Zinc-containing positive active material, preparation method thereof, positive plate and battery

Abstract

The invention provides a zinc-containing positive electrode active material and a preparation method thereof, a positive plate and a battery. The positive electrode active material comprises a zinc-containing positive electrode active material matrix and an oxide coating layer which coats the surface and comprises trivalent metal elements, a Zn element is doped in a zinc-containing positive electrode active material matrix, and an anti-position defect is introduced, so that the structural stability is improved; according to the zinc-containing positive electrode active material, a core-shell + concentration gradient structure is adopted, a first circular ring region (with the Zn content of 0.2-3%) serves as a transition layer, the concentration change between a sphere center region (with the Zn content of 0.3-6%) and a second circular ring region (with the Zn content of 0-1%) is smoothed, Zn element dissolution is reduced, and cracking caused by too large deformation difference of materials in a Zn-rich region and a Zn-poor region during charging and discharging can also be avoided. In addition, the oxide coating layer can capture dissolved Zn ions, and Zn element dissolution is further reduced. The synergistic effect improves the cycle life of the material and the battery capacity retention ratio.

Description

Technical Field

[0001] This invention relates to the field of batteries, and more particularly to a zinc-containing positive electrode active material, its preparation method, a positive electrode sheet, and a battery. Background Technology

[0002] With the rapid development of new energy vehicles and energy storage technologies, the energy density and cycle life of lithium-ion batteries have become key performance indicators. High-nickel or ultra-high-nickel cathode active materials have become a research hotspot due to their high specific capacity characteristics.

[0003] As the battery undergoes charge-discharge cycles, the crystal structure of high-nickel cathode active materials, especially ultra-high-nickel cathode materials, is prone to change. Throughout the charging process, the layered material gradually transitions from the O3 phase through the H1~3 phases, eventually becoming the O1 phase, with its volume initially increasing and then decreasing. This volume change within the particles induces internal stress, leading to particle breakage or microcrack formation, thus shortening the battery's cycle life.

[0004] Therefore, improving the cycle stability of high-nickel cathode active materials is an urgent problem to be solved. Summary of the Invention

[0005] This application provides a zinc-containing positive electrode active material and its preparation method, a positive electrode sheet, and a battery, thereby improving the cycle stability of high-nickel positive electrode active materials.

[0006] This application provides a zinc-containing positive electrode active material, comprising: a zinc-containing positive electrode active material matrix and an oxide coating layer covering at least a portion of the surface of the zinc-containing positive electrode active material matrix, wherein the oxide coating layer comprises a trivalent metal element;

[0007] The zinc-containing positive electrode active material is divided into three parts by a cross-section through the center of the sphere: a central region, a first annular region, and a second annular region. The first annular region is located between the central region and the second annular region. The annular width of the second annular region is 1 μm, and the annular width of the first annular region is 1 μm.

[0008] In the first annular region, the first molar percentage of Zn element among transition metal elements is 0.2% to 3%;

[0009] In the second annular region, the second molar percentage of Zn element among transition metal elements is 0% to 1%;

[0010] In the central region of the sphere, the third molar percentage of Zn element among transition metal elements is 0.3% to 6%;

[0011] The third molar percentage is greater than the first molar percentage, and the first molar percentage is greater than the second molar percentage.

[0012] Furthermore, the difference between the third molar percentage and the first molar percentage is less than 2%.

[0013] Furthermore, the molar percentage of Zn element in the second annular region is less than 20% of the Zn element in the zinc-containing positive electrode active material.

[0014] Furthermore, the chemical formula of the zinc-containing positive electrode active material is Li x Ni a Co b Mn c Zn y M z O m N n Wherein, 0.95≤x≤1.10, 0.6≤a≤1, 0≤b≤0.15, 0≤c≤0.35, 0.001≤y≤0.03, 0≤z≤0.02, 0≤n≤0.001, a+b+c+y+z=1, m+n=2, element M is selected from one or more of Na, Mg, Sc, Al, Ti, Ga, V, Cr, Fe, Y, Zr, Nb, Mo, Ta, and W, and element N is selected from one or more of F, Cl, Br, and S;

[0015] And / or, the first molar percentage is 0.2% to 1.18%, the second molar percentage is 0% to 0.65%, and the third molar percentage is 0.37% to 2.51%;

[0016] And / or, some Zn elements occupy Li element sites.

[0017] Furthermore, the oxide coating layer includes one or more of Al2O3, Cr2O3, Fe3O4, Ga2O3, and Mn2O3;

[0018] And / or, the oxide coating layer accounts for 0.16% to 1.11% of the mass percentage of the zinc-containing positive electrode active material.

[0019] Furthermore, the particle size Dv50 of the zinc-containing positive electrode active material is 9 μm ~ 18 μm;

[0020] And / or, the specific surface area of ​​the zinc-containing positive electrode active material is between 0.2 and 0.6 m². 2 / g;

[0021] And / or, the positive electrode active material satisfies 0.19≤I1(003)-I2(003)≤0.56, where I1 is the 2θ angle of the 003 peak of the positive electrode active material when the battery prepared by the positive electrode active material is charged to 100% SOC, and I2 is the 2θ angle of the 003 peak of the positive electrode active material when the battery prepared by the positive electrode active material is charged to 50% SOC, as determined by XRD.

[0022] Secondly, this application provides a method for preparing the zinc-containing positive electrode active material according to any one of the first aspects, comprising the following steps:

[0023] A first coprecipitation reaction is carried out between a first Zn source aqueous solution and a first other transition metal source aqueous solution to obtain a first hydroxide precursor core; in the first coprecipitation reaction, the molar percentage of Zn element in the first Zn source aqueous solution is 0.3% to 6% of the total molar percentage of the transition metal elements; the first other transition metal source aqueous solution includes nickel source, cobalt source, and manganese source;

[0024] A second Zn source aqueous solution and a second other transition metal source aqueous solution are introduced into a system including the first hydroxide precursor core to carry out a second coprecipitation reaction, thereby obtaining the second hydroxide precursor core. In the second coprecipitation reaction, the molar percentage of Zn element in the second Zn source aqueous solution relative to the total transition metal elements is 0.2-3%. The molar amount of Zn element in the second Zn source aqueous solution is less than the molar amount of Zn element in the first Zn source aqueous solution. The second other transition metal source aqueous solution includes a nickel source, a cobalt source, and a manganese source.

[0025] A third aqueous solution of another transition metal source is introduced into a system including the second hydroxide precursor core to perform a third coprecipitation and obtain a third hydroxide precursor core; the third aqueous solution of another transition metal source includes a nickel source, a cobalt source, and a manganese source.

[0026] The mixture of the third hydroxide precursor core, the doping element source, and the lithium source was sintered at 650~800℃ to obtain a zinc-containing cathode active material intermediate product.

[0027] The zinc-containing positive electrode active material intermediate product is mixed with a trivalent metal source and then sintered a second time at 600~700℃ to obtain the zinc-containing positive electrode active material.

[0028] Further, the step of mixing the zinc-containing positive electrode active material intermediate with a trivalent metal source and then performing a second sintering at 600-700°C to obtain the zinc-containing positive electrode active material includes:

[0029] The zinc-containing positive electrode active material intermediate product and the trivalent metal alkoxide were dispersed and mixed in an alcohol solvent atmosphere to obtain a dispersion.

[0030] The dispersion was sintered a second time at 600-700°C to obtain a zinc-containing positive electrode active material.

[0031] Thirdly, this application provides a positive electrode sheet, which includes the zinc-containing positive electrode active material as described in any one of the first aspects, or the zinc-containing positive electrode active material prepared by the preparation method described in the second aspect.

[0032] Fourthly, this application provides a battery comprising the positive electrode plate described in the third aspect.

[0033] The zinc-containing positive electrode active material of this application includes a zinc-containing positive electrode active material matrix and an oxide coating layer covering at least a portion of the surface of the zinc-containing positive electrode active material matrix. The oxide coating layer includes a trivalent metal element. The zinc-containing positive electrode active material is divided into a core region, a first annular region, and a second annular region through a cross-section of the core. The first annular region is located between the core region and the second annular region. The second annular region has a ring width of 1 μm, and the first annular region has a ring width of 1 μm. In the core region, the third molar percentage of Zn element in the transition metal element is 0.3% to 6%. In the first annular region, the first molar percentage of Zn element in the transition metal element is 0.2% to 3%. In the second annular region, the second molar percentage of Zn element in the transition metal element is 0% to 1%. The third molar percentage is greater than the first molar percentage, and the first molar percentage is greater than the second molar percentage. On the one hand, by doping with Zn, an appropriate amount of antisite defects are introduced into the bulk phase, which improves the structural stability, reduces microcracks in the material particles caused by charging and discharging, and improves the cycle life and capacity retention of the material. On the other hand, a core-shell structure with a concentration gradient is adopted. The first annular region (Zn content 0.2~3%) serves as a transition layer, smoothing the concentration change between the central region (Zn content 0.3~6%) and the second annular region (Zn content 0~1%). This reduces Zn dissolution and stress concentration at the Zn concentration gradient interface, preventing excessive deformation differences between the Zn-rich and Zn-poor regions during charging and discharging, which could lead to particle cracking. Furthermore, the oxide coating layer can capture dissolved Zn ions, further reducing Zn dissolution. These synergistic effects collectively improve the material's cycle life and battery capacity retention. Attached Figure Description

[0034] Figure 1 This is a schematic diagram of the structure of the zinc-containing positive electrode active material provided in this application;

[0035] Figure 2 This is a schematic diagram showing the distribution of different regions of the zinc-containing positive electrode active material in Example 1;

[0036] Figure 3The image shows the XRD pattern of the positive electrode active material of Comparative Example 1 at 100% SOC.

[0037] Figure 4 The image shows the XRD pattern of the positive electrode active material of Comparative Example 1 at 50% SOC.

[0038] Figure 5 This is a cross-sectional test example diagram of Example 2;

[0039] Figure 6 This is a Zn element distribution diagram for Example 2. Detailed Implementation

[0040] To make the objectives, technical solutions, and advantages of this application clearer, the technical solutions in the embodiments of this application will be clearly and completely described below in conjunction with the embodiments of this application. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0041] High-nickel and ultra-high-nickel materials mainly have the following problems:

[0042] (1) Changes in crystal structure: As the battery charge and discharge cycles proceed, the crystal structure of the positive electrode active material is prone to change. During the entire charging process, the layered material gradually changes from the O3 phase through the H1~3 phase, and finally becomes the O1 phase, with the volume first increasing and then decreasing.

[0043] (2) Internal stress of particles: High nickel content increases the inhomogeneity inside the lattice. Especially during deep charge and discharge, large volume changes will occur inside the particles, causing internal stress, which in turn leads to particle breakage or microcrack formation, shortening the cycle life of the battery.

[0044] (3) Surface phase transition: At high potential, the surface of the positive electrode active material is prone to oxidation, forming unstable phases such as rock-salt phase or spinel phase. These phase transitions will destroy the original layered structure, reduce the number of active lithium sites, and lead to irreversible capacity loss.

[0045] Therefore, introducing an appropriate amount of lithium ion and transition metal mixture (antisite defects) into the bulk phase helps maintain structural stability and improve battery capacity retention and cycle life. The formation of antisite defects can generate a pillar effect, hindering the relative movement between transition metal layers, i.e., preventing the formation of H1~3 phases, and also preventing the lattice change along the c-axis of the layered cathode material during charge and discharge. Calculation results show that the formation energy of Li / Zn mixture is only about half that of Li / Ni mixture, and the ionic radius of Zn is more suitable for entering Li layer sites. Therefore, by doping with Zn, an appropriate amount of antisite defects can be introduced into the bulk phase, improving structural stability, reducing microcracks in material particles caused by charge and discharge, and improving the material's cycle life and capacity retention. However, the presence of Zn may cause Zn ions to dissolve from the cathode material, forming Zn metal when the voltage reaches the redox potential of Zn ions. The movement of metallic Zn between the positive and negative electrodes may cause short circuits or puncture of the separator, reducing the battery's cycle stability and posing a safety risk. Therefore, a reverse Zn concentration gradient doping is formed by utilizing the high Zn concentration core inside the positive electrode active material and the low Zn concentration shell on the outer layer of the material. Through this structure, the Zn concentration in the core is relatively uniform, resulting in relatively uniform stress and strain under stress, thus improving structural stability, while the low Zn concentration shell on the outer layer reduces Zn dissolution.

[0046] Figure 1 This is a schematic diagram of the structure of the zinc-containing positive electrode active material provided in this application, as shown below. Figure 1 As shown, the zinc-containing positive electrode active material is divided into three parts by a cross-section through the center of the sphere: the center region, the first annular region, and the second annular region. The first annular region is located between the center region and the second annular region. The annular width of the second annular region is 1 μm, and the annular width of the first annular region is 1 μm.

[0047] In the central region, Zn accounts for 0.3% to 6% of the third molar percentage of transition metal elements.

[0048] In the first circular region, Zn accounts for 0.2% to 3% of the first molar percentage of transition metal elements.

[0049] In the second ring region, the Zn element accounts for 0% to 1% of the second molar percentage of transition metal elements.

[0050] The third molar percentage is greater than the first molar percentage, and the first molar percentage is greater than the second molar percentage.

[0051] The Zn ion radius is 0.74 Å, close to the Li ion radius of 0.76 Å. Therefore, Zn can preferentially occupy Li layer sites, forming stable Li / Zn antisite defects. First-principles calculations also show that Zn readily occupies Li sites. This application uses Zn as a dopant element, with the Zn element in the core region accounting for 0.3% to 6% of the third molar percentage of the transition metal element, for example, 0.3%, 0.5%, 1%, 2%, 3.5%, 5%, 6%, or any combination thereof. Within this range, the Zn element in the core region controls the Li / Zn antisite defect ratio to a suitable range, improving the material's structural stability and capacity retention, and reducing material strain during charge and discharge.

[0052] The zinc-containing cathode active material comprises a zinc-containing cathode active material matrix and an oxide coating layer covering at least a portion of the surface of the zinc-containing cathode active material matrix; the oxide coating layer comprises a trivalent metal element. The oxide coating layer effectively isolates the electrolyte from the zinc-containing cathode active material, reduces interfacial side reactions, and extends the lifespan of the zinc-containing cathode active material. The trivalent metal oxide more readily captures Zn ions, forming a spinel phase structure of AB₂O₄, reducing Zn ion dissolution; wherein, the A-site is a captured divalent element, and the B-site is a trivalent metal element in the oxide.

[0053] Specifically, the oxide can be selected from one or more of Al2O3, Cr2O3, Fe3O4, Ga2O3, and Mn2O3.

[0054] This application introduces a first annular region as a transition layer. In this first annular region, the first molar percentage of Zn element in the transition metal element can be 0.2%, 0.5%, 1%, 1.5%, 2%, 2.5%, 3%, or any combination thereof. The first annular region smooths the concentration change between the central region (Zn content 0.3~6%) and the second annular region (Zn content 0~1%), reducing stress concentration at the interface and thus effectively reducing the risk of particle cracking. In the second annular region, the second molar percentage of Zn element in the transition metal element can be 0%, 0.25%, 0.5%, 0.75%, 1.0%, or any combination thereof. Through Zn doping, the resulting Li / Zn antisite defects can also improve the structural stability of the second annular region.

[0055] In a simple core-shell structure, the abrupt change in Zn concentration between the Zn-rich core and the Zn-depleted shell can lead to significant differences in deformation during charging and discharging, easily causing stress concentration within the particles and resulting in cracking. In this application, the first annular region acts as a transition layer, preventing excessive differences in deformation between the Zn-rich and Zn-depleted regions during charging and discharging, which could lead to particle cracking.

[0056] In one implementation, Zn is uniformly distributed in the core region. This uniform Zn distribution stabilizes the crystal structure within the core region, ensuring its consistency. Therefore, the relatively uniform Zn distribution in the core results in a more uniform stress distribution, leading to more consistent volume expansion / contraction during charging and discharging within the core region. This reduces internal stress concentration and improves long-term cycle stability. Furthermore, the uniform Zn distribution in the core ensures consistent electronic / ionic conductivity, reducing local performance differences and contributing to stable capacity output.

[0057] In some embodiments, the difference between the third molar percentage of Zn element in the sphere core region and the first molar percentage of Zn element in the first annular region is less than 2%, so as to reduce the interfacial stress between the sphere core region and the first annular region and improve cycle stability.

[0058] In some embodiments, the molar percentage of Zn element in the second annular region relative to the Zn element in the zinc-containing cathode active material is less than 20%. For example, 0%, 2%, 5%, 10%, 15%, 19%, or any combination thereof. Having less than 20% Zn in the second annular region helps prevent Zn leaching and avoids excessive Zn doping from hindering the Li ion diffusion path.

[0059] Preferably, the first molar percentage is 0.2%~1.18%, the second molar percentage is 0%~0.65%, and the third molar percentage is 0.37%~2.51%. Within this range, the effect of inhibiting the leaching of Zn is better.

[0060] In some scenarios, zinc-containing cathode active materials are not perfectly spherical. For example, if damage occurs during the crushing process, it is necessary to repair the damaged area according to the spherical structure, divide the cross-section through the center of the sphere into three regions, and then further confirm the values ​​of the corresponding regions.

[0061] In some embodiments, the chemical formula of the zinc-containing positive electrode active material is Li x Ni a Co b Mn c Zn y M z O m N nWherein, 0.95≤x≤1.10, 0.6≤a≤1, 0≤b≤0.05, 0≤c≤0.05, 0.001≤y≤0.03, 0≤z≤0.02, 0≤n≤0.001, m+n=2, a+b+c+d+y+z=1, element M is selected from one or more of Na, Mg, Sc, Al, Ti, V, Cr, Fe, Y, Zr, Nb, Mo, Ta, W, and element N is selected from one or more of F, Cl, Br, S.

[0062] In some embodiments, the particle size Dv50 of the zinc-containing cathode active material is 9~18 μm. For example, 9 μm, 11 μm, 12 μm, 13.5 μm, 15 μm, 18 μm, or any combination thereof. A particle size within this range is beneficial for increasing the compaction density of the cathode material. Furthermore, the ring width of the first annular region is 1 μm, the ring width of the second annular region is 1 μm, and the ring width of both annular regions is 2 μm. To enhance the ability of the sphere-centered region to improve the structural stability of the material through Li / Zn antisite defects, the radius of the sphere-centered region is larger than the ring width of the two annular regions; therefore, the particle size Dv50 of the zinc cathode active material is greater than 9 μm. A particle size Dv50 less than 18 μm avoids the problem of restricted Li ion diffusion caused by excessively large particles.

[0063] In some embodiments, the specific surface area of ​​the zinc-containing positive electrode active material is between 0.2 and 0.6 m². 2 / g. For example, 0.2 m 2 / g, 0.3 m 2 / g, 0.35 m 2 / g, 0.4 m 2 / g, 0.45 m 2 / g, 0.5 m 2 / g, 0.6 m 2 / g, or any combination of the above. A specific surface area (0.2~0.6 m² / g) corresponds to a smoother particle surface, which is beneficial for reducing the contact area between the cathode material and the electrolyte, thereby reducing interfacial side reactions.

[0064] In some embodiments, the coating layer includes Al. Al is a redox inert element. Coating the outer layer with Al can effectively isolate the electrolyte from contact with the zinc-containing positive electrode active material, reduce interfacial side reactions, and improve the lifespan of the zinc-containing positive electrode active material.

[0065] In some embodiments, the oxide of the coating layer is Al2O3. In one specific implementation, Al2O3 is in a nanocrystalline state, possesses high chemical activity, is not subject to oxidation-reduction, and can effectively capture dissolved Zn. 2+This process forms a ZnAl2O4 spinel phase. This spinel phase has good affinity with the surface of ternary materials, making it less likely for the coating to detach. At the same time, ZnAl2O4 (band gap 3.8~3.9 eV) has a higher electrical conductivity than Al2O3 (band gap 8~9 eV), which can reduce the interfacial impedance of the material.

[0066] In some embodiments, the coating layer accounts for 0.16% to 1.11% of the zinc-containing positive electrode active material by mass. Within this mass percentage range, the coating layer effectively isolates the active material from the electrolyte, reducing the risk of oxygen release or thermal decomposition, while not significantly increasing Li ion diffusion resistance, thus balancing rate performance and cycle stability.

[0067] In some embodiments, the thickness of the coating layer is less than 100 nm. For example, 5 nm, 20 nm, 40 nm, and 80 nm. A thin coating layer (<100 nm) can effectively isolate the cathode material from the electrolyte, reduce zinc ion dissolution and surface side reactions; it also has lower diffusion resistance to Li ions, which is beneficial for rate performance and fast charge / discharge capability, and avoids the ion transport limitation problem that may be caused by a thick coating layer.

[0068] This application also provides a method for preparing a zinc-containing positive electrode active material, comprising the following steps:

[0069] S1. A first coprecipitation reaction is carried out between the first Zn source aqueous solution and the first other transition metal source aqueous solution to obtain the first hydroxide precursor core; in the first coprecipitation reaction solution, the molar percentage of Zn element in the first Zn source aqueous solution relative to the total transition metal elements is 0.3%~6%. The first other transition metal source aqueous solution includes nickel source, cobalt source, and manganese source.

[0070] S2. A second Zn source aqueous solution and a second other transition metal source aqueous solution are introduced into the system containing the first hydroxide precursor core to carry out a second coprecipitation reaction, obtaining the second hydroxide precursor core. In the second coprecipitation reaction solution, the molar percentage of Zn element in the second Zn source aqueous solution relative to the total transition metal elements is 0.2-3%; the molar amount of Zn element in the second Zn source aqueous solution is less than the molar amount of Zn element in the first Zn source aqueous solution. The second other transition metal source aqueous solution includes nickel source, cobalt source, and manganese source.

[0071] S3. A third aqueous solution of another transition metal source is introduced into the system containing the second hydroxide precursor core to perform a third coprecipitation, thereby obtaining the third hydroxide precursor core. The third aqueous solution of another transition metal source includes nickel, cobalt, and manganese sources.

[0072] S4. The mixture of the third hydroxide precursor core, the dopant source and the lithium source is sintered at 650~800℃ to obtain a zinc-containing cathode active material intermediate.

[0073] S5. After mixing the zinc-containing positive electrode active material intermediate with a trivalent metal source, a second sintering is carried out at 600~700℃ to obtain the zinc-containing positive electrode active material.

[0074] By controlling the amount of Zn added during precursor synthesis, the Zn content is maximized in the core region. No Zn is added to the outermost second ring region during precursor synthesis; instead, Zn diffuses from the inner core region and the first ring region to the second ring region via sintering, thus obtaining the aforementioned structure of the zinc-containing positive electrode active material.

[0075] In step S4, the dopant element in the dopant source is selected from one or more of Na, Mg, Sc, Al, Ti, Ga, V, Cr, Fe, Y, Zr, Nb, Mo, Ta, W, F, Cl, Br, and S.

[0076] In one implementation of step S5, the zinc-containing positive electrode active material is first dispersed in an alcohol solvent (e.g., ethanol), ultrasonically dispersed, and then a trivalent metal alkoxide is added for further dispersion and mixing (e.g., stirring for 2 hours) to obtain a dispersion. Subsequently, rotary evaporation is performed to obtain the process product. The process product is then subjected to a second sintering at 600-700°C to obtain a nickel-containing positive electrode active material coated with Al₂O₃ in a nanocrystalline state.

[0077] One specific preparation method includes the following steps:

[0078] Step 1: Weigh the Zn salt, Mn salt, Co salt and Ni salt according to the stoichiometric ratio, and prepare aqueous solutions of the salts respectively.

[0079] Step 2: Aqueous solutions of the four salts, a complexing agent, and a precipitant are added to the reactor under stirring to complete the first coprecipitation reaction, yielding the precursor core P1. Subsequently, the proportion of the Zn salt aqueous solution is reduced, and precursor core P1, Zn salt aqueous solution, nickel-cobalt-manganese salt aqueous solution, complexing agent aqueous solution, and precipitant aqueous solution are added simultaneously to complete the second coprecipitation reaction, yielding a nickel-cobalt-manganese-zinc hydroxide precursor core P2 with Zn reverse concentration gradient doping.

[0080] Step 3: Add Zn reverse concentration gradient doped precursor core P2, aqueous solutions of nickel, cobalt, and manganese salts, aqueous solutions of complexing agent and precipitant to complete the third coprecipitation reaction and form precursor P3 with nickel cobalt manganese hydroxide coating nickel cobalt manganese zinc hydroxide core.

[0081] Step 4: Drying to obtain the Zn inverse concentration gradient doped precursor P4.

[0082] Step 5: Mix the obtained precursor P4 and M element additive with the lithium source, and perform the first sintering at 650~800℃ in an atmosphere containing >95% oxygen to obtain Zn reverse concentration gradient doped ultra-high nickel cathode material P5.

[0083] Step 6: Disperse the positive electrode material P5 in ethanol, ultrasonically disperse it, add Al source solution, and then perform rotary evaporation to obtain the positive electrode material P6.

[0084] Step 7: The above cathode material P6 is sintered for the second time at 600~700℃ to obtain Al2O3-coated ultra-high nickel cathode material P7.

[0085] Through the above preparation steps, the zinc-containing positive electrode active material with the aforementioned Zn element distribution can be prepared.

[0086] This application also provides a positive electrode sheet, which includes any of the zinc-containing positive electrode active materials described above, or includes the zinc-containing positive electrode active material prepared by the above preparation method.

[0087] The positive electrode sheet of this application specifically includes a positive current collector and a positive active layer formed of positive active material disposed on the surface of the positive current collector.

[0088] In the specific preparation of the positive electrode sheet, for example, the positive electrode active material of this application can be dispersed with a conductive agent and a binder in an appropriate amount of N-methylpyrrolidone (NMP) solvent, and thoroughly stirred to form a uniform positive electrode slurry; the positive electrode slurry is uniformly coated on the positive electrode current collector, and after drying, rolling and slitting, the positive electrode sheet is obtained. In one specific embodiment, the positive electrode active layer comprises, by mass percentage, 70-99 wt% of positive electrode active material, 0.5-15 wt% of conductive agent, and 0.5-15 wt% of binder, and further comprises 80-98 wt% of positive electrode active material, 1-10 wt% of conductive agent, and 1-10 wt% of binder.

[0089] The positive current collector can be made of at least one of aluminum foil or nickel foil; the conductive agent can be selected from at least one of carbon black, acetylene black, graphene, Ketjen black, and carbon fiber; and the binder can be selected from at least one of polytetrafluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, polyethylene, polypropylene, polyvinyl alcohol, carboxymethyl cellulose, hydroxypropyl cellulose, diacetyl cellulose, polyvinyl chloride, carboxylated polyvinyl chloride, ethylene oxide-containing polymers, polyvinylpyrrolidone, and polyurethane.

[0090] This application also provides a battery including the above-described positive electrode.

[0091] It is conceivable that, in addition to the aforementioned positive electrode, the lithium-ion battery of this application also includes a negative electrode, an electrolyte, and a separator.

[0092] This application does not strictly limit the negative electrode active material in the negative electrode sheet. It can be at least one of the negative electrode active materials commonly used in lithium-ion batteries, such as graphite, hard carbon, soft carbon, mesophase carbon microspheres, silicon-based negative electrode materials (mainly including silicon suboxide and silicon-carbon negative electrode), and tin-based negative electrode materials (mainly including tin and tin alloy).

[0093] This application does not strictly limit the choice of electrolyte, which may include one or more solvents commonly used in lithium-ion battery electrolytes, as well as lithium salts commonly used in lithium-ion electrolytes. For example, the solvent may be ethylene carbonate, propylene carbonate, butene carbonate, fluoroethylene carbonate (FEC), dimethyl carbonate (DMC), diethyl carbonate (DEC), difluoroethylene carbonate (DFEC), dipropyl carbonate, methyl ethyl carbonate (EMC), ethyl acetate, ethyl propionate, propyl acetate, propyl propionate, sulfolane, γ-butyrolactone, etc.; the lithium salt may be one or more of lithium hexafluorophosphate (LiPF6), lithium bis(fluorosulfonyl)imide (LiFSI), and lithium bis(trifluoromethanesulfonyl)imide (LiTFSI).

[0094] This application does not strictly limit the choice of separator material. It can be one of the separator materials commonly used in lithium-ion batteries, such as polypropylene separator (PP), polyethylene separator (PE), polypropylene / polyethylene double-layer composite membrane (PP / PE), polyimide electrospun separator (PI), polypropylene / polyethylene / polypropylene triple-layer composite membrane (PP / PE / PP), cellulose nonwoven separator, and separator with ceramic coating.

[0095] In the preparation of lithium-ion batteries, the positive electrode, separator, and negative electrode are wound or stacked to obtain a bare cell, which is then packaged into a pre-stamped aluminum-plastic film bag. After the packaged battery is dried at 85°C, the electrolyte is injected into the dried battery. The battery undergoes resting, formation, and secondary sealing to complete the preparation of the lithium-ion battery.

[0096] The present application will be further described below through specific embodiments.

[0097] Example 1

[0098] The preparation method of the zinc-containing positive electrode active material in this embodiment includes the following steps:

[0099] Step 1: Weigh ZnSO4 salt, NiSO4 salt, CoSO4 salt, MnSO4 salt, and Al(OEt)3 according to the molar proportions of Zn, Ni, Co, Mn, and Al of 0.2%, 90%, 5%, 4.5%, and 0.3%, respectively. Prepare nickel-cobalt-manganese salt aqueous solutions from NiSO4, CoSO4, and MnSO4 salts; prepare an ethanol solution from Al salt; and prepare a Zn salt aqueous solution from ZnSO4 salt. Divide the nickel-cobalt-manganese salt aqueous solution into three portions according to a volume ratio of 3:3:4; and divide the Zn salt aqueous solution into two portions according to a volume ratio of 7:3.

[0100] Step 2: The first portion of nickel cobalt manganese salt aqueous solution (30%) (i.e., the first other transition metal source aqueous solution), the first portion of Zn salt aqueous solution (70%) (i.e., the first Zn source aqueous solution), ammonia solution, and sodium hydroxide solution are added in parallel under stirring conditions. The ammonia concentration is controlled at 6 g / L, the pH value is 11, the reaction temperature is 50℃, and the stirring speed is 250 rpm to complete the first coprecipitation reaction and obtain the first hydroxide precursor core with Zn doping.

[0101] Step 3: Add the second portion of nickel-cobalt-manganese salt aqueous solution (30%) (i.e., the second other transition metal source aqueous solution), the Zn-doped first hydroxide precursor core, the second portion of Zn salt aqueous solution (30%), the ammonia solution and the sodium hydroxide solution to the reactor. Control the ammonia concentration to 6.5 g / L, the pH value to 11, and the reaction temperature to 50°C to complete the second coprecipitation reaction and obtain the reverse concentration gradient Zn-doped second hydroxide precursor core.

[0102] Step 4: Add the second hydroxide precursor core doped with Zn in the reverse concentration gradient, the third portion of nickel cobalt manganese salt aqueous solution (40%) (i.e., the third other transition metal source aqueous solution), ammonia aqueous solution and sodium hydroxide aqueous solution to the reactor, control the ammonia concentration to 7 g / L, the pH value to 11.5, and the reaction temperature to 50℃ to complete the third coprecipitation reaction, and dry to obtain the third hydroxide precursor core doped with Zn in the reverse concentration gradient.

[0103] Step 5: Mix the third hydroxide precursor core, 2000 ppm ZrO2 and lithium hydroxide, wherein the molar ratio of the third hydroxide precursor core to LiOH is 1:1.03, and perform the first sintering under an oxygen atmosphere at a sintering temperature of 750℃ and a holding time of 20h to obtain a high nickel cathode material with Zn reverse concentration gradient doping.

[0104] Step 6: After mechanically crushing the positive electrode material, ultrasonically disperse it in ethanol for 30 minutes, then add Al(OEt)3 ethanol solution and stir at room temperature for 2 hours.

[0105] Step 7: Remove the ethanol solvent by rotary evaporation, and sinter the obtained material at 650°C for 8 hours to obtain an Al2O3-coated zinc-containing positive electrode active material with reverse concentration gradient doping.

[0106] Example 2

[0107] The preparation method in this embodiment is basically the same as that in Example 1. The difference is that in step 1, the molar proportions of Zn, Ni, Co, Mn and Al are 1.5%, 90%, 4.2%, 4%, and 0.3%, respectively.

[0108] Example 3

[0109] The difference from Example 2 is that, after the Ni, Co, and Mn salt solutions were prepared, the nickel-cobalt-manganese salt aqueous solution was divided into three portions in a ratio of 4:4:2. 40% of the nickel-cobalt-manganese salt solution was added for the first coprecipitation reaction, 40% for the second coprecipitation reaction, and 20% for the third coprecipitation reaction.

[0110] Example 4

[0111] Step 1: Weigh ZnSO4 salt, NiSO4 salt, CoSO4 salt, MnSO4 salt, and Al(OEt)3 according to the molar proportions of Zn, Ni, Co, Mn, and Al of 3%, 90%, 3.7%, 3%, and 0.3%, respectively. Prepare nickel-cobalt-manganese salt aqueous solutions from NiSO4, CoSO4, and MnSO4 salts, prepare an ethanol solution from Al salt, and prepare a Zn salt aqueous solution from ZnSO4 salt. Divide the nickel-cobalt-manganese salt aqueous solution into three portions according to a volume ratio of 3:3:4, and divide the Zn salt aqueous solution into two portions according to a volume ratio of 7:3.

[0112] Step 2: The first portion of nickel cobalt manganese salt aqueous solution (30%) (i.e., the first other transition metal source aqueous solution), the first portion of Zn salt aqueous solution (70%) (i.e., the first Zn source aqueous solution), ammonia solution, and sodium hydroxide solution are added in parallel under stirring conditions. The ammonia concentration is controlled at 6 g / L, the pH value is 11, the reaction temperature is 50℃, and the stirring speed is 250 rpm to complete the first coprecipitation reaction and obtain the first hydroxide precursor core with Zn doping.

[0113] Step 3: Add the second Ni, Co, Mn salt solution (30%) (i.e., the second aqueous solution of other transition metal sources), the Zn-doped first hydroxide precursor core, the second Zn salt aqueous solution (30%), the ammonia solution and the sodium hydroxide solution to the reactor. Control the ammonia concentration to 6.5 g / L, the pH value to 11, and the reaction temperature to 50 °C to complete the second coprecipitation reaction and obtain the reverse concentration gradient Zn-doped second hydroxide precursor core.

[0114] Step 4: Add the second hydroxide precursor core doped with Zn in the reverse concentration gradient, the third portion of nickel cobalt manganese salt aqueous solution (40%) (i.e., the third other transition metal source aqueous solution), ammonia aqueous solution and sodium hydroxide aqueous solution to the reactor, control the ammonia concentration to 7 g / L, the pH value to 11.5, and the reaction temperature to 50℃ to complete the third coprecipitation reaction, and dry to obtain the third hydroxide precursor core doped with Zn in the reverse concentration gradient.

[0115] Step 5: Mix the third hydroxide precursor core, 2000 ppm ZrO2 and lithium hydroxide, wherein the molar ratio of the third hydroxide precursor core to LiOH is 1:1.03, and perform the first sintering under an oxygen atmosphere at a sintering temperature of 750℃ and a holding time of 20h to obtain an ultra-high nickel cathode material with reverse concentration gradient doping of Zn.

[0116] Step 6: After mechanically crushing the positive electrode material, ultrasonically disperse it in ethanol for 30 minutes, then add Al(OEt)3 ethanol solution and stir at room temperature for 2 hours.

[0117] Step 7: Remove the ethanol solvent by rotary evaporation, and sinter the obtained cathode material at 650°C for 8 hours to obtain an Al2O3-coated zinc-containing cathode active material with reverse concentration gradient doping.

[0118] Example 5

[0119] The preparation method in this embodiment is basically the same as that in Example 1, except that in step 1, the molar proportions of Zn, Ni, Co, Mn and Al are 0.2%, 65%, 17.5%, 17%, and 0.3%, respectively.

[0120] Example 6

[0121] (1) Weigh ZnSO4, NiSO4 salt, CoSO4 salt, MnSO4 salt, and Al(OEt)3 according to the molar ratios of Zn, Ni, Co, Mn, and Al of 0.2%, 90%, 5%, 4.5%, and 0.3%, respectively. Prepare nickel-cobalt-manganese salt aqueous solutions from NiSO4, CoSO4, and MnSO4 salts, prepare an ethanol solution from Al salt, and prepare a Zn salt aqueous solution from ZnSO4 salt. Divide the nickel-cobalt-manganese salt aqueous solution into three portions according to a volume ratio of 3:3:4, and divide the Zn salt aqueous solution into two portions according to a volume ratio of 7:3.

[0122] (2) The first portion of nickel cobalt manganese salt aqueous solution (30%), the first portion of Zn salt aqueous solution (70%), ammonia aqueous solution and sodium hydroxide aqueous solution were added in parallel under stirring conditions. The ammonia concentration was controlled at 6 g / L, the pH value was 11, the reaction temperature was 50℃ and the stirring speed was 250 rpm to complete the first coprecipitation reaction and obtain a precursor core with Zn doping.

[0123] (3) Add the second Ni, Co, Mn salt solution (30%), Zn-doped precursor core P1, the second Zn salt aqueous solution (30%), ammonia solution and sodium hydroxide solution to the reactor, control the ammonia concentration to 6.5 g / L, the pH value to 11, and the reaction temperature to 50 °C, and complete the second coprecipitation reaction to obtain the reverse concentration gradient Zn-doped precursor core.

[0124] (4) Add the Zn precursor core with reverse concentration gradient, the third nickel cobalt manganese salt aqueous solution (40%), the ammonia solution and the sodium hydroxide solution to the reactor, control the ammonia concentration to 7 g / L, the pH value to 11.5, and the reaction temperature to 50℃ to complete the third coprecipitation reaction, and dry to obtain the Zn precursor with reverse concentration gradient.

[0125] (5) The precursor, 2000 ppm ZrO2 and lithium hydroxide were mixed, wherein the molar ratio of the precursor to LiOH was 1:1.03, and the first sintering was carried out in an oxygen atmosphere at a sintering temperature of 750℃ and a holding time of 20h to obtain an ultra-high nickel cathode material with Zn reverse concentration gradient doping.

[0126] (6) After mechanically crushing the material obtained in step 5, it is mechanically mixed with 3000 ppm Al2O3 powder and sintered at 650°C for 8 hours to obtain Al2O3-coated Zn reverse concentration gradient doped zinc positive electrode active material.

[0127] Example 7

[0128] The preparation method of this embodiment is basically the same as that of Example 1, except that Al(OEt)3 is replaced with Cr(OEt)3.

[0129] Example 8

[0130] The preparation method of this embodiment is basically the same as that of Example 1, except that in step 1, the molar proportions of Zn, Ni, Co, Mn and Al are 1.5%, 90.1%, 3.3%, 3%, and 2.1%, respectively.

[0131] According to the above molar ratio, the zinc-containing positive electrode active material prepared contains 1.11% alumina by mass.

[0132] Comparative Example 1:

[0133] (1) Weigh NiSO4 salt, CoSO4 salt, MnSO4 salt, and Al(OEt)3 according to the molar ratios of Ni, Co, Mn, and Al of 90%, 5%, 4.7%, and 0.3%, respectively. Prepare NiSO4 salt, CoSO4 salt, and MnSO4 salt into an aqueous solution of nickel, cobalt, and manganese salt, and prepare Al salt into an ethanol solution.

[0134] (2) Add nickel cobalt manganese salt aqueous solution, ammonia aqueous solution and sodium hydroxide aqueous solution to the reaction vessel, control the ammonia concentration to 7 g / L, the pH value to 11.5, and the reaction temperature to 50℃ to complete the coprecipitation reaction and obtain the precursor material.

[0135] (3) The precursor, 2000 ppm ZrO2, is mixed with lithium hydroxide, wherein the molar ratio of the precursor to LiOH is 1:1.03. The mixture is sintered for the first time in an oxygen atmosphere at a sintering temperature of 750℃ and a holding time of 20h to obtain an ultra-high nickel cathode material.

[0136] (4) After mechanically crushing the positive electrode material, it is ultrasonically dispersed in ethanol for 30 minutes, and then Al(OEt)3 ethanol solution is added and stirred at room temperature for 2 hours.

[0137] (5) The ethanol solvent was removed by rotary evaporation, and the obtained positive electrode material was sintered at 650°C for 8 hours to obtain zinc-containing positive electrode active material coated with Al2O3.

[0138] Comparative Example 2

[0139] (1) Weigh ZnSO4, NiSO4 salt, CoSO4 salt, MnSO4 salt, and Al(OEt)3 according to the molar ratios of Zn, Ni, Co, Mn, and Al of 2%, 90%, 4%, 3.7%, and 0.3%, respectively. Prepare nickel-cobalt-manganese salt aqueous solutions from NiSO4, CoSO4, and MnSO4 salts, prepare an ethanol solution from Al salt, and prepare a Zn salt aqueous solution from ZnSO4 salt.

[0140] (2) The nickel cobalt manganese salt aqueous solution, Zn salt aqueous solution, ammonia aqueous solution and sodium hydroxide aqueous solution were added in parallel under stirring conditions. The ammonia concentration was controlled at 6 g / L, the pH value was 11, the reaction temperature was 50℃, and the stirring speed was 250 rpm to complete the first coprecipitation reaction and obtain a precursor core with uniform Zn doping.

[0141] (3) The precursor, 2000 ppm ZrO2, is mixed with lithium hydroxide, wherein the molar ratio of the precursor to LiOH is 1:1.03. The mixture is sintered for the first time in an oxygen atmosphere at a temperature of 750°C and a holding time of 20 h to obtain a uniformly Zn-doped ultra-high nickel cathode material.

[0142] (4) After mechanically crushing the positive electrode material, it is ultrasonically dispersed in ethanol for 30 minutes, and then Al(OEt)3 ethanol solution is added and stirred at room temperature for 2 hours.

[0143] (5) The ethanol solvent was removed by rotary evaporation, and the obtained positive electrode material was sintered at 650°C for 8 hours to obtain zinc-containing positive electrode active material coated with Al2O3.

[0144] Comparative Example 3:

[0145] The difference from Example 1 is that the molar percentages of Zn, Ni, Co, Mn, and Al are 5%, 90%, 2.5%, 2.2%, and 0.3%, respectively.

[0146] Comparative Example 4

[0147] The difference from Example 4 is that all the Zn salt solution was added during the first coprecipitation reaction, while only nickel-cobalt-manganese salt solution was added during the second and third coprecipitation reactions, without adding Zn salt solution.

[0148] Comparative Example 5

[0149] The difference from Comparative Example 1 is that steps 4 and 5 are omitted.

[0150] Comparative Example 6

[0151] (1) Weigh ZnSO4, NiSO4 salt, CoSO4 salt, MnSO4 salt, and Al(OEt)3 according to the molar ratios of Zn, Ni, Co, Mn, and Al of 0.2%, 90%, 5%, 4.5%, and 0.3%, respectively. Prepare nickel-cobalt-manganese salt aqueous solutions from NiSO4, CoSO4, and MnSO4 salts, prepare an ethanol solution from Al salt, and prepare a Zn salt aqueous solution from ZnSO4 salt. Divide the nickel-cobalt-manganese salt aqueous solution into three portions according to a volume ratio of 3:3:4, and divide the Zn salt aqueous solution into two portions according to a volume ratio of 7:3.

[0152] (2) The first portion of nickel cobalt manganese salt aqueous solution (30%), the first portion of Zn salt aqueous solution (70%), ammonia aqueous solution and sodium hydroxide aqueous solution were added in parallel under stirring conditions. The ammonia concentration was controlled at 6 g / L, the pH value was 11, the reaction temperature was 50℃ and the stirring speed was 250 rpm to complete the first coprecipitation reaction and obtain a precursor core with Zn doping.

[0153] (3) Add the second Ni, Co, Mn salt solution (30%), Zn-doped precursor core P1, the second Zn salt aqueous solution (30%), ammonia solution and sodium hydroxide solution to the reactor, control the ammonia concentration to 6.5 g / L, the pH value to 11, and the reaction temperature to 50 °C, and complete the second coprecipitation reaction to obtain the reverse concentration gradient Zn-doped precursor core.

[0154] (4) Add the Zn precursor core with reverse concentration gradient, the third nickel cobalt manganese salt aqueous solution (40%), the ammonia solution and the sodium hydroxide solution to the reactor, control the ammonia concentration to 7 g / L, the pH value to 11.5, and the reaction temperature to 50℃ to complete the third coprecipitation reaction, and dry to obtain the Zn precursor with reverse concentration gradient.

[0155] (5) The precursor, 2000 ppm ZrO2 and lithium hydroxide are mixed, wherein the molar ratio of the precursor to LiOH is 1:1.03, and the first sintering is carried out in an oxygen atmosphere at a sintering temperature of 750℃ and a holding time of 20h to obtain a zinc-containing positive electrode active material with reverse concentration gradient doping of Zn.

[0156] Comparative Example 7

[0157] The difference from Example 1 is that Al(OEt)3 is replaced with Zr(OEt)4.

[0158] Test case

[0159] The test method for median particle size is GB / T19077.1-2016; the test method for BET is GB / T19587-2017.

[0160] Figure 2 This is a schematic diagram showing the distribution of different regions in the zinc-containing positive electrode active material of Example 1. (Refer to...) Figure 1 The S3 region represents the center region, the S2 region represents the first annular region, and the S3 region represents the second annular region. The Zn element content percentage was tested in each region. The test results of each embodiment and comparative example are detailed in Table 1.

[0161] XRD (003) Peak Difference Test: The test was conducted using an X-ray diffractometer (Bruker D8AA25 instrument, Cu target, 40kV voltage, 40mA current, Soller 2.5). Batteries were prepared using the zinc-containing positive electrode active materials from each example and comparative example, following the same method as in Test Example 2 below. XRD scans were performed on the zinc-containing positive electrode active material samples charged to 50% SOC and 100% SOC, and the diffraction patterns were recorded to determine the peak difference of the (003) peak at 100% SOC and 50% SOC. Figure 3 The image shows the XRD pattern of the positive electrode active material of Comparative Example 1 at 100% SOC. Figure 4 The XRD pattern of the positive electrode active material of Comparative Example 1 at 50% SOC clearly shows the shift of the (003) peak, indicating a significant structural change. The test results of the peak position difference of the (003) peak in each embodiment and comparative example are detailed in Table 2.

[0162] The powder of the positive electrode active material to be tested was dispersed in epoxy resin, mixed evenly, and then cured in a mold. After curing, the resin block was subjected to multi-stage grinding and polishing with sandpaper and polishing cloth until a fresh, flat cross-section of the material particles was exposed, and the surface was free of scratches. An argon ion polisher (CP, Cross Section Polisher) was then used to polish the cross-section. The cross-section of the positive electrode active material particles was analyzed by elemental surface scanning using an electron probe microanalysis (EPMA) system. The accelerating voltage was set to 15 kV, and characteristic X-rays of Zn (Kα series), Ni (Kα series), Co (Kα series), and Mn (Kα series) were selected for detection. The molar percentage of Zn was measured. (Example: Material testing in Example 2) Figure 5 This is an example diagram of the cross-sectional test in Example 2. The test was conducted using a line scan method, and the Zn element distribution test results are as follows. Figure 6 As shown. In Figure 6 In China, according to Figure 5 The cross-section of the positive electrode active material particles is divided according to the size of the particles. The outermost 1μm layer is the second annular region (i.e., region A in the figure), the innermost 1μm layer is the first annular region (i.e., region B in the figure), and the innermost layer is the spherical core region (i.e., region C in the figure). The mass content of Zn element at the center position of each layer is taken as the molar percentage of that layer. The first molar percentage of Zn element in the first annular region (region B) is represented by the molar percentage of Zn element at the black dot position in the figure. The second molar percentage of Zn element in the second annular region (region A) is represented by the molar percentage of Zn element at the red dot position in the figure. The third molar percentage of Zn element in the spherical core region (region C) is represented by the molar percentage of Zn element at the yellow dot position in the figure. Thus, the molar percentage of Zn element in the transition metal element in each annular region can be determined.

[0163] The molar percentage of Zn in the second annular region relative to the Zn in the cathode material was tested using the aforementioned linear scanning method. The mass distribution of Zn on the linear scanning line was determined by integrating the area of ​​the second annular region and dividing by the total area.

[0164] Mass percentage test of coating oxide: Weigh a certain mass of zinc-containing positive electrode active material, dissolve it in aqua regia, and determine the content of metal elements in the coating layer using ICP-OES or ICP-MS, and then calculate the mass percentage of metal oxide.

[0165] Zn element site testing: X-ray diffraction (XRD) tests were performed on the zinc-containing positive electrode active materials of each embodiment to obtain XRD patterns. By refining (fitting the XRD patterns), the positions of the doped Zn elements can be determined, and some Zn elements occupy lithium sites.

[0166] Table 1

[0167]

[0168] Table 2

[0169]

[0170] Test Example 2

[0171] After the zinc-containing positive electrode active materials from all examples and comparative examples were fabricated into positive electrode sheets, they were assembled with negative electrode sheets, electrolytes, and separators according to the following method to obtain a lithium-ion battery. The method includes:

[0172] 1) The positive electrode active materials from the examples and comparative examples were mixed with conductive carbon black and PVDF at a weight ratio of 96%:2%:2%, respectively, and dispersed to obtain a positive electrode slurry. This slurry was coated onto an aluminum foil current collector, with a positive electrode areal density of 4.12 g / cm³. 3 The positive electrode sheet is prepared by rolling.

[0173] 2) Artificial graphite, styrene-diene rubber (SBR), sodium carboxymethyl cellulose, and conductive carbon black are mixed in a weight ratio of 94%:3%:2%:1%. The mixture is dispersed in water and then mixed using a double planetary mixer to obtain a negative electrode slurry. This slurry is coated onto a copper current collector, followed by rolling and drying to obtain a negative electrode sheet.

[0174] 3) Assemble the positive electrode, negative electrode, and separator into a lithium-ion battery and inject a non-aqueous electrolyte. The electrolyte is prepared by mixing ethylene carbonate (EC): diethyl carbonate (DEC): propylene carbonate (PC) in a mass ratio of 2:5:3. Then, add 5% fluoroethylene carbonate (FEC) and 13% lithium hexafluorophosphate (LiPF6) by mass of the total electrolyte.

[0175] First-cycle discharge specific capacity test: The prepared batteries of each embodiment and comparative example were subjected to charge-discharge tests at 25°C. The charge-discharge regime was as follows: constant current charging at 0.1C to 4.50V, then constant voltage charging at 4.50V until the current decreased to 0.02C, followed by resting for 5 minutes, and then constant current discharging at 0.1C to 2.5V. The discharge capacity Q was recorded and divided by the mass of zinc-containing positive electrode active material used in each battery to obtain the first-cycle discharge specific capacity. The test results are detailed in Table 3.

[0176] Cyclic testing: At 25℃, the capacitor is charged at a constant current rate of 0.5C to 4.50V, then charged at a constant voltage rate of 0.05C to 4.50V, and finally discharged at a discharge rate of 1C to 3.0V. This charge-discharge cycle is repeated 300 times. The discharge capacity Q1 at the first cycle and the discharge capacity Q at the 300th cycle are measured. 300 The capacity retention rate Q after 300 cycles is calculated using the following formula: Capacity retention rate Q = Q 300 / Q1*100%. See Table 3 for detailed test results.

[0177] Zn leaching test: After 300 cycles, the negative electrode of each example and comparative battery was dissolved in aqua regia. The dissolved aqua regia was then injected into an ICP-OES instrument to measure the emission spectral intensity of Zn. The Zn leaching amount in the test sample was calculated based on the standard curve of the Zn standard solution. The test results are detailed in Table 3.

[0178] Table 3

[0179]

[0180] In Example 2, the total Zn doping content in the material was increased from 0.2% to 1.5%. Compared with Example 1, the capacity decreased in the first week, the capacity retention rate increased, and there was slight Zn dissolution.

[0181] Compared with Example 2, Example 3 reduced the amount of raw materials used in the third co-precipitation stage during the synthesis phase, making it easier for Zn to diffuse to the boundary, resulting in an increase in the molar percentage of Zn in the second ring region and an increase in Zn dissolution under the same conditions.

[0182] In Example 4, the total Zn doping content in the material was increased to 3%, and the difference between the third molar percentage and the first molar percentage was 3.44%. Compared with Example 2, Zn dissolution increased, and the capacity in the first week continued to decrease.

[0183] Example 5 uses a material composition with molar proportions of Zn, Ni, Co, Mn, and Al of 0.2%, 65%, 17.5%, 17%, and 0.3%, respectively. Due to the decrease in Ni content, the capacity decreased significantly compared to Example 1, while the capacity retention rate increased significantly, and no Zn dissolution was observed.

[0184] In Example 6, Al2O3 coating was performed by sintering a mixture of cathode material and Al2O3. The overall performance was similar to that of Example 1, with slight Zn leaching, indicating that the coating layer obtained by the powder sintering doping method had insufficient Zn capture effect.

[0185] In Example 8, as the Al coating amount increased, the initial capacity of the material decreased. However, due to the thick coating layer more effectively absorbing the diffused Zn ions and suppressing interfacial side reactions, the cycle retention rate was significantly improved, and the Zn dissolution amount was greatly reduced.

[0186] As can be seen from the comparison between Comparative Example 1 and Examples 1 and 2, a small amount of Zn doping has little effect on capacity. Increasing the doping amount will reduce capacity, but can effectively improve capacity retention.

[0187] As can be seen from Comparative Example 2, uniform Zn doping is more conducive to improving capacity retention, but it will cause Zn element dissolution to intensify, resulting in safety risks.

[0188] In Comparative Example 3, the Zn doping amount was 5%. Compared with Example 1 and Example 2, the capacity in the first week further decreased, the capacity retention rate further improved, and the Zn dissolution amount continued to increase.

[0189] Compared with Example 4, Comparative Example 4 showed a more concentrated Zn concentration distribution, a slight decrease in the first-cycle capacity, and a significant decrease in capacity retention.

[0190] Comparative Example 5 uses a ternary cathode material without Zn doping or coating. It has a high initial capacity, but poor capacity retention.

[0191] Comparative Example 6 followed the same process as Example 1, but without Al2O3 coating. Due to stronger interfacial side reactions, its initial capacity was similar to that of Example 1, but its capacity retention was significantly lower, and Zn was dissolved. Compared to Comparative Example 5, Comparative Example 6 also lacked Al2O3 coating, and since Comparative Example 5 did not have Zn doping, its capacity retention decreased.

[0192] Although coating with Zr element in Comparative Example 7 can improve cycle stability to some extent (compared to no coating), the amount of Zn dissolution is still very high because Zr cannot form a stable spinel structure with Zn to "lock" Zn ions like Al can.

[0193] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A zinc-containing positive electrode active material, characterized in that, include: A zinc-containing positive electrode active material matrix and an oxide coating layer covering at least a portion of the surface of the zinc-containing positive electrode active material matrix, wherein the oxide coating layer comprises a trivalent metal element; The zinc-containing positive electrode active material is divided into three parts by a cross-section through the center of the sphere: a central region, a first annular region, and a second annular region. The first annular region is located between the central region and the second annular region. The annular width of the second annular region is 1 μm, and the annular width of the first annular region is 1 μm. In the first annular region, the first molar percentage of Zn element among transition metal elements is 0.2% to 3%; In the second annular region, the second molar percentage of Zn element among transition metal elements is 0% to 1%; In the central region of the sphere, the third molar percentage of Zn element among transition metal elements is 0.3% to 6%; The third molar percentage is greater than the first molar percentage, and the first molar percentage is greater than the second molar percentage.

2. The zinc-containing positive electrode active material according to claim 1, characterized in that, The difference between the third molar percentage and the first molar percentage is less than 2%.

3. The zinc-containing positive electrode active material according to claim 1, characterized in that, In the second annular region, the molar percentage of Zn element in the zinc-containing positive electrode active material is less than 20%.

4. The zinc-containing positive electrode active material according to any one of claims 1-3, characterized in that, The chemical formula of the zinc-containing positive electrode active material is Li x Ni a Co b Mn c Zn y M z O m N n Wherein, 0.95≤x≤1.10, 0.6≤a≤1, 0≤b≤0.15, 0≤c≤0.35, 0.001≤y≤0.03, 0≤z≤0.02, 0≤n≤0.001, a+b+c+y+z=1, m+n=2, element M is selected from one or more of Na, Mg, Sc, Al, Ti, Ga, V, Cr, Fe, Y, Zr, Nb, Mo, Ta, and W, and element N is selected from one or more of F, Cl, Br, and S; And / or, the first molar percentage is 0.2% to 1.18%, the second molar percentage is 0% to 0.65%, and the third molar percentage is 0.37% to 2.51%; And / or, some Zn elements occupy Li element sites.

5. The zinc-containing positive electrode active material according to any one of claims 1-3, characterized in that, The oxide coating layer includes one or more of Al2O3, Cr2O3, Fe3O4, Ga2O3, and Mn2O3; And / or, the oxide coating layer accounts for 0.16% to 1.11% of the mass percentage of the zinc-containing positive electrode active material.

6. The zinc-containing positive electrode active material according to any one of claims 1-3, characterized in that, The particle size Dv50 of the zinc-containing positive electrode active material is 9μm ~ 18μm; And / or, the specific surface area of ​​the zinc-containing positive electrode active material is between 0.2 and 0.6 m². 2 / g; And / or, the positive electrode active material satisfies 0.19≤I1(003)-I2(003)≤0.56, where I1 is the 2θ angle of the 003 peak of the positive electrode active material when the battery prepared by the positive electrode active material is charged to 100% SOC, and I2 is the 2θ angle of the 003 peak of the positive electrode active material when the battery prepared by the positive electrode active material is charged to 50% SOC, as determined by XRD.

7. A method for preparing a zinc-containing positive electrode active material according to any one of claims 1-6, characterized in that, Includes the following steps: A first coprecipitation reaction is carried out between a first Zn source aqueous solution and a first other transition metal source aqueous solution to obtain a first hydroxide precursor core; in the first coprecipitation reaction, the molar percentage of Zn element in the first Zn source aqueous solution is 0.3% to 6% of the total molar percentage of the transition metal elements; the first other transition metal source aqueous solution includes nickel source, cobalt source, and manganese source; A second Zn source aqueous solution and a second other transition metal source aqueous solution are introduced into a system including the first hydroxide precursor core to carry out a second coprecipitation reaction and obtain the second hydroxide precursor core. In the second coprecipitation reaction, the molar percentage of Zn element in the second Zn source aqueous solution is 0.2-3% of the total transition metal elements; the molar amount of Zn element in the second Zn source aqueous solution is less than the molar amount of Zn element in the first Zn source aqueous solution; the second other transition metal source aqueous solution includes nickel source, cobalt source, and manganese source; A third aqueous solution of another transition metal source is introduced into a system including the second hydroxide precursor core to perform a third coprecipitation and obtain a third hydroxide precursor core; the third aqueous solution of another transition metal source includes a nickel source, a cobalt source, and a manganese source. The mixture of the third hydroxide precursor core, the doping element source, and the lithium source was sintered at 650~800℃ to obtain a zinc-containing cathode active material intermediate product. The zinc-containing positive electrode active material intermediate product is mixed with a trivalent metal source and then sintered a second time at 600~700℃ to obtain the zinc-containing positive electrode active material.

8. The method for preparing the zinc-containing positive electrode active material according to claim 7, characterized in that, The process involves mixing the zinc-containing positive electrode active material intermediate with a trivalent metal source and then performing a second sintering at 600-700°C to obtain the zinc-containing positive electrode active material, comprising: The zinc-containing positive electrode active material intermediate product and the trivalent metal alkoxide were dispersed and mixed in an alcohol solvent atmosphere to obtain a dispersion. The dispersion was sintered a second time at 600-700°C to obtain a zinc-containing positive electrode active material.

9. A positive electrode plate, characterized in that, The positive electrode sheet includes the zinc-containing positive electrode active material according to any one of claims 1-6, or the zinc-containing positive electrode active material prepared by the preparation method of the zinc-containing positive electrode active material according to claim 7 or 8.

10. A battery, characterized in that, The battery includes the positive electrode as described in claim 9.

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