Lithium-rich nickel-based cathode materials and their preparation methods, cathode sheets and secondary batteries

Abstract

This application provides lithium-rich nickel-based cathode materials, their preparation methods, and batteries. The lithium-rich nickel-based cathode materials include lithium-rich materials and high-valence cations N doped into the lithium-rich materials. The general structural formula of the lithium-rich materials is: Li… 1+x Ni y M z O s M is a transition metal, 0 < x ≤ 2, 0 ≤ y < 1, 0 < z ≤ 1, 1 ≤ s ≤ 4; the high-valence cation N is a metal ion with a valence state ≥ +3. The lithium-rich nickel-based cathode material of this application uses lithium-rich material doped with high-valence cation N. Doping with high-valence cation N can increase the cell parameters and Ig of the lithium-rich nickel-based cathode material. (003) / I (104) This effectively increases the interlayer spacing of the layered structure and reduces cation mixing, which helps suppress the migration of transition metal ions to lithium sites and accelerates Li... + The diffusion and transfer of oxygen can alleviate the release of lattice oxygen and the transformation from layered to spinel structure, thereby improving the rate performance and stability of the material.

Description

Technical Field

[0001] This application belongs to the field of lithium battery material technology, and more specifically, relates to lithium-rich nickel-based cathode materials and their preparation methods, cathode sheets and secondary batteries. Background Technology

[0002] Lithium-ion batteries are a type of rechargeable battery with advantages such as high operating voltage, high energy density, long cycle life, low self-discharge rate, and low pollution. They are widely used in electric vehicles, portable electronic devices, and energy storage systems. With the continuous development of the new energy vehicle industry, the requirements for energy products (lithium-ion batteries) are becoming increasingly stringent, especially regarding product safety, charge / discharge specific capacity, and cycle life.

[0003] Cathode materials are a key component of lithium-ion batteries. Among them, lithium-rich layered materials are considered crucial materials for next-generation high-performance lithium-ion batteries due to their outstanding advantages such as high specific capacity, low cost, and good thermal stability. However, when the charging voltage of lithium-rich cathode materials reaches above 4.5V, lattice oxygen undergoes irreversible release, and transition metals occupy the lithium sites left by the lithium extraction. This results in the incomplete re-insertion of lithium extracted during charging during discharging, leading to significant irreversible capacity loss in lithium-rich layered cathode materials. Furthermore, the migration of transition metals and the release of lattice oxygen cause a phase transition, transforming the material from a layered structure to a spinel phase, thus degrading the material's cycle performance and rate capability. Summary of the Invention

[0004] Based on this, this application provides a lithium-rich nickel-based cathode material and its preparation method, cathode sheet, and secondary battery to solve the technical problems existing in the prior art. When the charging voltage of the lithium-rich cathode material reaches 4.5V or above, lattice oxygen is irreversibly released, and at the same time, the transition metal occupies the lithium sites left by the original lithium extraction, resulting in the lithium extracted during charging not being completely reinserted during discharge. Therefore, the lithium-rich layered cathode material has a large irreversible capacity loss. At the same time, the migration of the transition metal and the release of lattice oxygen cause the material to undergo a phase transition, changing from the original layered structure to the spinel phase, and the cycle performance and rate performance of the material also degrade.

[0005] To achieve the above objectives, the technical solution adopted in this application is as follows:

[0006] Firstly, a lithium-rich nickel-based cathode material is provided, comprising a lithium-rich material and a high-valence cation N doped in the lithium-rich material, wherein the general structural formula of the lithium-rich material is: Li 1+x Ni y M z O s M is a transition metal, 0 < x ≤ 2, 0 ≤ y < 1, 0 < z ≤ 1, 1 ≤ s ≤ 4; the high-valence cation N is a metal ion with a valence state ≥ +3.

[0007] Optionally, the transition metal M includes at least one of Mn, Co, Fe, and Cr;

[0008] And / or, high-valence cations N include Al 3+ Ce 3+ Ce 4+ Sn 4+ Ti 4+ Cr 3+ Zr 4+ 、Nb 5+ W 5+ V 5+ Mo 6+ At least one of them.

[0009] Optionally, the high-valence cation N includes metal ions N1 and N2, each of which is independently Al. 3+ Ce 3+ Ce 4+ Sn 4+ Ti 4+ Cr 3+ Zr 4+ 、Nb 5+ W 5+ V 5+ Mo 6+ One of them, metal ions N1 and metal ions N2 are different; the general structural formula of lithium-rich nickel-based cathode materials is: Li 1+x Ni a M b N1 c N2 d O2, where 0.85≤a≤0.95, 0≤b≤0.15, 0≤c≤0.015, and 0≤d≤0.01.

[0010] Optionally, M is Co, metal ion N1 is Ti, metal ion N2 is Al, and the general structural formula of lithium-rich nickel-based cathode material is: Li 1+x Ni a Co b Ti c Al d O2.

[0011] Optionally, the lithium-rich nickel-based cathode material has a polyhedral morphology.

[0012] And / or, the lithium-rich nickel-based cathode material has a hexagonal crystal system, and the unit cell of the lithium-rich nickel-based cathode material includes three edge lengths: a0, b0, and c0, where a0 = b0 ≠ c0. I of the cell of lithium-rich nickel-based cathode material (003) / I (104) The value range is 1.2-1.5.

[0013] Optionally, the outer surface of the lithium-rich nickel-based cathode material has a coating layer, which includes a polyanionic material;

[0014] And / or, the outer surface of the lithium-rich nickel-based cathode material has a coating layer, which includes a polyanionic metal phosphate.

[0015] Secondly, a method for preparing a lithium-rich nickel-based cathode material is provided, which is used to prepare the lithium-rich nickel-based cathode material as described above. The preparation method includes the following steps:

[0016] Nickel salt, metallic M salt, and high-valence cation N salt are mixed to obtain mixed metal salt solution A;

[0017] The complexing agent, precipitant and mixed metal salt solution A are mixed and coprecipitated to obtain mixture B, which includes the hydroxide precursor of lithium-rich nickel cathode material.

[0018] The mixture B was centrifuged, washed and dried to obtain the hydroxide precursor;

[0019] Lithium-rich nickel-based cathode materials are obtained by mixing lithium source with hydroxide precursor and reacting them through high-temperature solid-state synthesis.

[0020] Optionally, the high-valent cation N salt includes high-valent cation N1 salt and high-valent cation N2 salt, and the molar ratio of nickel, M, N1, and N2 in the nickel salt, metallic M salt, high-valent cation N1 salt, and high-valent cation N2 salt is: a:b:c:d, 0.9≤a≤0.95, 0.5≤b≤0.1, 0≤c≤0.01, 0≤d≤0.01;

[0021] And / or, the complexing agent is an ammonia solution, and the precipitant is an inorganic alkaline solution.

[0022] Thirdly, a positive electrode sheet is provided, comprising the above-described lithium-rich nickel-based positive electrode material or the lithium-rich nickel-based positive electrode material prepared by the above-described method.

[0023] Fourthly, a secondary battery is provided, including a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, wherein the positive electrode is the aforementioned positive electrode.

[0024] The beneficial effects of this application are as follows:

[0025] 1. The lithium-rich nickel-based cathode material provided in this application adopts a high-valence cation N-doped lithium-rich material. High-valence cation N doping can increase the cell parameters and Ig of the lithium-rich nickel-based cathode material. (003) / I (104)This effectively increases the interlayer spacing of the layered structure and reduces cation mixing, which helps suppress the migration of transition metal ions to lithium sites and accelerates Li... + The diffusion and transfer of oxygen alleviate the release of lattice oxygen and the transformation from layered to spinel structure, thereby improving the rate performance and stability of the material. Compared with the prior art, the lithium-rich nickel-based cathode material of this application is more stable and has significantly improved cycle performance and rate performance.

[0026] 2. The polyanionic metal phosphate coating of this application can effectively reduce alkaline impurities on the surface of lithium-rich nickel-based cathode materials, alleviate the material homogenization process, and improve the cycle life and safety of the battery.

[0027] 3. The method for preparing lithium-rich nickel-based cathode material provided in this application synthesizes a uniformly doped hydroxide precursor in one step through a co-precipitation reaction. Then, the hydroxide precursor is mixed with a lithium source and a high-valence cation-doped lithium-rich nickel-based cathode material is prepared by a high-temperature solid-state synthesis method. The preparation process is simple and controllable, which is conducive to industrial production.

[0028] 4. The secondary battery provided in this application has a positive electrode comprising the lithium-rich nickel-based positive electrode material provided in this application, wherein the cell parameters and I of the lithium-rich nickel-based positive electrode material are... (003) / I (104) The large value and stable crystal structure solve the problem of irreversible release of lattice oxygen when the charging voltage reaches 4.5V or above, thereby improving the stability of the secondary battery. Attached Figure Description

[0029] The present invention will be further described below with reference to the accompanying drawings and embodiments. In the accompanying drawings:

[0030] Figure 1 This is a field emission scanning electron microscope image of the lithium-rich nickel-based cathode material precursor of Example 1 of this application;

[0031] Figure 2 Al is the embodiment of this application 1 3+ Ti 4+ Field emission scanning electron microscope image of lithium-rich nickel-based cathode material doped with dual high-valence cations;

[0032] Figure 3 Al is the embodiment of this application 1 3+ Ti 4+ Refined Rietveld structure diagram of lithium-rich nickel-based cathode material doped with two high-valence cations. Detailed Implementation

[0033] To make the technical problems, technical solutions, and beneficial effects to be solved by this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and are not intended to limit the scope of this application.

[0034] This application provides a lithium-rich nickel-based cathode material, comprising a lithium-rich material and a high-valence cation N doped in the lithium-rich material. The general structural formula of the lithium-rich material is: Li 1+x Ni y M z O s M is a transition metal, 0 < x ≤ 2, 0 ≤ y < 1, 0 < z ≤ 1, 1 ≤ s ≤ 4; the high-valence cation N is a metal ion with a valence state ≥ +3.

[0035] The lithium-rich nickel-based cathode material provided in this application has a layered structure and is a lithium-rich material doped with high-valence cation N. High-valence cation N doping can increase the cell parameters and Ig of the lithium-rich nickel-based cathode material. (003) / I (104) This effectively increases the interlayer spacing of the layered structure and reduces cation mixing, which helps suppress the migration of transition metal ions to lithium sites and accelerates Li... + The diffusion and transfer of oxygen can alleviate the release of lattice oxygen and the transformation from layered to spinel structure, thereby improving the rate performance and stability of the material.

[0036] Compared with the prior art, the lithium-rich nickel-based cathode material of this application embodiment is more stable than the lithium-rich cathode material, and its cycle performance and rate performance are significantly improved.

[0037] Lithium-rich nickel-based cathode materials possess high specific energy and specific capacity. However, their surface is prone to structural transformation during charge and discharge, gradually shifting to a spinel structure and eventually a non-conductive rock salt structure, thus affecting their cycle stability. Furthermore, cation mixing during cycling causes rapid capacity decay, and residual alkali easily forms on the particle surface, leading to surface side reactions. Incorporating transition metals into lithium-rich nickel-based cathode materials can mitigate these problems.

[0038] In some embodiments, the transition metal M includes at least one of Mn, Co, Fe, and Cr, which can form lithium-rich materials with excellent electrical properties. When cobalt is added to a lithium-rich nickel-based material system, a higher cobalt content accelerates the Li-Li conversion process. + The higher the transmission rate, the better the performance; when adding manganese to lithium-rich nickel-based material systems, the higher the manganese content, the more stable the structure and the better the safety performance; the addition of appropriate amounts of iron and cadmium can stabilize the structure of the material.

[0039] Optionally, the high-valence cation N includes Al3+ Ce 3+ / Ce 4+ Sn 4+ Ti 4+ Cr 3+ Zr 4+ 、Nb 5+ W 5+ V 5+ Mo 6+ At least one of them, for example in some embodiments, the high-valent cation N can be Al. 3+ Ce 3+ Ce 4+ Sn 4+ Ti 4+ Cr 3+ Zr 4+ 、Nb 5+ W 5+ V 5+ Mo 6+ Any of the following, or the high-valence cation N is Al 3+ and Ce 3+ Or Al 3+ and Ce 4+ , or Al 3+ and Ti 4 + , or Cr 3+ and Zr 4+ , or Nb 5+ and W 5+ , or Al 3+ and V 5+ , or Al 3+ and Mo 6+ And so on. Generally, lithium-rich nickel-based cathode materials, due to Ni... 2+ radius and Li + radius Similarly, Ni at site 3b 2+ Easy to migrate to the vacant Li + At the site, during discharge, it is affected by Ni 2+ Li occupied + The position can no longer receive Li. + This mixing will lead to Li + The migration of cations is hindered, leading to the loss of active lithium. Furthermore, cation mixing can cause the formation and accumulation of harmful phases in the material, thus affecting its cycle stability. This application's embodiments, by doping with high-valence cations, can effectively increase the cell parameters and Ig of lithium-rich nickel-based cathode materials. (003) / I (104)This increases the interlayer spacing of the layered structure and reduces cation mixing, ultimately improving the rate capability and stability of lithium-rich nickel-based cathode materials.

[0040] In some embodiments, the high-valence cation N includes metal ions N1 and N2, each of which is independently Al. 3+ Ce 3+ Ce 4+ Sn 4+ Ti 4+ Cr 3+ Zr 4+ 、Nb 5+ W 5+ V 5+ Mo 6+ One of them, metal ions N1 and metal ions N2 are different; the general structural formula of lithium-rich nickel-based cathode materials is: Li 1+x Ni a M b N1 c N2 d O2, where 0.85≤a≤0.95, 0≤b≤0.15, 0≤c≤0.015, 0≤d≤0.01. It can be understood that by doping with two or more high-valence cations, the problem of cation mixing in lithium-rich nickel-based cathode materials can be further reduced or resolved. Furthermore, the doping of two higher-order cations can effectively hinder the migration of Ni elements during charging, suppress the formation of NiO, and stabilize the matrix material, thereby improving the structural integrity of lithium-rich nickel-based cathode materials and ultimately alleviating capacity decay.

[0041] Optionally, M is Co, metal ion N1 is Ti, metal ion N2 is Al, and the general structural formula of lithium-rich nickel-based cathode material is: Li 1+x Ni a Co b Ti c Al d O2. In this embodiment, Al 3+ Ti 4+ High-valence cation co-doping can increase the cell parameters and I(003) / I(104) value of lithium-rich nickel-based cathode materials, thereby effectively increasing the interlayer spacing of the layered structure and reducing cation mixing. This helps to suppress the migration of transition metal ions to lithium sites and accelerate the Li-Li transition. + The diffusion and transfer of oxygen can alleviate the release of lattice oxygen and the transformation from layered to spinel structure, thereby improving the rate capability and stability of the material.

[0042] When preparing lithium-rich nickel-based cathode materials using the preparation method of this application, lithium-rich nickel-based cathode materials with a polyhedral particle structure can be produced. Lithium-rich nickel-based cathode materials with an octahedral morphology exhibit good structural stability and are less prone to rapid cracking during charge and discharge. Furthermore, lithium-rich nickel-based cathode materials also have high tap density, resulting in higher overall energy density in the assembled battery. Further, the particle size of the lithium-rich nickel-based cathode material is 400nm-700nm. This particle size range can effectively balance the rate performance and tap density of the lithium-rich nickel-based cathode material, and can be directly applied to the battery manufacturing process.

[0043] In some embodiments, the lithium-rich nickel-based cathode material is hexagonal in crystal structure, and the unit cell of the lithium-rich nickel-based cathode material includes three edge lengths: a0, b0, and c0, wherein a0 = b0 ≠ c0. I of the cell of lithium-rich nickel-based cathode material (003) / I (104) The value range is 1.2-1.5.

[0044] In some embodiments, the outer surface of the lithium-rich nickel-based cathode material has a coating layer, which includes a polyanionic material. Typically, the surface of the lithium-rich nickel-based cathode material contains free lithium, and the coating layer is used to isolate the free lithium from the external environment, reduce direct contact between the free lithium and the external environment, slow down the dissolution of the lithium-rich nickel-based cathode material by the electrolyte, and improve the stability and storability of the lithium-rich nickel-based cathode material.

[0045] Optionally, the outer surface of the lithium-rich nickel-based cathode material has a coating layer, which is a polyanionic metal phosphate, such as LiZr(PO4)3. The metal phosphate coating layer can effectively reduce alkaline impurities on the surface of the lithium-rich nickel-based cathode material, alleviate the material homogenization process, and improve the cycle life and safety of the battery.

[0046] This application also provides a method for preparing the above-mentioned lithium-rich nickel-based cathode material, which includes the following steps:

[0047] S01: Mix nickel salt, metallic M salt, and high-valence cation N salt to obtain mixed metal salt solution A.

[0048] Mixed metal salt solutions are the main reactants for coprecipitation reactions, providing nickel, metal M, N and other metal elements for hydroxide precursors.

[0049] Understandably, the amounts of nickel salt, metallic M salt, and high-valence cation N salt added are based on the proportions of each element in the hydroxide precursor.

[0050] Optionally, when the high-valent cation N salt includes high-valent cation N1 salt and high-valent cation N2 salt, the molar ratio of nickel, M, N1, and N2 in the nickel salt, metal M salt, high-valent cation N1 salt, and high-valent cation N2 salt is: a:b:c:d, 0.9≤a≤0.95, 0.5≤b≤0.1, 0≤c≤0.01, 0≤d≤0.01. That is, the high-valent cation N salt includes two high-valent cation metals N1 and N2. In this case, the general structural formula of the final lithium-rich nickel-based cathode material is applicable to Li 1+x Ni a M b N1 c N2 d O2.

[0051] In some embodiments, the nickel salt, the metal M salt, and the high-valence cation N salt are each independently a sulfate, acetate, carbonate, or nitrate of the corresponding metal. Since acetate has a pungent odor and nitrate will produce harmful gases during the sintering stage, sulfate is generally chosen for reasons of odor irritation and experimental safety.

[0052] Therefore, when metal M is Co, high-valence cation N1 is Ti, and high-valence cation N2 is Al, the nickel salt, metal M salt, high-valence cation N1 salt, and high-valence cation N2 salt can be selected as NiSO4·6H2O, CoSO4·7H2O, Ti(SO4)2, and Al2(SO4)3·18H2O, respectively.

[0053] Optionally, the concentration of the mixed metal salt solution A is 1 mol / L to 3 mol / L, and the total concentration of all metals in the mixed metal salt solution A is 1 mol / L to 3 mol / L.

[0054] The complexing agent, precipitant, and mixed metal salt solution A are mixed and subjected to a co-precipitation reaction to obtain mixture B, which includes the hydroxide precursor of lithium-rich nickel-based cathode material.

[0055] The complexing agent, precipitant, and mixed metal salt solution A undergo a co-precipitation reaction to generate a hydroxide precursor precipitate. Mixture B contains liquid and precipitate particles.

[0056] Understandably, the solution after mixing the complexing agent, precipitant, and mixed metal salt solution A has an alkaline pH to ensure the smooth formation of the hydroxide precursor. Optionally, the pH of the reaction solution is 10-12.

[0057] In some embodiments, the coprecipitation reaction is carried out under stirring and heating conditions to accelerate the reaction rate and improve reaction uniformity, avoiding agglomeration during the reaction. Optionally, the stirring speed is 200 rpm-400 rpm, and the heating temperature is 25°C-60°C.

[0058] In some embodiments, a complexing agent, a precipitant, and a mixed metal salt solution A are added separately. The complexing agent is added at a rate of 5-10 ml / min, the precipitant is added at a rate of 5-10 ml / min, and the mixed metal salt solution A is added at a rate of 2-5 ml / min. The reaction rate is controlled by controlling the addition rate of the reactants, and the morphology of the hydroxide precursor precipitate is adjusted.

[0059] In some embodiments, the complexing agent is an ammonia solution. The precipitant is an inorganic alkaline solution, such as sodium hydroxide or potassium hydroxide.

[0060] S03: Mixture B is centrifuged, washed and dried to obtain the hydroxide precursor.

[0061] Remove impurities from mixture B to reduce their impact.

[0062] S04: The lithium source and hydroxide precursor are mixed and reacted by high-temperature solid-state synthesis to obtain lithium-rich nickel-based cathode material.

[0063] The lithium source and hydroxide precursor undergo a synthesis reaction at high temperature to generate lithium-rich nickel-based cathode material.

[0064] In some embodiments, the high-temperature solid-state synthesis method is carried out in a protective atmosphere of nitrogen or argon to avoid introducing too much oxygen during the reaction process, which would affect crystal formation.

[0065] In some embodiments, the method of mixing a lithium source with a hydroxide precursor and reacting them via a high-temperature solid-state synthesis method includes the following steps:

[0066] The lithium source and hydroxide precursor are mixed and then placed in a high-temperature atmosphere tube furnace. Under a protective atmosphere, the temperature is raised to 400℃-500℃ at a heating rate of (2-10)℃ / min and held for sintering for 2-5 hours. Then, a second heating is carried out to raise the temperature to 700℃-800℃ and held for 12-24 hours to obtain the lithium-rich cathode material.

[0067] The first stage of heating is mainly used to melt the lithium source to prepare for the synthesis reaction. In the second stage of heating, the molten lithium source and hydroxide precursor undergo a synthesis reaction. The temperature of 700℃-800℃ can provide sufficient reaction energy to make the synthesis reaction proceed in the forward direction.

[0068] Optionally, the molar ratio of lithium to hydroxide precursor in the lithium source is (1-2.5):1. By controlling the molar ratio of lithium to hydroxide precursor, the proportion of each element in the crystal can be controlled to obtain lithium-rich nickel-based cathode material crystals with larger unit cell parameters.

[0069] In some embodiments, the lithium source can be LiOH·H2O, which is a common lithium source material that is readily available and has good reaction performance.

[0070] The method for preparing lithium-rich nickel-based cathode materials provided in this application involves a one-step co-precipitation reaction to synthesize a uniformly doped hydroxide precursor. Then, the hydroxide precursor is mixed with a lithium source and a high-valence cation-doped lithium-rich nickel-based cathode material is prepared by a high-temperature solid-state synthesis method. The preparation process is simple and controllable, which is conducive to industrial production.

[0071] This application also provides a positive electrode sheet, comprising the above-described lithium-rich nickel-based positive electrode material or the lithium-rich nickel-based positive electrode material obtained by the above-described preparation method. The positive electrode sheet of this application includes a current collector and a positive electrode active layer bonded to the surface of the current collector, wherein the positive electrode active layer is doped with the lithium-rich nickel-based positive electrode material described in this application. Because the positive electrode sheet of this application contains the above-described lithium-rich nickel-based positive electrode material, it exhibits superior cycle performance and rate capability.

[0072] In some embodiments, the mass content of lithium-rich nickel-based cathode material in the cathode active layer can be 70 wt% to 90 wt%. In addition to the lithium-rich nickel-based cathode material, the electrode active layer also includes a binder and a conductive agent.

[0073] The content of the binder in the positive electrode active layer can be 5wt% to 15wt%. In some embodiments, the binder can be a commonly used positive electrode binder, such as one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methylcellulose, methylcellulose, carboxymethylcellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivatives.

[0074] The content of the conductive agent in the positive electrode active layer can be 5wt% to 15wt%; in some embodiments, the conductive agent can be a commonly used conductive agent, such as one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nanotubes.

[0075] This application also provides a secondary battery, which includes necessary components such as a positive electrode, a negative electrode, a separator, and an electrolyte, as well as other necessary or auxiliary components. The positive electrode is the same as that in this application embodiment, specifically a positive electrode with a lithium-rich nickel-based positive electrode material in its active layer. The secondary battery provided in this application embodiment uses the lithium-rich nickel-based positive electrode material provided in this application for its positive electrode, and the cell parameters and I0 of the lithium-rich nickel-based positive electrode material are... (003) / I (104)The large value and stable crystal structure solve the problem of irreversible release of lattice oxygen when the charging voltage reaches 4.5V or above, thereby improving the stability of the battery.

[0076] The following examples illustrate this point.

[0077] Example 1

[0078] The lithium-rich nickel-based cathode material in this embodiment is doped with Al. 3+ Ti 4+ The lithium-rich nickel cathode material, with dual high-valence cations and cobalt as the transition metal M, has a polyanionic coating layer on its outer surface.

[0079] The preparation method of the lithium-rich nickel-based cathode material in this embodiment includes the following steps:

[0080] Step 1: Add 0.095 mol NiSO4·6H2O, 0.003 mol CoSO4·7H2O, 0.001 mol Ti(SO4)2 and 0.001 mol Al2(SO4)3·18H2O to 49 ml of deionized water to obtain a clear 2 mol / L metal salt solution.

[0081] Step 2: Take 25wt% ammonia water, dilute it with deionized water, and prepare ammonia solutions with molar concentrations of 0.5mol / L and 3mol / L as reaction complexing agents.

[0082] Step 3: Add 80g of NaOH to 500mL of deionized water to prepare a 4mol / L NaOH solution as a precipitant.

[0083] Step 4: Add 100 ml of the prepared 0.5 mol / L ammonia solution to the coprecipitation reaction apparatus. While stirring at 300 rpm and heating at 50°C, simultaneously add NaOH solution at a flow rate of 6 ml / min, ammonia solution at a flow rate of 5 ml / min, and 2 mol / L metal salt solution at a flow rate of 3 ml / min using a peristaltic pump. The pH of the reaction solution is maintained at 11.5.

[0084] Step 5: After reacting for 18 hours, the resulting precipitate is centrifuged, washed, and dried to obtain Al. 3+ Ti 4+ Hydroxide precursors for lithium-rich nickel cathode materials doped with dual high-valence cations, the morphology of the hydroxide precursors are as follows: Figure 1 As shown.

[0085] Step 6: Mix LiOH·H2O with the above hydroxide precursor at a molar ratio of 1.05:1, and then place the mixture in a ball mill and ball mill at a frequency of 25 Hz for 30 min.

[0086] Step 7: Transfer the ball-milled sample to a high-temperature atmosphere tube furnace, heat it to 450°C at a heating rate of 2°C / min under a protective argon atmosphere, and hold it for 3 hours for sintering. Then, perform a second heating stage, heating it to 750°C and holding it for 12 hours. The sintered product is then ground and sieved to obtain lithium-rich nickel cathode material.

[0087] Step 8: Add 20g of the lithium-rich cathode material prepared in Step 7 to 100ml of anhydrous ethanol and disperse it. Stir it with ultrasound to form a uniformly dispersed turbid liquid A. Add 0.362g of Zr(SO4)2·4H2O and 0.132g of LiH2PO4 to deionized water and stir to dissolve them into a clear solution B. While continuously stirring solution B, slowly add turbid liquid A dropwise. Then heat at 50℃ and stir at 300rpm until the solution is completely evaporated. Then transfer the solid to a vacuum oven and dry it overnight at 110℃ under vacuum.

[0088] Step 9: Transfer the dried sample to a tube furnace under an argon atmosphere and heat it to 700°C at a heating rate of 5°C / min. Hold the temperature for 4 hours. After sintering, grind and sieve the product to obtain a lithium-rich nickel cathode material doped with double high-valence cations coated with LiZr(PO4)3.

[0089] Example 2

[0090] This embodiment provides a Cr 3+ Sn 4+ The lithium-rich nickel-based cathode material doped with dual high-valence cations is prepared in this embodiment using a method that is largely the same as the method in Example 1, except that:

[0091] (1) In step 1, Ti(SO4)2 is changed to Cr2(SO4)3;

[0092] (2) In step 1, Al2(SO4)3·18H2O is changed to Sn(SO4)2.

[0093] Comparative Example 1

[0094] This comparative example provides a lithium-rich nickel-based low-cobalt cathode material, the structural formula of which is: Li 1+x Ni y Co z O sExcept for the absence of high-valence cations, the preparation method of the lithium-rich nickel-based cathode material in this comparative example is the same as that in Example 1.

[0095] Comparative Example 2

[0096] This embodiment provides a lithium-rich nickel-based low-manganese cathode material, the structural formula of which is: Li 1+x Ni y Mn z O s The preparation method of the lithium-rich nickel-based cathode material in this comparative example is largely the same as that in Example 1, except that it is not doped with high-valence cations.

[0097] (1) In addition to not being doped with high-valence cations;

[0098] (2) In step 1, CoSO4·7H2O is changed to MnSO4·4H2O.

[0099] Performance testing

[0100] Furthermore, in order to verify the progressiveness of the embodiments of this application, the lithium-rich nickel-based materials of Embodiment 1, Embodiment 2, Comparative Example 1 and Comparative Example 2 were subjected to the following performance tests.

[0101] 1. Appearance and morphology test

[0102] Please see Figure 1 , Figure 1 The image shows a field emission scanning electron microscope image of the lithium-rich nickel-based cathode material precursor of Example 1. It can be seen from the image that it consists of spherical particles composed of small thin flakes, with a size of about 3.5 μm.

[0103] Please see Figure 2 , Figure 2 Al of Example 1 3+ Ti 4+ Field emission scanning electron microscope image of lithium-rich nickel cathode material doped with dual high-valence cations. The image shows that it is an octahedron of varying sizes, with a particle size of approximately 400-700 nm.

[0104] Please see Figure 3 , Figure 3 Al of Example 1 3+ Ti 4+ A refined Rietveld structure diagram of a lithium-rich nickel-based cathode material doped with two high-valence cations. Based on the refined structure, its unit cell parameters can be derived as follows: Furthermore, c0 / a0 = 4.934, indicating that the material has a relatively good crystal structure. Its I (003) / I (104)The value is 1.5, which is greater than 1.2, and the proportion of Ni at the Li site is 0.0307, ​​indicating that the degree of cation mixing in this material is low.

[0105] 2. Method for evaluating the effectiveness of electricity collection:

[0106] A) Battery assembly:

[0107] ① Positive electrode sheet: The positive electrode materials prepared in Example 1, Example 2, Comparative Example 1 and Comparative Example 2 were used as active materials. The active materials were mixed with polyvinylidene fluoride and SP-Li in a mass ratio of 80:10:10 and ball-milled to obtain a positive electrode slurry. The positive electrode slurry was coated on the surface of aluminum foil and dried in positive air at 120°C for 2 hours to obtain positive electrode sheets.

[0108] ② Negative electrode: Lithium metal sheet;

[0109] ③ Electrolyte: Mix ethylene carbonate and methyl ethyl carbonate in a volume ratio of 3:7, and add 1 mol / L LiPF6 to form an electrolyte;

[0110] ④Separator: Polypropylene microporous separator;

[0111] ⑤ Lithium-ion battery assembly: Lithium-ion batteries are assembled in an inert atmosphere glove box according to the assembly sequence of negative electrode sheet-separator-electrolyte-positive electrode sheet; wherein, the lithium-ion batteries corresponding to the positive electrode materials of Examples 1 and 2 are batteries A1 and A2 respectively, and the lithium-ion batteries corresponding to the positive electrode materials of Comparative Examples 1 and 2 are batteries B1 and B2 respectively.

[0112] B) Performance Testing:

[0113] The electrochemical performance of batteries A1, A2, B1, and B2 was tested under the following conditions: the assembled batteries were placed at room temperature for 6 hours before charge-discharge testing was performed. The charge-discharge voltage was 2.0-4.7V and the rate was 0.1C. The test results are shown in Table 1 below. The rate performance of the batteries was tested at 0.1C, 0.5C, 1C, and 2C, and the results are shown in Table 2.

[0114] Table 1

[0115]

[0116] Table 2

[0117]

[0118] As can be seen from the battery test results in Table 1, the two Al types coated with polyanionic polymers... 3+ Ti 4+ and Cr 3+ Sn 4+The lithium-rich nickel-based cathode material doped with dual high-valence cations has a significantly higher first-cycle discharge specific capacity and capacity retention after 50 cycles than the same polyanionic coated but undoped Li-based cathode material. 1+x Ni y Co z O s and Li 1+x Ni y Mn z O s This indicates that doping with high-valence cations can significantly improve the discharge capacity of the material, enhance structural stability, and increase capacity retention. Among them, Al... 3+ Ti 4+ The lithium-rich nickel-based cathode material doped with two high-valent cations achieved a first-cycle discharge specific capacity of 256 mAh / g, which is higher than that of Cr. 3+ Sn 4+ The lithium-rich cathode material doped with two high-valence cations has higher efficiency, indicating that Al... 3+ Ti 4+ The doping effect of dual high-valence cations is higher than that of Cr. 3 + Sn 4+ The doping effect of dual high-valence cations is mainly Al 3+ Ti 4+ Doping with dual high-valent cations can further expand the interlayer spacing and accelerate the Li... + The diffusion and transfer of these substances are significant. However, the two types of high-valence cation doping have essentially the same effect on the structural stability of the bulk material, meaning that these high-valence cations can effectively alleviate the problem of Li-Ni mixing.

[0119] Table 2 shows the rate performance results of each cathode material: the lithium-rich cathode material doped with high-valence cations exhibits excellent rate performance, indicating that high-valence cation doping can effectively improve the crystal structure of the material and accelerate the lithium enrichment process. + The diffusion and transfer of Li can still be effectively completed under high current load. + The de-embedding, in which Al 3+ Ti 4+ The effect of doping with two high-valence cations is more significant. Furthermore, as shown in Table 1, undoped Li... 1+x Ni y Co z O s and Li 1+x Ni y Mn z O s The initial discharge capacity of Li is basically the same, but the capacity retention rate is different. 1+x Ni y Mn z O sIt must be greater than Li 1+x Ni y Co z O s Because the addition of Mn can improve the structural stability of the material system, however, in terms of rate performance, Li 1+x Ni y Co z O s It must be greater than Li 1+x Ni y Mn z O s Because the addition of Co can improve the Li content of the material system. + Diffusion rate.

[0120] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A lithium-rich nickel-based cathode material, characterized in that: This includes a lithium-rich nickel-based cathode material and a high-valence cation N doped in the lithium-rich nickel-based cathode material. The high-valence cation N includes metal ions N1 and N2, and each of the metal ions N1 and N2 is independently Al. 3+ Ce 3+ Ce 4+ Sn 4+ Ti 4+ Cr 3+ Zr 4+ 、Nb 5+ W 5+ V 5+ Mo 6+ One of them, wherein the metal ions N1 and N2 are different; The general structural formula of the lithium-rich nickel-based cathode material is: Li 1+ x Ni a M b N1 c N2 d O2, wherein M is a transition metal, 0 < x ≤ 2, 0.85 ≤ a ≤ 0.95, 0 ≤ b ≤ 0.15, 0 < c ≤ 0.015, 0 < d ≤ 0.01; and the lithium-rich nickel-based cathode material has a polyhedral particle morphology, is hexagonal in crystal, and its unit cell includes three edges of lengths a0, b0, and c0, where a0 = b0 ≠ c0. The I of the cell of the lithium-rich nickel-based cathode material (003) / I (104) The value range is 1.2-1.5; The transition metal M includes at least one of Mn, Co, Fe, and Cr.

2. The lithium-rich nickel-based cathode material as described in claim 1, characterized in that: M is Co, N1 is Ti, N2 is Al, and the general structural formula of the lithium-rich nickel-based cathode material is: Li 1+x Ni a Co b Ti c Al d O2.

3. The lithium-rich nickel-based cathode material as described in any one of claims 1 to 2, characterized in that: The outer surface of the lithium-rich nickel-based cathode material has a coating layer, which includes a polyanionic material. And / or, the outer surface of the lithium-rich nickel-based cathode material has a coating layer comprising a polyanionic metal phosphate.

4. A method for preparing a lithium-rich nickel-based cathode material, characterized in that: The method for preparing the lithium-rich nickel-based cathode material as described in any one of claims 1 to 3 includes the following steps: Nickel salt, metallic M salt, and high-valence cation N salt are mixed to obtain mixed metal salt solution A; A complexing agent, a precipitant and a mixed metal salt solution A are mixed and a co-precipitation reaction is carried out to obtain a mixture B, wherein the mixture B includes the hydroxide precursor of the lithium-rich nickel-based cathode material; The mixture B was subjected to centrifugation, washing and drying to obtain the hydroxide precursor; The lithium source is mixed with the hydroxide precursor and reacted by a high-temperature solid-state synthesis method to obtain the lithium-rich nickel-based cathode material.

5. The method for preparing the lithium-rich nickel-based cathode material as described in claim 4, characterized in that: The high-valent cation N salt includes high-valent cation N1 salt and high-valent cation N2 salt. The molar ratio of nickel, M, N1, and N2 in the nickel salt, metallic M salt, high-valent cation N1 salt, and high-valent cation N2 salt is: a:b:c:d, 0.9≤a≤0.95, 0.5≤b≤0.1, 0<c≤0.01, 0<d≤0.01; And / or, the complexing agent is an ammonia solution, and the precipitant is an inorganic alkaline solution.

6. A positive electrode plate, characterized in that: This includes the lithium-rich nickel-based cathode material as described in any one of claims 1 to 3, or the lithium-rich nickel-based cathode material obtained by the preparation method described in claim 4 or 5.

7. A secondary battery, comprising a positive electrode, a negative electrode, and a separator disposed between the positive electrode and the negative electrode, characterized in that: The positive electrode is the positive electrode as described in claim 6.

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