Lithium battery positive electrode active material and preparation method, positive electrode and lithium battery thereof

Abstract

A lithium battery positive electrode active material and preparation method, as well as a positive electrode and lithium battery, wherein the positive electrode active material comprises layered lithium composite oxide grains and Li7MO6 phases distributed at the grain interfaces of the lithium composite oxide, where M is Bi, Sb, or Ta. Preparation of the material required for the present invention requires atmosphere control during the sintering process, and the sintering process must be carried out in two controlled steps, each consisting of four steps. Due to the presence of the intergranular Li7MO6 phase in the positive electrode active material, the total lithium ion content of the positive electrode material can be significantly increased, which has practical positive implications for both the material's capacitance and the replenishment of lithium ions during cycling.

Description

Technical Field

[0001] The invention relates to a positive electrode active material for a lithium battery and a method for preparing the material, and also relates to a positive electrode of a lithium battery using the positive electrode active material and a lithium battery. Background Art

[0002] Lithium batteries are primarily composed of positive electrode materials, negative electrode materials, separators, and electrolytes. Cathode materials account for over 40% of a lithium battery's total cost, and their performance directly impacts various performance indicators. Therefore, cathode materials play a core role in lithium batteries. Currently commercialized cathode materials for lithium batteries include lithium cobalt oxide, lithium manganese oxide, lithium iron phosphate, and ternary materials. With my country's rapid economic development, the demand for new battery materials continues to increase. Coupled with strong demand for new, efficient, and environmentally friendly battery materials in products such as mobile phones, laptops, digital cameras, camcorders, and automobiles, my country's new battery materials market is expected to continue to expand. As the future of battery development, the market for lithium batteries' cathode materials holds promising prospects. Furthermore, the widespread adoption of mobile phones and the large-scale commercialization of new energy vehicles will create new opportunities for lithium battery cathode materials. While the market for lithium battery cathode materials is vast, developing materials that can improve the specific capacity performance of lithium battery cathode materials remains a challenge for those skilled in the field. Summary of the Invention

[0003] The present invention aims to provide a lithium battery positive electrode active material that is beneficial to improving the electrochemical performance of lithium ion battery positive electrode materials, and to provide a method for preparing the lithium battery positive electrode active material.

[0004] The lithium battery positive electrode active material of the present invention comprises a layered structure lithium composite oxide crystal grain having a chemical formula 1; and a Li7MO6 phase distributed at the interface of the lithium composite oxide crystal grain, wherein M is Bi, Sb or Ta;

[0005] 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.

[0006] In the present invention, it is preferred that x and y cannot be 0 at the same time.

[0007] In the present invention, it is preferred that 0.9≤a≤1.3, 0.3≤x≤1, and 0.01≤y≤0.7.

[0008] The atomic ratio of M atoms in Li7MO6 in the positive electrode active material to (NixAyB1-xy) atoms in the layered positive electrode material is 0.1% to 8%, preferably 0.3% to 5%.

[0009] The Li7MO6 phase is distributed along the interface of the layered cathode material grains.

[0010] Since the Li7MO6 phase of the present invention is distributed along the interface of the layered positive electrode material grains, there is no definite orientation relationship between the Li7MO6 phase and the layered positive electrode material, and its orientation is random. This distribution form of Li7MO6 is beneficial for lithium replenishment.

[0011] Preferably, the average grain size of the Li7MO6 phase in the present invention is 50 nm to 20 μm.

[0012] Preferably, the particles composed of the Li7MO6 phase have an average particle size of 0.05 μm to 1 μm.

[0013] The lithium composite oxide of the present invention can be LiCoO2, LiMnO2, LiNiO2, Li(Ni 0.75 Mn 0.25 )O2、Li(Ni 0.9 Co 0.06 Mn 0.04 )O2, etc.

[0014] The lithium battery positive electrode active material of the present invention is prepared by the following method.

[0015] The raw materials required for preparing the lithium composite oxide chemical formula 1 and Li7MO6 are mixed, including the following preparation steps:

[0016] The sintering was performed twice in an oxygen-deficient atmosphere and an air atmosphere, respectively, and each sintering process included two steps.

[0017] First sintering: sintering is carried out in two steps in an oxygen-deficient atmosphere; the oxygen-deficient atmosphere means that the volume content of oxygen in the atmosphere is less than 21%;

[0018] The partial pressure of the protective gas and air in the oxygen-deficient atmosphere is 1 / 5 to 1 / 2;

[0019] Step A, heating to 300°C to 480°C and keeping warm to remove moisture;

[0020] Step B, heating to 570℃~650℃ and keeping warm, then cooling to room temperature; forming Li7MO6 phase embryo

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

[0022] Step C, heating to 750°C to 830°C and keeping warm;

[0023] Step D: heating to 850°C to 920°C and keeping warm.

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

[0025] The inventors have discovered through research that in order to prepare the material required by the present invention, it is necessary to control the atmosphere during the sintering process, and the sintering process must also be divided into two and four steps of controlled sintering.

[0026] In one embodiment of the present invention, the preferred temperature includes step A, heating to 320°C to 470°C and maintaining the temperature;

[0027] In another embodiment of the present invention, it is further preferred to include step A, heating to 350° C. to 450° C. and maintaining the temperature.

[0028] In one embodiment of the present invention, the process preferably includes step B of heating the temperature to 580° C. to 620° C. and maintaining the temperature.

[0029] In one embodiment of the present invention, the preferred temperature includes step C, heating to 790°C to 810°C and maintaining the temperature;

[0030] In one embodiment of the present invention, the preferred temperature includes step D, heating to 860°C to 900°C and maintaining the temperature;

[0031] In one embodiment of the present invention, the holding time in step A is 200 minutes to 500 minutes; preferably 240 minutes to 400 minutes; more preferably 240 minutes to 380 minutes.

[0032] In one embodiment of the present invention, the holding time in step B is 120 minutes to 500 minutes; preferably 200 minutes to 500 minutes; more preferably 240 minutes to 400 minutes.

[0033] In one embodiment of the present invention, the holding time in step C is 60 minutes to 240 minutes; preferably 60 minutes to 200 minutes; more preferably 100 minutes to 200 minutes.

[0034] In one embodiment of the present invention, the holding time in step D is 350 minutes to 800 minutes; preferably 360 minutes to 720 minutes; and more preferably 400 minutes to 650 minutes.

[0035] In step A of the present invention, since the goal is to remove moisture from the raw materials, any preferred embodiment with a relatively high temperature and holding time is acceptable.

[0036] The purpose of the present invention is also to use the lithium battery positive electrode active material to prepare a lithium battery positive electrode.

[0037] A further object of the present invention is to use the lithium battery positive electrode active material to prepare a lithium battery positive electrode. The lithium battery positive electrode is used to prepare a lithium battery.

[0038] 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.

[0039] During the preparation of the active positive electrode material for lithium-ion batteries of the present invention, after the formation of the layered lithium composite oxide crystals, a Li7MO6 phase is successfully generated between the crystals. The XRD pattern of the present invention shows that, except for the diffraction peak of the layered lithium composite oxide, all other diffraction peaks coincide with those of the Li7MO6 phase. This material has not been reported in the prior art.

[0040] The precursor is preferably hydroxide, and the lithium precursor is preferably lithium hydroxide monohydrate or lithium carbonate.

[0041] The addition of a high-lithium-ion-content phase to the layered positive electrode active material for lithium-ion batteries of the present invention allows the material itself to possess a relatively high relative content of lithium ions, which in turn translates to a higher theoretical specific capacity for the lithium-ion battery positive electrode material, significantly enhancing the electrochemical performance of the material. The lithium-ion content of the Li7BiO6 phase in the present invention is very high, and although bismuth atoms are a main-group element, they possess unique electrochemical properties. Therefore, the addition of a small amount of the Li7BiO6 phase to the layered positive electrode material for lithium-ion batteries, in addition to providing an additional lithium source, should also benefit the conductive properties of the positive electrode material.

[0042] The significance of this invention lies in the fact that it is the first to successfully form a pure Li7MO6 phase within a layered cathode material for lithium-ion batteries, a process far more challenging than producing a single pure Li7MO6 phase. The inventors developed the present material by chance during their ongoing research and development process. Further detailed research and development revealed the necessary control requirements, leading to the product of the present invention. The presence of the intergranular Li7MO6 phase within the cathode active material significantly increases the total lithium ion content of the cathode material, significantly impacting both the material's capacity and the replenishment of lithium ions during cycling. BRIEF DESCRIPTION OF THE DRAWINGS

[0043] Figure 1 The Li(Ni 0.75 Mn 0.25 )Diffraction patterns of O2 phase and Li7BiO6 phase.

[0044] Figure 2 is a scanning electron microscope image of the sample of Example 1, Figure 2a It is the microstructural characteristics and energy spectrum analysis results of the Li7BiO6 phase when the grains are cut. Figure 2b It is a microstructural image of grains without cross sections.

[0045] Figure 3 The Li(Ni 0.75 Mn 0.25 )Diffraction patterns of O2 phase and Li7BiO6 phase.

[0046] Figure 4 The Li(Ni 0.75 Mn 0.25 )Diffraction patterns of O2 phase and Li7BiO6 phase.

[0047] Figure 5 The Li(Ni 0.75 Mn 0.25 )Diffraction patterns of O2 phase and a small amount of Li7BiO6 phase samples.

[0048] Figure 6 The diffraction pattern of the sample prepared in Comparative Example 1.

[0049] Figure 7 The diffraction pattern of the sample prepared in Comparative Example 2 is shown.

[0050] Figure 8 The diffraction pattern of the sample prepared in Comparative Example 3 is shown.

[0051] Figure 9 The diffraction pattern of the sample prepared in Comparative Example 4 was obtained. DETAILED DESCRIPTION

[0052] The samples prepared by the present invention are first subjected to composition analysis using inductively coupled plasma, followed by phase analysis using an X-ray diffractometer to determine which phases are present in the samples, and finally, scanning electron microscopy and transmission electron microscopy are used to analyze the morphology, structure and distribution characteristics of the various phases in the samples.

[0053] Example 1

[0054] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and Bi2O3.According to Li:Bi:(Ni 0.75 Mn 0.25) in a molar ratio of 1.1:0.01:1. After mixing, the mixture is thoroughly ground and then placed in a magnesium oxide crucible. Sintering is carried out in two steps. The first step is carried out in an argon atmosphere sintering furnace with an argon volume content of 30%. The temperature is first kept at 400°C for 300 minutes, then kept at 600°C for 300 minutes, and then cooled to room temperature. The second step is sintering in an air atmosphere. The temperature is first raised normally to 800°C, kept at this temperature for 150 minutes, and then raised to 875°C. After continuing to keep this temperature for 600 minutes, a sample containing only layered lithium-ion battery positive electrode material and Li7BiO6 phase is obtained.

[0055] X-ray powder polycrystal 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 0.75 Mn 0.25 )O2(This phase does not exist in the database, use Li 0.99 NiO2 is substituted, and its crystal structure and lattice constant are exactly the same), the rest of the diffraction peaks are consistent with those of Li7BiO6 very well.

[0056] Microstructure observation and energy spectrum analysis were completed under a field emission scanning electron microscope. The scanning electron microscope used was a JSM-7900F model from JEOL. Some grains in the sample were cut into planes using a cross-section polisher. The working state of the scanning electron microscope is shown in Figure 2. Figure 2a After the grain is cut, Li(Ni 0.75 Mn 0.25 ) Microstructure and energy spectrum analysis results of O2 phase and Li7BiO6 phase; Figure 2b When the grains are not cut, Li(Ni 0.75 Mn 0.25 )Microstructure of O2 phase and Li7BiO6 phase. Figure 2a It is the microstructural characteristics and energy spectrum analysis results of the Li7BiO6 phase when the grains are cut. Figure 2b It is a microstructure image of grains without cross sections. From the backscattered electron microscopy image of the scanning electron microscope, it can be seen that the grain interface ( Figure 2a ) and grain boundaries without cross-section ( Figure 2b ) can be seen to have a white interface phase, and the results of the composition analysis are as follows Figure 2aAs shown in Figure 2, the energy spectrum results show that the phase contains a considerable amount of bismuth and oxygen. The reason why nickel and manganese appear in the results is that the white phase is too small, and the electron beam passes through the white phase and hits the lithium-ion battery positive electrode material. In addition, the atomic number of lithium is too small to be analyzed by energy spectrum. Combined with the X-ray diffraction results, it can be judged that the white phase at the grain boundary should be the Li7BiO6 phase. From the results of Figure 2, it can be seen that the Li7BiO6 phase tends to be distributed at the grain boundaries of the positive electrode material grains in the layered structure of the lithium-ion battery positive electrode material. It may be that the Li7BiO6 phase sticks several surrounding positive electrode material grains together. This microstructural feature makes the Li7BiO6 phase very effective in achieving the lithium replenishment effect.

[0057] Example 2

[0058] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and Bi2O3.According to Li:Bi:(Ni 0.75 Mn 0.25 ) in a molar ratio of 1.1:0.015:1, and after mixing, they are fully ground and then loaded into a magnesium oxide crucible. Sintering is carried out in two steps. The first step is carried out in an argon atmosphere with an argon volume content of 40%. First, the temperature is kept at 400°C for 300 minutes, then the temperature is continuously raised to 600°C and kept for 300 minutes, and then cooled to room temperature. The second step is sintering in an air atmosphere. First, the temperature is normally raised to 800°C, kept for 150 minutes, and then the temperature is raised to 875°C in 60 minutes. The temperature is continued to be kept for 600 minutes to obtain a sample containing only layered structure lithium-ion battery positive electrode material and Li7BiO6 phase.

[0059] X-ray powder polycrystal 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, use (Li 0.95 Ni 0.05 )(Ni 0.79 Mn 0.21 )O2 is replaced, and its crystal structure and lattice constant are exactly the same), the rest of the diffraction peaks are in good agreement with those of Li7BiO6. Figure 1 Compared with the X-ray diffraction results of Example 1, the most obvious difference is that the content of Li7BiO6 phase is significantly increased, and the diffraction peak curve of this phase is more standard and the peak width is narrower, indicating that the grains of this phase are coarser than those in Example 1.

[0060] Example 3

[0061] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and Bi2O3.According to Li:Bi:(Ni 0.75 Mn 0.25 ) in a molar ratio of 1.1:0.01:1, grind thoroughly after mixing, and then put into a magnesium oxide crucible. Sintering is carried out twice. The first time is in an argon atmosphere with an argon volume content of 20%. First, it is kept at 400°C for 300 minutes, then heated to 620°C and kept for 300 minutes, and then cooled to room temperature. The second time is sintering in an air atmosphere. First, the temperature is normally raised to 800°C, and after keeping it warm for 200 minutes, it is heated to 875°C and kept warm for 480 minutes to obtain a sample containing only layered structure lithium-ion battery positive electrode materials and Li7BiO6 phases. The most important thing about this step is to increase the sintering time of the first step of the second time at 800°C.

[0062] X-ray powder polycrystal 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, use (Li 0.95 Ni 0.05 )(Ni 0.79 Mn 0.21 )O2 is replaced, and its crystal structure and lattice constant are exactly the same), the rest of the diffraction peaks are consistent with Li7BiO6, but the intensity of the diffraction peaks is very low, especially with Figure 1 In comparison, the results obtained by different processes with the same composition are quite different, indicating that when the preparation process changes slightly, the chance of forming Li7BiO6 phase becomes lower. In fact, when we further increase the sintering time at 875℃ to 900 minutes or reduce it to 300 minutes, the Li7BiO6 phase completely disappears, indicating that the process conditions have high control requirements.

[0063] Example 4

[0064] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and Bi2O3.According to Li:Bi:(Ni 0.75 Mn 0.25) in a molar ratio of 1.1:0.015:1. After mixing, they are thoroughly ground and then placed in a magnesium oxide crucible. Sintering is carried out in two steps. The first step is carried out in an argon atmosphere sintering furnace with an argon volume content of 40%. First, the temperature is kept at 400°C for 300 minutes, then the temperature is raised to 600°C and kept for 300 minutes, and then cooled to room temperature. The second step is sintering in an air atmosphere. The temperature is first raised normally to 800°C, kept for 180 minutes, and then raised to 900°C. After continuing to keep the temperature for 600 minutes, a sample containing only layered lithium-ion battery positive electrode material and Li7BiO6 phase is obtained.

[0065] X-ray powder polycrystal diffraction experiments were performed on a Rigaku D / Max 2500 diffractometer from Japan. Figure 5 The diffraction pattern shows that, aside from the main phase Li(Ni0.75Mn0.25)O2 (this phase does not exist in the database, so Li0.99NiO2 was used instead, with the same crystal structure and lattice constant), the remaining diffraction peaks in the sintered sample closely match those of Li7BiO6, with virtually no diffraction peaks from other impurity phases. This indicates that under the current process, in addition to forming the layered structure of the lithium-ion battery cathode material phase, the remaining lithium reacts with bismuth to form the Li7BiO6 phase.

[0066] Comparative Example 1

[0067] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and Bi2O3.According to Li:Bi:(Ni 0.75 Mn 0.25 ) in a molar ratio of 1.1:0.01:1, and after mixing, they were thoroughly ground and then loaded into a magnesium oxide crucible. Sintering was carried out in two steps. The first step was carried out in an argon atmosphere sintering furnace with an argon volume content of 30%. First, the temperature was kept at 400°C for 300 minutes, then the temperature was raised to 600°C and kept for 300 minutes, and then cooled to room temperature. The second step was sintering in an air atmosphere, directly raising the temperature to 875°C in one step, continuing to keep the temperature for 600 minutes, and then cooling to obtain the experimental sample. This step omitted the short time of keeping the temperature at 800°C.

[0068] X-ray powder polycrystal 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, use Li 0.99This indicates that if the intermediate temperature of 800℃ is omitted in the second step of sintering, not only the Li7BiO6 phase cannot be formed, but also other trace phases will not appear. At this time, all the added Bi is dissolved into the matrix lithium-ion battery layered positive electrode material phase.

[0069] Comparative Example 2

[0070] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and Bi2O3.According to Li:Bi:(Ni 0.75 Mn 0.25 ) in a molar ratio of 1.1:0.01:1. After mixing, the mixture was thoroughly ground and then placed into a magnesium oxide crucible. Sintering was carried out twice. The first time was in an oxygen atmosphere sintering furnace with an oxygen volume content of 35%. First, the temperature was kept at 400°C for 300 minutes, then the temperature was raised to 600°C and kept for 300 minutes, and then cooled to room temperature. The second time was sintered in an air atmosphere. The temperature was first raised to 800°C for 150 minutes, kept for 150 minutes, and then raised to 875°C for 60 minutes. The temperature was continued to be kept for 600 minutes and then cooled to obtain the experimental sample.

[0071] X-ray powder polycrystal diffraction experiments were performed on a Rigaku D / Max 2500 diffractometer from Japan. Figure 6 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, use Li 0.99 NiO2 is replaced, and its crystal structure and lattice constant are exactly the same), and more small peaks appear. Analysis shows that these small diffraction peaks are consistent with (Li 0.27 Ni 0.73 )O phase matches Li2O2, indicating that when sintered at low temperature in an oxygen atmosphere, no Li7BiO6 phase is obtained under this composition, but a small amount of (Li 0.27 Ni 0.73 )O phase and Li2O2 phase. The existence of the latter two phases will have an adverse effect on the electrochemical performance of lithium-ion battery cathode materials.

[0072] Comparative Example 3

[0073] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and Bi2O3.According to Li:Bi:(Ni 0.75 Mn 0.25) in a molar ratio of 1.1:0.01:1, mixed well, and thoroughly ground before being placed into a magnesium oxide crucible. All sintering was performed under an argon atmosphere with a volume content of 30%. The first step was to hold the temperature at 400°C for 300 minutes, then raise the temperature to 600°C and hold it for 300 minutes before cooling to room temperature. The second step, also in an argon atmosphere, was to raise the temperature to 800°C over 150 minutes, hold it for 150 minutes, then raise the temperature to 875°C over 60 minutes, hold it for another 600 minutes, and then cool it to obtain the experimental sample.

[0074] X-ray powder polycrystal diffraction experiments were performed on a Rigaku D / Max 2500 diffractometer from Japan. Figure 6 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, use Li 0.99 NiO2 phase is replaced, and its crystal structure and lattice constant are exactly the same), and more small peaks appear. Analysis shows that these small diffraction peaks are consistent with (Li 0.27 Ni 0.73 )O, NiO2 and Li 0.3 The results show that the bismuth-containing samples cannot obtain the Li7BiO6 phase under the sintering process in an argon atmosphere, and bismuth is only dissolved in the positive electrode material of the lithium-ion battery as a doping element.

[0075] Comparative Example 4

[0076] For raw materials (Ni 0.75 Mn 0.25 )(OH)2,Li(OH).H2O and Bi2O3.According to Li:Bi:(Ni 0.75 Mn 0.25 ) in a molar ratio of 1.1:0.015:1, and after mixing, they are fully ground and then loaded into a magnesium oxide crucible. The sintering process is almost the same as that in Example 4, except that the final sintering time at 900°C is extended to 15 hours. The specific process is: sintering is carried out twice, the first time is carried out in an argon atmosphere sintering furnace with an argon volume content of 30%, first keeping it at 400°C for 300 minutes, then heating it to 600°C and keeping it for 300 minutes, and then cooling it to room temperature. The second time is sintering in an air atmosphere, first heating it normally to 800°C, keeping it warm for 180 minutes, then heating it to 900°C, and continuing to keep it warm for 900 minutes to obtain the experimental sample.

[0077] X-ray powder polycrystal diffraction experiments were performed on a Rigaku D / Max 2500 diffractometer from Japan. Figure 9It 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, use Li 0.99 NiO2 phase is replaced, and its crystal structure and lattice constant are exactly the same). The diffraction peak of Li7BiO6 phase is also very obvious. However, different from Example 4, a relatively obvious diffraction peak appears at the position of 18° in the diffraction pattern. After analysis, it is determined that this peak should correspond to Li 0.27 Ni 0.73 O phase. This result shows that if the sintering time is too long during the last high-temperature sintering step, other impurity phases will appear.

Claims

1. A positive electrode active material for a lithium battery, characterized in that: It includes a layered structure lithium composite oxide crystal grains shown in Chemical Formula 1; and a Li7MO6 phase distributed at the interface of the lithium composite oxide crystal grains, wherein M is Bi, Sb or Ta; 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 at least one metal element selected from Mn, Al, Mg, Cr, Nb, Mo and Cu.

2. A lithium battery positive electrode active material 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: 0.9≤a≤1.3, 0.3≤x≤1, 0.01≤y≤0.

7.

4. The positive electrode active material for a lithium battery according to claim 1, wherein: The atomic ratio of M atoms in Li7MO6 in the positive electrode active material to (NixAyB1-xy) atoms in the layered positive electrode material is 0.1% to 8%.

5. A lithium battery positive electrode active material according to claim 4, characterized in that: The atomic ratio of M atoms in Li7MO6 in the positive electrode active material to (NixAyB1-xy) atoms in the layered positive electrode material is 0.3% to 5%.

6. The positive electrode active material for a lithium battery according to claim 1, characterized in that: The Li7MO6 phase is distributed along the interface of the layered cathode material grains.

7. The positive electrode active material for a lithium battery according to claim 1, characterized in that: The average grain size of Li7MO6 phase is 50nm~20μm.

8. 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 Li7MO6 are mixed, wherein M is Bi, Sb or Ta; 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 at least one metal element selected from Mn, Al, Mg, Cr, Nb, Mo and Cu; The method comprises the following preparation steps: The sintering was performed twice in an oxygen-deficient atmosphere and an air atmosphere, respectively, and each sintering process included two steps of preparation. First sintering: two-step preparation in an oxygen-deficient atmosphere; The partial pressure of the protective gas and air in the oxygen-deficient atmosphere is 1 / 5 to 1 / 2; Step A, heating to 300°C to 480°C and keeping warm for 200 minutes to 500 minutes; Step B, heating to 570°C to 650°C and keeping the temperature for 120 minutes to 500 minutes, and then cooling to room temperature to allow the Li7MO6 phase embryo to begin to grow; Second sintering: prepared by two-step sintering in air atmosphere; Step C, heating to 750°C to 830°C and keeping the temperature for 60 minutes to 240 minutes; Step D: heating to 850° C. to 920° C. and keeping the temperature therefor for 350 to 800 minutes.

9. The method for preparing a positive electrode active material for a lithium battery according to claim 8, wherein: The protective gas is argon or nitrogen.

10. The method for preparing a positive electrode active material for a lithium battery according to claim 8, characterized in that: In the steps, step A, heating to 350°C to 450°C and keeping warm; and / or step B, heating to 580°C to 620°C and keeping warm; and / or step C, heating to 790°C to 810°C and keeping warm; and / or step D, heating to 860°C to 900°C and keeping warm.

11. The method for preparing a positive electrode active material for a lithium battery according to claim 8, wherein: In the steps, the insulation time of step A is 240 minutes to 400 minutes; and / or the insulation time of step B is 200 minutes to 500 minutes; and / or the insulation time of step C is 60 minutes to 200 minutes; and / or the insulation time of step D is 360 minutes to 720 minutes.

12. A lithium battery positive electrode active material according to any one of claims 1 to 7 used in a lithium battery positive electrode.

13. The lithium battery positive electrode according to claim 12 is used for preparing a lithium battery.

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