A lithium vanadium phosphate positive electrode material, a positive electrode sheet including the positive electrode material, and a battery

Abstract

This invention provides a lithium vanadium phosphate cathode material, a cathode sheet comprising the cathode material, and a battery, wherein the cathode material comprises a lithium vanadium phosphate matrix; and the peak intensity I of the (121) crystal plane in the X-ray diffraction pattern of the cathode material is... 121 Peak intensity I of (211) crystal plane 211 The ratio I 121 / I 211 The value ranges from 0.60 to 0.99. Compared with conventional lithium vanadium phosphate cathode materials, the lithium vanadium phosphate cathode material provided by this invention has a specific spherical structure, which allows for more complete contact with the electrolyte during charging and discharging. Furthermore, the lithium vanadium phosphate cathode material provided by this invention has a smaller particle size, resulting in a shorter migration distance for lithium ions during cycling. The carbon coating layer on the material surface has a higher degree of graphitization, greater conductivity, and superior electrochemical performance.

Description

Technical Field

[0001] This invention relates to the field of lithium-ion battery technology, and particularly to a lithium vanadium phosphate cathode material, a cathode sheet including the cathode material, and a battery. Background Technology

[0002] With the development of technology, lithium-ion batteries have been widely used in recent years due to their many advantages, such as high specific energy, good cycle performance, high operating voltage, no memory effect, and environmental friendliness. However, lithium-ion batteries still have a series of problems, making the development of safer, more stable, and environmentally friendly electrode materials particularly important. Current research has found that the overall performance of lithium-ion batteries is mainly limited by their positive electrode.

[0003] Monoclinic lithium vanadium phosphate materials have a typical NASCION structure. Due to their high reversible capacity, high energy density, and good stability, they have become a highly promising cathode material for commercial lithium-ion batteries. However, the low intrinsic conductivity and lithium-ion diffusion rate of lithium vanadium phosphate itself have hindered its commercialization. Conventional lithium vanadium phosphate cathode materials are mostly irregular amorphous structures with large particle sizes, resulting in a small specific surface area, which cannot fully contact the electrolyte. In addition, the lithium-ion transport path is large, resulting in poor electrochemical performance. Summary of the Invention

[0004] To address the issues of insufficient contact with electrolyte and poor electrochemical performance caused by the large particle size and irregular amorphous structure of conventional lithium vanadium phosphate materials when used as battery materials, this invention provides a lithium vanadium phosphate cathode material, a cathode sheet including the cathode material, and a battery. The cathode material of this invention is a lithium vanadium phosphate cathode material with a near-spherical structure. The particle size of the cathode material is smaller than that of conventional lithium vanadium phosphate (particle size distribution of 0.05μm to 3.5μm), which allows for more sufficient contact with the electrolyte, easier lithium ion insertion and extraction, and thus better electrochemical performance.

[0005] The objective of this invention is achieved through the following technical solution:

[0006] A cathode material comprising a lithium vanadium phosphate matrix; wherein, in an X-ray diffraction pattern, the peak intensity I of the (121) crystal plane of the cathode material is... 121 Peak intensity I of (211) crystal plane 211 The ratio I 121 / I 211 The value ranges from 0.60 to 0.99.

[0007] According to an embodiment of the present invention, in the X-ray diffraction pattern of the cathode material, the peak intensity I of the (121) crystal plane is... 121 Peak intensity I of (211) crystal plane 211The ratio I 121 / I 211 It is 0.80 to 0.86, for example, 0.81, 0.82, 0.83, 0.84, 0.85 or 0.86.

[0008] According to an embodiment of the present invention, in the X-ray diffraction pattern of the cathode material, the peak of the (121) crystal plane is sharp, indicating that the cathode material has good crystallinity and good electrochemical performance.

[0009] According to an embodiment of the present invention, the chemical formula of the lithium vanadium phosphate matrix is ​​Li. x V 2-y M y (PO4) z Where 1≤x≤3, 0≤y≤2, 0≤z≤1; M is selected from at least one of Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, Ti, Mg, Ca, Sr, and Zr.

[0010] According to an embodiment of the present invention, the chemical formula of the lithium vanadium phosphate matrix is ​​Li3V2(PO4)3.

[0011] According to embodiments of the present invention, the cathode material further includes a carbon material. Exemplarily, the carbon material is mixed in a lithium vanadium phosphate matrix. The carbon material can effectively improve the conductivity of the cathode material, resulting in better electrochemical performance.

[0012] According to an embodiment of the present invention, the cathode material further includes a carbon coating layer. Exemplarily, the carbon coating layer coats the outer surface of a lithium vanadium phosphate substrate. The carbon coating layer can effectively improve the conductivity of the cathode material, thereby enhancing its electrochemical performance.

[0013] According to an embodiment of the present invention, the coating may be a partial coating or a complete coating.

[0014] According to an embodiment of the present invention, the mass of the carbon coating layer and / or the carbon material accounts for 10wt% to 15.5wt% of the total mass of the cathode material, for example, 10wt%, 11wt%, 12wt%, 13wt%, 14wt%, 15wt% or 15.5wt%.

[0015] According to an embodiment of the present invention, the thickness of the carbon coating layer is 2nm to 30nm, for example, 3nm, 3.5nm, 4nm, 4.5nm, 5nm, 6nm, 7nm, 8nm, 9nm, 10nm, 12nm, 15nm, 16nm, 18nm, 20nm, 22nm, 25nm, 26nm, 27nm or 30nm.

[0016] According to the embodiment of the present application, the content of the carbon coating layer and / or carbon material in the positive electrode material is determined by TG thermal gravimetric test on the positive electrode material, and the higher the carbon content is, the better the electrical performance of the positive electrode material is. Specifically, when the positive electrode material is subjected to TG thermal gravimetric test, the mass of the positive electrode material changes with the increase of temperature, and the difference of weight loss between two platforms (the stage where the mass change of the positive electrode material tends to be flat with the increase of temperature) is the content of the carbon coating layer and / or carbon material in the positive electrode material.

[0017] According to the embodiment of the present application, the Raman spectrum of the positive electrode material contains a D band characteristic peak with an intensity of I -1 in the region of Raman shift of 1338-1344 cm D , a G band characteristic peak with an intensity of I -1 in the region of Raman shift of 1598-1602 cm G , and 0.77≤I D / I G ≤0.95.

[0018] According to the embodiment of the present application, the Raman spectrum of the positive electrode material contains a D band characteristic peak with an intensity of I D in the region of Raman shift of 1338-1344 cm -1 , a G band characteristic peak with an intensity of I G in the region of Raman shift of 1598-1602 cm D , and 0.81≤I G / I D ≤0.83.

[0019] According to the embodiment of the present application, the graphitization degree of the carbon coating layer and / or carbon material in the positive electrode material is determined by Raman spectrum test on the positive electrode material, and the lower the I G / I (去离子水) ratio is, the higher the graphitization degree of the carbon coating layer and / or carbon material is, and the better the conductive performance of the carbon coating layer and / or carbon material is.

[0020] According to the embodiment of the present application, the positive electrode material is a spheroid particle.

[0021] According to the embodiment of the present application, the positive electrode material satisfies:

[0022] 1.02≤a / b≤1.97;

[0023] wherein a is the length of the long axis of the positive electrode material, and b is the length of the short axis of the positive electrode material.

[0024] According to the embodiment of the present application, the positive electrode material satisfies:

[0025] 1.12≤a / b≤1.20;

[0026] wherein a and b are defined as above.

[0027] For example, a / b is 1.12, 1.13, 1.14, 1.15, 1.16, 1.17, 1.18, 1.19 or 1.20.

[0028] According to an embodiment of the present application, the length of the long axis a of the positive electrode material is 0.1 μm to 3.5 μm, preferably 0.12 μm to 1.87 μm, such as 0.14 μm to 0.23 μm.

[0029] According to an embodiment of the present application, the length of the short axis b of the positive electrode material is 0.07 μm to 3.18 μm, preferably 0.11 μm to 2.25 μm, such as 0.12 μm to 0.20 μm.

[0030] It is known in the art that a standard circle such as Figure 6 has equal length of long and short axis a, b, i.e. a / b is 1, and the greater the a / b ratio, the more the circle deviates from a sphere, and the positive electrode material of the present application satisfies 1.02≤a / b≤1.97, indicating that the positive electrode material of the present application has a spherical structure.

[0031] According to an embodiment of the present application, the particle size distribution of the positive electrode material is 0.05 μm to 3.5 μm, preferably 0.15 μm to 0.23 μm, such as 0.15 μm, 0.16 μm, 0.17 μm, 0.18 μm, 0.19 μm, 0.2 μm, 0.21 μm, 0.22 μm, 0.23 μm, 0.5 μm, 1 μm, 1.5 μm, 2 μm, 2.5 μm, 3 μm or 3.5 μm. The particle size of the positive electrode material of the present application is smaller than that of conventional lithium vanadium phosphate, and can be more fully contacted with electrolyte, making it easier for lithium ions to be deintercalated, and making it have better electrochemical performance.

[0032] According to an embodiment of the present application, the first discharge specific capacity of the positive electrode material under 1C condition is greater than 120 mAh / g, such as 120.6 mAh / g to 130.8 mAh / g.

[0033] The present application also provides a preparation method of the positive electrode material, which comprises the following steps:

[0034] (1) mixing deionized water, a dispersing agent, a lithium source, a vanadium source, a phosphorus source, an M source and a reducing agent to form a sol-gel by reaction, drying to prepare a precursor;

[0035] (2) pre-sintering the precursor, and then sintering to prepare the positive electrode material.

[0036] According to an embodiment of the present application, in step (1), the temperature of the mixing is 60-90℃.

[0037] According to an embodiment of the present application, in step (1), the dispersant is selected from at least one of polyethylene glycol, ethanol, acetone, methanol. The dispersant can inhibit the agglomeration of particles during the preparation of the spherical-like lithium vanadium phosphate cathode material, thereby obtaining a spherical-like lithium vanadium phosphate cathode material with a particle size distribution of 0.05-3.5 μm.

[0038] According to an embodiment of the present application, in step (1), the lithium source is selected from at least one of lithium carbonate, lithium hydroxide, lithium oxide.

[0039] According to an embodiment of the present application, in step (1), the vanadium source is selected from at least one of V2O5, V2O3, VO, VO2, ammonium metavanadate.

[0040] According to an embodiment of the present application, in step (1), the phosphorus source is selected from at least one of ammonium dihydrogen phosphate, diammonium hydrogen phosphate, ammonium phosphate, phosphoric acid.

[0041] According to an embodiment of the present application, in step (1), the M source is selected from at least one of an oxide of M, such as an oxide of Fe, an oxide of Co, an oxide of Mn, an oxide of Cu, an oxide of Zn, an oxide of Al, an oxide of Sn, an oxide of B, an oxide of Ga, an oxide of Cr, an oxide of Ti, an oxide of Mg, an oxide of Ca, an oxide of Sr, an oxide of Zr.

[0042] According to an embodiment of the present application, in step (1), the reducing agent is selected from at least one of citric acid, oxalic acid, ascorbic acid.

[0043] According to an embodiment of the present application, in step (1), the volume ratio V of the deionized water to the dispersant is 1-4:1. (去离子水) / V (分散剂) .

[0044] According to an embodiment of the present application, in step (1), the molar ratio of Li:V:P:M in the lithium source, the vanadium source, the phosphorus source and the M source is (x-x+0.5):2-y:z:y.

[0045] According to an embodiment of the present application, in step (1), the molar ratio n of the vanadium source to the reducing agent is 0.75-2:1. (钒源) :n (还原剂) .

[0046] According to an embodiment of the present application, in step (1), the mixing is, for example, dispersing the dispersant in deionized water, adding a reducing agent, controlling the rotation speed at 400-600 r / min to make the reducing agent fully dissolved; adding a vanadium source and an M source, reacting for 30-50 min; adding a phosphorus source and a lithium source, reacting for 30-50 min, to form a sol-gel.

[0047] According to an embodiment of the present application, in step (1), the drying is drying at 100-130 ℃ for 10-14 h.

[0048] According to an embodiment of the present application, in step (1), the obtained precursor is ground with a mortar for 20-40 min and sieved (600-800 mesh).

[0049] According to an embodiment of the present application, in step (2), the pre-sintering and sintering are performed in a tube furnace.

[0050] According to an embodiment of the present application, in step (2), the pre-sintering temperature is 300-400 ℃, the pre-sintering time is 3-5 h, and the pre-sintering atmosphere is an inert atmosphere (such as nitrogen), and the heating rate is 4-7 ℃ / min.

[0051] According to an embodiment of the present application, in step (2), after pre-sintering, grinding is preferably performed before sintering again.

[0052] According to an embodiment of the present application, in step (2), the grinding is performed in a planetary grinding machine, and is, for example, fully ground at 600-800 r / min for 4-6 h.

[0053] According to an embodiment of the present application, in step (2), the sintering temperature is 750-900 ℃, the sintering time is 8-14 h, the sintering atmosphere is an inert atmosphere (such as nitrogen), and the heating rate is 4-7 ℃ / min.

[0054] The present application also provides a positive electrode sheet, which comprises the above positive electrode material.

[0055] According to an embodiment of the present application, the positive electrode sheet comprises a current collector and a positive electrode material layer; the positive electrode material layer is arranged on at least one surface of the current collector; and the positive electrode material layer comprises the above positive electrode material.

[0056] According to an embodiment of the present application, the positive electrode material layer further comprises a conductive agent and a binder.

[0057] According to an embodiment of the present application, the mass percentage of each component in the positive electrode material layer is: 75-98 wt% of the positive electrode material, 1-15 wt% of the conductive agent, and 1-10 wt% of the binder.

[0058] Preferably, the mass percentage of each component in the positive electrode material layer is: 80-96wt% of the positive electrode material, 3-10wt% of the conductive agent, and 1-10wt% of the binder.

[0059] According to an embodiment of the present application, the thickness of the positive electrode material layer is 3-30μm, preferably 5-15μm.

[0060] According to an embodiment of the present application, the conductive agent includes but is not limited to: carbon-based materials, metal-based materials, conductive polymers, or mixtures thereof. In some embodiments, the carbon-based materials are selected from natural graphite, artificial graphite, carbon black, acetylene black, ketjen black, carbon fiber, or any combination thereof. In some embodiments, the metal-based materials are selected from metal powder, metal fiber, copper, nickel, aluminum, silver. In some embodiments, the conductive polymer is a polyphenylene derivative.

[0061] According to an embodiment of the present application, the current collector includes but is not limited to: aluminum foil, carbon-coated aluminum foil, perforated aluminum foil, stainless steel foil, polymer substrate coated with conductive metal, and any combination thereof.

[0062] According to an embodiment of the present application, the binder includes but is not limited to: polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), styrene butadiene rubber (SBR), nitrile butadiene rubber (NBR), water-based acrylic resin, polyvinyl alcohol, polyvinyl butyral, polyurethane, fluorinated rubber, carboxymethyl cellulose (CMC), polyacrylic acid (PAA).

[0063] According to an embodiment of the present application, the positive electrode sheet can be prepared according to conventional methods in the art. Typically, the positive electrode material and optional conductive agent, binder are dispersed in a solvent (e.g. NMP) to form a uniform positive electrode slurry, the positive electrode slurry is coated on the current collector, and after drying and other processes, the positive electrode sheet is obtained.

[0064] The present application also provides a battery comprising the above-mentioned positive electrode material, or comprising the above-mentioned positive electrode sheet.

[0065] The present application has the following advantages:

[0066] The present application provides a lithium vanadium phosphate positive electrode material, and a positive electrode sheet and a battery comprising the same. Compared with conventional lithium vanadium phosphate positive electrode materials, the lithium vanadium phosphate positive electrode material provided by the present application has a specific spherical structure, can contact the electrolyte more fully during charging and discharging, has a smaller particle size, a shorter migration distance of lithium ions during cycling, a higher graphitization degree of the carbon coating layer on the surface of the lithium vanadium phosphate matrix and / or the carbon material mixed in the lithium vanadium phosphate matrix, a larger electrical conductivity, and a more excellent electrochemical performance. Attached Figure Description

[0067] Figure 1 The images are scanning electron microscope (SEM) images of the cathode materials prepared in Example 1 and Comparative Example 3, where a represents Example 1 (left image) and b represents Comparative Example 3 (right image).

[0068] Figure 2 The image shows the XRD pattern of the cathode material prepared in Example 1.

[0069] Figure 3 The images show the Raman spectra of the cathode materials prepared in Example 1 and Comparative Example 3. The one with higher intensity is Example 1, and the one with lower intensity is Comparative Example 3.

[0070] Figure 4 The graph shows the cycle performance of the batteries prepared in Example 1 and Comparative Example 3.

[0071] Figure 5 The TG curves are for the cathode materials prepared in Example 1 and Comparative Example 3.

[0072] Figure 6 This is a schematic diagram of the major and minor axes of the particles. Detailed Implementation

[0073] The present invention will be further described in detail below with reference to specific embodiments. It should be understood that the following embodiments are merely illustrative and explanatory of the present invention and should not be construed as limiting the scope of protection of the present invention. All technologies implemented based on the above content of the present invention are covered within the scope of protection intended by the present invention.

[0074] Unless otherwise specified, the experimental methods used in the following examples are conventional methods; unless otherwise specified, the reagents and materials used in the following examples are commercially available.

[0075] The X-ray diffraction pattern of the cathode material in this invention is determined using an X-ray diffraction apparatus, such as a Cu-Kα ray diffractometer, to measure the peak intensity I of the (121) crystal plane of the cathode material. 121 Peak intensity I of (211) crystal plane 211 Calculate I 121 / I 211 .

[0076] The Raman spectra of the cathode material in this invention were measured using, for example, a Raman Dual-100 dual-wavelength confocal Raman spectrometer. The Raman spectra of the cathode material were measured at a Raman shift of 1340 cm⁻¹. -1 The characteristic peak intensity I of the D band within the region D 1600cm -1 The characteristic peak intensity I of the G-band within the region G And calculate I D / IG .

[0077] The SEM image of the positive electrode material in the present application is tested by using, for example, a JSM-6490LV scanning electron microscope.

[0078] The particle size distribution of the positive electrode material in the present application is obtained by a laser particle size tester.

[0079] The long and short axis a and b of the positive electrode material in the present application are obtained by SEM image analysis.

[0080] The thickness of the carbon coating layer in the present application is obtained by TEM testing.

[0081] The mass proportion of the carbon coating layer and / or carbon material in the present application is obtained by TG curve analysis, specifically, a first platform (a stage in which the mass change of the positive electrode material tends to be flat as the temperature rises) appears when the temperature is 100-370℃, a second platform (a stage in which the mass change of the positive electrode material tends to be flat as the temperature rises) appears when the temperature is 450-600℃, and the difference in weight loss corresponding to the two platforms is the content of the carbon coating layer and / or carbon material in the positive electrode material.

[0082] Example 1

[0083] (1) Preparation of the positive electrode material:

[0084] A sol-gel method is adopted, and 40ml of deionized water is mixed with a dispersant polyethylene glycol under the condition of a water bath at 80℃ (V (去离子水) / V (聚乙二醇) = 2), the lithium source, vanadium source and phosphorus source are lithium hydroxide, vanadium pentoxide and ammonium dihydrogen phosphate respectively, and are weighed according to the molar ratio of Li:V:P (3.1:2:3), and citric acid (n (钒源) :n (柠檬酸) = 1) is also weighed.

[0085] The weighed reducing agent citric acid is added to the polyethylene glycol aqueous solution, and the rotor is put in to make the reducing agent citric acid dissolve fully; vanadium pentoxide is added to the solution to make it fully; ammonium dihydrogen phosphate and lithium hydroxide are added to the mixed solution respectively; the reaction is continued until a sol-gel is formed; the precursor is obtained after drying (drying temperature 110℃); after grinding (30min), it is put into a tube furnace for pre-sintering (nitrogen atmosphere, 350℃, 4h), and after cooling, the pre-sintered material is ball milled using a planetary mill (400r / min speed, ball milling for 2h), and then sintered again (nitrogen atmosphere, 850℃, 12h), and the positive electrode material is obtained after natural cooling.

[0086] The positive electrode material prepared above is subjected to XRD, SEM and Raman, and the test results are shown in Table 1.

[0087] (2) Preparation of the battery:

[0088] 1) Preparation of the positive electrode sheet

[0089] The above positive electrode material, polyvinylidene fluoride (PVDF), SP (super P) and carbon nanotubes (CNT) are mixed in a mass ratio of 80:10:10, N-methyl pyrrolidone (NMP) is added, and stirring is carried out under the action of a vacuum stirrer until the mixed system becomes a positive electrode active paste with uniform fluidity; the positive electrode active paste is uniformly coated on one surface of an aluminum foil; the coated aluminum foil is dried, then rolled, and cut to obtain the desired positive electrode sheet.

[0090] 2) Preparation of the negative electrode sheet

[0091] The negative electrode active material artificial graphite, sodium carboxymethyl cellulose (CMC-Na), butadiene rubber, and conductive carbon black (SP) are mixed in a mass ratio of 94.5:2.5:1.5:1.5, deionized water is added, and a negative electrode active paste is obtained under the action of a vacuum stirrer; the negative electrode active paste is uniformly coated on both surfaces of a copper foil; the coated copper foil is dried at room temperature, then transferred to a 80°C oven for drying for 10h, and then cold-pressed and cut to obtain the negative electrode sheet.

[0092] 3) Preparation of the electrolyte

[0093] In an argon-filled glove box (H2O<0.1ppm, O2<0.1ppm), EC / PC / DEC is mixed uniformly in a mass ratio of 1:1:1, then 1mol / L of fully dried lithium hexafluorophosphate (LiPF6) is quickly added thereto, stirred uniformly, and after passing the water content and free acid detection, the desired electrolyte is obtained.

[0094] 4) Preparation of the battery

[0095] The positive electrode sheet of step 1), the negative electrode sheet of step 2), and the separator are stacked in the order of positive electrode sheet, separator, and negative electrode sheet, then wound to obtain a battery cell; the battery cell is placed in an outer packaging aluminum foil, the electrolyte of step 3) is injected into the outer packaging, and after passing the vacuum packaging, standing, formation, shaping, sorting, and other processes, the battery is obtained. The battery of the present application has a charge-discharge range of 3.0-4.3V.

[0096] (3) Performance test:

[0097] The battery was placed in an environment of (25±3) °C, and rested for 3 hours. When the battery body reached (25±3) °C, the battery was charged to 4.4 V at 1C, then charged to a cutoff current of 0.05C at 4.4 V constant voltage, then discharged to 3 V at 1C and 5C, respectively, and the first discharge specific capacity of the battery under the conditions of 1C and 5C and the initial capacity Q0 of the battery under the condition of 1C were recorded. The battery was charged to 4.4 V at 1C, then charged to a cutoff current of 0.05C at 4.4 V constant voltage, then discharged to 3 V at 1C, and the cycle was repeated for 200 times. The discharge capacity of the previous cycle was taken as the capacity Q2 of the battery, the capacity retention rate (%) was calculated, and the results were recorded in Table 2. The calculation formula used is as follows: capacity retention rate (%) = Q2 / Q0 x 100%.

[0098] Example 2

[0099] According to the process steps of Example 1, the difference is that the sintering condition temperature of Example 2 is 900 °C.

[0100] Example 3

[0101] According to the process steps of Example 1, the difference is that the lithium source of Example 3 is lithium carbonate.

[0102] Example 4

[0103] According to the process steps of Example 1, the difference is that the reducing agent of Example 4 is oxalic acid.

[0104] Example 5

[0105] According to the process steps of Example 1, the difference is that the dispersing agent of Example 5 is ethanol.

[0106] Example 6

[0107] According to the process steps of Example 1, the difference is that Example 6 is weighed according to the molar ratio of Li:V:P (3.5:2:3).

[0108] Comparative Example 1

[0109] According to the process steps of Example 1, the difference is that in Comparative Example 1, the molar ratio of Li:V:P in the lithium source, vanadium source, and phosphorus source is 4:2:3, and no dispersing agent is added.

[0110] Comparative Example 2

[0111] According to the process steps of Example 1, the difference is that in Comparative Example 2, no grinding is performed, and the pre-sintering process is directly performed, and no dispersing agent is added.

[0112] Comparative Example 3

[0113] The process steps of Example 1 were followed except that in Comparative Example 3, the pre-sintering temperature was 400°C for 4h and no dispersant was added.

[0114] Comparative Example 4

[0115] The process steps of Example 1 were followed except that in Comparative Example 4, the drying temperature was 150°C and no dispersant was added.

[0116] Comparative Example 5

[0117] The process steps of Example 1 were followed except that in Comparative Example 5, n (钒源) : n (柠檬酸) was 2 and no dispersant was added.

[0118] Comparative Example 6

[0119] The process steps of Example 1 were followed except that in Comparative Example 6, V (去离子水) / V (聚乙二醇) was 6:1.

[0120] Table 1 Performance test results of the positive electrode materials and batteries prepared in the examples and comparative examples

[0121]

[0122] Comparing Comparative Example 1 and Examples 2-6, it can be seen that the greater the ratio of the peak intensity of the (121) crystal plane to the peak intensity of the (211) crystal plane I 121 / I 211 , the better the crystallinity of the prepared positive electrode material; the smaller the ratio of the long axis to the short axis of the positive electrode material, the closer the prepared positive electrode material is to a spherical shape; the smaller the particle size distribution of the positive electrode material, the better the positive electrode material can be fully contacted with the electrolyte during charging and discharging; the lower the ratio I D / I G , the higher the graphitization degree of the carbon coating layer on the surface of the positive electrode material, which can effectively enhance the electrical conductivity of the positive electrode material. In summary, the positive electrode material of Example 1 has the best electrochemical performance, with a first discharge specific capacity of 130.8 mAh / g (theoretical specific capacity of 133 mAh / g) under 1C conditions, a capacity retention rate of 99.8% after 200 cycles, and a discharge specific capacity of 119.0 mAh / g under 5C conditions.

[0123] Comparing Comparative Example 1 and Comparative Examples 1-6, it can be seen that the ratio of the peak intensity of the (121) crystal plane to the peak intensity of the (211) crystal plane I 121 / I 211At the same time, the ratio of long axis to short axis of the positive electrode material is increased, the particle of the obtained positive electrode material tends to be irregular block, and the particle size is also obviously increased, the larger particle size leads to that the positive electrode material cannot be fully contacted with electrolyte during the cycle; the I D / I G The ratio is also significantly increased, which indicates that the graphitization degree of the carbon coating layer on the surface of the positive electrode material is reduced, the conductivity of the positive electrode material is reduced, and the electrochemical performance of the positive electrode material is reduced, the battery of the comparative example 1 has only 80.2 mAh / g of the initial discharge specific capacity under the condition of 1C, and the capacity retention rate after the cycle is only 96.4%, and the electrochemical performance under the condition of high-rate discharge is worse.

[0124] In summary, the positive electrode material of the present application has higher crystallinity, smaller particle size, higher graphitization degree of the carbon coating layer on the surface of the material, and the particle tends to be spherical, can be fully contacted with electrolyte, and the smaller particle size, the shorter migration distance of lithium ion, and the higher graphitization degree can improve the conductivity of the material, so that the material can exhibit excellent electrochemical performance during the cycle.

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

Claims

1. A positive electrode material, characterized by, The positive electrode material includes a lithium vanadium phosphate base; the positive electrode material has a peak intensity I 121 of a (121) crystal face in an X-ray diffraction pattern 211 The ratio I 121 / I 211 is 0.60 to 0.

99. The positive electrode material satisfies: 1.12≤a / b≤1.20; wherein a is a long axis length of the positive electrode material, in units of μm; b is a short axis length of the positive electrode material, in units of μm; The particle size distribution of the positive electrode material is 0.15 μm-3.5 μm.

2. The positive electrode material of claim 1, wherein, The positive electrode material further comprises a carbon material; the carbon material is mixed in the lithium vanadium phosphate matrix.

3. The positive electrode material of claim 1, wherein, When the positive electrode material is subjected to TG thermal gravimetric testing, a first platform appears at a temperature of 100-370 ℃, and a second platform appears at a temperature of 450-600 ℃.

4. The positive electrode material according to any one of claims 1 to 3, characterized in that, The positive electrode material further comprises a carbon coating layer; the carbon coating layer is coated on the outer surface of the lithium vanadium phosphate matrix.

5. The positive electrode material according to claim 4, characterized in that, The thickness of the carbon coating layer is 2 nm-30 nm.

6. The positive electrode material of claim 4, wherein, The mass of the carbon coating layer and / or the carbon material accounts for 10 wt%-15.5 wt% of the total mass of the positive electrode material.

7. The cathode material of claim 4, wherein, The Raman spectrum of the positive electrode material contains a D band characteristic peak with an intensity I -1 in the region of 1338-1344 cm D -1, a G band characteristic peak with an intensity I -1 in the region of 1598-1602 cm G -1, and 0.77≤I D / I G ≤0.

95.

8. The cathode material of claim 1, wherein, The positive electrode material is a spherical-like particle; and / or, the long axis length a of the positive electrode material is 0.1 μm-3.8 μm; the short axis length b of the positive electrode material is 0.07 μm-3.18 μm.

9. The cathode material of claim 1, wherein, The chemical formula of the lithium vanadium phosphate base is Li x V 2- y M y (PO4) z wherein 1≤x≤3, 0≤y≤2, 0≤z≤1; M is selected from at least one of Fe, Co, Mn, Cu, Zn, Al, Sn, B, Ga, Cr, Ti, Mg, Ca, Sr, Zr.

10. A positive electrode sheet, comprising the positive electrode material according to any one of claims 1-9.

11. A battery, comprising the positive electrode material according to any one of claims 1-9, or comprising the positive electrode sheet according to claim 10.

Images