Positive electrode material, preparation method therefor, and use thereof

Abstract

A positive electrode material, a preparation method therefor, and a use thereof. The positive electrode material comprises a base material and lithium oxalate particles covering at least part of the surface of the base material; and the particle size of the lithium oxalate particles is less than 200 nm. The lithium oxalate particles having the particle size less than 200 nm are loaded on the surface of the base material, thereby exerting the lithium supplementing effect of lithium oxalate to the maximum extent; and the positive electrode material is applied to a battery, thereby facilitating increase of the capacity and initial efficiency of the battery.

Description

A positive electrode material and its preparation method and application

[0001] This application claims priority to the Chinese patent application filed with the China Patent Office on December 4, 2023, with application number 202311649120.X and application name “A positive electrode material, its preparation method and application”, the entire contents of which are incorporated by reference into this application. Technical Field

[0002] The present application belongs to the technical field of lithium-ion batteries, and specifically relates to a positive electrode material and a preparation method and application thereof. Background Art

[0003] During the first cycle of a lithium-ion battery, a solid electrolyte interface (SEI) will form on the surface of the negative electrode, resulting in irreversible lithium loss. At this stage, the lithium replenishment methods in batteries are mainly divided into positive electrode lithium replenishment and negative electrode lithium replenishment. Among them, positive electrode lithium replenishment is achieved by adding a small amount of high-capacity lithium replenisher during the homogenization process of the positive electrode material. However, the current chemical stability of the lithium replenisher is poor, the decomposition voltage is high, and the binding with the positive electrode material is poor, making it difficult to play the role of lithium replenishment. Therefore, additional catalysts, binders, etc. need to be added. The residues left on the positive electrode side of such a lithium replenishment system after delithiation will affect the impedance of the battery and catalyze the gas production of the electrolyte, thereby causing the capacity and first efficiency of the battery to decrease. In addition, the preparation process is more complicated and the production cost is high. Therefore, how to balance improving the capacity and first efficiency of the battery is a technical problem that needs to be solved urgently in this field.

[0004] Summary of the Invention

[0005] The present application provides a positive electrode material, which maximizes the lithium replenishing effect of lithium oxalate by loading lithium oxalate particles with a particle size of less than 200 nm on the surface of a base material. The positive electrode material is applied to a battery, which is beneficial to improving the capacity and initial efficiency of the battery.

[0006] The present application also provides a method for preparing a positive electrode material, which can produce the above-mentioned positive electrode material with excellent performance by inducing a rapid exothermic reaction among a matrix material, a compound containing oxalate, and a lithium source, so that lithium oxalate particles with a particle size of less than 200 nm are covered on the surface of the matrix material. The preparation process is simple and easy to operate, which is conducive to mass production.

[0007] The present application also provides a positive electrode sheet. Since it includes the above-mentioned positive electrode material, applying the positive electrode sheet to a battery is beneficial to improving the capacity and initial efficiency of the battery.

[0008] The present application also provides a battery, which has both excellent capacity and initial efficiency due to the inclusion of the above-mentioned positive electrode sheet.

[0009] In a first aspect of the present application, a positive electrode material is provided, comprising a base material and lithium oxalate particles covering at least a portion of a surface of the base material;

[0010] The particle size of the lithium oxalate particles is less than 200 nm.

[0011] The positive electrode material as described above, wherein the lithium oxalate particles are distributed in a dotted manner on the surface of the base material;

[0012] The particle size of the lithium oxalate particles is 5 to 100 nm.

[0013] The positive electrode material as described above, wherein the positive electrode material comprises, in parts by mass: 90-99.9 wt % of matrix material and 0.1-10 wt % of lithium oxalate.

[0014] The positive electrode material as described above, wherein the matrix material comprises a positive electrode active material and a carbon layer coated on the surface of the positive electrode active material;

[0015] The lithium oxalate particles cover the surface of the carbon layer.

[0016] The positive electrode material as described above, wherein the positive electrode material comprises, in parts by mass: 95-99 wt% of matrix material and 1-5 wt% of lithium oxalate; and / or, the matrix material comprises, in parts by mass: 95-99 wt% of positive electrode active material and 1-5 wt% of carbon layer.

[0017] The positive electrode material as described above, wherein the chemical formula of the positive electrode active material is Li a Fe b M c N d (PO4) e , where 0.9≤a≤1.1, 0.25≤b≤1.0, 0≤c≤0.75, 0≤d≤0.1, 0.9≤e≤1.1;

[0018] Wherein, M includes Mn;

[0019] N includes at least one of Mg, Al, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, P, S, and F.

[0020] The positive electrode material as described above, wherein the growth rate of the specific surface area of ​​the positive electrode material relative to the specific surface area of ​​the base material is ≥2.5%.

[0021] A second aspect of the present application provides a method for preparing the positive electrode material according to the first aspect, comprising the following steps: subjecting a matrix material, a compound containing oxalate, and a lithium source to high-speed mechanical dispersion or thermal initiation to obtain the positive electrode material;

[0022] The time for the high-speed mechanical dispersion treatment and the thermal initiation is no more than 10 minutes.

[0023] The preparation method as described above, wherein the rotation speed of the high-speed mechanical dispersion treatment is 800 to 3000 rpm and the time is 0.5 to 10 minutes; or

[0024] The thermal initiation temperature is 100-300° C., and the time is 0.5-10 minutes.

[0025] The preparation method as described above, wherein, before thermal initiation, it further comprises premixing the matrix material, the compound containing oxalate, and the lithium source;

[0026] The temperature of the premix does not exceed 15°C.

[0027] The preparation method as described above, wherein the compound containing oxalate comprises at least one of ammonium oxalate, oxalic acid and hydrates thereof; and / or,

[0028] The lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium citrate; and / or,

[0029] The molar ratio of the oxalate in the oxalate-containing compound to the lithium in the lithium source is (0.4-10):1.

[0030] In a third aspect of the present application, a positive electrode sheet is provided, which comprises the positive electrode material described in the first aspect or the positive electrode material prepared by the preparation method described in the second aspect.

[0031] A fourth aspect of the present application provides a lithium-ion battery, comprising the positive electrode sheet described in the third aspect.

[0032] The implementation of this application has at least the following beneficial effects:

[0033] The positive electrode material provided in the present application includes a base material and lithium oxalate particles covering the surface of the base material. The lithium oxalate particles themselves have good chemical stability and do not undergo chemical reactions under normal circumstances. The lithium oxalate particles can decompose and release lithium elements during the charging process, providing additional lithium elements for the positive electrode material. Lithium oxalate is inexpensive, has a high capacity, and leaves no residue after decomposing and releasing lithium elements. In addition, due to the small particle size of the lithium oxalate particles, the contact area between the lithium oxalate particles and the base material is increased, forming a good bond, which can enable the lithium oxalate particles to be firmly and tightly covered on the surface of the base material, avoiding falling off and losing electrical contact, and maximizing the lithium replenishing effect of lithium oxalate. Applying this positive electrode material to the battery is beneficial to improving the capacity and initial efficiency of the battery.

[0034] The preparation method of the positive electrode material provided in the present application is to limit the solid phase mixing of the base material, the compound containing oxalate, and the lithium source, so that the compound containing oxalate and the lithium source react to form lithium oxalate and generate heat. At the same time, under the heat conditions, the lithium oxalate particles can be covered on the surface of the base material. In addition, by limiting the reaction time, the lithium oxalate particles can be nucleated in large quantities without growing up, and lithium oxalate particles with a particle size of less than 200 nm can be synthesized in situ on the surface of the base material, thereby obtaining the above-mentioned positive electrode material with excellent performance. The preparation process is simple and easy to operate, which is conducive to mass production. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] FIG1 is a SEM image of the positive electrode material in Example 1 of the present application;

[0036] FIG2 is a SEM image of the positive electrode material in Example 20 of the present application at the first magnification;

[0037] FIG3 is a SEM image of the positive electrode material in Example 20 of the present application at a second magnification;

[0038] FIG4 is an SEM image of carbon-coated lithium iron phosphate A1 in Example 1 and Comparative Example 1 of the present application;

[0039] FIG5 is an SEM image of lithium nickel manganese oxide A3 in Example 20 of the present application and Comparative Example 3;

[0040] FIG6 is a SEM image of lithium oxalate of Comparative Example 4 of the present application;

[0041] FIG7 is an XRD diffraction pattern of lithium oxalate in Comparative Examples 4-6 of the present application;

[0042] FIG8 is a SEM image of lithium oxalate in Comparative Example 7. DETAILED DESCRIPTION

[0043] To make the purpose, technical solutions, and advantages of this application more clear, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are part of the embodiments of this application, not all of the embodiments. Based on the embodiments of this application, all other embodiments obtained by ordinary technicians in this field without making creative efforts are within the scope of protection of this application.

[0044] In a first aspect of the present application, a positive electrode material is provided, comprising a matrix material and lithium oxalate particles covering at least a portion of a surface of the matrix material; the particle size of the lithium oxalate particles is less than 200 nm.

[0045] The matrix material serves as the core of the positive electrode material, and the lithium oxalate particles cover part or all of the surface of the matrix material. In this case, the lithium oxalate particles can serve as a lithium-replenishing layer. The particle size of the lithium oxalate particles is less than 200 nm, which can be observed using a scanning electron microscope (SEM).

[0046] According to the research of this application, the above-mentioned positive electrode material is applied to the battery, which is conducive to improving the capacity and first effect of the battery. This is because, during the charging process, the lithium oxalate particles decompose and release the lithium element, and the lithium element is embedded in the negative electrode to supplement the irreversible capacity of the first charge and discharge, reducing the loss of lithium element in the matrix material during the charge and discharge process. Secondly, lithium oxalate is cheap, stable, high in capacity, and has no residue after decomposition and release of lithium element. In addition, the particle size of the lithium oxalate particles is less than 200nm, which helps to increase the contact area between the lithium oxalate particles and the matrix material, forming a good combination, so that the lithium oxalate particles are firmly and tightly covered on the surface of the matrix material, avoiding falling off and losing electrical contact, and maximizing the lithium supplementation effect of lithium oxalate. The positive electrode material is applied to the battery, which is conducive to improving the capacity and first effect of the battery.

[0047] The lithium oxalate particles are distributed in a dotted manner on the surface of the matrix material, and the dotted distribution area is dense and uniform, which avoids the agglomeration of the lithium oxalate particles, is conducive to achieving effective coating of the outer surface of the matrix material, and promotes the decomposition of lithium oxalate.

[0048] On the one hand, the smaller the particle size of lithium oxalate particles, the easier it is to decompose and release lithium ions at a lower voltage; on the other hand, the smaller the particle size of lithium oxalate particles, the larger the specific surface area, and the larger the contact area between the lithium oxalate particles and the matrix material, which can form a good bond with the matrix material to ensure electrical contact, thereby ensuring the decomposition of lithium oxalate.

[0049] In some embodiments, the particle size of the lithium oxalate particles is 5 to 100 nm. If the particle size of the lithium oxalate particles is too large, it is difficult to decompose and form a good bond with the matrix material, which is not conducive to the lithium oxalate's lithium supplementation effect. By further limiting the particle size of the lithium oxalate particles to 5 to 100 nm, it is beneficial to achieve a uniform and dense distribution of the lithium oxalate particles on the surface of the matrix material, thereby achieving maximum coverage of the outer surface of the matrix material and exerting the lithium oxalate's lithium supplementation effect.

[0050] The present application does not limit the mass content of lithium oxalate. For example, in some embodiments, the positive electrode material includes, by mass, 90 to 99.9 wt % of the matrix material and 0.1 to 10 wt % of lithium oxalate. Preferably, the positive electrode material includes, by mass, 95 to 99 wt % of the matrix material and 1 to 5 wt % of lithium oxalate, which is beneficial to maximize the capacity and initial efficiency of the battery.

[0051] Because the decomposition voltage of lithium oxalate is relatively high (about 4.7 V), the positive electrode material provided in this application is particularly suitable for use in high-voltage systems, allowing more lithium ions to be released and achieving a higher specific capacity.

[0052] This application does not limit the specific type of matrix material, and conventional positive electrode active materials in the field can be selected as needed, such as lithium cobalt oxide, ternary positive electrode materials, lithium manganese oxide, lithium nickel manganese oxide, lithium-rich manganese-based materials and other high-voltage system materials.

[0053] In order to broaden the applicability of the positive electrode material, in some embodiments, the matrix material includes a positive electrode active material and a carbon layer coated on the surface of the positive electrode active material, and lithium oxalate is coated on the surface of the carbon layer, specifically the surface of the carbon layer away from the positive electrode active material. By coating the carbon layer on the surface of the positive electrode active material, conductivity can be provided to lithium oxalate to reduce the decomposition voltage of lithium oxalate, thereby ensuring that the lithium oxalate particles can effectively play a lithium supplement role even in a low voltage system. At this time, due to the small particle size of the lithium oxalate particles, they are covered on the surface of the carbon layer, which can make the lithium oxalate particles firmly and tightly covered on the surface of the carbon layer to avoid falling off, thereby maximizing the lithium effect of lithium oxalate. Applying this positive electrode material to batteries is beneficial to improving the capacity and initial efficiency of the batteries.

[0054] The present application does not limit the specific mass percentages of the positive electrode active material and the carbon layer, which can be adjusted according to actual needs. For example, in some embodiments, the matrix material includes, by mass, 95-99 wt % of the positive electrode active material and 1-5 wt % of the carbon layer.

[0055] The present application does not limit the specific type of positive electrode active material. For example, the positive electrode active material includes at least one of lithium iron phosphate, lithium manganese iron phosphate, and lithium nickel manganese oxide. In some embodiments, the chemical formula of the positive electrode active material is Li a Fe b Mc N d (PO4) e , wherein 0.9≤a≤1.1, 0.25≤b≤1.0, 0≤c≤0.75, 0≤d≤0.1, and 0.9≤e≤1.1; wherein M includes Mn; and N includes at least one of Mg, Al, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, P, S, and F.

[0056] Because the particle size of lithium oxalate particles is less than 200 nm, the specific surface area of ​​the positive electrode material increases relative to the specific surface area of ​​the matrix material. In some embodiments, the specific surface area of ​​the positive electrode material increases by 2.5% or more relative to the specific surface area of ​​the matrix material. Growth rate = (specific surface area of ​​positive electrode material - specific surface area of ​​matrix material) / specific surface area of ​​matrix material. By limiting the range of increase in the specific surface area of ​​the positive electrode material, lithium oxalate, with its high lithium replenishment performance, can be used in most positive electrode materials.

[0057] The second aspect of the present application provides a method for preparing the positive electrode material provided in the first aspect, comprising the following steps: subjecting the matrix material, the compound containing oxalate, and the lithium source to high-speed mechanical dispersion treatment or thermal initiation to obtain the positive electrode material; wherein the time for the high-speed mechanical dispersion treatment and the thermal initiation does not exceed 10 minutes.

[0058] Most lithium oxalate lithium supplements in the prior art are prepared by preparing a carbon material, a catalyst, and lithium oxalate into a lithium oxalate lithium supplement composite material, which is then mixed with a base material to form a slurry. Under the joint action of the catalyst and the carbon material, the decomposition of lithium oxalate is promoted to release lithium elements. However, in the lithium oxalate lithium supplement composite material, it is difficult for lithium oxalate and the carbon material and the catalyst to form a good bond, which makes it difficult for lithium oxalate to separate from the carbon material and the catalyst during the homogenization process, resulting in difficulty in fully reducing the decomposition voltage. Moreover, due to the introduction of a large amount of carbon materials and catalysts, the cost of the lithium supplement additive is expensive, which limits its application in cost-effective positive electrode systems, especially its application in carbon-coated lithium iron phosphate systems. However, the present application forms a stable bond by in-situ growing lithium oxalate on the base material. When the surface of the base material is a carbon layer, the carbon layer is used to provide conductivity to lithium oxalate to reduce the decomposition voltage of lithium oxalate. In this method, lithium oxalate will not lose contact with the carbon layer, and the use of excessive carbon materials and catalysts can be avoided, further reducing the cost of the battery system.

[0059] The high-speed mechanical dispersion treatment can be directly carried out in a high-speed mixer, that is, the matrix material, the compound containing oxalate, and the lithium source are directly placed in the high-speed mixer for high-speed mechanical dispersion treatment.

[0060] Before thermal initiation, the matrix material, the compound containing oxalate, and the lithium source are premixed. The premixing can be carried out in a high-speed mixer. In order to avoid overheating of the high-speed mixer during the mixing stage, which may cause the raw materials to react prematurely, the premixing temperature is usually kept below 15°C. Specifically, circulating cooling water may be used as an aid. For example, circulating cooling water may be used for cooling during premixing, and the temperature of the circulating cooling water shall not exceed 15°C.

[0061] High-speed mechanical dispersion and thermal initiation essentially utilize heat to induce a rapid reaction between the oxalate-containing compound and the lithium source to generate lithium oxalate particles that coat the surface of the substrate. By limiting the high-speed mechanical dispersion and thermal initiation times to no more than 10 minutes, the extremely rapid reaction speed allows lithium oxalate to nucleate in large quantities without growing, thereby forming lithium oxalate particles with a particle size of less than 200nm. Simultaneously, the reaction between the oxalate-containing compound and the lithium source releases a large amount of heat, which thermodynamically allows the adjacent reactants to reach reaction conditions. This allows the lithium oxalate particles to heterogeneously nucleate on the surface of the substrate and adhere firmly and densely to the substrate surface, forming a good coating.

[0062] In some embodiments, the high-speed mechanical dispersion treatment speed is 800-3000 rpm, for example, 800 rpm, 1000 rpm, 1200 rpm, 1500 rpm, 2000 rpm, 2500 rpm, 3000 rpm or a range consisting of any two thereof, and the time is 0.5-10 min, preferably 1-3 min; the thermal initiation temperature is 100-300°C, for example, 100°C, 200°C, 300°C or a range consisting of any two thereof, and the time is 0.5-10 min.

[0063] The present application does not limit the specific type and addition amount of the oxalate-containing compound and the lithium source, as long as the oxalate-containing compound and the lithium source can react to form lithium oxalate. For example, the oxalate-containing compound includes at least one of ammonium oxalate, oxalic acid, and hydrates thereof; and / or the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, and lithium citrate; and / or the ratio of the molar amount of oxalate in the oxalate-containing compound to the molar amount of lithium in the lithium source is (0.4-10):1, preferably (1-4):1.

[0064] It should be noted that after the mixture is subjected to high-speed mechanical dispersion treatment or thermal initiation, post-treatment is also included. For example, the mixture is subjected to high-speed mechanical dispersion treatment or thermal initiation, and after water washing, filtration, and drying, the positive electrode material is obtained.

[0065] In a third aspect of the present application, a positive electrode sheet is provided, which includes the positive electrode material of the first aspect or the positive electrode material prepared by the preparation method of the second aspect.

[0066] The positive electrode sheet of the present application can also be prepared by conventional technical means in the field. Specifically, the above-mentioned positive electrode material, conductive agent, and binder can be uniformly dispersed in a solvent to obtain a positive electrode active layer slurry, and then the positive electrode active layer slurry is coated on at least one functional surface of the positive electrode current collector. After drying, the positive electrode sheet of the present application can be obtained.

[0067] In a fourth aspect of the present application, a lithium-ion battery is provided, wherein the lithium-ion battery includes the positive electrode sheet provided in the third aspect.

[0068] The lithium-ion battery of the present application includes, in addition to the positive electrode sheet, a separator, a negative electrode sheet, and an electrolyte. The composition of the negative electrode sheet can refer to conventional negative electrode sheets in the art, and the separator can also adopt separators conventionally used in the art, such as PP film, PE film, etc. The lithium-ion battery of the present application can be prepared using conventional methods in the art. Specifically, the positive electrode sheet, separator, and negative electrode sheet can be stacked in sequence, and then a battery cell can be obtained through a lamination or winding process. The above-mentioned lithium-ion battery can then be obtained through processes such as baking, liquid injection, formation, and packaging.

[0069] The present invention is further described below by means of specific examples and comparative examples. Unless otherwise specified, the reagents, materials and instruments used below are all conventional reagents, materials and instruments, which are all commercially available, and the reagents and materials involved can also be synthesized by conventional synthesis methods.

[0070] Example 1

[0071] (1) 10 kg of precursor FePO4, 2.5 kg of lithium carbonate, 0.5 kg of glucose, and 87 g of TiO2 were mixed and sand-ground until the Dv50 of the solid particles was ≤ 500 nm to obtain a sand-ground slurry; the sand-ground slurry was spray-dried to obtain a composite precursor powder; the precursor powder was heated to 300° C. at 5° C. / min under nitrogen and kept warm for 3 h, then heated to 750° C. at 2° C. / min and kept warm for 10 h, then heated to 780° C. at 2° C. / min and kept warm for 2 h to obtain carbon-coated lithium iron phosphate A1; the carbon-coated lithium iron phosphate A1 includes lithium iron phosphate and a carbon layer coated on the surface of the lithium iron phosphate;

[0072] (2) 1 kg of carbon-coated lithium iron phosphate A1, 9.4 g of lithium hydroxide, and 24.0 g of oxalic acid dihydrate were added to a high-speed mixer and mixed at 2000 rpm for 3 min; the reaction product was added to 3 L of ethanol, stirred and washed for 5 min, and filtered and dried to obtain a positive electrode material, which was recorded as D1.

[0073] Example 2

[0074] The preparation process is basically the same as that in Example 1, except that "9.4 g lithium hydroxide, 24.0 g oxalic acid dihydrate" in step (2) is replaced by "2.4 g lithium hydroxide, 6.0 g oxalic acid dihydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D2.

[0075] Example 3

[0076] The preparation process is basically the same as that in Example 1, except that "9.4 g lithium hydroxide, 24.0 g oxalic acid dihydrate" in step (2) is replaced by "4.7 g lithium hydroxide, 12.0 g oxalic acid dihydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D3.

[0077] Example 4

[0078] The preparation process is basically the same as that in Example 1, except that "9.4 g lithium hydroxide, 24.0 g oxalic acid dihydrate" in step (2) is replaced by "14.1 g lithium hydroxide, 36.0 g oxalic acid dihydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D4.

[0079] Example 5

[0080] The preparation process is basically the same as that in Example 1, except that "9.4 g lithium hydroxide, 24.0 g oxalic acid dihydrate" in step (2) is replaced by "18.8 g lithium hydroxide, 48.0 g oxalic acid dihydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D5.

[0081] Example 6

[0082] The preparation process is basically the same as that in Example 1, except that "9.4 g lithium hydroxide, 24.0 g oxalic acid dihydrate" in step (2) is replaced by "23.5 g lithium hydroxide, 60.0 g oxalic acid dihydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D6.

[0083] Example 7

[0084] The preparation process is basically the same as that in Example 1, except that "9.4 g lithium hydroxide, 24.0 g oxalic acid dihydrate" in step (2) is replaced by "47 g lithium hydroxide, 120.0 g oxalic acid dihydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D7.

[0085] Example 8

[0086] The preparation process is basically the same as that in Example 1, except that "9.4 g lithium hydroxide, 24.0 g oxalic acid dihydrate" in step (2) is replaced by "9.4 g lithium hydroxide, 48.0 g oxalic acid dihydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D8.

[0087] Example 9

[0088] The preparation process is basically the same as that in Example 1, except that "9.4 g lithium hydroxide, 24.0 g oxalic acid dihydrate" in step (2) is replaced by "9.4 g lithium hydroxide, 36.0 g oxalic acid dihydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D9.

[0089] Example 10

[0090] The preparation process is basically the same as that in Example 1, except that "9.4 g lithium hydroxide, 24.0 g oxalic acid dihydrate" in step (2) is replaced by "14.1 g lithium hydroxide, 24.0 g oxalic acid dihydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D10.

[0091] Example 11

[0092] The preparation process is basically the same as that in Example 1, except that "9.4 g lithium hydroxide, 24.0 g oxalic acid dihydrate" in step (2) is replaced by "18.8 g lithium hydroxide, 24.0 g oxalic acid dihydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D11.

[0093] Example 12

[0094] The preparation process is basically the same as that in Example 1, except that "9.4 g lithium hydroxide, 24.0 g oxalic acid dihydrate" in step (2) is replaced by "9.4 g lithium hydroxide, 27.9 g ammonium oxalate monohydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D12.

[0095] Example 13

[0096] The preparation process is basically the same as that of Example 1, except that "9.4 g lithium hydroxide, 24.0 g oxalic acid dihydrate" in step (2) is replaced by "14.5 g lithium carbonate, 24.0 g oxalic acid dihydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D13.

[0097] Example 14

[0098] The preparation process is basically the same as that of Example 1, except that "9.4 g lithium hydroxide, 24.0 g oxalic acid dihydrate" in step (2) is replaced by "14.5 g lithium carbonate, 27.9 g ammonium oxalate monohydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D14.

[0099] Example 15

[0100] 1 kg of carbon-coated lithium iron phosphate A1, 4.7 g of lithium hydroxide, and 12 g of oxalic acid dihydrate were added to a high-speed mixer and stirred intermittently at 500 rpm for 30 seconds. During the stirring process, circulating cooling water was used for cooling for 1 minute, and this was repeated 5 times. The stirred materials were placed in a corundum sagger and placed in a muffle furnace preheated to 200°C and heated for 5 minutes. The reaction product was added to 3 L of ethanol, stirred and washed for 5 minutes, and then filtered and dried to obtain the positive electrode material D15.

[0101] Example 16

[0102] The preparation process is basically the same as that of Example 15, except that "4.7 g lithium hydroxide, 12 g oxalic acid dihydrate" are replaced by "9.4 g lithium hydroxide, 24.0 g oxalic acid dihydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D16.

[0103] Example 17

[0104] The preparation process is basically the same as that of Example 15, except that "4.7 g lithium hydroxide, 12 g oxalic acid dihydrate" are replaced by "14.1 g lithium hydroxide, 36.0 g oxalic acid dihydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D17.

[0105] Example 18

[0106] The preparation process is basically the same as that of Example 15, except that "4.7 g lithium hydroxide, 12 g oxalic acid dihydrate" are replaced by "9.4 g lithium hydroxide, 27.9 g ammonium oxalate monohydrate", and other conditions remain unchanged to obtain a positive electrode material, which is recorded as D18.

[0107] Example 19

[0108] (1) 10 kg of precursor FePO4, 6.13 kg of lithium carbonate, 11.54 kg of manganese carbonate, 11.55 kg of ammonium dihydrogen phosphate, 1.04 kg of glucose, and 1.95 kg of PEG-2000 were mixed and sand-ground until the Dv50 of the solid particles was ≤ 450 nm to obtain a sand-ground slurry; the sand-ground slurry was spray-dried to obtain a composite precursor powder; the precursor powder was heated to 350 ° C at 5 ° C / min under nitrogen and kept warm for 3 h, and then heated to 700 ° C at 2 ° C / min and kept warm for 10 h to obtain carbon-coated lithium manganese iron phosphate A2.

[0109] (2) 1 kg of carbon-coated lithium manganese iron phosphate A2, 9.4 g of lithium hydroxide, and 24.0 g of oxalic acid dihydrate were added to a high-speed mixer and mixed at 2000 rpm for 3 min; the reaction product was added to 3 L of ethanol, stirred and washed for 5 min, and filtered and dried to obtain a positive electrode material, which was recorded as D19.

[0110] Example 20

[0111] (1) 10 kg of precursor Ni 0.5 Mn 1.5 (OH)4, 2.21 kg of lithium carbonate, and 128 g of Ta2O5 were added to a high-speed mixer and mixed and stirred until uniform to obtain a mixture; the mixture was sintered at 960°C for 15 hours, then cooled to room temperature at a rate of 1°C / min, crushed, and sieved to obtain lithium nickel manganese oxide A3;

[0112] (2) 1 kg of lithium nickel manganese oxide A3, 9.4 g of lithium hydroxide, and 24.0 g of oxalic acid dihydrate were added to a high-speed mixer and stirred intermittently at 500 rpm for 30 s. During the stirring process, circulating cooling water was used for cooling for 1 min, and this process was repeated 5 times. The stirred materials were placed in a corundum sagger and placed in a muffle furnace preheated to 200 ° C and heated for 5 min. The reaction product was added to 3 L of ethanol, stirred and washed for 5 min, and the positive electrode material was obtained after filtration and drying, which was recorded as D20.

[0113] Comparative Example 1

[0114] 10 kg of precursor FePO4, 2.5 kg of lithium carbonate, 0.5 kg of glucose, and 87 g of TiO2 were mixed and sand-milled until the Dv50 of the solid particles was ≤ 500 nm to obtain a sand-milled slurry; the sand-milled slurry was spray-dried to obtain a composite precursor powder; the precursor powder was heated to 300 ° C at 5 ° C / min under nitrogen, kept warm for 3 hours, then heated to 750 ° C at 2 ° C / min, kept warm for 10 hours, and then heated to 780 ° C at 2 ° C / min, kept warm for 2 hours for sintering to obtain carbon-coated lithium iron phosphate A1, which is the positive electrode material of this comparative example.

[0115] Comparative Example 2

[0116] 10 kg of precursor FePO4, 6.13 kg of lithium carbonate, 11.54 kg of manganese carbonate, 11.55 kg of ammonium dihydrogen phosphate, 1.04 kg of glucose, and 1.95 kg of polyethylene glycol (PEG-2000) were mixed and sand-milled until the Dv50 of the solid particles was ≤ 450 nm to obtain a sand-milled slurry; the sand-milled slurry was spray-dried to obtain a composite precursor powder; the precursor powder was heated to 350 ° C. at 5 ° C. / min under nitrogen and kept warm for 3 h, and then heated to 700 ° C. at 2 ° C. / min and kept warm for 10 h to obtain carbon-coated lithium manganese iron phosphate A2, which is the positive electrode material of this comparative example.

[0117] Comparative Example 3

[0118] 10kg of precursor Ni 0.5 Mn 1.5(OH)4, 2.21kg lithium carbonate, and 128g Ta2O5 were added to a high-speed mixer and mixed and stirred until uniform to obtain a mixture; the mixture was sintered at 960°C for 15h, then cooled to room temperature at a rate of 1°C / min, and then crushed and sieved to obtain lithium nickel manganese oxide A3, which is the positive electrode material of this comparative example.

[0119] Comparative Example 4

[0120] 188 g of lithium hydroxide and 480 g of oxalic acid dihydrate were added to a high-speed mixer and rapidly mixed at 2000 rpm for 3 minutes to react; the reaction product was added to 5 L of ethanol, stirred and washed for 5 minutes, and filtered and dried to obtain lithium oxalate C1.

[0121] Comparative Example 5

[0122] The preparation process is basically the same as that of Comparative Example 4, except that "480 g of oxalic acid dihydrate" is replaced by "480 g of ammonium oxalate monohydrate", and other conditions remain unchanged to obtain lithium oxalate C2.

[0123] Comparative Example 6

[0124] The preparation process is basically the same as that of Comparative Example 4, except that "188 g of lithium hydroxide" is replaced by "188 g of lithium carbonate" and other conditions remain unchanged to obtain lithium oxalate C3.

[0125] Comparative Example 7

[0126] A 5% mass concentration oxalic acid aqueous solution was prepared and freeze-dried to obtain lithium oxalate particles with a particle size of 500 nm. 20 g of lithium oxalate particles were stirred and mixed with 1 kg of carbon-coated lithium iron phosphate A1 using a high-speed mixer to obtain the positive electrode material D21 of this comparative example.

[0127] Test example

[0128] Electrochemical performance test: The positive electrode materials in Examples 1-20 and Comparative Examples 1-3 and 7 were assembled into button-type half-cells with a specification of CR2430 (the negative electrode was a metal lithium sheet), and the 0.1C charge and discharge capacity and the first coulombic efficiency (first efficiency) were tested at a temperature of 40°C; among them, the voltage window of Examples 1-19 and Comparative Examples 1, 2, and 7 was 2.0~4.5V, and the nominal capacity was 170mAh / g, and the voltage window of Example 20 and Comparative Example 3 was 3.5~4.95V, and the nominal capacity was 150mAh / g.

[0129] The test results are shown in Table 1.

[0130] Table 1

[0131] The SEM image of carbon-coated lithium iron phosphate A1 is shown in Figure 4, and the SEM image of the positive electrode material in Example 1 is shown in Figure 1. Since the particles of carbon-coated lithium iron phosphate A1 are small and the particle size of the lithium oxalate formed is also very small, it cannot be clearly identified in the SEM. Example 20 uses lithium nickel manganese oxide A3 with larger particles as the base material. The SEM image of lithium nickel manganese oxide A3 is shown in Figure 5. Since the particles of lithium nickel manganese oxide A3 are large and the surface is smooth and flat, the growth of lithium oxalate on its surface can be very clearly observed. According to the SEM images of the positive electrode material in Example 20 (Figures 2 and 3), it can be seen that a large number of lithium oxalate particles are attached to the surface of lithium nickel manganese oxide A3, and the particle size of most lithium oxalate particles is less than 100nm.

[0132] The SEM image of lithium oxalate C1 prepared in Comparative Example 4 is shown in Figure 6 , which indicates that the particle size of the produced lithium oxalate is 100-300 nm. The XRD diffraction patterns of lithium oxalates C1, C2, and C3 prepared in Comparative Examples 4-6 are shown in Figure 7 . All diffraction peaks closely match those of the standard PDF card for lithium oxalate (PDF#24-0646), confirming that the product produced by the reaction is lithium oxalate.

[0133] The SEM image of the lithium oxalate prepared by freeze-drying in Comparative Example 7 is shown in FIG8 . As can be seen from FIG8 , the particle size of the generated lithium oxalate is about 500 nm.

[0134] According to Table 1, the positive electrode material provided by the present application can improve the capacity and the first effect. After research, the applicant believes that: the present application can make lithium oxalate particles with a particle size of less than 200nm adhere to the surface of the base material through in-situ synthesis and control of reaction conditions and time, forming a good bond, and can make the lithium oxalate particles firmly and tightly covered on the surface of the base material to avoid falling off, thereby maximizing the lithium supplementation effect of lithium oxalate, thereby improving the capacity and the first effect, avoiding the defects of the prior art of adding additional catalysts and carbon materials, and reducing production costs. In addition, the present application can synthesize lithium oxalate particles in situ on the surface of the base material, and the preparation process is simple and easy to operate, which is suitable for mass production.

[0135] The above describes in detail the preferred embodiments and experimental verifications of the present application. It should be understood that ordinary skill in the art can make numerous modifications and variations based on the concepts of the present application without inventive effort. Therefore, any technical solutions that can be derived by those skilled in the art based on the concepts of the present application through logical analysis, reasoning, or limited experimentation on the basis of the existing technology should be within the scope of protection defined by the claims.

Claims

1. A cathode material, wherein, it includes a matrix material and lithium oxalate particles covering at least part of the surface of the matrix material; the particle size of the lithium oxalate particles is less than 200 nm.

2. The cathode material according to claim 1, wherein, the lithium oxalate particles are dot - distributed on the surface of the matrix material; the particle size of the lithium oxalate particles is 5 - 100 nm.

3. The cathode material according to claim 2, wherein, the cathode material comprises, by mass fraction: 90 - 99.9 wt% of the matrix material and 0.1 - 10 wt% of lithium oxalate.

4. The cathode material according to any one of claims 1 - 3, wherein, the matrix material includes a cathode active material and a carbon layer coated on the surface of the cathode active material; the lithium oxalate particles cover the surface of the carbon layer.

5. The cathode material according to claim 4, wherein, the cathode material comprises, by mass fraction: 95 - 99 wt% of the matrix material and 1 - 5 wt% of lithium oxalate; and / or, the matrix material comprises, by mass fraction: 95 - 99 wt% of the cathode active material and 1 - 5 wt% of the carbon layer.

6. The cathode material according to claim 5, wherein, The chemical formula of the positive electrode active material is Li a Fe b M c N d (PO 4 ) e , where 0.9 ≤ a ≤ 1.1, 0.25 ≤ b ≤ 1.0, 0 ≤ c ≤ 0.75, 0 ≤ d ≤ 0.1, 0.9 ≤ e ≤ 1.1; wherein, M includes Mn; N includes at least one of Mg, Al, Ca, Sc, Ti, V, Cr, Fe, Co, Cu, Zn, Ga, Sr, Y, Zr, Nb, Mo, Ru, Ta, W, B, Si, Ge, Sb, Te, P, S, F.

7. The cathode material according to claim 6, wherein, the growth rate of the specific surface area of the cathode material relative to the specific surface area of the matrix material is ≥2.5%.

8. A preparation method of the cathode material according to any one of claims 1 - 7, wherein, it includes the following steps: After performing high - speed mechanical dispersion treatment or thermal initiation on the matrix material, a compound containing oxalate, and a lithium source, the cathode material is obtained; wherein, the time of the high - speed mechanical dispersion treatment and the thermal initiation does not exceed 10 min.

9. The preparation method according to claim 8, wherein, the rotation speed of the high - speed mechanical dispersion treatment is 800 - 3000 rpm, and the time is 0.5 - 10 min; or, the temperature of the thermal initiation is 100 - 300 °C, and the time is 0.5 - 10 min.

10. The preparation method according to claim 9, wherein, before thermal initiation, it further includes premixing the matrix material, a compound containing oxalate, and a lithium source; the temperature of the premixing does not exceed 15 °C.

11. The preparation method according to any one of claims 8 - 10, wherein, the compound containing oxalate includes at least one of ammonium oxalate, oxalic acid and its hydrates.

12. The preparation method according to any one of claims 8 - 11, wherein, the lithium source includes at least one of lithium hydroxide, lithium carbonate, lithium nitrate, lithium acetate, lithium citrate.

13. The preparation method according to any one of claims 8 - 12, wherein, the molar ratio of oxalate in the compound containing oxalate to lithium in the lithium source is (0.4 - 10):

1.

14. A cathode plate, wherein, The positive electrode sheet includes the positive electrode material described in any one of claims 1-7 or the positive electrode material prepared by the preparation method described in any one of claims 8-13.

15. A lithium-ion battery, wherein, the lithium-ion battery includes the positive electrode sheet described in claim 14.

Images