnel-type, 0 < x < 1; the particle size of the layered oxide is 2-20 μm; The organic ligand includes a first organic ligand and a second organic ligand, the first organic ligand is selected from one or more of isophthalic acid, phthalic acid, terephthalic acid, trimesic acid, 1,2,4-benzene tricarboxylic acid and 1,3,5-benzene tricarboxylic acid; the second organic ligand has the structure shown in the above formula (1), wherein R1-R6 are the same or different, and each is independently selected from one of hydrogen, methyl, ethyl, n-propyl, isopropyl, n-butyl, isobutyl, tert-butyl, vinyl, propenyl, allyl, alkenyl, butadienyl, ethynyl, propynyl and butynyl; The solvent is selected from one or more of acetonitrile, ethanol, ethylene glycol, methanol, propanol, tetrahydrofuran and N,N-dimethylformamide.

8. The method of claim 7, wherein, The weight ratio of the layered oxide: the first metal source: the first organic ligand: the second organic ligand is 1000: 0.05-70: 0.15-84: 0.15-84.

9. The method according to any one of claims 6 to 8, characterized in that, The conditions of the contact reaction include: in a solvent thermal reaction kettle, the reaction temperature is 100-300°C, and the reaction time is 5-36h.

10. The positive electrode material prepared by the method according to any one of claims 6-9.

11. A positive electrode sheet of a sodium ion battery, comprising the positive electrode material according to any one of claims 1-5 and 10.

12. A sodium ion battery, comprising the positive electrode sheet according to claim 11.

Images