A positive electrode material and its preparation method and application

Abstract

The present invention discloses a positive electrode material and a preparation method and application thereof, comprising the following steps: mixing a positive electrode material body, a coating agent containing M and a coating agent containing N, and then performing heat treatment; the heat treatment comprises a first heat treatment and a second heat treatment; the temperature of the first heat treatment is 550° C. to 750° C.; the temperature of the second heat treatment is 250° C. to 550° C.; the M is selected from at least one of B, W, Nb, Mo, Sb, Sr, Sn and Mo; the N is selected from at least one of Ni, Co, Mn, Zr, Al, Mg, Ti, Sr, W, Y, Zn, La, Ce and F; after the heat treatment, the coating agent containing M forms Li e M f O g or an oxide containing M. The positive electrode material prepared by the preparation method of the present invention can improve the structural stability of the surface interface and grain boundary of the positive electrode material, thereby improving the use stability of the positive electrode material.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy materials, and specifically relates to a positive electrode material and a preparation method and application thereof. Background Art

[0002] Lithium-ion batteries, due to their high operating voltage and excellent cycle performance, are widely used in new energy vehicles, mobile devices, energy storage power stations, and other fields. With the continuous development of technology, people are also placing higher demands on lithium-ion batteries. The design and development of electrode materials with higher capacity, higher power, higher energy density, and better cycle stability has become a research hotspot in the new energy field.

[0003] Currently, modifying traditional lithium-ion battery cathode materials to charge to higher voltages and increase capacity while ensuring safety and stability is a key technological approach for the development of high-energy-density lithium-ion batteries. However, charging cathode materials to higher voltages or releasing more lithium ions can lead to adverse consequences such as crystal structure breakdown, particle structure destruction, gas evolution, transition metal dissolution, and increased surface and interfacial side reactions. These can lead to failures such as capacity decay, poor electrochemical performance, and reduced safety.

[0004] Therefore, it is currently urgent to provide a positive electrode material to improve the stability of the positive electrode material under high-voltage conditions. Summary of the Invention

[0005] The present invention aims to solve at least one of the technical problems existing in the prior art. To this end, the present invention provides a method for preparing a positive electrode material, wherein the obtained positive electrode material has high structural stability at the surface interface and grain boundaries, thereby having high high-voltage stability.

[0006] The present invention also provides a positive electrode material prepared by the above preparation method.

[0007] The present invention also provides an application of the positive electrode material in a secondary battery.

[0008] According to a first embodiment of the present invention, a method for preparing a positive electrode material is provided, comprising the following steps:

[0009] A method for preparing a positive electrode material comprises the following steps:

[0010] The positive electrode material body, the coating agent containing M and the coating agent containing N are mixed and then heat treated;

[0011] The heat treatment includes a first heat treatment and a second heat treatment;

[0012] The temperature of the first heat treatment is 550°C to 750°C;

[0013] The temperature of the second heat treatment is 250°C to 550°C;

[0014] The M is selected from at least one of B, W, Nb, Mo, Sb, Sr, Sn and Mo;

[0015] The N is selected from at least one of Ni, Co, Mn, Zr, Al, Mg, Ti, Sr, W, Y, Zn, La, Ce and F;

[0016] After the heat treatment, the coating agent containing M forms Li e M f O g or an oxide containing M, wherein 1≤e≤5, 1≤f≤10, 1≤g≤10;

[0017] After the heat treatment, the N-containing coating agent forms Li e N f O g Or an oxide containing N, wherein 1≤e≤5, 1≤f≤10, 1≤g≤10.

[0018] A method for preparing a positive electrode material according to an embodiment of the present invention has at least the following beneficial effects:

[0019] Grain boundaries are interfaces between grains of the same structure but different orientations; they are difficult to observe with the naked eye, or even with conventional scanning electron microscopy. In cathode materials, grain boundaries are vulnerable sites. During long-term cycling, or even high-voltage charge and discharge, cracks can easily form at these boundaries, ultimately leading to disintegration and failure of the cathode material. Conventional technologies have made it difficult to achieve microscopic control of grain boundaries.

[0020] The present invention is provided with a first heat treatment (high temperature platform) of 550°C to 750°C and a second heat treatment (low temperature platform) of 250°C to 550°C. According to the type of M, the coating agent containing M is a low melting point coating agent or a compound that can react with the surface of the positive electrode material body (mainly residual lithium). Under the first heat treatment (high temperature platform) of 550°C to 750°C, the coating agent containing M is converted into a liquid phase or generates a compound on the surface of the positive electrode material body that is easy to infiltrate the grain boundary (the gap between the primary spheres on the secondary sphere surface) and diffuses along the grain boundary and (or) the surface layer into the interior of the material (shallow doping), forming a quasi-in-situ grain boundary strengthening layer (Li e M f O g ) while achieving surface doping; From the type of N, we can see that the N-containing coating agent has a high melting point. Under the first heat treatment (high temperature platform), the N-containing coating agent will not melt to form a liquid phase. The low temperature platform promotes the high melting point N-containing coating agent to form a liquid phase on the surface of the positive electrode material. e N fO g The island-shaped coating layer (which does not form a continuous coating layer) improves the ionic conductivity of the resulting cathode material. The synergistic effect of the two coating agents prevents the formation of intragranular cracks at the grain boundaries of the resulting cathode material, which accelerates the structural degradation of the fresh surface. This in turn prevents the formation of a disordered surface reconstruction layer of the cathode material, ultimately improving the structural stability of the surface interface and grain boundaries of the resulting cathode material, thereby enhancing the performance of the resulting cathode material under high pressure.

[0021] According to some preferred embodiments of the present invention, M is selected from at least one of B, W, Nb, Mo, Sb, Sr, and Sn.

[0022] According to some preferred embodiments of the present invention, the M is selected from at least one of B, W and Nb.

[0023] According to some preferred embodiments of the present invention, the N is selected from at least one of Zr, Mg, Ti and F.

[0024] According to some preferred embodiments of the present invention, the M-containing coating agent includes at least one of B2O3, WO3, Nb2O5 and H3BO3.

[0025] According to some preferred embodiments of the present invention, the N-containing coating agent includes at least one of TiO2, MgO, LiF and ZrO2.

[0026] According to some embodiments of the present invention, the cathode material body includes at least one of a polycrystalline material, a quasi-single crystal material, and a single crystal material.

[0027] According to some embodiments of the present invention, the first heat treatment lasts for 0.5 h to 5 h.

[0028] According to some embodiments of the present invention, the second heat treatment lasts for 3 hours to 8 hours.

[0029] The second heat treatment (low temperature platform) has a relatively long holding time, which promotes the formation of an island coating layer (Li e N f O g ). It mainly reacts with the residual lithium on the surface of the positive electrode material. Residual lithium is an unavoidable presence in the positive electrode material and has a negative impact on the performance of the positive electrode material. Therefore, the preparation method provided by the present invention can also improve the comprehensive performance of the obtained positive electrode material by removing the residual lithium on the surface of the positive electrode material.

[0030] According to some embodiments of the present invention, the method for preparing the positive electrode material body includes mixing a precursor and a lithium source, sintering the mixture, and crushing the mixture.

[0031] According to some embodiments of the present invention, the lithium source includes at least one of LiOH and Li2CO3.

[0032] According to some embodiments of the present invention, the lithium source includes at least one of fine powder LiOH, coarse particle LiOH, battery grade Li2CO3, quasi battery grade Li2CO3, and industrial Li2CO3.

[0033] According to some embodiments of the present invention, the sintering temperature is 750-1050°C.

[0034] According to some embodiments of the present invention, the molar ratio of lithium in the lithium source to the transition metal in the precursor is 1 to 1.1:1.

[0035] During the sintering process, Li (lithium source) will volatilize, and some of it will exist on the surface of the positive electrode material in the form of residual lithium. Therefore, it is necessary to ensure that the lithium source is slightly excessive.

[0036] According to some embodiments of the present invention, the sintering atmosphere includes oxygen.

[0037] According to some embodiments of the present invention, the volume concentration of oxygen is 22-99.99%.

[0038] According to some embodiments of the present invention, the preparation method further comprises adding additives during the mixing process.

[0039] According to some embodiments of the present invention, the additive includes at least one element selected from the group consisting of Ni, Co, Mn, Zr, Al, Mg, Ti, Sr, W, Y, Mo, Sb, Nb, Sn, Zn, La, Ce, B, and F.

[0040] The elements in the above additives form strong chemical bonds with the oxygen in the cathode material, stabilizing the lattice structure and improving the high voltage performance of the resulting cathode material.

[0041] According to some embodiments of the present invention, the preparation method further comprises screening, removing iron and packaging the positive electrode material.

[0042] According to a second embodiment of the present invention, a positive electrode material prepared by the preparation method is provided.

[0043] The positive electrode material comprises a positive electrode material body, and the surface of the positive electrode material body has a grain boundary;

[0044] The first coating is Li e M f O g and at least one of an oxide containing M, wherein the first coating is concentrated at the grain boundary;

[0045] The second coating is distributed on the surface of the positive electrode material body.

[0046] According to some embodiments of the present invention, the positive electrode material is LiNi x Co y Mn z R a O2@M b N c , 0 <x≤1,0≤y≤0.3,0≤z≤0.6,0.001≤a≤0.01,0.001≤b≤0.005,0.001≤c≤0.008,x+y+z+a=1。

[0047] R is an element in the additive. The presence of R ensures the improvement of the high-voltage performance of the positive electrode material after doping, while avoiding the reduction of the specific capacity of the obtained positive electrode material.

[0048] When the cathode material is polycrystalline, the first coating is also concentrated in the gaps between the primary particles. Because these gaps are also vulnerable areas of polycrystalline materials, the first coating concentrated in these gaps also has the effect of hindering electrolyte penetration and improving the bonding strength between primary particles, which has a positive impact on improving the high-voltage performance of the resulting cathode material.

[0049] According to a third aspect of the present invention, an embodiment of the present invention provides an application of the positive electrode material in a secondary battery.

[0050] According to some embodiments of the present invention, the test voltage of the secondary battery is 2.8-4.25V.

[0051] Other features and advantages of the present invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0052] The above and / or additional aspects and advantages of the present invention will become apparent and readily understood from the following description of the embodiments with reference to the accompanying drawings, in which:

[0053] Figure 1 This is a SEM image of the positive electrode material obtained in Example 1;

[0054] Figure 2 This is a SEM image of the positive electrode material obtained in Example 1;

[0055] Figure 3 This is the SEM image of the positive electrode material obtained in Comparative Example 1. DETAILED DESCRIPTION

[0056] The following describes embodiments of the present invention in detail. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals throughout represent the same or similar elements or elements having the same or similar functions. The embodiments described below with reference to the accompanying drawings are exemplary and are intended only to explain the present invention and are not to be construed as limiting the present invention. Unless otherwise specified, the materials and reagents used in the embodiments are commercially available.

[0057] Example 1

[0058] This embodiment discloses a method for preparing a positive electrode material, and the specific steps are as follows:

[0059] S1. Ni 0.70 Co 0.05 Mn 0.25 (OH)2 precursor is mixed evenly with powder LiOH, ZrO2, and Al2O3 and then sintered at high temperature in an oxygen atmosphere. 0.70 Co 0.05 Mn 0.25 (OH)2 and LiOH are fed in a molar ratio of Li / (Ni+Co+Mn) of 1.05. The addition amounts of ZrO2 and Al2O3 are 4000ppm and 1000ppm respectively (based on the mass of Zr / Al in ZrO2 / Al2O3 relative to the precursor). The oxygen volume concentration during the sintering process is 95% and the sintering temperature is 915℃. The sintered product is pre-treated by coarse crushing and enters the next process. After coarse crushing, the particle size D v 50 is controlled at 8±0.5μm.

[0060] S2. The crushed and pre-treated material from step S1 is uniformly mixed with a low-melting-point coating agent, B2O3 (a coating agent containing M, where M is B), and a high-melting-point coating agent, TiO2 (a coating agent containing N, where N is Ti), and then subjected to a secondary sintering process. The added amounts of the coating agents, B2O3 and TiO2, are 1000ppm and 1500ppm, respectively (based on the B / Ti ratio in the B2O3 / TiO2 ratio relative to the mass of the cathode material obtained in step S1). During the secondary sintering process, the high-temperature platform, T1, is maintained at 550°C for 2 hours; the low-temperature platform, T2, is maintained at 450°C for 6 hours. The sintered product is then screened, de-ironed, and packaged to obtain the finished product.

[0061] The effect of coating agent on grain boundary infiltration is as follows Figure 1 As shown;

[0062] The coating agent containing M generates compounds that easily infiltrate the grain boundary (the gap between the primary spheres on the secondary sphere surface) and diffuses into the material along the grain boundary and (or) the surface (shallow doping), forming an in-situ grain boundary strengthening layer (Li e M f Og ) while achieving surface doping.

[0063] Figure 2 Schematic diagram of the overall coating effect of the positive electrode material in this embodiment.

[0064] An island-shaped coating layer is formed on the surface of the positive electrode material body.

[0065] Example 2

[0066] This embodiment discloses a method for preparing a positive electrode material, and the specific steps are as follows:

[0067] S1. Ni 0.82 Co 0.06 Mn 0.12 The (OH)2 precursor is mixed evenly with coarse particles of LiOH, additives Y2O3 and Sb2O3, and then sintered at high temperature in an oxygen atmosphere. 0.82 Co 0.06 Mn 0.12 (OH)2 and LiOH were added in a molar ratio of Li / (Ni+Co+Mn) of 1.03. The amounts of Y2O3 and Sb2O3 additives were 2000ppm and 2000ppm respectively (based on the Y / Sb in Y2O3 / Sb2O3 as a percentage of the precursor mass). The oxygen concentration during the sintering process was 98% by volume and the sintering temperature was 840°C. The sintered product was pre-treated by coarse crushing and then entered the next process. After coarse crushing, the particle size was D v 50 is controlled at 10±0.5μm.

[0068] S2. The crushed and pre-treated material from step S1 is mixed evenly with WO3, which readily reacts with residual lithium on the surface of the positive electrode material, and MgO, a high-melting-point coating agent containing M, and then subjected to secondary sintering. The coating agents WO3 and MgO are added in amounts of 1500 ppm and 1000 ppm, respectively (based on the W / Mg ratio of the WO3 / MgO ratio to the mass of the positive electrode material). The secondary sintering process is conducted at a high-temperature platform (T1) of 750°C for a holding time of 0.5 hours, and at a low-temperature platform (T2) of 400°C for a holding time of 5 hours. The sintered product is screened, iron removed, and packaged to obtain the finished product.

[0069] Example 3

[0070] This embodiment discloses a method for preparing a positive electrode material, and the specific steps are as follows:

[0071] S1. Ni 0.55 Co 0.12 Mn 0.33 (OH)2 precursor, mixed with battery grade Li2CO3, additive MO3, La2O3, and then sintered at high temperature in an oxygen atmosphere. 0.55 Co0.12 Mn 0.33 (OH)2 and Li2CO3 are fed in a molar ratio of Li / (Ni+Co+Mn) of 1.06. The addition amounts of MO3 and La2O3 are 2500ppm and 1000ppm respectively (based on the M / La ratio of MO3 / La2O3 to the precursor mass). The oxygen volume concentration during the sintering process is 22% and the sintering temperature is 950℃. The sintered product is pre-treated by coarse crushing and enters the next process. After coarse crushing, the particle size D v 50 is controlled at 4.5±0.5μm.

[0072] S2. The crushed and pre-treated material from step S1 is mixed evenly with Nb2O5, a material that readily reacts with residual lithium on the surface of the positive electrode material, and a high-melting-point coating agent, LiF, followed by secondary sintering. The coating agents Nb2O5 and LiF are added in amounts of 1500ppm and 1000ppm, respectively (based on the Nb / F ratio of the Nb2O5 / LiF ratio to the mass of the positive electrode material). The secondary sintering process is conducted at a high-temperature platform (T1) of 700°C for a holding time of 1 hour, and at a low-temperature platform (T2) of 550°C for a holding time of 6 hours. The sintered product is then screened, iron removed, and packaged to obtain the finished product.

[0073] Example 4

[0074] This embodiment discloses a method for preparing a positive electrode material, and the specific steps are as follows:

[0075] S1. Ni 0.60 Co 0.07 Mn 0.33 (OH)2 precursor, industrial Li2CO3, additive CeO2, ZnO are mixed evenly and sintered at high temperature in oxygen atmosphere. 0.60 Co 0.07 Mn 0.33 (OH)2 and Li2CO3 were added in a molar ratio of Li / (Ni+Co+Mn) of 1.07. The addition amounts of CeO2 and ZnO were 1500ppm and 1200ppm respectively (based on the mass of Ce / Zn in CeO2 / ZnO relative to the precursor). The oxygen concentration during the sintering process was 40% and the sintering temperature was 930℃. The sintered product was pre-treated by coarse crushing and then entered the next process. After coarse crushing, the particle size was D v 50 is controlled at 5.5±0.5μm.

[0076] S2. The crushed and pre-treated material from step S1 is mixed uniformly with a low-melting-point coating agent, H3BO3, and a high-melting-point coating agent, ZrO2, and then subjected to secondary sintering. The added amounts of H3BO3 and ZrO2 are 800 ppm and 1500 ppm, respectively (based on the ratio of B to Zr in H3BO3 / ZrO2 relative to the mass of the positive electrode material). The secondary sintering process is conducted at a high-temperature platform, T1, of 600°C for 3 hours, and a low-temperature platform, T2, of 450°C for 7 hours. The sintered product is screened, iron removed, and packaged to obtain the finished product.

[0077] Comparative Example 1

[0078] This comparative example discloses a method for preparing a positive electrode material, which differs from Example 1 in that the low-melting-point coating agent B2O3 is not added, and the other conditions are the same.

[0079] Figure 3 This is the SEM image of the island-shaped coating formed in Comparative Example 1.

[0080] In Comparative Example 1, the coating agent did not infiltrate the grain boundaries.

[0081] Comparative Example 2

[0082] This comparative example discloses a method for preparing a positive electrode material, which differs from Example 2 in that the low-temperature platform in step S2 is not included, and the other conditions are the same.

[0083] Test Example 1

[0084] This test example examined the charge and discharge performance of the positive electrode materials of Examples 1-4 and Comparative Examples 1-2. The test results are shown in Table 1. The test method involved mixing the positive electrode material, acetylene black, and PVDF in a mass ratio of 9.2:0.5:0.3 using N-methylpyrrolidone as the solvent to form a slurry. The slurry was then coated onto aluminum foil and dried at 80°C with forced air for 8 hours, followed by vacuum drying at 120°C for 12 hours to obtain the positive electrode. The battery was assembled in an argon-protected glove box. The negative electrode was a lithium metal sheet, the separator was a polypropylene film, and the electrolyte was 1M LiPF6-EC / DMC (1:1, v / v). A 2032-type button cell case was used. The resulting button cell was subjected to electrochemical performance testing, and the capacity retention rate was calculated as the ratio of the gram-specific capacity after the Nth charging cycle to the gram-specific capacity after the first charging cycle. The specific test mechanism is: discharge at a rate of 0.1C at 2.8-4.25V, then cycle 100 times at a rate of 1C / 1C at 2.8-4.25V, and record the cycle capacity retention rate after 100 cycles.

[0085] Table 1 Performance test results

[0086]

[0087] In Examples 1 to 4, the present invention sets a high temperature and a low temperature platform. The high temperature platform promotes the M coating agent to transform into a liquid phase or to form a compound that is easy to infiltrate the grain boundary on the surface of the positive electrode material and diffuses along the grain boundary and (or) the surface layer into the material to form an in-situ grain boundary strengthening layer (Li e M f O g ) while achieving surface doping; the low temperature platform holding time is relatively long, which promotes the high melting point coating agent to form an island coating layer on the surface, improves the ionic conductivity of the positive electrode material, and thus improves the performance of the positive electrode material. In comparative example 1, there is no low melting point coating agent, so it is impossible to form an in-situ grain boundary strengthening layer (Li e M f O g ) while achieving surface doping; Comparative Example 2 does not include the setting of a low-temperature platform, so it is impossible to promote the high-melting-point coating agent to form an island-shaped coating layer on the surface, thereby affecting the use efficiency of the positive electrode material.

[0088] The embodiments of the present invention are described in detail above with reference to the accompanying drawings, but the present invention is not limited to the above embodiments. Various changes can be made within the scope of knowledge possessed by ordinary technicians in the relevant technical field without departing from the scope of the present invention.

Claims

1. A method for preparing a positive electrode material for a lithium ion battery, characterized in that: The following steps are involved: The positive electrode material body, the coating agent containing M and the coating agent containing N are mixed and then heat treated; The heat treatment includes a first heat treatment and a second heat treatment; The temperature of the first heat treatment is 550°C to 750°C; The temperature of the second heat treatment is 250°C to 550°C; The second heat treatment time is 3h~8h; The first heat treatment is a high temperature platform. During the first heat treatment, the M-containing coating agent is transformed into a liquid phase or forms a compound on the surface of the cathode material that is easy to infiltrate the grain boundary. During the first heat treatment, the N-containing coating agent does not melt to form a liquid phase; The second heat treatment is a low-temperature platform, which promotes the high-melting-point N-containing coating agent to form an island-shaped coating layer on the surface of the positive electrode material. The M-containing coating agent includes at least one of B2O3, WO3, Nb2O5 and H3BO3; The N-containing coating agent includes at least one of TiO2, MgO and ZrO2; After the heat treatment, the coating agent containing M forms Li e M f O g or an oxide containing M, wherein 1≤e≤5, 1≤f≤10, 1≤g≤10; After the heat treatment, the N-containing coating agent forms Li e N f O g Or an oxide containing N, wherein 1≤e≤5, 1≤f≤10, 1≤g≤10.

2. The method for preparing a positive electrode material for a lithium ion battery according to claim 1, wherein: The time of the first heat treatment is 0.5h~5h.

3. The method for preparing a positive electrode material for a lithium ion battery according to claim 1, wherein: The preparation method of the positive electrode material body comprises mixing a precursor and a lithium source, sintering the mixture, and crushing the mixture.

4. The method for preparing a positive electrode material for a lithium ion battery according to claim 3, wherein: The lithium source includes at least one of LiOH and Li2CO3.

5. A lithium ion battery positive electrode material prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The positive electrode material comprises a positive electrode material body, and the surface of the positive electrode material body has a grain boundary; The first coating is Li e M f O g and at least one of an oxide containing M, wherein the first coating is concentrated at the grain boundary; The second coating is distributed on the surface of the positive electrode material body.

6. The lithium-ion battery cathode material according to claim 5, characterized in that The positive electrode material has the following chemical formula LiNi x Co y Mn z R a O2@M b N c , where 0 <x≤1,0≤y≤0.3,0≤z≤0.6,0.001≤a≤0.01,0.001≤b≤0.005,0.001≤c≤0.008,x+y+z+a=1。 7. The lithium-ion battery positive electrode material according to claim 6, characterized in that The R is an additive, and the element is at least one of Ni, Co, Mn, Zr, Al, Mg, Ti, Sr, W, Y, Mo, Sb, Nb, Sn, Zn, La, Ce, B and F.

8. Use of the lithium-ion battery positive electrode material according to claim 6 or 7 in a secondary battery.

Images