Al-La doped core-interlayer@bnt composite positive electrode active material and preparation and application thereof

Abstract

The application belongs to the field of lithium ion battery materials, and particularly relates to an Al-La doped core-intermediate layer@BNT composite positive electrode active material, which comprises a core, an intermediate layer for coating the core and a shell for coating the intermediate layer, the core and the intermediate layer are Al and La double metal doped positive electrode active materials, the core is a layered structure material, the intermediate layer has a spinel phase or / and a rock salt phase, and the shell is a sodium bismuth titanate material. The application also comprises preparation and application of the material. Researches show that the core, the intermediate layer and the shell material are controlled, and the combination of the hierarchical structure can realize synergy, can improve the capacity, the rate and the long cycle stability of the positive electrode active material, and can effectively improve the electrochemical performance under extreme conditions such as high temperature and high current.

Description

Technical Field

[0001] The present invention relates to the field of lithium ion materials, and in particular to the field of positive electrode materials. Background Art

[0002] Lithium-ion batteries are now widely used in portable electronic devices, electric vehicles (EVs), and smart grids. The key to their energy density and lifespan lies in their positive and negative electrode materials. Since negative electrode materials have made rapid progress and offer stable performance, positive electrode materials play a greater role in battery performance.

[0003] Cathode materials primarily include layered lithium cobalt oxide, layered lithium nickel oxide, spinel lithium manganese oxide, layered ternary materials, and layered lithium-rich manganese-based cathode materials. In practical applications, these cathode materials suffer from low first-cycle efficiency, cycling stability, and significant voltage decay, particularly for high-nickel ternary cathode materials and lithium-rich manganese-based cathode materials. This is primarily due to the irreversible transformation of the cathode material's crystal structure under high voltage, coupled with side reactions between residual lithium on the cathode material's surface and the electrolyte. Therefore, a synergistic strategy is urgently needed to properly and comprehensively address these issues.

[0004] For example, the Chinese patent application publication number CN105938899A discloses a method for coating a modified lithium battery positive electrode material with a LiAlO2 fast ion conductor. The method first ball-mills aluminum hydroxide and the positive electrode material, then dissolves them in a lithium-containing solution, and obtains a coating material by evaporating and sintering. The obtained coating material has excellent electrochemical properties. The Chinese patent application publication number CN111370689A discloses a ruthenium and aluminum co-doped lithium cobalt oxide positive electrode material. Under the co-doping effect of aluminum and ruthenium, its discharge specific capacity is significantly improved, and the cycle stability at 4.5V and 4.6V is also improved. However, the above method does not properly solve the problems of internal structural degradation of the material and interface side reactions, so it has certain limitations in application. Summary of the Invention

[0005] In order to solve the problem of unsatisfactory capacity, rate and long cycle performance of positive electrode materials, the first purpose of the present invention is to provide an Al-La doped core-intermediate layer@BNT composite positive electrode active material (also referred to as composite positive electrode active material in the present invention), aiming to improve the capacity, rate and long cycle performance of the material through the combination of materials and three-layer layer-by-layer structure.

[0006] The second purpose of the present invention is to provide a preparation method of the Al-La doped core-intermediate layer@BNT composite positive electrode active material and its application in lithium-ion batteries.

[0007] A third object of the present invention is to provide a lithium-ion battery comprising the composite positive electrode active material.

[0008] An Al-La doped core-intermediate layer@BNT composite positive electrode active material, comprising a core, an intermediate layer coating the core, and a shell coating the intermediate layer, wherein the core and the intermediate layer are positive electrode active materials doped with Al and La bimetallic materials, wherein the core is a layered structure material, and the intermediate layer has a spinel phase and / or a rock salt phase;

[0009] The shell is made of sodium bismuth titanate material (BNT layer).

[0010] The novel material described in this invention comprises a three-layer structure, wherein the core and middle layer are a bimetallic hybrid cathode active material of Al and La, and the BNT is the shell. Research in this invention has shown that the control of the core, middle layer, and shell materials, and the combination of the hierarchical structure, can achieve synergy, synergistically improving the capacity, rate capability, and long-cycle stability of the cathode active material. Furthermore, it can effectively improve its electrochemical performance under extreme conditions, such as high temperature and high current.

[0011] In the present invention, the combination of the bimetallic type of Al and La is one of the keys to improving the synergy of the three-layer hierarchical structure and improving the electrochemical performance. In the present invention, Al and La can be used to dope the positive electrode active materials known in the industry to obtain the core and intermediate layer materials. In the present invention, the positive electrode active material before doping can be, for example, a lithium-containing oxide containing at least one metal of Ni / Co / Mn, and can further be one or more of lithium cobalt oxide, lithium nickel oxide, high nickel ternary material, and lithium-rich material.

[0012] In the materials of the core and the intermediate layer, the molar content of Al and La in the total metal is less than or equal to 8 mol%, preferably 0.1 to 0.5 mol%.

[0013] As a preference, the chemical formula of the core and the intermediate layer materials is Li 1.2-x TM 1-y M d O 2-z , where 0 <x<0.3,0<y<0.2,0<z<0.4,TM为过渡金属,M为掺杂元素La和Al,0<d / (1-y)<8%。

[0014] The chemical formula of the sodium bismuth titanate material is Na x Bi 1-x TiO3, of which 0 <x<1,优选地,x为0.4~0.6。

[0015] Preferably, the shell has a thickness of 1 to 15 nm, and the intermediate layer has a thickness of 1 nm to 20 nm.

[0016] The present invention also provides a method for preparing the composite positive electrode active material, comprising the following steps:

[0017] Step (1):

[0018] The positive electrode precursor, lithium source, Al source and La source are combined and calcined to obtain material 1;

[0019] Step (2):

[0020] The material 1 is mixed with a BNT precursor source, and then calcined at 500-700° C. to obtain the composite positive electrode active material.

[0021] In the present invention, by combining steps (1) and (2), a novel three-layer structure of an Al / La bimetallic doped core, an intermediate layer, and a BNT surface coating can be constructed. The material prepared by the preparation method has excellent capacity, rate capability, and long cycle performance, particularly excellent electrochemical performance under extreme conditions.

[0022] In the present invention, the positive electrode precursor and the Al source and La source are pre-calcined, and then the subsequent BNT precursor source is calcined. This can construct the core phase and structure of Al-La. In addition, it is also beneficial to further induce and adjust the Al-La hybrid intermediate layer and its phase structure during the calcination stage, thereby synergistically improving the electrochemical properties of the obtained material.

[0023] In the present invention, the positive electrode precursor may be a positive electrode precursor material known in the industry, for example, the positive electrode precursor is at least one of a transition metal oxide, a transition metal hydroxide, and a transition metal carbonate;

[0024] Preferably, the lithium source is at least one of lithium carbonate, lithium bicarbonate, and organic acid lithium;

[0025] Preferably, the Al source is at least one of oxides, nitrates, and organic acid salts.

[0026] Preferably, the La source is at least one of oxides, nitrates, and organic acid salts.

[0027] In the present invention, the compounding is solid phase compounding or liquid phase compounding.

[0028] Preferably, the molar ratio of the precursor source (calculated as TM (transition metal)) to the lithium source (calculated as Li) is 1:1 to 1.5.

[0029] Preferably, the Al source (calculated as Al) accounts for 0.1% to 3% of the molar amount of the precursor source, preferably 0.1% to 0.5%.

[0030] Preferably, the La source (calculated as La) is 0.1% to 3% of the molar amount of the precursor source, preferably 0.1 to 0.3%.

[0031] In the present invention, the calcination atmosphere in step (1) is an oxygen-containing atmosphere, which is at least one of oxygen, a mixture of oxygen and protective gas, and air. Considering the convenience of the preparation process and the effect of the obtained material, the calcination atmosphere is air.

[0032] In step (1), the roasting process includes a first roasting stage and a second roasting stage, wherein the temperature of the first roasting stage is 400-600° C.; preferably, the first roasting stage time is greater than or equal to 3 hours, preferably 5-8 hours;

[0033] Preferably, the temperature of the second stage calcination is 800-1000° C.; preferably, the second stage calcination time is greater than or equal to 10 hours, preferably 10 to 20 hours.

[0034] In step (2), the BNT precursor source includes a Na source, a Bi source, and a Ti source; which are one or more of the nitrates, sulfates, carbonates, acetates, chlorides, oxides, and organic salts of the respective elements.

[0035] Preferably, in the BNT precursor source, the molar ratio of Na, Bi and Ti is x:1-x:1, where x is the content of Na element and 0 <x<1;

[0036] Preferably, the molar ratio of the material 1 to the BNT precursor source is 1:0.001-0.15; preferably 1:0.01-0.05.

[0037] In the present invention, controlling the calcination temperature in step (2) is beneficial to forming a BNT layer with good morphology. In addition, it is also beneficial to further induce the phase and structure of the intermediate layer, thereby further synergistically improving the electrochemical properties of the prepared material.

[0038] Preferably, the calcination stage is carried out in an oxygen-containing atmosphere. The oxygen-containing atmosphere is at least one of oxygen, a mixture of oxygen and protective gas, and air. Considering the convenience of the preparation process and the effect of the obtained material, the calcination atmosphere is air.

[0039] Preferably, the temperature of the calcination stage is 650-700°C.

[0040] Preferably, the calcination time is 1 to 5 hours.

[0041] The preferred method for preparing the positive electrode active material of the present invention comprises the following steps:

[0042] (I) uniformly mixing a certain amount of an Al-containing compound, a La-containing compound and a lithium-ion battery cathode material precursor;

[0043] (II) The mixture is sintered in air or oxygen, firstly heat-treated at 400-600° C. for at least 3 hours, preferably 5-8 hours, and then heat-treated at 800-1000° C. for at least 10 hours to prepare Material 1.

[0044] (III) Dissolve the compound containing Bi, Na, and Ti in an ethanol / water mixed solution, mix uniformly for 2 hours, add material 1, and then mix for more than 1 hour. Evaporate at 60-80° C. to obtain a mixed powder.

[0045] (IV) sintering the mixed powder at 500-700° C. for at least 2 hours to obtain the composite positive electrode material.

[0046] The present invention also provides a use of the composite positive electrode active material as a positive electrode active material for a lithium-ion battery. Preferably, the composite positive electrode active material is used to prepare a positive electrode for a lithium-ion battery. Preferably, the composite positive electrode active material is used to prepare a positive electrode material for a lithium-ion battery.

[0047] The present invention can be used to prepare lithium-ion batteries and their positive electrode components using the positive electrode active material of the present invention, based on existing methods. For example, the positive electrode active material, binder, and conductive agent can be slurried and solidified to form a positive electrode by coating, and the positive electrode, separator, and negative electrode can be stacked to form a lithium-ion battery.

[0048] The present invention also provides a lithium ion battery containing the composite positive electrode active material.

[0049] Preferably, the positive electrode contains the composite positive electrode active material.

[0050] In the present invention, BNT is used to sinter and coat the bulk phase doped with La and Al, which can induce the formation of an intermediate layer and help adjust its phase and structure, improve the material level interface effect, and thus help to achieve the synergistic reduction of the covalency of TM-O, promote the localization of oxygen covalent electrons, improve the redox of cations and anions, and inhibit the irreversible phase change of the structure during the cycle; in addition, it is also beneficial to promote Li + of O n- The migration of the electrolyte into the electrolyte reduces the interfacial side reactions, thereby synergistically improving the cycle stability and rate performance of the material. At the same time, the material's ionic conductivity and electronic conductivity are also significantly improved.

[0051] Compared with the prior art, the advantages of the present invention are as follows:

[0052] 1. The present invention provides a novel Al-La hybrid core-intermediate layer@BNT composite cathode active material. Through the combined control of the materials and hierarchical structure, the capacity, rate, and cycle performance of the material can be synergistically improved, especially helping to improve the electrochemical performance of the material under extreme conditions such as high temperature and high current.

[0053] 2. The present invention pre-calcines the Al-La material and then calcines it with the BNT source. This is beneficial for regulating and inducing the physical phase and structure of the intermediate layer, and is beneficial for preparing the three-layer material while taking into account synergy. Through the preparation method, the electrochemical properties of the prepared material can be improved.

[0054] 3. The preparation process of the material of the present invention is simple, pollution-free, and low-cost, which is conducive to promoting the commercial application of the material. BRIEF DESCRIPTION OF THE DRAWINGS

[0055] Figure 1 XRD comparison patterns of Example 1 and Comparative Example 1;

[0056] Figure 2 HRTEM characterization images of Example 1 and Comparative Example 1;

[0057] Figure 3 Comparison of first cycle performance between Example 1 and Comparative Example 1 (0.1C, 2-4.7V);

[0058] Figure 4 Comparison of 500-cycle performance between Example 1 and Comparative Example 1 (2-4.65V);

[0059] Figure 5 Comparison of cycle performance between Example 1 and Comparative Example 1 (2-4.9V);

[0060] Figure 6 Comparison of rate performance between Example 1 and Comparative Example 1;

[0061] Figure 7 Performance comparison chart of Example 1 and Comparative Example 1 at 55°C (2-4.65V); DETAILED DESCRIPTION

[0062] Example 1:

[0063] Step (1):

[0064] 1g of lithium-rich manganese-based cathode material (Mn 0.53 Ni 0.27)CO3 precursor was mixed with Li2CO3(0.42 g), Al2O3(0.0033 g) and lanthanum nitrate (0.0036 g) and sintered in air at 500 °C (T1) for 5 h and then at 900 °C (T2) for 15 h to obtain material 1 (Li 1.165 Mn 0.530 Ni 0.266 Al 0.003 La 0.001 O2).

[0065] Step (2):

[0066] Material 1 was added to an ethanol / water solution of 0.0082 g bismuth nitrate, 0.0014 g sodium acetate and 0.01 g of tetrabutyl titanate, the coating chemical formula was Bi 0.5 Na 0.5 TiO3, mixed for 2 h, the solution was evaporated at 70 °C, the obtained solid powder was sintered in air, heated to 650 °C at a rate of 2 °C / min and kept for 3 h to obtain modified lithium-rich manganese-based positive electrode material Li 1.165 Mn 0.530 Ni 0.266 Al 0.003 La 0.001 O2@1% Bi 0.5 Na 0.5 TiO3. The XRD pattern of the prepared material is shown in Figure 1 , and the HRTEM pattern is shown in Figure 2 .

[0067] As can be seen from Figure 1 and Figure 2 , the material is composed of a layered main phase, an intermediate rock salt phase and a surface BNT coating phase, wherein the BNT is about 7 nm thick and the intermediate rock salt phase is about 2 nm thick.

[0068] Electrochemical performance determination:

[0069] The modified lithium-rich manganese-based positive electrode material finally prepared by the above method, acetylene black and PVDF were mixed at a mass ratio of 8:1:1 to prepare a slurry, which was uniformly coated on an aluminum foil, cut into positive electrode sheets with a diameter of 12 mm, lithium metal sheets were used as negative electrodes, Celgard 2400 was used as a separator, a 1M LiPF6 solution of EC / DMC (volume ratio 1:1) was used as an electrolyte, and CR2016 type button cells were assembled in an argon-filled glove box, which is the battery of Example 1.

[0070] As a result, the modified material can release an ultra-high specific capacity of about 260 mAh / g at a voltage of 2.0-4.7 V Figure 3), the capacity retention rate is 95% after 200 cycles at 2.0-4.65V voltage and 30℃, and 78.57% after 500 ultra-long cycles ( Figure 4 ).

[0071] In addition, this modification method increases the normal charge cut-off voltage (4.8V) of the lithium-rich material to 4.9V, and its capacity retention rate after 200 cycles at 4.9V and 30°C is 85.76% ( Figure 5 ), which is much better than the performance reported in Comparative Example 1 and other literature and patents.

[0072] The modified material can release a specific capacity of 160 mAh / g at an ultra-high rate of 10C ( Figure 6 ).

[0073] After 200 cycles at 2.0-4.65V and 55℃, the capacity retention rate is still 68% ( Figure 7 ).

[0074] Example 2:

[0075] Compared with Example 1, the only difference is that the ratio of Al and La is adjusted. The chemical formula of the prepared material 1 is Li 1.165 Mn 0.528 Ni 0.265 Al 0.005 La 0.002 O2, the chemical formula after coating is Li 1.165 Mn 0.528 Ni 0.265 Al 0.005 La 0.002 O2@1%Bi 0.5 Na 0.5 TiO3.

[0076] The battery was assembled in the manner of Example 1 and electrochemical performance was measured. The results were as follows: after 200 cycles at 2-4.65V and 30°C, the capacity retention rate was 94%, after 500 cycles, the capacity retention rate was 76%. After 200 cycles at 2-4.9V and 30°C, the capacity retention rate was 85%, and the release capacity at 10C was 155 mAh / g.

[0077] After 200 cycles at 2.0-4.65V and 55°C, the capacity retention rate is still 64%.

[0078] Example 3:

[0079] Compared with Example 1, the only difference is that the sintering mechanism of step 1 is changed, mainly the T2 temperature is changed. The difference in step 1 is: first sintering at 500°C for 5 hours and then sintering at 800°C for 15 hours. Other processes and operations are the same as Example 1.

[0080] The battery was assembled in the manner of Example 1 and electrochemical performance was measured. The results were as follows: after 200 cycles at 2-4.65 V and 30° C., the capacity retention rate was 91%, after 500 cycles, the capacity retention rate was 75%, after 200 cycles at 2-4.9 V and 30° C., the capacity retention rate was 71%, and the release capacity at 10 C was 149 mAh / g.

[0081] After 200 cycles at 2.0-4.65V and 55°C, the capacity retention rate is still 60%.

[0082] Example 4:

[0083] Compared with Example 1, the only difference is that the sintering mechanism of step 1 is changed, mainly the T2 temperature is changed. The difference in step 1 is: first sintering at 500°C for 5 hours and then sintering at 1000°C for 15 hours. Other processes and operations are the same as Example 1.

[0084] The battery was assembled in the manner of Example 1 and electrochemical performance was measured. The results were as follows: after 200 cycles at 2-4.65 V and 30° C., the capacity retention rate was 90%, after 500 cycles, the capacity retention rate was 65%, after 200 cycles at 2-4.9 V and 30° C., the capacity retention rate was 74%, and the release capacity at 10 C was 152 mAh / g.

[0085] After 200 cycles at 2.0-4.65V and 55°C, the capacity retention rate is still 61%.

[0086] Example 5:

[0087] Compared with Example 1, the only difference is that the raw material of BNT in step 2 is adjusted so that the content of the synthesized BNT coating is 5%, and the chemical formula after coating is Li 1.165 Mn 0.530 Ni 0.266 Al 0.003 La 0.001 O2@5%Bi 0.5 Na 0.5 TiO3.

[0088] The battery was assembled in the manner of Example 1 and electrochemical performance was measured. The results were as follows: after 200 cycles at 2-4.65 V and 30° C., the capacity retention rate was 89%, after 500 cycles, the capacity retention rate was 64%, after 200 cycles at 2-4.9 V and 30° C., the capacity retention rate was 72%, and the release capacity at 10 C was 151 mAh / g.

[0089] After 200 cycles at 2.0-4.65V and 55°C, the capacity retention rate is still 58%.

[0090] Example 6:

[0091] Compared with Example 1, the only difference is that the sintering temperature of the coating in step 2 is adjusted to 700° C., and the other processes and operations are the same as Example 1.

[0092] The battery was assembled in the manner of Example 1 and electrochemical performance was measured. The results were as follows: after 200 cycles at 2-4.65 V and 30° C., the capacity retention rate was 92%, after 500 cycles, the capacity retention rate was 74%, after 200 cycles at 2-4.9 V and 30° C., the capacity retention rate was 76%, and the release capacity at 10 C was 157 mAh / g.

[0093] After 200 cycles at 2.0-4.65V and 55°C, the capacity retention rate is still 63%.

[0094] Example 7:

[0095] Compared with Example 1, the only difference is that the sintering temperature of the coating in step 2 is adjusted to 500° C., and the other processes and operations are the same as Example 1.

[0096] The battery was assembled in the manner of Example 1 and electrochemical performance was measured. The results were as follows: after 200 cycles at 2-4.65 V and 30° C., the capacity retention rate was 91%, after 500 cycles, the capacity retention rate was 70%, after 200 cycles at 2-4.9 V and 30° C., the capacity retention rate was 70%, and the release capacity at 10 C was 150 mAh / g.

[0097] After 200 cycles at 2.0-4.65V and 55°C, the capacity retention rate is still 65.3%.

[0098] Example 8:

[0099] Compared with Example 1, the only difference is that the mixed materials are sintered in an oxygen atmosphere, and the obtained material 1 is a ternary material with the chemical formula of LiNi 0.799 Mn 0.097 Co 0.1 Al 0.003 La 0.001O2. After coating, the chemical formula is LiNi 0.799 Mn 0.097 Co 0.1 Al 0.003 La 0.001 O2@1%Bi 0.5 Na 0.5 TiO3.

[0100] The battery was assembled in the manner of Example 1 and the electrochemical performance was measured. The results were as follows: the capacity retention rate was 79% after 200 cycles at 2.8-4.3V and 30°C, and the capacity retention rate was 65% after 200 cycles at 2.8-4.5V and 30°C.

[0101] After 200 cycles at 2.8-4.3V and 55°C, the capacity retention rate is still 51.5%.

[0102] Comparative Example 1:

[0103] Compared with Example 1, the only difference is that in step 1, Al2O3 and lanthanum nitrate are not added, and step 2 is not performed. Other operations and parameters are the same as in Example 1. The chemical formula of the prepared material 1 is Li 1.165 Mn 0.533 Ni 0.267 O2.

[0104] The battery was assembled in the manner of Example 1 and the electrochemical properties were measured. The results were as follows: the initial discharge capacity was 235 mAh / g at 2-4.7 V, the capacity retention rate was 60.41% after 200 cycles at 2-4.65 V and 30°C, the capacity retention rate was 57.53% after 200 cycles at 2-4.9 V and 30°C, the release capacity was 115 mAh / g at 10C, and the capacity retention rate was 47% after 200 cycles at a high temperature of 2.0-4.65 V and 55°C.

[0105] Comparative Example 2:

[0106] Compared with Example 1, the only difference is that in step 1, no Al2O3 and lanthanum nitrate are added, and the subsequent step 2 is carried out. The chemical formula of the material finally obtained is Li 1.165 Mn 0.533 Ni 0.267 O2@1%Bi 0.5 Na 0.5 TiO3.

[0107] The battery was assembled in the manner of Example 1 and the electrochemical properties were measured. The results were as follows: the initial discharge capacity was 235 mAh / g at 2-4.7 V, the capacity retention rate was 79.1% after 200 cycles at 2-4.65 V and 30°C, the capacity retention rate was 67% after 200 cycles at 2-4.9 V and 30°C, the release capacity was 137 mAh / g at 10C, and the capacity retention rate was still 56.2% after 200 cycles at a high temperature of 2.0-4.65 V and 55°C.

[0108] Comparative Example 3:

[0109] Compared with Example 1, the only difference is that only Al is doped without adding La, and the molar amount of Al is the same as that of Example 1 (Al-La molar amount). Other processes and parameters are the same as Example 1.

[0110] The battery was assembled in the manner of Example 1 and the electrochemical properties were measured. The results were as follows: the capacity retention rate was 68% after 200 cycles at 2-4.65 V and 30°C, the capacity retention rate was 59% after 200 cycles at 2-4.9 V, the release capacity was 135 mAh / g at 10C, and the capacity retention rate was still 49.9% after 200 cycles at a high temperature of 2.0-4.65 V and 55°C.

[0111] Comparative Example 4:

[0112] Compared with Example 1, the only difference is that only La is doped without adding Al, and the molar amount of La is the same as that of Example 1 (Al-La molar amount). Other processes and parameters are the same as Example 1.

[0113] The battery was assembled in the manner of Example 1 and the electrochemical properties were measured. The results were as follows: the capacity retention rate was 72% after 200 cycles at 2-4.65 V and 30°C, the capacity retention rate was 63% after 200 cycles at 2-4.9 V and 30°C, the release capacity was 138 mAh / g at 10C, and the capacity retention rate was still 51.3% after 200 cycles at a high temperature of 2.0-4.65 V and 55°C.

[0114] Comparative Example 5:

[0115] Compared with Example 1, the only difference is that an equimolar amount of neodymium nitrate is used to replace the lanthanum nitrate, and the other processes and parameters are the same as those in Example 1.

[0116] The battery was assembled in the manner of Example 1 and the electrochemical properties were measured. The results were as follows: the capacity retention rate was 74% after 200 cycles at 2-4.65 V and 30°C, the capacity retention rate was 68% after 200 cycles at 2-4.9 V and 30°C, the release capacity was 143 mAh / g at 10C, and the capacity retention rate was still 53% after 200 cycles at a high temperature of 2.0-4.65 V and 55°C.

[0117] Comparative Example 6:

[0118] Compared with Example 1, the only difference is that the treatment in step 2 is not performed, and the other processes and parameters are the same as those in Example 1.

[0119] The battery was assembled in the manner of Example 1 and the electrochemical properties were measured. The results were as follows: the capacity retention rate was 89% after 200 cycles at 2-4.65 V and 30°C, the capacity retention rate was 65% after 200 cycles at 2-4.9 V and 30°C, the release capacity was 140 mAh / g at 10C, and the capacity retention rate was still 52.3% after 200 cycles at a high temperature of 2.0-4.65 V and 55°C.

[0120] Comparative Example 7:

[0121] Compared with Example 1, the only difference is that equimolar Ba 0.5 Na 0.5 TiO3 replaces the Bi 0.5 Na 0.5 TiO3, other processes and operations are the same as in Example 1, and the chemical formula of the final material is Li 1.165 Mn 0.530 Ni 0.26 6Al 0.003 La 0.001 O2@1%Ba 0.5 Na 0.5 TiO3.

[0122] The battery was assembled in the manner of Example 1 and the electrochemical properties were measured. The results were as follows: the capacity retention rate was 81% after 200 cycles at 2-4.65 V and 30°C, the capacity retention rate was 61% after 200 cycles at 2-4.9 V and 30°C, the release capacity was 139 mAh / g at 10C, and the capacity retention rate was still 54.3% after 200 cycles at a high temperature of 2.0-4.65 V and 55°C.

[0123] Comparative Example 8:

[0124] The steps are substantially the same as those in Example 1, with the only difference being that the calcination temperature in step 2 is 400° C. The other processes and operations are the same as those in Example 1.

[0125] The battery was assembled in the manner of Example 1 and the electrochemical properties were measured. The results were as follows: after 200 cycles at 2-4.65 V and 30°C, the capacity retention rate was 65%, after 200 cycles at 2-4.9 V and 30°C, the capacity retention rate was 60%, the release capacity at 10C was 133 mAh / g, and after 200 cycles at a high temperature of 2.0-4.65 V and 55°C, the capacity retention rate was still 50.5%.

[0126] Comparative Example 9:

[0127] The steps are substantially the same as those in Example 1, with the only difference being that the calcination temperature in step 2 is 800° C. The other processes and operations are the same as those in Example 1.

[0128] The battery was assembled in the manner of Example 1 and the electrochemical properties were measured. The results were as follows: after 200 cycles at 2-4.65 V and 30°C, the capacity retention rate was 63%, after 200 cycles at 2-4.9 V and 30°C, the capacity retention rate was 61%, the release capacity at 10C was 134 mAh / g, and after 200 cycles at a high temperature of 2.0-4.65 V and 55°C, the capacity retention rate was still 49.4%.

Claims

1. A method for preparing a composite positive electrode active material, characterized in that: The following steps are involved: Step (1): A positive electrode precursor, a lithium source, an Al source, and a La source are combined and then calcined to obtain material 1; the positive electrode precursor is at least one of a transition metal oxide, a transition metal hydroxide, and a transition metal carbonate; the molar ratio of the positive electrode precursor to the lithium source is 1:1-1.5; the Al source is 0.1%-3% of the molar amount of the positive electrode precursor; the La source is 0.1%-3% of the molar amount of the positive electrode precursor; Step (2): The material 1 is mixed with a BNT precursor source, and then calcined at 500-700° C. to obtain the composite positive electrode active material; The BNT precursor source includes a Na source, a Bi source, and a Ti source; which is one or more of the nitrates, sulfates, carbonates, acetates, chlorides, oxides, and organic salts of each element; In the BNT precursor source, the molar ratio of Na, Bi and Ti is x:1-x:1, where x is the content of Na element and 0 <x<1; The molar ratio of the material 1 to the BNT precursor source is 1:0.001-0.15; The composite positive electrode active material is an Al-La doped core-intermediate layer@BNT, comprising a core, an intermediate layer covering the core, and a shell covering the intermediate layer. The core and intermediate layer are positive electrode active materials doped with Al and La bimetallic materials, wherein the core is a layered structure material and the intermediate layer has a spinel phase and / or a rock salt phase. The shell is made of sodium bismuth titanate material; In steps (1) and (2), the atmosphere during the calcination stage is air.

2. The method for preparing a composite positive electrode active material according to claim 1, wherein: In the core and the intermediate layer materials, the molar content of Al and La in the total metal is 0.1-0.5 mol%; The chemical formula of the material of the core and the intermediate layer is Li 1.2-x TM 1-y M d O 2-z , where 0 < x < 0.3, 0 < y < 0.2, 0 < z < 0.4, TM is a transition metal, M is a doping element La and Al, and 0 < d / (1 - y) < 8%; The chemical formula of the sodium bismuth titanate material is Na x Bi 1-x TiO3, of which 0 <x<1。 3. The method for preparing a composite positive electrode active material according to claim 1, wherein: In step (1), the lithium source is at least one of lithium carbonate, lithium bicarbonate, and lithium hydroxide; The Al source is at least one of oxides, nitrates, and organic acid salts; The La source is at least one of oxides, nitrates, and organic acid salts.

4. The method for preparing a composite positive electrode active material according to claim 1, wherein: The compounding is solid phase compounding or liquid phase compounding.

5. The method for preparing a composite positive electrode active material according to claim 1, wherein: In step (1), the roasting process includes a first roasting stage and a second roasting stage, wherein the temperature of the first roasting stage is 400-600°C; the temperature of the second roasting stage is 800-1000°C.

6. The method for preparing a composite positive electrode active material according to claim 5, wherein: In step (1), the first roasting time is 5 to 8 hours; The second roasting time is 10~20h.

7. A composite positive electrode active material prepared by the preparation method according to any one of claims 1 to 6.

8. An application of a composite positive electrode active material prepared by the preparation method according to any one of claims 1 to 6, characterized in that: Used as positive electrode active material in lithium-ion batteries.

9. The use according to claim 8, characterized in that It is used to prepare the positive electrode of lithium-ion batteries.

10. The use according to claim 9, characterized in that It is used to prepare positive electrode materials for lithium-ion batteries.

11. A lithium ion battery, characterized in that: A composite positive electrode active material prepared by the preparation method according to any one of claims 1 to 6.

12. The lithium-ion battery according to claim 11, wherein The positive electrode contains the composite positive electrode active material.

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