A composite cathode material and a battery comprising the same

Abstract

The application provides a composite positive electrode material and a battery comprising the composite positive electrode material, wherein the composite positive electrode material comprises lithium iron phosphate and boron-nitrogen co-doped biomass carbon, and the boron-nitrogen co-doped biomass carbon has a porous sheet structure and a layered structure. The lithium iron phosphate is attached to the surface of the porous sheet structure and / or embedded in the layered structure, which is an in-situ generated structure, and the lithium iron phosphate is combined with the biomass carbon material very closely, so that the conductivity of the positive electrode material is greatly improved; meanwhile, the introduction of boron elements and nitrogen elements provides conductive cavities and lone pair electrons, so that the conductivity of the composite positive electrode material is further enhanced.

Description

TECHNICAL FIELD

[0001] The present application relates to a boron-nitrogen co-doped biomass carbon and lithium iron phosphate composite composite cathode material and a battery containing the composite cathode material, and belongs to the technical field of lithium ion batteries, in particular to the field of development of lithium ion battery cathodes. BACKGROUND

[0002] In recent years, the new energy industry has developed rapidly, and the application field has been continuously expanded, especially in the electric vehicle industry. Therefore, the application of energy storage devices represented by lithium ion batteries has been promoted. The cathode material is an essential main material for lithium ion batteries, which determines the battery capacity and voltage system. Lithium iron phosphate is widely used in lithium ion battery cathode materials due to its low cost, environmental friendliness and excellent safety.

[0003] Lithium iron phosphate has an olivine structure, and lithium ions can only diffuse in one dimension (perpendicular to the 010 crystal plane), which limits the capacity and rate performance of lithium iron phosphate. The most commonly used lithium iron phosphate cathode in the industry is carbon-coated lithium iron phosphate prepared by solid-phase synthesis using sucrose as a carbon source. This carbon-coated method to some extent enhances the electrical conductivity and improves the capacity. However, this carbon-coated method involves the regulation of coating amount and type. If the coating amount is too high, it will increase the cost and reduce the tap density of the material, etc. Therefore, it is of great significance to develop other types of composite materials.

[0004] With the progress and development of society, people consume more and more energy, especially non-renewable energy such as fossil energy. The consumption of these energy sources is accompanied by the emission of a large amount of greenhouse gases, which exacerbates environmental pollution and other problems. Therefore, finding alternative energy sources for fossil energy is also an important task. Biomass resources are considered an important candidate due to their low price, abundant reserves and renewability. However, the current development and processing methods of biomass resources are not mature enough, and some agricultural and forestry waste is directly burned, producing a large amount of CO2 and causing environmental pollution and other problems. Therefore, it is of great significance to reasonably develop and utilize biomass resources. SUMMARY

[0005] In order to improve the deficiencies of the prior art, the purpose of the present application is to provide a composite cathode material and a battery comprising the composite cathode material, wherein the composite cathode material comprises lithium iron phosphate and boron-nitrogen co-doped biomass carbon, the electronic conductivity and ionic conductivity of the composite cathode material are high, the obtained battery has good room temperature cycle performance and low temperature cycle performance, and the battery does not have the problem of lithium precipitation.

[0006] The purpose of the present application is achieved by the following technical solutions:

[0007] A composite positive electrode material, comprising lithium iron phosphate and boron-nitrogen co-doped biomass carbon, the boron-nitrogen co-doped biomass carbon having a porous sheet structure and a layered structure, the lithium iron phosphate being attached to the surface of the porous sheet structure and / or embedded in the layered structure.

[0008] According to an embodiment of the present application, the mass ratio of the lithium iron phosphate and the boron-nitrogen co-doped biomass carbon is 85-92:15-8, for example 85:15, 86:14, 87:13, 88:12, 89:11, 90:10, 91:9 or 92:8.

[0009] According to an embodiment of the present application, the boron-nitrogen co-doped biomass carbon comprises nitrogen elements and boron elements, the amount of the nitrogen elements being 1%-3%, for example 1%, 2% or 3%, and the amount of the boron elements being 1%-3%, for example 1%, 2% or 3%. Herein, the amount of the nitrogen elements is the percentage of the mass of the nitrogen elements in the total mass of the composite positive electrode material, and the amount of the boron elements is the percentage of the mass of the boron elements in the total mass of the composite positive electrode material.

[0010] According to an embodiment of the present application, the boron-nitrogen co-doped biomass carbon comprises carbon elements, the amount of the carbon elements being 2%-13%, for example 2%, 3%, 4%, 5%, 6%, 7%, 8%, 9%, 10%, 11%, 12% or 13%. Herein, the amount of the carbon elements is the percentage of the mass of the carbon elements in the total mass of the composite positive electrode material.

[0011] According to an embodiment of the present application, the boron-nitrogen co-doped biomass carbon has a median particle size of 100 nm-200 μm, for example 100 nm, 150 nm, 200 nm, 300 nm, 400 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, 150 μm, 180 μm or 200 μm.

[0012] According to an embodiment of the present application, the lithium iron phosphate has a median particle size of 0.5 μm-1.5 μm, for example 0.5 μm, 0.6 μm, 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, 1.2 μm, 1.3 μm, 1.4 μm or 1.5 μm.

[0013] According to embodiments of the present application, the boron-nitrogen co-doped biomass carbon has a porosity of 75% to 85%, such as 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, or 85%.

[0014] According to embodiments of the present application, the porous sheet-like structure is a structure having a porous nanosheet morphology. The porous sheet-like structure has a thickness of 20 nm to 150 nm (such as 20 nm, 30 nm, 40 nm, 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, or 150 nm) and a pore size of 50 nm to 500 nm (such as 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, or 500 nm).

[0015] According to embodiments of the present application, the layered structure is a structure having a layered morphology of porous nanosheet components. The layered structure has a thickness of 50 nm to 2 μm (such as 50 nm, 60 nm, 70 nm, 80 nm, 90 nm, 100 nm, 110 nm, 120 nm, 130 nm, 140 nm, 150 nm, 180 nm, 200 nm, 220 nm, 250 nm, 280 nm, 300 nm, 320 nm, 350 nm, 380 nm, 400 nm, 420 nm, 450 nm, 480 nm, 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, or 2 μm).

[0016] According to embodiments of the present application, the composite cathode material has a median particle size of 500 nm to 200 μm, such as 500 nm, 600 nm, 700 nm, 800 nm, 900 nm, 1 μm, 2 μm, 5 μm, 8 μm, 10 μm, 15 μm, 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, 50 μm, 60 μm, 70 μm, 80 μm, 90 μm, 100 μm, 120 μm, 150 μm, 180 μm, or 200 μm.

[0017] According to embodiments of the present application, the composite cathode material has an electronic conductivity of 2.49 to 5.56 mS / cm.

[0018] According to the embodiment of the present application, the lithium iron phosphate is attached to the surface of the porous sheet structure and / or embedded in the layered structure, thereby improving the conductivity of the composite positive electrode material; meanwhile, the introduction of boron and nitrogen elements provides conductive holes and lone pair electrons, further enhancing the conductivity of the composite positive electrode material, and the two elements also have a synergistic effect, making the lithium ion diffusion faster, reducing the battery impedance, and improving the lithium precipitation problem of the battery; compared with the conventional lithium iron phosphate, the battery including the composite positive electrode material of the present application has higher cycle capacity and retention rate, and due to the reduced impedance, the low-temperature performance and lithium precipitation problem of the battery including the composite positive electrode material of the present application are also significantly improved.

[0019] The present application also provides a preparation method of the composite positive electrode material, which comprises the following steps:

[0020] The biomass carbon source, the boron source, the nitrogen source, the iron source, the phosphorus source and the lithium source are mixed and subjected to high-temperature solid-phase reaction to prepare the composite positive electrode material.

[0021] According to the embodiment of the present application, the high-temperature solid-phase reaction is carried out under the protection of an inert atmosphere.

[0022] According to the embodiment of the present application, the inert atmosphere is nitrogen or argon. Preferably, it is nitrogen.

[0023] According to the embodiment of the present application, the boron source is selected from at least one of H3BO3, B2O3, sodium tetraborate, sodium perborate and phenylboronic acid, and preferably H3BO3.

[0024] According to the embodiment of the present application, the nitrogen source is selected from at least one of p-phenylenediamine, melamine and urea, and preferably p-phenylenediamine.

[0025] According to the embodiment of the present application, the iron source is selected from at least one of FeSO4, FeCO3, FeCl2, Fe(Ac)2 and Fe(C2O4)2, and preferably Fe(C2O4)2.

[0026] According to the embodiment of the present application, the phosphorus source is selected from NH4H2PO4 or (NH4)2HPO4, and preferably NH4H2PO4.

[0027] According to the embodiment of the present application, the lithium source is selected from one or more of lithium oxide, lithium hydroxide, lithium carbonate, lithium phosphate, lithium phosphite, lithium hydrogen phosphate, lithium dihydrogen phosphate, lithium oxalate, lithium acetate, lithium polyacrylate, lithium stearate, lithium formate, lithium citrate, lithium tartrate, lithium oleate, lithium benzoate, lithium methoxide and lithium ethoxide, and preferably lithium oxalate.

[0028] According to the embodiment of the present application, the iron source, the phosphorus source and the lithium source are fed in an atomic ratio of Fe:P:Li of 1:1:1.

[0029] According to an embodiment of the present application, the total mass of the boron source, the nitrogen source and the biomass carbon source accounts for 8% to 15% of the total mass of the mixed system.

[0030] According to an embodiment of the present application, the mass of the boron source accounts for 1% to 3% of the total mass of the mixed system.

[0031] According to an embodiment of the present application, the mass of the nitrogen source accounts for 1% to 3% of the total mass of the mixed system.

[0032] According to an embodiment of the present application, the mass of the biomass carbon source accounts for 2% to 13% of the total mass of the mixed system.

[0033] According to an embodiment of the present application, the temperature rising rate of the high-temperature solid-phase reaction is 2 to 10℃ / min, for example, 2℃ / min, 3℃ / min, 4℃ / min, 5℃ / min, 6℃ / min, 7℃ / min, 8℃ / min, 9℃ / min or 10℃ / min.

[0034] According to an embodiment of the present application, the temperature of the high-temperature solid-phase reaction is 500℃ to 900℃, for example, 500℃, 600℃, 700℃, 800℃ or 900℃.

[0035] According to an embodiment of the present application, the time of the high-temperature solid-phase reaction is 6h to 12h, for example, 6h, 7h, 8h, 9h, 10h, 11h or 12h.

[0036] According to an embodiment of the present application, the method further comprises: naturally cooling to room temperature, washing with distilled water and ethanol for 2-3 times respectively, to prepare the composite cathode material.

[0037] According to an embodiment of the present application, the biomass carbon source is prepared by carbonizing and activating a fruit shell type biomass material.

[0038] According to an embodiment of the present application, the biomass carbon obtained after the high-temperature solid-phase reaction of the biomass carbon source has a porous sheet structure and a layered structure, which can allow the lithium iron phosphate particles to adhere to the surface of the porous sheet structure and / or be embedded in the layered structure, to achieve a better contact effect.

[0039] According to an embodiment of the present application, the biomass carbon source is prepared by the following method:

[0040] 1) screening fruit shell type biomass materials with a median particle size of 2mm or less, carbonizing under an inert atmosphere to obtain a carbonized precursor;

[0041] 2) mixing the activating agent and the carbonized precursor, removing water by heating, and preparing the biomass carbon source by activation treatment in an inert atmosphere.

[0042] In step 1), the carbonization temperature is 450-550℃, for example, 450℃, 460℃, 470℃, 480℃, 490℃, 500℃, 510℃, 520℃, 530℃, 540℃ or 550℃; and the carbonization time is 0.5-3h, for example, 0.5h, 1h, 1.5h, 2h, 2.5h or 3h.

[0043] In step 1), the shell biomass material is selected from at least one of coconut shell, walnut shell and jujube pit. The shell biomass material is rich in cellulose, and the biomass carbon source formed has low ash content, high strength, and is easy to form a porous sheet structure and a layered structure.

[0044] In step 1), the shell biomass material with a median particle size of 2mm or less can obtain a biomass carbon source with a porous sheet structure and a layered structure, and the smaller the size of the shell biomass material, the larger the specific surface area, and the more active the reaction, which is more conducive to forming a porous sheet structure and a layered structure.

[0045] In step 2), the activating agent is selected from at least one of KOH, HCl, H3PO4, H2SO4, ZnCl2 and K2CO3, and is preferably KOH.

[0046] In step 2), the mass ratio of the activating agent to the carbonized precursor is 3:1-5:1, and is preferably 4:1.

[0047] In step 2), the heating temperature is 150-200℃, and the time is 3-6h.

[0048] In step 2), the activation temperature is 700-800℃, and the time is 1-4h.

[0049] According to the embodiment of the present application, the preparation method of the biomass carbon source comprises the following steps:

[0050] Step 1: Take coconut shells, crush them, and then screen particles of 2mm or less from them; wash them with distilled water and ethanol three times, and dry them in an oven at 110℃ for standby;

[0051] Step 2: Put the dried coconut shells into a reaction kettle, and exhaust by introducing an inert gas.

[0052] Step 3: Set the heating rate to 10℃ / min, heat to 500℃, and keep for 1h to obtain a carbonized precursor.

[0053] Step four: mix a certain amount of activator and carbonized precursor according to a certain mass ratio, put into a reaction kettle, heat to 150 DEG C and keep for 4h to remove moisture;

[0054] Step five: empty by passing in inert gas, set the temperature rising rate to 5 DEG C / min, heat to 750 DEG C and keep for 2h.

[0055] Step six: after the reaction, wash with hydrochloric acid, distilled water and ethanol for 2-3 times, then put into an oven at 80 DEG C for drying.

[0056] The application also provides application of the composite cathode material in a lithium ion battery.

[0057] The application provides a cathode sheet, which comprises the composite cathode material.

[0058] According to an embodiment of the application, the cathode sheet comprises a current collector and a cathode active material layer on at least one side surface of the current collector, and the cathode active material layer comprises the composite cathode material.

[0059] According to an embodiment of the application, the current collector is a single-surface aluminum foil, a double-surface aluminum foil or a porous aluminum foil.

[0060] According to an embodiment of the application, the mass of the composite cathode material accounts for 93-98 wt% of the total mass of the cathode active material layer, for example 96-97 wt%, preferably 96.5 wt%.

[0061] According to an embodiment of the application, the cathode active material layer further comprises a binder and a conductive agent.

[0062] According to an embodiment of the application, the binder is at least one of PVDF, PTFE, polyacrylate and polyacrylic acid.

[0063] According to an embodiment of the application, the conductive agent is at least one of graphite, carbon black, acetylene black, graphene and carbon nanotube.

[0064] The application also provides a preparation method of the cathode sheet, which comprises the following steps: coating a slurry containing the composite cathode material on one side or both sides of a current collector to obtain the cathode sheet.

[0065] The application also provides application of the cathode sheet in a battery.

[0066] The application provides a battery, which comprises the composite cathode material or the cathode.

[0067] According to an embodiment of the application, the battery comprises a negative electrode sheet, a separator and an electrolyte.

[0068] The negative electrode sheet comprises a current collector and a negative electrode slurry on the surface of the current collector.

[0069] Preferably, the current collector in the negative electrode sheet is a single-facet copper foil, a double-facet copper foil or a porous copper foil.

[0070] Preferably, the negative electrode slurry comprises a negative electrode active material and an additive.

[0071] Preferably, the negative electrode active material is at least one of graphite, silicon, silicon monoxide, hard carbon, soft carbon and lithium titanate; and the additive comprises at least one of a conductive agent, a negative electrode binder and a dispersing agent, for example, the conductive agent is at least one of graphite, carbon black, acetylene black, graphene and carbon nanotubes; the negative electrode binder is SBR; and the dispersing agent is sodium carboxymethyl cellulose or lithium carboxymethyl cellulose.

[0072] According to an embodiment of the present application, the negative electrode sheet is prepared by a method comprising the following steps:

[0073] (1) mixing a negative electrode active material, a conductive agent, a binder and a dispersing agent uniformly to obtain a negative electrode slurry;

[0074] (2) coating the negative electrode slurry on the surface of a current collector, and baking to obtain a negative electrode sheet.

[0075] According to an embodiment of the present application, the mass ratio of the negative electrode active material, the conductive agent, the negative electrode binder and the dispersing agent is not particularly limited. For example, the mass ratio of the negative electrode active material, the conductive agent, the negative electrode binder and the dispersing agent can be 95:2:1.8:1.2; and exemplarily, the mass ratio of artificial graphite, carbon black, SBR and CMC is 95:2:1.8:1.2.

[0076] According to an embodiment of the present application, the battery is assembled by a positive electrode sheet, a separator, a negative electrode sheet and an electrolyte. For example, the positive electrode sheet, the negative electrode sheet and the separator are assembled into an electric core by winding or stacking in the industry, and then packaged by an aluminum plastic film, and then sequentially subjected to baking, electrolyte injection, formation and two-sealing processes to obtain a lithium ion battery.

[0077] The present application has the following advantages:

[0078] The application provides a composite positive electrode material and a battery comprising the composite positive electrode material, the composite positive electrode material comprising lithium iron phosphate and boron-nitrogen co-doped biomass carbon, the boron-nitrogen co-doped biomass carbon having a porous sheet structure and a layered structure. The lithium iron phosphate is attached to the surface of the porous sheet structure and / or embedded in the layered structure, which is an in-situ generated structure, and the lithium iron phosphate is combined with the biomass carbon material very closely, greatly improving the conductivity of the positive electrode material. Meanwhile, the introduction of boron elements and nitrogen elements provides conductive cavities and lone pair electrons, further enhancing the conductivity of the composite positive electrode material, and the two elements also have a synergistic effect, so that lithium ions diffuse faster, the battery impedance is reduced, and the lithium precipitation problem of the battery is improved. Compared with conventional lithium iron phosphate, the battery comprising the composite positive electrode material of the application has higher cycle capacity and retention rate, and due to the reduced impedance, the low-temperature performance and lithium precipitation problem of the battery comprising the composite positive electrode material of the application are also obviously improved. BRIEF DESCRIPTION OF DRAWINGS

[0079] Figure 1 EIS diagram of the battery of Example 1 and Comparative Example 1 at 25℃ 100% SOC.

[0080] Figure 2 Cycle performance diagram of the battery of Example 1 and Comparative Example 1 at 25℃.

[0081] Figure 3 SEM diagram of the B, N co-doped biomass carbon of Example 1.

[0082] Figure 4 XPS diagram of the B, N co-doped biomass carbon of Example 1. DETAILED DESCRIPTION

[0083] The application will be described in further detail below with reference to specific examples. It should be understood that the following examples are only illustrative and explanatory of the application, and should not be interpreted as limiting the scope of protection of the application. Any technology achieved based on the above description of the application is included in the scope of protection intended by the application.

[0084] The experimental methods used in the following examples are conventional methods unless otherwise specified; the reagents, materials, etc. used in the following examples can be obtained from commercial channels unless otherwise specified.

[0085] The electrochemical impedance involved in the following examples and comparative examples is measured by using an electrochemical workstation (model CHI600E) produced by Shanghai Chenhua, the test frequency is 10KHz-0.01Hz, the alternating current amplitude is 5mV, and the results are shown in Figure 1

[0086] ​The cycle performance involved in the following examples and comparative examples is measured by Land battery test system of Wuhan Blue Electric Co., Ltd., and the process is as follows:

[0087] Voltage range 3.75V-2.0V

[0088] 1. 1C constant current discharge to 2.0V;

[0089] 2. Stand for 30 min;

[0090] 3. 1C constant current constant voltage full charging (cut-off current is 0.05C);

[0091] 4. Stand for 30 min;

[0092] 5. 1C constant current discharge to 2.0V; so cycle for 300 times, and the results are shown in Figure 2 .

[0093] The batteries prepared in the examples and comparative examples are subjected to performance test, and the test items include low temperature performance (12℃ 3C lithium precipitation, -20℃ discharge) and cycle retention rate, and the test process is as follows:

[0094] Low temperature performance: -20℃ discharge: the full battery is placed in a low temperature box at -20℃, and discharged at 0.2C, and the discharge capacity retention rate is calculated.

[0095] 12℃ 3C lithium precipitation: the battery is placed in a low temperature box at 12℃, and discharged at 0.5C to 2V, and charged to 3.75V at 3C cross current constant voltage, and the cut-off current is 0.05C. Cycle for 20 times, and disassemble the battery to observe the interface condition.

[0096] Example 1

[0097] 1. A certain amount of coconut shell is placed in a mortar, crushed and ground with a pestle, and then sieved through a mesh to obtain particles below 2mm, and then washed with deionized water and anhydrous ethanol for three times and dried for standby use.

[0098] 2. A certain amount of standby coconut shell is placed in a reaction kettle, and nitrogen is introduced into the reaction kettle to be evacuated for 5-10min.

[0099] 3. The heating rate is set to 10℃ / min to heat to 500℃ and keep for 1h to obtain carbonized precursor.

[0100] 4. The carbonized precursor and 50wt% KOH solution are taken in a mass ratio of 1:4, mixed uniformly, and then placed in a reaction kettle, heated to 150℃ for 4h, then evacuated by introducing nitrogen, and then the heating rate is adjusted to 5℃ / min to heat to 750℃, and kept for 2h to obtain biomass carbon source, and then washed with hydrochloric acid, deionized water and anhydrous ethanol for 2-3 times and dried for standby use.

[0101] 5. Take appropriate amounts of Fe(C2O4)2, NH4H2PO4 and Li2CO3 according to the molar ratio of 2:2:1, then take appropriate amounts of H3BO3, p-phenylenediamine, biomass carbon source and the above mixture according to the mass ratio of 2:2:5:91, and directly place them in a reaction kettle, evacuate after purging with nitrogen, and then heat to 700℃ at a rate of 5℃ / min for 10h, then naturally cool to room temperature, and wash 2-3 times with deionized water and anhydrous ethanol to obtain the final product, boron-nitrogen co-doped biomass carbon and lithium iron phosphate composite positive electrode material.

[0102] Lithium ion battery preparation process:

[0103] Disperse the above-mentioned composite positive electrode material, binder PVDF and conductive carbon black in N-methyl pyrrolidone, and after stirring, obtain a uniformly dispersed positive electrode slurry, wherein the solid content includes 96.5wt% of the composite positive electrode, 1.5wt% of PVDF and 2wt% of conductive carbon black, the solid content of the positive electrode slurry is 67.5wt%, and the viscosity is 21745mPa·s. The positive electrode slurry is uniformly coated on both sides of an aluminum foil, dried at 100-130℃ for 4h, and compacted using a roller compactor, and the compacted density is 2.6-3.2g / cm 3 , to obtain a positive electrode sheet;

[0104] Mix and disperse graphite, binder SBR, thickening agent CMC and conductive agent conductive carbon black in deionized water to obtain a negative electrode slurry, wherein the solid content includes 95wt% of graphite, 1.2wt% of CMC, 2wt% of conductive carbon black and 1.8wt% of SBR, the solid content of the negative electrode slurry is 44-46wt%, and the viscosity is 6561mPa·s. The slurry is uniformly coated on both sides of a copper foil, dried at 70-100℃ for 5h, and compacted using a roller compactor, and the compacted density is 1.4-1.7g / cm 3 , to obtain a negative electrode sheet;

[0105] Winding and packaging the positive electrode sheet, the negative electrode sheet and the separator (PP / PE / PP composite film, thickness 8μm, porosity 42%) into an electric core, then injecting electrolyte, forming, hot pressing and double sealing to obtain a lithium ion battery.

[0106] Example 2

[0107] The steps for synthesizing the composite positive electrode material are the same as in Example 1, except that the biomass raw material is changed from coconut shell to walnut shell.

[0108] Example 3

[0109] The steps for synthesizing the composite positive electrode material are the same as in Example 1, except that the biomass raw material is changed from coconut shell to jujube shell.

[0110] Comparative Example 1

[0111] Compared with Example 1, the difference is that no boron source, nitrogen source and biomass carbon source are added, and the contents of other substances and the preparation process are the same as those of Example 1.

[0112] Comparative Example 2

[0113] Compared with Example 1, the difference is that no boron source and nitrogen source are added, and the contents of other substances and the preparation process are the same as those of Example 1.

[0114] Comparative Example 3

[0115] Compared with Example 1, the difference is that no boron source is added, and the contents of other substances and the preparation process are the same as those of Example 1.

[0116] Comparative Example 4

[0117] Compared with Example 1, the difference is that no nitrogen source is added, and the contents of other substances and the preparation process are the same as those of Example 1.

[0118] Comparative Example 5

[0119] Compared with Example 1, the difference is that the carbon source is replaced by glucose, and the contents of other substances and the preparation process are the same as those of Example 1.

[0120] Figure 1 EIS diagram of the battery of Example 1 and Comparative Example 1 at 25℃ 100% SOC. Figure 2 Cycle performance diagram of the battery of Example 1 and Comparative Example 1 at 25℃. Figure 3 SEM diagram of the B, N co-doped biomass carbon of Example 1. Figure 4 XPS diagram of the B, N co-doped biomass carbon of Example 1.

[0121] From Figure 1 It can be seen that the Rct of the battery of Example 1 is smaller than that of Comparative Example 1, indicating that the introduction of boron-nitrogen co-doped biomass carbon in Example 1 reduces the electrochemical impedance of the lithium ion battery; at the same time, Figure 2 The results also show that the capacity and retention rate of the battery of Example 1 are higher than those of Comparative Example 1. This indicates that the in-situ composite anode material prepared by one-step high-temperature synthesis has improved conductivity and lithium ion transmission rate. Figure 3 The SEM diagram of the B, N co-doped biomass carbon source of Example 1 shows a porous sheet structure and a layered structure. Figure 4 The XPS diagram of the B, N co-doped biomass carbon source of Example 1 shows that B and N elements are doped into the carbon material.

[0122] Comparative Examples 2 to 4 used biomass as a precursor, and had a porous sheet structure and a layered structure similar to Example 1. However, Comparative Example 5 used glucose as a precursor, and could not obtain the porous sheet structure and the layered structure of the present application.

[0123] Table 1 shows the results of performance tests of lithium ion batteries of Comparative Examples 1 to 5 and Examples 1 to 3.

[0124]

[0125] The above describes the embodiments of the present application. However, the present application is not limited to the above-described embodiments. Any modification, equivalent replacement, improvement, and the like made within the spirit and principle of the present application should be included in the scope of the present application.

Claims

1. A composite cathode material, characterized in that, The composite cathode material comprises lithium iron phosphate and boron-nitrogen co-doped biomass carbon. The boron-nitrogen co-doped biomass carbon has a porous sheet-like structure and a layered structure. The lithium iron phosphate is attached to the surface of the porous sheet-like structure and / or embedded in the layered structure. The median particle size of the boron-nitrogen co-doped biomass carbon is 0.5 μm to 200 μm. The median particle size of the lithium iron phosphate is 0.5 μm to 1.5 μm. The boron-nitrogen co-doped biomass carbon includes nitrogen, carbon, and boron. The mass percentage of nitrogen in the composite cathode material is 1% to 3%, the mass percentage of boron in the composite cathode material is 1% to 3%, and the mass percentage of carbon in the composite cathode material is 2% to 13%. The mass ratio of lithium iron phosphate and boron nitrogen co-doped biomass carbon is 85~92:15~8.

2. The composite cathode material according to claim 1, characterized in that, The porosity of the boron-nitrogen co-doped biomass carbon is 75%~85%.

3. The composite cathode material according to claim 1, characterized in that, The thickness of the porous sheet structure is 20nm~150nm, and the pore size is 50nm~500nm; the thickness of the layered structure is 50nm~2μm.

4. The composite cathode material according to claim 1, characterized in that, The median particle size of the composite cathode material is 500 nm to 200 μm.

5. The composite cathode material according to any one of claims 1-4, characterized in that, The composite cathode material is prepared by mixing a biomass carbon source, a boron source, a nitrogen source, an iron source, a phosphorus source, and a lithium source, and then carrying out a high-temperature solid-phase reaction to obtain the composite cathode material; the temperature of the high-temperature solid-phase reaction is 500°C~900°C.

6. A positive electrode, said positive electrode comprising the composite positive electrode material according to any one of claims 1-5.

7. A battery comprising the composite positive electrode material according to any one of claims 1-5, or the battery comprising the positive electrode according to claim 6.

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