Lithium ion battery positive electrode active material and preparation thereof and positive electrode and lithium battery

Abstract

A lithium battery positive electrode active material, including a layered lithium composite oxide crystal grain; and a Li8MO6 phase embedded in the layered lithium composite oxide crystal grain in a granular form, wherein M is Zr, Sn, Pb or Hf; the material of the present invention can have a relatively high relative content of lithium ions, which means that the theoretical specific capacity of the lithium ion battery positive electrode material is relatively high, which is of great significance for improving the electrochemical cycle performance of the lithium ion battery positive electrode material. The present invention generates a Li8MO6 phase with a high lithium content inside the lithium composite oxide crystal grain; it has a good prospect for lithium supplementation.

Description

Technical Field

[0001] The invention relates to a positive electrode active material for a lithium ion battery and a method for preparing the material, and also includes a positive electrode of a lithium battery and a lithium battery in which the positive electrode active material is used. Background Art

[0002] Lithium batteries are mainly composed of positive electrode materials, negative electrode materials, diaphragms and electrolytes. Positive electrode materials account for more than 40% of the total cost of lithium batteries, and the performance of positive electrode materials directly affects the various performance indicators of lithium batteries, so lithium battery positive electrode materials occupy a core position in lithium batteries. At present, the positive electrode materials of lithium batteries that have been commercialized include products such as lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate and ternary materials. With the rapid development of my country's economy, the demand for new battery materials continues to increase, coupled with the strong demand for new, efficient and environmentally friendly battery materials for products such as mobile phones, laptops, digital cameras, camcorders, and automobiles, my country's new battery materials market will continue to expand. As the future development direction of batteries, lithium batteries have a promising market for positive electrode materials. At the same time, the promotion of mobile phones and the large-scale commercialization of new energy vehicles will bring new opportunities for lithium battery positive electrode materials.

[0003] The rate performance and cycle performance of layered cathode materials for lithium-ion batteries have always been issues of great concern to researchers. After multiple cycles, the electrochemical performance of cathode materials generally shows a significant decrease. It is generally believed that the reason for the deterioration of cycle performance is that part of the crystal layered structure in the cathode material is destroyed, and lithium ions cannot be normally embedded. The reasons for the destruction of the crystal structure of layered cathode materials are relatively complex, among which excessive deintercalation of lithium ions is an important factor. An effective way to prevent excessive deintercalation is to add lithium supplement materials to lithium-ion batteries, so that when the battery forms the SEI film (solid electrolyte interface film) in the first cycle, part of the lithium ions can be provided by the lithium supplement phase, so that the battery can have enough lithium for deintercalation and embedding while ensuring the capacity in subsequent cycles. There are many phases used to replenish lithium in lithium-ion batteries, such as orthorhombic Li2NiO2, but these lithium replenishing phases are generally added by physical methods, that is, after preparing the layered structure positive electrode material, a small amount of Li2NiO2 phase is mixed in. Although this method of addition can also increase the total amount of lithium in the material, the phases are independent grains, and the lithium replenishment effect is not very good. Therefore, finding a more efficient lithium replenishing phase in the existing positive electrode materials to improve the specific capacity and rate performance of lithium battery positive electrode materials is still a difficult problem that technicians need to face. Summary of the invention

[0004] The purpose of the present invention is to provide a lithium battery positive electrode active material which is beneficial to improving the electrochemical performance of the lithium ion battery positive material, and to provide a preparation method for the lithium battery positive electrode active material.

[0005] The purpose of the present invention also includes providing a lithium battery positive electrode made of the lithium battery positive electrode active material and showing the microstructure distribution characteristics of the active material in the matrix.

[0006] The present invention also aims to provide a lithium battery using the lithium battery positive electrode material.

[0007] The lithium battery positive electrode active material of the present invention comprises a layered lithium composite oxide crystal grain having a chemical formula 1; and a Li8MO6 phase embedded in the layered lithium composite oxide crystal grain in a granular form, wherein M is Zr, Sn, Pb or Hf;

[0008] Chemical formula 1 is: Lia(NixAyB1-xy)O2 0.9≤a≤1.5,0≤x≤1,0≤y≤0.7, A is selected from Co or Mn, and B can be selected from at least one metal element of Mn, Al, Mg, Cr, Nb, Mo and Cu.

[0009] In the present invention, it is preferred that x and y cannot be 0 at the same time.

[0010] In the present invention, 1.05≤a≤1.5, 0.3≤x≤1, and 0≤y≤0.5 are preferred.

[0011] The atomic ratio of the M atom in Li8MO6 in the positive electrode active material to the (NixAyB1-xy) (A is selected from Co or Mn, and B can be selected from at least one metal element selected from Mn, Al, Mg, Cr, Nb, Mo and Cu) in the layered positive electrode material is 0.001~0.1, preferably 0.005~0.05.

[0012] The size of the Li8MO6 phase in the positive electrode active material is about 20-300nm, and it is in the form of particles embedded in the interior of the grains of the layered lithium-ion battery positive electrode material Lia(NixAyB1-xy)O2 (A is selected from Co or Mn, and B can be selected from at least one metal element among Mn, Al, Mg, Cr, Nb, Mo and Cu.). From the formation mechanism and morphology of the active material Li8MO6 phase, it can be judged that there will be no definite orientation relationship between this phase and the grains of the layered lithium-ion battery positive electrode material Lia(NixAyB1-xy)O2 (A is selected from Co or Mn, and B can be selected from at least one metal element among Mn, Al, Mg, Cr, Nb, Mo and Cu.).

[0013] Preferably, the average grain size of the Li8MO6 phase in the present invention is 20 to 300 nm.

[0014] Preferably, the particles composed of Li8MO6 phase have an average particle size of 30-50nm.

[0015] The lithium battery positive electrode active material of the present invention is prepared by the following method.

[0016] The raw materials required for preparing the lithium composite oxide chemical formula 1 and Li8MO6 are mixed, including the following preparation steps:

[0017] The sintering is performed twice in an oxygen-deficient atmosphere and in an air atmosphere respectively, and each sintering comprises two steps of preparation;

[0018] First sintering: prepared in an oxygen-deficient atmosphere; the oxygen-deficient atmosphere refers to an atmosphere in which the volume content of oxygen is less than 21%;

[0019] Step A, heating to 320°C to 500°C and keeping warm to remove moisture;

[0020] Step B, heating to 550°C to 700°C and then cooling to room temperature, so that the Li8MO6 phase embryo begins to grow;

[0021] Second sintering: two-step sintering in air atmosphere;

[0022] Step C, heating to 770°C to 840°C and keeping warm;

[0023] Step D, heating to 860°C to 950°C and keeping warm.

[0024] The preferred protective gas in the present invention is argon, nitrogen or hydrogen.

[0025] In the oxygen-deficient atmosphere, the partial pressure of the protective gas and air in the oxygen-deficient atmosphere is 1 / 10-5 / 10;

[0026] Wherein, when the protective gas is hydrogen, the partial pressure of hydrogen and air cannot be higher than 3 / 10.

[0027] The volume ratio of argon, nitrogen or hydrogen to air in the protective gas in the oxygen-deficient atmosphere is preferably 1 / 10 to 3 / 10;

[0028] The inventors have found through research that in order to prepare the material required by the present invention, it is necessary to perform the atmosphere control treatment according to the present invention during the sintering process, and the sintering process must also be controlled in two times and four steps.

[0029] In one embodiment of the present invention, the preferred temperature includes step A, heating to 350°C to 450°C and maintaining the temperature.

[0030] In one embodiment of the present invention, it is preferred to include step B, heating to 590° C. to 660° C. and maintaining the temperature.

[0031] In one embodiment of the present invention, the preferred temperature includes step C, heating to 780°C to 820°C and maintaining the temperature.

[0032] In one embodiment of the present invention, the preferred temperature includes step D, heating to 870°C to 920°C and maintaining the temperature.

[0033] In one embodiment of the present invention, the insulation time of step A is 150 minutes to 450 minutes; preferably 240 minutes to 450 minutes.

[0034] In one embodiment of the present invention, the insulation time of step B is 150 minutes to 600 minutes; preferably 200 minutes to 500 minutes.

[0035] In one embodiment of the present invention, the insulation time of step C is 60 minutes to 300 minutes; preferably 90 minutes to 200 minutes.

[0036] In one embodiment of the present invention, the insulation time of step D is 300 minutes to 900 minutes; preferably 500 minutes to 720 minutes.

[0037] In the present invention, it is necessary to control the corresponding sintering atmosphere according to the requirements of the present invention.

[0038] In step A of the present invention, since the goal is to remove moisture from the raw material, any preferred embodiment with a relatively high temperature and a relatively long holding time is acceptable.

[0039] The purpose of the present invention is also to use the lithium battery positive electrode active material to prepare a lithium battery positive electrode.

[0040] A further purpose of the present invention is to use the lithium battery positive electrode active material to prepare a lithium battery positive electrode, and to use the lithium battery positive electrode to prepare a lithium battery.

[0041] The raw materials include a lithium precursor, a precursor required to form a lithium composite oxide of Chemical Formula 1, and an oxide of M.

[0042] In the preparation process of the active positive electrode material for lithium ion batteries of the present invention, after the layered lithium composite oxide crystal grains are formed, the Li8MO6 phase is successfully generated inside the crystal grains for the first time. The XRD diagram of the present invention shows that, except for the diffraction peak of the layered lithium composite oxide, the remaining diffraction peaks all overlap with the Li8MO6 phase. There is no related report on this material in the prior art.

[0043] The precursor is preferably a hydroxide, and the lithium precursor is preferably lithium hydroxide monohydrate or lithium carbonate.

[0044] The addition of the high lithium ion content Li8MO6 phase in the layered positive electrode active material of the lithium ion battery of the present invention enables the material itself to have a higher relative content of lithium ions, which means that the theoretical specific capacity of the lithium ion battery positive electrode material is higher, which is of great significance for improving the electrochemical cycle performance of the lithium ion battery positive electrode material. After the active positive electrode material of the present invention is formed, a high lithium content Li8MO6 phase is endogenously generated inside the lithium composite oxide grains. Since this phase appears when the positive electrode material is formed, it can be generated or precipitated inside the layered structure phase, so there is no definite orientation relationship between this phase and the layered lithium ion battery positive electrode material Lia (NixAyB1-xy) O2 grains; the formation timing, distribution mode and chemical composition of this phase determine that it must have good lithium supplement prospects. The endogenous Li8MO6 phase inside the layered structure lithium ion battery positive electrode material should also bring benefits to the conductive properties of the positive electrode material in addition to providing an additional lithium source.

[0045] The significance of the present invention also lies in that the present invention is the first to successfully form a pure Li8MO6 phase inside a layered positive electrode material for a lithium-ion battery, which is much more difficult than preparing a single pure Li8MO6 phase. The inventor also prepared the material of the present invention due to accidental factors during the continuous research and development process. Through further detailed research and development by the inventor, the corresponding control requirements were discovered, and the product of the present invention was further obtained. Due to the presence of the intracrystalline Li8MO6 phase in the positive electrode active material, the present invention can significantly increase the total lithium ion content of the positive electrode material, which has practical positive significance for the material capacity and the replenishment of lithium ions during the cycle process. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 The sample Li(Ni) prepared in Example 1 0.9 Co 0.06 Mn 0.04 )Diffraction patterns of O2 phase and Li8ZrO6 phase.

[0047] Figure 2 The sample Li(Ni) prepared in Example 1 0.9 Co 0.06 Mn 0.04 )SEM images of O2 phase and Li8ZrO6 phase.

[0048] Figure 3 The sample Li(Ni) prepared in Example 2 0.75 Mn 0.25 )Diffraction patterns of O2 phase and Li8ZrO6 phase.

[0049] Figure 4 The sample Li(Ni 0.75 Mn 0.25)Diffraction patterns of O2 phase and Li8ZrO6 phase.

[0050] Figure 5 These are the diffraction patterns of the Li(Ni0.75Mn0.25)O2 phase and Li8ZrO6 phase of the samples prepared in Example 4.

[0051] Figure 6 The Li(Ni 0.75 Mn 0.25 )Microstructure and energy spectrum results of O2 phase and Li8ZrO6 phase.

[0052] Figure 7 The Li(Ni 0.75 Mn 0.25 )Diffraction patterns of O2 phase and Li8ZrO6 phase

[0053] Figure 8 This is the X-ray pattern of the sample prepared in Comparative Example 1.

[0054] Fig. 9 This is the X-ray pattern of the sample prepared in Comparative Example 2.

[0055] Fig.10 This is the X-ray pattern of the sample prepared in Comparative Example 3.

[0056] Fig.11 This is the X-ray pattern of the sample prepared in Comparative Example 4. DETAILED DESCRIPTION

[0057] The analysis and detection of the material of the present invention adopts ICP component analysis, X-ray powder polycrystalline diffraction phase analysis and scanning electron microscope microscopic analysis, among which the emphasis is on X-ray powder polycrystalline diffraction phase analysis. Phase analysis is used to determine which phases are contained in the final sample, and scanning electron microscopy is used to determine the microscopic distribution of each phase.

[0058] Example 1

[0059] For raw materials (Ni 0.9 Co 0.06 Mn 0.04 )(OH)2,Li(OH).H2O and ZrO2.According to Li:Zr:(Ni 0.9 Co 0.06 Mn 0.04) in a molar ratio of 1.1:0.01:1 to mix the raw materials. After thorough mixing and grinding, sinter in a magnesium oxide crucible. Sintering is carried out in two steps and four steps. The first time, it is placed in a box-type sintering furnace protected by an argon atmosphere, in which the ratio of argon to air is about 15% (volume ratio). First, heat to 400°C in 90 minutes and keep warm for 300 minutes to fully decompose the crystal water in the raw materials. Then heat to 600°C within 90 minutes and keep warm for 300 minutes. This stage is mainly to decompose the hydroxide into the corresponding oxide. The purpose of adding argon is to make the decomposed oxide in an oxygen-deficient state, laying the foundation for the formation of the target phase Li8ZrO6 at a higher temperature. The second sintering is also a two-stage sintering, which is completed in an air atmosphere. First, heat to 800°C within 150 minutes, keep warm for 150 minutes, then heat to 875°C within 60 minutes, and keep warm for 600 minutes to obtain a Li(Ni 0.9 Co 0.06 Mn 0.04 )O2 phase and Li8ZrO6 phase samples.

[0060] X-ray powder polycrystalline diffraction experiments were performed on a Rigaku D / Max 2500 diffractometer from Japan. Figure 1 It is the diffraction result. From the diffraction pattern, it can be seen that in addition to the main phase Li (Ni 0.9 Co 0.06 Mn 0.04 )O2(This phase does not exist in the database, so we can only use Li 0.99 NiO2 is substituted, and its crystal structure is exactly the same), the rest of the diffraction peaks coincide very well with those of Li8ZrO6.

[0061] Scanning electron microscopy analysis was performed under a JEOL JSM-7900F field emission scanning electron microscope. The SEM sample was cut into a plane using a JEOL 1B-19530CP cross-section polisher. The SEM works as follows: Figure 2 As shown. From the scanning electron microscope photo, we can see that there are several small particles inside the cut grains, which are brighter when backscattered electron imaging is performed. The results of the composition analysis are shown in the upper right figure, indicating that the small bright blocks contain a relatively high amount of zirconium. Considering that the lithium content cannot be measured by energy spectrum analysis, combined with the X-ray diffraction results, it can be determined that the brighter small particles should be Li8ZrO6 phase, because zirconium has a relatively large atomic number, so it appears brighter when backscattered imaging. This result shows that the large grains sintered should be Li(Ni 0.9 Co 0.06 Mn 0.04 )O2 phase, a small amount of Li8ZrO6 phase is generated in these phases.

[0062] Example 2

[0063] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and ZrO2.According to Li:Zr:(Ni 0.75 Mn 0.25 ) in a molar ratio of 1.1:0.01:1 to proportion the raw materials. After thorough mixing and grinding, sintering is carried out in a magnesium oxide crucible. The sintering is carried out in two steps and four steps. The first time, it is placed in a box-type sintering furnace protected by an argon atmosphere, in which the ratio of argon to air is about 25%. First, heat it to 400°C in 90 minutes and keep it warm for 300 minutes to fully decompose the crystal water in the raw materials. Then heat it to 620°C in 90 minutes and keep it warm for 300 minutes. This stage is mainly to decompose the hydroxide into the corresponding oxide. The purpose of adding argon is to make the decomposed oxide in an oxygen-deficient state, laying the foundation for the formation of the target phase Li8ZrO6 phase at a higher temperature. The second sintering is also a two-stage sintering, which is completed in an air atmosphere. First, heat it to 800°C in 150 minutes, keep it warm for 150 minutes, then heat it to 900°C in 60 minutes, and keep it warm for 900 minutes to obtain a Li(Ni 0.75 Mn 0.25 )O2 phase and Li8ZrO6 phase samples.

[0064] X-ray powder polycrystalline diffraction experiments were performed on a Rigaku D / Max 2500 diffractometer from Japan. Figure 3 It is the diffraction result. From the diffraction pattern, it can be seen that in addition to the main phase Li (Ni 0.75 Mn 0.25 )O2(This phase does not exist in the database, so we can only use Li 0.99 NiO2 is substituted, and its crystal structure is exactly the same), the rest of the diffraction peaks coincide very well with those of Li8ZrO6.

[0065] Example 3

[0066] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and ZrO2.According to Li:Zr:(Ni 0.75 Mn 0.25) is mixed with raw materials in a molar ratio of 1.1:0.015:1. After thorough mixing and grinding, sintering is carried out in a magnesium oxide crucible. Sintering is carried out in two steps and four steps. The first time, it is placed in a box-type sintering furnace protected by an argon atmosphere, in which the ratio of argon to air is about 25%. First, heat it to 400°C in 90 minutes and keep it warm for 300 minutes to fully decompose the crystal water in the raw materials. Then heat it to 600°C within 90 minutes and keep it warm for 300 minutes. This stage is mainly to decompose the hydroxide into the corresponding oxide. The purpose of adding argon is to make the decomposed oxide in an oxygen-deficient state, laying the foundation for the formation of the target phase Li8ZrO6 phase at a higher temperature. The second sintering is also a two-stage sintering, which is completed in an air atmosphere. First, heat it to 800°C within 150 minutes, keep it warm for 180 minutes, then heat it to 875°C within 60 minutes, and keep it warm for 600 minutes to obtain a Li(Ni 0.75 Mn 0.25 )O2 phase and Li8ZrO6 phase samples.

[0067] X-ray powder polycrystalline diffraction experiments were performed on a Rigaku D / Max 2500 diffractometer from Japan. Figure 4 It is the diffraction result. From the diffraction pattern, it can be seen that in addition to the main phase Li (Ni 0.75 Mn 0.25 )O2(This phase does not exist in the database, so we can only use Li 0.99 NiO2 is substituted, and its crystal structure is exactly the same), the rest of the diffraction peaks coincide very well with those of Li8ZrO6.

[0068] Example 4

[0069] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and SnO2.According to Sn:(Ni 0.75 Mn 0.25) is one percent to proportion the raw materials. After thorough mixing and grinding, sintering is carried out in a magnesium oxide crucible. The sintering is carried out in two steps and four steps. The first time, it is placed in a box-type sintering furnace protected by an argon atmosphere, in which the ratio of argon to air is about 15%. First, heat it to 400°C in 90 minutes and keep it warm for 300 minutes to fully decompose the crystal water in the raw materials. Then heat it to 600°C within 90 minutes and keep it warm for 300 minutes. This stage is mainly to decompose the hydroxide into the corresponding oxide. The purpose of adding argon is to make the decomposed oxide in an oxygen-deficient state, laying the foundation for the formation of the target phase Li8SnO6 phase at a higher temperature. The second sintering is also a two-stage sintering, which is completed in an air atmosphere. First, heat it to 800°C within 150 minutes, keep it warm for 150 minutes, then heat it to 875°C within 60 minutes, and keep it warm for 600 minutes to obtain a Li(Ni 0.75 Mn 0.25 )O2 phase and Li8SnO6 phase samples.

[0070] X-ray powder polycrystalline diffraction experiments were performed on a Rigaku D / Max 2500 diffractometer from Japan. Figure 5 It is the diffraction result. From the diffraction pattern, it can be seen that in addition to the main phase Li (Ni 0.75 Mn 0.25 )O2(This phase does not exist in the database, so we can only use Li 0.99 NiO2 is substituted, and its crystal structure is exactly the same), the rest of the diffraction peaks coincide very well with those of Li8SnO6.

[0071] Scanning electron microscopy analysis was performed under a JEOL JSM-7900F field emission scanning electron microscope. The SEM sample was cut into a plane using a JEOL 1B-19530CP cross-section polisher. The SEM results are shown in Figure 2. Figure 6 As shown in the SEM photo,

[0072] There are several small particles inside the cut grains, which are brighter in backscattered electron imaging. The results of the composition analysis are shown in the upper right figure, indicating that the small bright blocks contain a relatively high amount of zirconium. Considering that the lithium content cannot be measured in the energy spectrum analysis, combined with the X-ray diffraction results, it can be determined that the brighter small particles should be Li8ZrO6 phases, because zirconium has a relatively large atomic number, so it appears brighter in backscattered imaging. This result shows that the large sintered grains should be Li(Ni0.75Mn0.25)O2 phases, and a small amount of Li8SnO6 phases are generated in these phases.

[0073] Example 5

[0074] For raw materials (Ni 0.75 Mn0.25 )(OH)2,Li(OH).H2O and ZrO2.According to Li:Zr:(Ni 0.75 Mn 0.25 ) in a molar ratio of 1.2:0.02:1 to proportion the raw materials. After thorough mixing and grinding, sintering is carried out in a magnesium oxide crucible. Sintering is carried out in two steps and four steps. The first time, it is placed in a box-type sintering furnace protected by an argon atmosphere, in which the ratio of argon to air is about thirty-five percent. First, heat up to 400°C in 90 minutes and keep warm for 300 minutes to fully decompose the crystal water in the raw materials. Then heat up to 610°C in 90 minutes and keep warm for 300 minutes. This stage is mainly to decompose the hydroxide into the corresponding oxide. The purpose of adding argon is to make the decomposed oxide in an oxygen-deficient state, laying the foundation for the formation of the target phase Li8ZrO6 phase at a higher temperature. The second sintering is also a two-stage sintering, which is completed in an air atmosphere. First, heat up to 800°C in 150 minutes, keep warm for 150 minutes, then heat up to 875°C in 60 minutes, and keep warm for 600 minutes to obtain a Li(Ni 0.75 Mn 0.25 )O2 phase and Li8ZrO6 phase samples.

[0075] X-ray powder polycrystalline diffraction experiments were performed on a Rigaku D / Max 2500 diffractometer from Japan. Figure 7 It is the diffraction result. From the diffraction pattern, it can be seen that in addition to the main phase Li (Ni 0.75 Mn 0.25 )O2(This phase does not exist in the database, so we can only use Li 0.99 NiO2 is replaced, and its crystal structure is exactly the same), the rest of the diffraction peaks are consistent with Li8ZrO6 very well. Among the small diffraction peaks, except for those matching Li8ZrO6, there are basically no impurity peaks elsewhere, indicating that the samples prepared under this process have only generated the desired Li8ZrO6 phase in addition to the layered structure of the lithium-ion battery positive electrode material phase.

[0076] Comparative Example 1

[0077] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and ZrO2.According to Li:Zr:(Ni 0.75 Mn 0.25) is 1.1:0.01:1 to match the raw materials. After fully mixing and grinding, sinter in a magnesium oxide crucible. Sintering in an argon atmosphere below 600°C is the same as the previous example, but the sintering at 800°C is omitted at high temperature, and the second sintering in the air is directly to 875°C. The specific process is as follows: Sintering is carried out in two steps. The first time is placed in a box-type sintering furnace protected by an argon atmosphere, in which the ratio of argon to air is about 15%. First, heat it to 400°C in 90 minutes, keep it warm for 300 minutes, so that the crystal water in the raw materials is fully decomposed, and then heat it to 600°C within 90 minutes, keep it warm for 300 minutes, and then cool the furnace to suffocation. The second sintering is directly heated to 875°C within 150 minutes, keep it warm for 600 minutes, and then cool it to obtain the experimental sample.

[0078] X-ray powder polycrystalline diffraction experiments were performed on a Rigaku D / Max 2500 diffractometer from Japan. Figure 8 It is the diffraction result. From the diffraction pattern, it can be seen that in addition to the main phase Li (Ni 0.75 Mn 0.25 )O2(This phase does not exist in the database, so we can only use Li 0.99 NiO2 is substituted, and its crystal structure is exactly the same), no diffraction peaks that match Li8ZrO6 are found. After careful analysis, it is determined that a trace amount of (Li 0.275 Ni 0.725 )O. Our experience shows that the presence of this phase will deteriorate the electrochemical performance of lithium-ion battery cathode materials.

[0079] Comparative Example 2

[0080] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and ZrO2.According to Li:Zr:(Ni 0.75 Mn 0.25 ) in a molar ratio of 1.1:0.01:1 to proportion the raw materials. After fully mixing and grinding, use a magnesium oxide crucible for sintering. The temperature and steps of the entire sintering are the same as the example process, except that all sintering is carried out in the air. The specific process is as follows: The sintering is carried out in two steps. The first time, the temperature is raised to 400°C in 90 minutes and kept warm for 300 minutes to fully decompose the crystal water in the raw materials. Then, the temperature is raised to 600°C within 90 minutes, and the furnace is cooled to suffocation after keeping warm for 300 minutes. The second sintering is directly heated to 800°C within 150 minutes, kept warm for 150 minutes, and then heated to 900°C within 60 minutes. After keeping warm for 600 minutes, the experimental sample is obtained by cooling.

[0081] X-ray powder polycrystalline diffraction experiments were performed on a Rigaku D / Max 2500 diffractometer from Japan. Fig. 9 It is the diffraction result. From the diffraction pattern, it can be seen that in addition to the main phase Li (Ni 0.75 Mn 0.25 )O2(This phase does not exist in the database, so we can only use Li 0.99 NiO2 is substituted, and its crystal structure is exactly the same). A diffraction peak is found near 17°, which may be consistent with Li8ZrO6, but the strongest peak near 19° has no intensity at all. Combined with the two very small diffraction peaks near 40° and 50° behind the diffraction pattern, it is judged that the diffraction peak near 17° should belong to Li2NiO2. In addition to this trace phase, there may be (Li 0.275 Ni 0.725 )O phase.

[0082] Comparative Example 3

[0083] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and ZrO2.According to Li:Zr:(Ni 0.75 Mn 0.25 ) is 1.1:0.01:1 to proportion the raw materials. After fully mixing and grinding, sintering is carried out in a magnesium oxide crucible. The temperature and steps of the entire sintering are the same as those in the previous example, except that the low-temperature part is sintered in an oxygen atmosphere. The specific process is as follows: the sintering is carried out in two steps and four steps. The first step is to sinter in an oxygen atmosphere (oxygen volume content 40%). First, the temperature is raised to 400°C in 90 minutes and kept warm for 300 minutes to fully decompose the crystal water in the raw materials. Then, the temperature is raised to 600°C within 90 minutes, and the furnace is cooled to suffocation after keeping warm for 300 minutes. The second sintering is carried out in the air, directly raising the temperature to 800°C within 150 minutes, keeping warm for 150 minutes, and then raising the temperature to 900°C within 60 minutes. After keeping warm for 600 minutes, the experimental sample is obtained by cooling.

[0084] X-ray powder polycrystalline diffraction experiments were performed on a Rigaku D / Max 2500 diffractometer from Japan. Fig.10 It is the diffraction result. From the diffraction pattern, it can be seen that in addition to the main phase Li (Ni 0.75 Mn 0.25 )O2(This phase does not exist in the database, so we can only use Li 0.99NiO2 is substituted, and its crystal structure is exactly the same). A diffraction peak is found near 17°, which may be consistent with Li8ZrO6, but the strongest peak near 19° has no intensity at all. Combined with the two very small diffraction peaks near 40° and 50° behind the diffraction pattern, it is judged that the diffraction peak near 17° should belong to Li2NiO2. In addition to this trace phase, there may be (Li 0.275 Ni 0.725 )O phase. This result is very close to that of sintering in air, and the desired Li8ZrO6 phase is not present.

[0085] Comparative Example 4

[0086] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and ZrO2.According to Li:Zr:(Ni 0.75 Mn 0.25 ) in a molar ratio of 1.1:0.01:1 to proportion the raw materials. After fully mixing and grinding, sintering is carried out in a magnesium oxide crucible. The temperature and steps of the entire sintering are the same as those in the previous example, except that the entire sintering is carried out in an argon atmosphere (argon volume content 30%). The specific process is as follows: the sintering is carried out in two steps. The first time is sintering in an argon atmosphere. First, the temperature is raised to 400°C in 90 minutes and kept warm for 300 minutes to fully decompose the crystal water in the raw materials. Then, the temperature is raised to 600°C within 90 minutes, and the furnace is cooled to suffocation after keeping warm for 300 minutes. The second sintering is still carried out in an argon atmosphere. The temperature is directly raised to 800°C within 150 minutes, and after keeping warm for 150 minutes, the temperature is raised to 875°C within 60 minutes. After keeping warm for 600 minutes, the experimental sample is obtained by cooling.

[0087] X-ray powder polycrystalline diffraction experiments were performed on a Rigaku D / Max 2500 diffractometer from Japan. Fig.11 It is the diffraction result. From the diffraction pattern, it can be seen that in addition to the main phase Li (Ni 0.75 Mn 0.25 )O2(This phase does not exist in the database, so we can only use Li 0.99 NiO2 is substituted, and its crystal structure is exactly the same), the remaining small diffraction peaks can basically coincide with the Li6ZrO7 phase, indicating that under the condition of an all-argon atmosphere, Li8ZrO6 phase cannot be sintered, but Li6ZrO7 phase with a slightly lower lithium content can be obtained.

Claims

1. A positive electrode active material for a lithium battery, characterized in that: It includes a layered lithium composite oxide crystal grain having a chemical formula 1; and a Li8MO6 phase embedded in the layered lithium composite oxide crystal grain in a granular form, wherein M is Zr, Sn, Pb or Hf; Chemical formula 1 is: Lia(NixAyB1-xy)O2, 0.9≤a≤1.5, 0≤x≤1, 0≤y≤0.7, A is selected from Co or Mn, and B is selected from at least one metal element of Mn, Al, Mg, Cr, Nb, Mo and Cu.

2. The positive electrode active material for a lithium battery according to claim 1, characterized in that: x and y cannot be 0 at the same time.

3. The positive electrode active material for a lithium battery according to claim 1, characterized in that: In Chemical Formula 1, 1.05≤a≤1.5, 0.3≤x≤1, 0≤y≤0.

5.

4. The positive electrode active material for a lithium battery according to claim 1, characterized in that: The atomic ratio of M atoms in Li8MO6 to (NixAyB1-xy) atoms in the lithium composite oxide Lia(NixAyB1-xy)O2 is 0.001~0.

1.

5. The positive electrode active material according to claim 1, characterized in that: The size of the Li8MO6 phase in the positive electrode active material is between 20-300 nm.

6. A method for preparing a positive electrode active material for a lithium battery, characterized in that: The raw materials required for preparing the lithium composite oxide chemical formula 1 and Li8MO6 are prepared and mixed, wherein M is Zr, Sn, Pb or Hf; Chemical formula 1 is: Lia (Nix A y B1-xy) O2, wherein 0.9 ≤ a ≤ 1.5, 0 ≤ x ≤ 1, 0 ≤ y ≤ 0.7, A is selected from Co or Mn, and B is selected from at least one metal element selected from Mn, Al, Mg, Cr, Nb, Mo and Cu; The method comprises the following preparation steps: Sintering is performed twice in an oxygen-deficient atmosphere and in an air atmosphere respectively, and each sintering comprises two steps; First sintering: prepared in an oxygen-deficient atmosphere; the oxygen-deficient atmosphere refers to an atmosphere in which the volume content of oxygen is less than 21%; Step A, heating to 320℃~500℃ and keeping warm, Step B, heating to 550°C to 700°C, keeping the temperature, and then cooling to room temperature; Second sintering: sintering in air atmosphere; Step C, heating to 770°C to 840°C and keeping warm; Step D, heating to 860°C to 950°C and keeping warm; The obtained product is a layered lithium composite oxide crystal grain having a structure shown in Chemical Formula 1; and a Li8MO6 phase embedded in the layered lithium composite oxide crystal grain in a granular form.

7. The preparation method according to claim 6, characterized in that: The oxygen-deficient atmosphere contains protective gas and air; the protective gas is argon, nitrogen or hydrogen.

8. The preparation method according to claim 7, characterized in that: The volume ratio of the protective gas to air in the oxygen-deficient atmosphere is 1 / 10 to 5 / 10, wherein the volume ratio does not exceed 3 / 10 when the protective gas is hydrogen.

9. The preparation method according to any one of claims 6 to 8, characterized in that: In the steps, step A, heating to 350°C-450°C and keeping warm; and / or step B, heating to 590°C-660°C and keeping warm; and / or step C, heating to 780°C-820°C and keeping warm; and / or step D, heating to 870°C-920°C and keeping warm.

10. The preparation method according to any one of claims 6 to 8, characterized in that: In the steps described, The holding time of step A is 150 minutes to 450 minutes. The holding time of step B is 150 minutes to 600 minutes. The holding time of step C is 60 minutes to 300 minutes. The holding time of step D is 300 minutes to 900 minutes.

11. An application of a positive electrode active material for a lithium battery as claimed in any one of claims 1 to 5, characterized in that: The applications include use in positive electrodes for lithium batteries.

12. The use of a positive electrode active material for a lithium battery according to claim 11, characterized in that: The lithium battery positive electrode active material is used for a lithium battery positive electrode, and the lithium battery positive electrode is used for a lithium battery.

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