Gradient lithium-rich manganese-based positive electrode material, preparation method and application thereof, and lithium ion battery positive electrode plate

Abstract

The invention provides a gradient lithium-rich manganese-based positive electrode material, a preparation method and application thereof, and a lithium ion battery positive electrode plate, and belongs to the technical field of lithium ion batteries. According to the gradient lithium-rich manganese-based positive electrode material provided by the invention, the oxide containing rare earth elements is used as the coating layer to form the cathode protection layer, so that the rate capability and the cycle performance of the lithium-rich manganese-based positive electrode material are improved; the doping amount of rare earth elements in the lithium-rich manganese-based positive electrode material is controlled to be gradually increased from inside to outside, so that an energy barrier in a lithium ion migration process is influenced, and the migration rate of lithium ions is favorably improved; the radius of the rare earth atoms is relatively large, so that a three-dimensional ion channel in the positive electrode material can be expanded, and the migration rate of lithium ions is further improved; the gradient doping of the rare earth elements effectively inhibits the structural change of the electrode material in the charge-discharge process, improves the capacity retention ratio and rate capability of the lithium ion battery, can further promote the uniform diffusion of lithium ions, and improves the capacity retention ratio of the battery.

Description

Technical Field

[0001] The present invention relates to the technical field of lithium-ion batteries, and in particular to a gradient lithium-rich manganese-based positive electrode material, a preparation method and application thereof, and a lithium-ion battery positive electrode sheet. Background Art

[0002] With the depletion of energy, the search for clean and efficient energy has become a current research hotspot. In terms of travel, electric vehicles, as an environmentally friendly and efficient way of travel, are gradually replacing traditional fuel vehicles. The power core of electric vehicles is the battery device. One of the key materials that provide energy in the battery is the positive electrode material. Currently, the commercial lithium-ion battery positive electrode materials mainly include lithium manganese oxide, lithium iron phosphate, lithium cobalt oxide, nickel cobalt manganese oxide, etc. The actual specific capacity is 110~220mAh / g, which is far lower than the specific capacity of the negative electrode material. Therefore, the positive electrode material has become the key to further improving the performance of lithium-ion batteries.

[0003] In 2004, the Argonne National Laboratory in the United States synthesized xLi2MnO3·(1-x)LiMO2 (M=Ni, Co, Mn) lithium-rich manganese-based positive electrode materials for the first time, with a specific capacity of up to 250mAh / g and an operating voltage of 3.6V. Due to its high energy density and operating voltage, lithium-rich manganese-based positive electrode materials are expected to become the positive electrode materials for the next generation of commercial high-energy lithium batteries. However, the low first coulombic efficiency, severe voltage decay, and low cycle and rate performance of batteries prepared using lithium-rich manganese-based positive electrode materials limit their practical applications.

[0004] At present, the research on lithium-rich manganese-based positive electrode materials is mainly to improve the cycle stability and specific capacity of the battery by doping or coating the lithium-rich manganese-based positive electrode materials. The first cycle specific capacity at 0.1C reaches 276.2mAh / g. However, after the electrode made of such lithium-rich manganese-based positive electrode materials is used to form a battery, the ion migration resistance of the battery is relatively high, generally above 40Ω, and the capacity retention rate is poor, only reaching 96%. Summary of the invention

[0005] The purpose of the present invention is to provide a gradient lithium-rich manganese-based positive electrode material and its preparation method and application, and a lithium-ion battery positive electrode sheet. The gradient lithium-rich manganese-based positive electrode material provided by the present invention can improve the ion migration performance and capacity retention rate of the battery.

[0006] In order to achieve the above-mentioned object of the invention, the present invention provides the following technical solutions:

[0007] The present invention provides a gradient lithium-rich manganese-based positive electrode material having a core-shell structure, including a core center, a core surface layer and a coating layer arranged in sequence from the inside to the outside;

[0008] The composition of the core center is shown in Formula I

[0009] xLi2MnO3·(1-x)LiTMM a O2 Formula I,

[0010] The composition of the core surface layer is shown in Formula II

[0011] yLi2MnO3·(1-y)LiTMM b O2 Formula II,

[0012] In the formula I and formula II, 0<y<x<1, 0.01<a<b<4, TM is Ni, Co and Mn, and M is a rare earth element;

[0013] The coating layer is an oxide containing rare earth elements.

[0014] Preferably, the molar ratio of Ni, Co and Mn in the gradient lithium-rich manganese-based positive electrode material is (14-30):(5-11):(50-90).

[0015] Preferably, the rare earth element includes one or more of lanthanum, cerium, praseodymium, neodymium or yttrium.

[0016] Preferably, the coating layer has a thickness of 2 to 50 nm.

[0017] The present invention also provides a method for preparing the gradient lithium-rich manganese-based positive electrode material described in the above technical solution, comprising the following steps:

[0018] 1) mixing a metal source solution with an alkali solution, a complexing agent solution and a rare earth salt solution in parallel to perform a coprecipitation reaction to obtain a layered oxide precursor; the metal source solution is a solution containing nickel ions, cobalt ions and manganese ions; during the coprecipitation reaction, adjusting the ratio of nickel, cobalt and manganese in the reaction system and the concentration of rare earth ions as the reaction progresses;

[0019] 2) The layered oxide precursor obtained in step 1) is mixed with a lithium source and then sintered to obtain a gradient lithium-rich manganese-based positive electrode material.

[0020] Preferably, in step 1), the total concentration of nickel ions, cobalt ions and manganese ions in the metal source solution is 0.2-4 mol / L.

[0021] Preferably, the pH value of the co-precipitation reaction in step 1) is 7-12, and the temperature is 40-70°C.

[0022] Preferably, the sintering in step 2) includes a first sintering and a second sintering performed sequentially, wherein the first sintering temperature is 400-700° C. and the holding time is 4-10 hours; the second sintering temperature is 600-1000° C. and the holding time is 6-24 hours.

[0023] The present invention also provides the application of the gradient lithium-rich manganese-based positive electrode material described in the above technical solution in a lithium-containing energy storage device.

[0024] The present invention also provides a lithium-ion battery positive electrode sheet, comprising a current collector and a conductive agent, a binder and an active material coated on the current collector, wherein the active material is the gradient lithium-rich manganese-based positive electrode material described in the above technical solution.

[0025] The present invention provides a gradient lithium-rich manganese-based positive electrode material having a core-shell structure, comprising a core center, a core surface layer and a coating layer arranged in sequence from the inside to the outside; the composition of the core center is as shown in Formula I xLi2MnO3·(1-x)LiTMM a O2 formula I, the composition of the core surface layer is shown in formula II yLi2MnO3·(1-y)LiTMM b O2 formula II, in formula I and formula II, 0<y<x<1, 0.01<a<b<4, TM is Ni, Co and Mn, and M is a rare earth element; the coating layer is an oxide containing a rare earth element. The positive electrode material provided by the present invention uses an oxide containing rare earth elements as a coating layer to form a cathode protection layer, which inhibits the structural change of the surface phase of the lithium-rich manganese-based positive electrode material, the escape of lattice oxygen, the oxidation of the electrolyte and the dissolution of the salt, thereby improving the rate performance and cycle performance of the lithium-rich manganese-based positive electrode material; by controlling the ratio of the two structural units of monoclinic Li2MnO3 and rhombic LiTMO2 in the inner core from the inside to the outside, the structural stability of the material during the charge and discharge process is improved, thereby improving the capacity retention rate, discharge specific capacity and safety performance of the lithium-rich manganese-based positive electrode material in the lithium ion battery; by controlling the doping amount of rare earth elements in the lithium-rich manganese-based positive electrode material to gradually increase from the inside to the outside, the energy barrier in the lithium ion migration process is affected, which helps to improve the migration rate of lithium ions; and the radius of rare earth atoms is large, which can expand the three-dimensional ion channel in the positive electrode material and further improve the migration rate of lithium ions; through the gradient doping of rare earth elements, the structural change of the electrode material during the charge and discharge process is effectively inhibited, the capacity retention rate and rate performance of the lithium ion battery are improved, and the uniform diffusion of lithium ions can be further promoted to improve the capacity retention rate of the battery. The results of the embodiment show that the gradient lithium-rich manganese-based positive electrode material provided by the present invention has an ion migration resistance of 20 to 24Ω; the gradient lithium-rich manganese-based positive electrode material provided by the present invention is used to make an electrode, which is assembled into a 2032 button battery, and activated for 3 cycles under the conditions of voltage 2.0 to 4.8V and current density 0.1C, and then a charge and discharge cycle test is carried out under the conditions of voltage 2.0 to 4.8V and current density 0.1C, and the capacity retention rate for 100 cycles is 99.2 to 99.8%. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 Schematic diagram of the structure of the gradient lithium-rich manganese-based positive electrode material prepared in Example 1. DETAILED DESCRIPTION

[0027] All raw materials of the present invention have no particular limitation on their sources and can be purchased from the market or prepared according to conventional methods known to those skilled in the art.

[0028] There is no particular limitation on the purity of all raw materials in the present invention. The present invention preferably uses high-purity or conventional purity in the field of lithium-ion batteries.

[0029] The present invention provides a gradient lithium-rich manganese-based positive electrode material having a core-shell structure, including a core center, a core surface layer and a coating layer arranged in sequence from the inside to the outside;

[0030] The composition of the core center is shown in Formula I

[0031] xLi2MnO3·(1-x)LiTMM a O2 Formula I,

[0032] The composition of the core surface layer is shown in Formula II

[0033] yLi2MnO3·(1-y)LiTMM b O2 Formula II,

[0034] In the formula I and formula II, 0<y<x<1, 0.01<a<b<4, TM is Ni, Co and Mn, and M is a rare earth element;

[0035] The coating layer is an oxide containing rare earth elements.

[0036] The gradient lithium-rich manganese-based positive electrode material provided by the present invention includes a core center, and the composition of the core center is shown in Formula I. As an embodiment of the present invention, x in Formula I can be 0.5 or 0.4; a in Formula I can be 0.01 or 0.1. In an embodiment of the present invention, x in Formula I is 0.5 and a is 0.01.

[0037] The gradient lithium-rich manganese-based positive electrode material provided by the present invention also includes a core surface layer arranged outside the core center, and the composition of the core surface layer is shown in Formula II. As an embodiment of the present invention, y in Formula II can be 0.4 or 0.2; b in Formula II can be 0.5 or 2.0.

[0038] In the present invention, there is a gradually transitioning intermediate layer between the core center and the core surface layer, and the phase structure and the doping amount of rare earth elements of the intermediate layer are between those of the core center and the core surface layer.

[0039] In the present invention, TM in Formula I and Formula II is Ni, Co and Mn. As an embodiment of the present invention, the TM can be Ni0.42 Mn 0.42 Co 0.16 .

[0040] In the present invention, M in Formula I and Formula II is a rare earth element, and the rare earth element preferably includes one or more of lanthanum, cerium, praseodymium, neodymium or yttrium. As an embodiment of the present invention, the rare earth element can be lanthanum and cerium, cerium and praseodymium, praseodymium and neodymium, or neodymium and yttrium.

[0041] The gradient lithium-rich manganese-based positive electrode material provided by the present invention also includes a coating layer coated on the outside of the core surface layer. In the present invention, the coating layer is an oxide containing rare earth elements, preferably one or more of lanthanum-containing oxides, cerium-containing oxides, praseodymium-containing oxides, neodymium-containing oxides or yttrium-containing oxides. As an embodiment of the present invention, the rare earth element-containing oxide can be lanthanum-containing oxides and cerium-containing oxides, cerium-containing oxides and praseodymium-containing oxides, praseodymium-containing oxides and neodymium-containing oxides, or neodymium-containing oxides and yttrium-containing oxides. As another embodiment of the present invention, the lanthanum-containing oxide includes lanthanum oxide and lithium lanthanum oxide, the cerium-containing oxide includes cerium oxide and lithium cerium oxide, the praseodymium-containing oxide includes praseodymium oxide and lithium praseodymium oxide, the neodymium-containing oxide includes neodymium oxide and lithium neodymium oxide, and the yttrium-containing oxide includes yttrium oxide and lithium yttrium oxide. When the coating layer contains multiple rare earth oxides, the present invention has no requirement on the ratio of each rare earth oxide.

[0042] In the present invention, the thickness of the coating layer is preferably 2 to 50 nm, more preferably 10 to 40 nm, and further preferably 20 to 30 nm. As an embodiment of the present invention, the thickness of the coating layer may be 2 nm, 3 nm, 4 nm, 5 nm, 10 nm, 15 nm, 20 nm, 25 nm, 30 nm, 35 nm, 40 nm, 45 nm or 50 nm. The present invention limits the thickness of the coating layer to the above range, which is conducive to further improving the rate performance and cycle performance of the positive electrode material.

[0043] In the present invention, the molar ratio of Ni, Co, and Mn in the gradient lithium-rich manganese-based positive electrode material is preferably (14-30): (5-11): (50-90). As an embodiment of the present invention, the molar ratio of Ni, Co, and Mn in the lithium-rich manganese-based positive electrode material can be 14:5:50, 18:7:50, 20:8:60, 25:10:80, or 30:11:70.

[0044] The present invention uses an oxide containing rare earth elements as a coating layer to form a cathode protection layer, thereby inhibiting the structural change of the surface phase of the lithium-rich manganese-based positive electrode material, the escape of lattice oxygen, the oxidation of the electrolyte and the dissolution of the salt, thereby improving the rate performance and cycle performance of the lithium-rich manganese-based positive electrode material; by controlling the ratio of the two structural units of monoclinic Li2MnO3 and rhombic LiTMO2 in the inner core from the inside to the outside, the structural stability of the material during the charge and discharge process is improved, thereby improving the capacity retention rate, discharge specific capacity and safety performance of the lithium-rich manganese-based positive electrode material in the lithium-ion battery; by controlling the doping amount of rare earth elements in the lithium-rich manganese-based positive electrode material to gradually increase from the inside to the outside, the energy barrier in the lithium ion migration process is affected, which helps to improve the migration rate of lithium ions; and the radius of rare earth atoms is relatively large, which can expand the three-dimensional ion channel in the positive electrode material and further improve the migration rate of lithium ions; through the gradient doping of rare earth elements, the structural change of the electrode material during the charge and discharge process is effectively inhibited, the capacity retention rate and rate performance of the lithium-ion battery are improved, and the uniform diffusion of lithium ions can be further promoted to improve the capacity retention rate of the battery.

[0045] The present invention also provides a method for preparing the gradient lithium-rich manganese-based positive electrode material described in the above technical solution, comprising the following steps:

[0046] 1) mixing a metal source solution with an alkali solution, a complexing agent solution and a rare earth salt solution in parallel to perform a coprecipitation reaction to obtain a layered oxide precursor; the metal source solution is a solution containing nickel ions, cobalt ions and manganese ions; during the coprecipitation reaction, adjusting the ratio of nickel ions, cobalt ions and manganese ions in the reaction system and the concentration of rare earth ions as the reaction progresses;

[0047] 2) The layered oxide precursor obtained in step 1) is mixed with a lithium source and then sintered to obtain a gradient lithium-rich manganese-based positive electrode material.

[0048] The invention mixes a metal source solution with an alkali solution, a complexing agent solution and a rare earth salt solution in parallel to carry out a coprecipitation reaction to obtain a layered oxide precursor.

[0049] In the present invention, the metal source solution is preferably a mixed solution of a nickel salt, a cobalt salt and a manganese salt. As an embodiment of the present invention, the nickel salt may be any one or more of nickel nitrate, nickel acetate, nickel chloride or nickel sulfate; the cobalt salt may be any one or more of cobalt nitrate, cobalt acetate, cobalt chloride or cobalt sulfate; the manganese salt may be any one or more of manganese nitrate, manganese acetate, manganese chloride or manganese sulfate.

[0050] In the present invention, the total concentration of nickel ions, cobalt ions and manganese ions in the metal source solution is preferably 0.2 to 4 mol / L, more preferably 1 to 3 mol / L. As an embodiment of the present invention, the total concentration of nickel ions, cobalt ions and manganese ions in the metal source solution can be 0.2 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L or 4 mol / L. The total concentration of nickel ions, cobalt ions and manganese ions affects the speed of the coprecipitation reaction. The ion concentration within the above range is conducive to the stable coprecipitation reaction.

[0051] In the present invention, the alkali in the alkaline solution is preferably any one or more of sodium carbonate, sodium bicarbonate, ammonium bicarbonate, ammonium carbonate, sodium hydroxide, potassium hydroxide or lithium hydroxide. Using the above alkaline solution to control the pH value of the reaction system is conducive to the coprecipitation reaction.

[0052] In the present invention, the concentration of the alkaline solution is preferably 0.1-6 mol / L, more preferably 1-5 mol / L, and further preferably 2-4 mol / L; as an embodiment of the present invention, the concentration of the alkaline solution can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L or 6 mol / L. The concentration of the alkaline solution within the above range is conducive to the coprecipitation reaction.

[0053] In the present invention, the complexing agent is preferably any one or more of citric acid solution, oxalic acid solution, ammonia water or ethylenediaminetetraacetic acid solution. The use of the above complexing agent is conducive to the coordinated progress of the coprecipitation reaction and the complexation.

[0054] In the present invention, the concentration of the complexing agent is preferably 0.1-6 mol / L, more preferably 1-5 mol / L, and further preferably 2-4 mol / L; as an embodiment of the present invention, the concentration of the complexing agent can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L or 6 mol / L. The concentration of the complexing agent within the above range is conducive to the coordinated coprecipitation reaction and complexation.

[0055] In the present invention, the rare earth salt in the rare earth salt solution preferably includes any one or more of lanthanum sulfate, lanthanum chloride, lanthanum nitrate, cerium sulfate, cerium chloride, cerium nitrate, praseodymium sulfate, praseodymium chloride, praseodymium nitrate, neodymium sulfate, neodymium chloride, neodymium nitrate, yttrium sulfate, yttrium chloride or yttrium nitrate.

[0056] In the present invention, the concentration of the rare earth salt solution is preferably 0.1-6 mol / L, more preferably 1-5 mol / L, and further preferably 2-4 mol / L; as an embodiment of the present invention, the concentration of the rare earth salt solution can be 0.1 mol / L, 0.5 mol / L, 1 mol / L, 1.5 mol / L, 2 mol / L, 2.5 mol / L, 3 mol / L, 3.5 mol / L, 4 mol / L, 4.5 mol / L, 5 mol / L, 5.5 mol / L or 6 mol / L. The concentration of the rare earth salt solution within the above range is beneficial to the obtained coating layer containing rare earth oxides, and further improves the structural stability and electrochemical activity of the positive electrode material.

[0057] In the present invention, during the coprecipitation reaction, the ratio of nickel ions, cobalt ions, and manganese ions in the reaction system and the concentration of rare earth ions are adjusted as the reaction progresses. The present invention adjusts the ratio of nickel ions, cobalt ions, and manganese ions in the reaction system and the concentration of rare earth ions during the coprecipitation reaction, so that the layered oxide precursor generated by the coprecipitation reaction presents a gradient phase structure and a gradient rare earth doping amount.

[0058] The present invention preferably adjusts the ratio of nickel ions, cobalt ions, and manganese ions in the reaction system and changes the concentration of rare earth ions by adjusting the concentrations of the metal source solution and the rare earth salt solution during co-current mixing.

[0059] As an embodiment of the present invention, the metal source solution can be obtained by mixing a first metal source solution and a second metal source solution, and the proportion of manganese ions in the first metal source solution to the total amount of nickel ions, cobalt ions and manganese ions is higher than the corresponding proportion in the second metal source solution; the ratio of nickel ions, cobalt ions and manganese ions in the metal source solution is adjusted by adjusting the mixing ratio of the first metal source solution and the second metal source solution during parallel mixing; the ratio of nickel ions, cobalt ions and manganese ions in the metal source solution can also be changed by gradually injecting the second metal source solution into a fixed amount of the first metal source solution at a certain rate.

[0060] As an embodiment of the present invention, the rare earth salt solution can be obtained by mixing an initial rare earth salt solution and deionized water, and the concentration of rare earth ions in the rare earth salt solution can be adjusted by adjusting the ratio of the initial rare earth salt solution and the deionized water; the concentration of rare earth ions in the rare earth salt solution can also be changed by gradually injecting the initial rare earth salt solution into a fixed amount of deionized water at a certain rate.

[0061] In the present invention, the pH value of the coprecipitation reaction is preferably 7 to 12, more preferably 8 to 10. As an embodiment of the present invention, the pH value of the coprecipitation reaction can be 7.0, 7.5, 8.0, 8.5, 9.0, 9.5, 10.0, 10.5, 11.0, 11.5 or 12.0. The pH value of the coprecipitation reaction affects the speed of the coprecipitation reaction and the complexation. The present invention limits the pH value of the coprecipitation reaction to the above range, which is conducive to coordinating the speed of the coprecipitation reaction and the complexation to obtain a layered oxide precursor with a stable structure.

[0062] In the present invention, the temperature of the coprecipitation reaction is preferably 40 to 70° C., more preferably 50 to 60° C. As an embodiment of the present invention, the temperature of the coprecipitation reaction may be 40° C., 45° C., 50° C., 55° C., 60° C., 65° C. or 70° C. The temperature of the coprecipitation reaction affects the growth rate of the precursor. The present invention limits the temperature of the coprecipitation reaction to the above range, which is beneficial to improving the sphericity and densification of the precursor.

[0063] After obtaining the layered oxide precursor, the present invention mixes the layered oxide precursor with a lithium source and then sintering to obtain a gradient lithium-rich manganese-based positive electrode material.

[0064] In the present invention, the lithium source preferably includes any one or more of lithium hydroxide, lithium carbonate, lithium oxalate or lithium acetate.

[0065] In the present invention, the molar ratio of the metal element in the layered oxide precursor to the lithium in the lithium source is preferably 1:n, wherein 1<n≤5; as an embodiment of the present invention, the value of n may be 1.5, 2, 2.5, 3, 3.5, 4, 4.5 or 5. The present invention limits the molar ratio of the metal element in the layered oxide precursor to the lithium in the lithium source within the above range, which can further increase the lithium content of the positive electrode material, and is beneficial to improving the electrochemical activity of the positive electrode material.

[0066] In the present invention, the sintering preferably includes a first sintering and a second sintering performed sequentially. The present invention promotes the preliminary decomposition of the precursor and the lithium source through the first sintering, so that the lithium source and the precursor are in full contact, and it is also beneficial to reduce the stress and pores generated during the sintering process; the lithium source and the precursor undergo a solid solution reaction through the second sintering to form a positive electrode material; the present invention is beneficial to further improve the electrochemical performance and structural stability of the positive electrode material through the first sintering and the second sintering performed sequentially.

[0067] In the present invention, the temperature of the first sintering is preferably 400-700° C., more preferably 500-600° C. As an embodiment of the present invention, the temperature of the first sintering may be 400° C., 450° C., 500° C., 550° C., 600° C., 650° C. or 700° C. The present invention limits the temperature of the first sintering to the above range, which is conducive to sufficient contact between the precursor and the lithium source.

[0068] In the present invention, the holding time of the first sintering is preferably 4 to 10 hours, more preferably 6 to 8 hours. In an embodiment of the present invention, the holding time of the first sintering may be 4 hours, 5 hours, 6 hours, 7 hours, 8 hours, 9 hours or 10 hours. The present invention limits the holding time of the first sintering to the above range, which is conducive to fully mixing the precursor with the lithium source and reducing the stress and pores generated by sintering.

[0069] In the present invention, the temperature of the second sintering is preferably 600-1000° C., more preferably 700-900° C. As an embodiment of the present invention, the temperature of the second sintering may be 600° C., 650° C., 700° C., 750° C., 800° C., 850° C., 900° C., 950° C. or 1000° C. The present invention limits the temperature of the second sintering to the above range, which is conducive to the solid solution reaction between the precursor and the lithium source.

[0070] In the present invention, the holding time of the second sintering is preferably 6 to 24 hours, more preferably 10 to 20 hours, and further preferably 14 to 18 hours. In an embodiment of the present invention, the holding time of the second sintering can be 6 hours, 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours or 24 hours. The present invention limits the holding time of the second sintering to the above range, which is conducive to the full reaction of the precursor and the lithium source and improves the structural stability of the positive electrode material.

[0071] The present invention has no special requirements for the sintering environment, as long as the layered oxide precursor and the lithium source can be sintered. In an embodiment of the present invention, the sintering is performed in air.

[0072] The present invention adjusts the ratio of nickel ions, cobalt ions and manganese ions and the concentration change of rare earth ions during the coprecipitation reaction, so that the positive electrode material presents a gradient phase structure and a gradient rare earth element doping amount; during the coprecipitation process, the rare earth elements on the surface of the precursor cannot be completely doped into the lattice, and the excess rare earth elements are enriched on the surface of the material to produce a very thin nano-coating layer, the specific components of which are rare earth oxides and lithium-containing rare earth oxides.

[0073] The present invention also provides the application of the gradient lithium-rich manganese-based positive electrode material described in the above technical solution in a lithium-containing energy storage device.

[0074] The present invention has no particular limitation on the specific manner of the application, and any application manner familiar to those skilled in the art may be adopted.

[0075] The present invention also provides a lithium-ion battery positive electrode sheet, comprising a current collector and a conductive agent, a binder and an active material coated on the current collector, wherein the active material is the gradient lithium-rich manganese-based positive electrode material described in the above technical solution.

[0076] The present invention has no special requirements on the types and amounts of the current collector, conductive agent and binder, and the types and amounts well known to those skilled in the art can be used.

[0077] The technical solutions in the present invention will be described clearly and completely below in conjunction with the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0078] Example 1

[0079] A gradient lithium-rich manganese-based positive electrode material, the gradient lithium-rich manganese-based positive electrode material is a core-shell structure, the core center is 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 Y 0.01 )O2, the outer core is 0.3Li2MnO3·0.7Li(Ni 0.42 Mn 0.42 Co 0.16 Y 0.3 )O2, a coating layer is provided on the surface of the core, the coating layer is LiYO2 and Y2O3, and the average thickness of the coating layer is 12nm.

[0080] The preparation method of the above-mentioned gradient lithium-rich manganese-based positive electrode material is:

[0081] (1) dissolving nickel sulfate, cobalt sulfate and manganese sulfate in deionized water to prepare solution A and solution B with a concentration of 2 mol / L, respectively, wherein the molar ratio of Ni, Co and Mn in solution A is 0.21:0.08:0.71, and the molar ratio of Ni, Co and Mn in solution B is 0.343:0.1305:0.5265; preparing a 0.4 mol / L yttrium sulfate solution;

[0082] (2) 600 mL of solution B was gradually injected into 600 mL of solution A being stirred through a constant flow pump, 600 mL of yttrium sulfate solution was gradually injected into 600 mL of deionized water being stirred, while solution B and yttrium sulfate solution were injected, solution A and solution B being mixed were added into the reactor through a constant flow pump, yttrium sulfate solution and deionized water being mixed were added into the reactor through a constant flow pump, 2 mol / L Na2CO3 solution and 2 mol / L ammonia water were independently added into the reactor through a constant flow pump in parallel, the pH value of the mixed solution in the reactor was controlled to be 8.7, the mixture was stirred at a stirring rate of 1000 rpm, the mixed solution was heated, the reaction temperature was controlled to be 55°C, the reaction was carried out for 10 hours, and a layered oxide precursor was obtained;

[0083] (3) The layered oxide precursor obtained in step (2) and Li2CO3 are uniformly mixed in a ratio of 1.6:1 between the amount of lithium and the total amount of Ni, Mn and Co, and the mixture is pre-sintered at 500°C for 5 h in an air atmosphere, and then heated to 900°C and kept for 10 h to obtain the gradient lithium-rich manganese-based positive electrode material.

[0084] Example 1 The structural diagram of the gradient lithium-rich manganese-based positive electrode material prepared is as follows Figure 1 As shown, there is a phase structure gradient and a gradient distribution of the Y element from the inner core center to the outer core layer, and the outer shell is a coating layer containing Y oxide.

[0085] Example 2

[0086] A gradient lithium-rich manganese-based positive electrode material, the gradient lithium-rich manganese-based positive electrode material is a core-shell structure, the core center is 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 Ce 0.01 )O2, the outer core is 0.4Li2MnO3·0.6Li(Ni 0.42 Mn 0.42 Co 0.16 Ce 0.86 )O2, a coating layer is provided on the surface of the core, the coating layer is LiCeO2 and Ce2O3, and the average thickness of the coating layer is 10nm.

[0087] The preparation method of the above-mentioned gradient lithium-rich manganese-based positive electrode material is:

[0088] (1) dissolving nickel sulfate, cobalt sulfate and manganese sulfate in deionized water to prepare solution A and solution B with a concentration of 2 mol / L, respectively, wherein the molar ratio of Ni, Co and Mn in solution A is 0.21:0.08:0.71, and the molar ratio of Ni, Co and Mn in solution B is 0.2765:0.1055:0.618; preparing a 2 mol / L cerium sulfate solution;

[0089] (2) 600 mL of solution B was gradually injected into 600 mL of solution A being stirred through a constant flow pump, 600 mL of cerium sulfate solution was gradually injected into 600 mL of deionized water being stirred, while solution B and cerium sulfate solution were injected, solution A and solution B being mixed were added into the reactor through a constant flow pump, the mixed solution of cerium sulfate solution and deionized water was added into the reactor through a constant flow pump, 2 mol / L Na2CO3 solution and 2 mol / L ammonia water were independently added into the reactor through a constant flow pump, the pH value of the mixed solution in the reactor was controlled to be 10.2, the mixture was stirred at a stirring rate of 1000 rpm, the mixed solution was heated, the reaction temperature was controlled to be 55°C, the reaction was carried out for 20 hours, and a lithium-rich layered oxide precursor was obtained;

[0090] (3) The lithium-rich layered oxide precursor described in step (2) and Li2CO3 are uniformly mixed in a ratio of 1.6:1 between the amount of lithium and the total amount of Ni, Mn and Co, and the mixture is pre-sintered at 500°C for 5 h in an air atmosphere, and then heated to 900°C and kept for 10 h to obtain the gradient lithium-rich manganese-based positive electrode material.

[0091] Example 3

[0092] A gradient lithium-rich manganese-based positive electrode material, the gradient lithium-rich manganese-based positive electrode material is a core-shell structure, the core center is 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 Nd 0.01 )O2, the outer core layer is 0.2Li2MnO3·0.8Li(Ni 0.42 Mn 0.42 Co 0.16 Nd 3.25 )O2, a coating layer is provided on the surface of the core, the coating layer is LiNdO2 and Nd2O3, and the average thickness of the coating layer is 15nm.

[0093] The preparation method of the above-mentioned gradient lithium-rich manganese-based positive electrode material is:

[0094] (1) dissolving nickel sulfate, cobalt sulfate and manganese sulfate in deionized water to prepare solution A and solution B with a concentration of 1 mol / L, respectively, wherein the molar ratio of Ni, Co and Mn in solution A is 0.21:0.08:0.71, and the molar ratio of Ni, Co and Mn in solution B is 0.409:0.156:0.435; preparing a 4.8 mol / L neodymium sulfate solution;

[0095] (2) 600 mL of solution B was gradually injected into 600 mL of solution A being stirred by a constant flow pump, 600 mL of neodymium sulfate solution was gradually injected into 600 mL of deionized water being stirred, while solution B and neodymium sulfate solution were injected, solution A and solution B being mixed were added into the reactor by a constant flow pump, the mixed solution of neodymium sulfate solution and deionized water was added into the reactor by a constant flow pump, 2 mol / L Na2CO3 solution and 2 mol / L ammonia water were independently added into the reactor by constant flow pumps, the pH value of the mixed solution in the reactor was controlled to be 8.7, the mixture was stirred at a stirring rate of 1000 rpm, the mixed solution was heated, the reaction temperature was controlled to be 55°C, the reaction was carried out for 40 hours, and a lithium-rich layered oxide precursor was obtained;

[0096] (3) The lithium-rich layered oxide precursor described in step (2) and Li2CO3 are uniformly mixed in a ratio of 1.6:1 between the molar number of lithium and the total molar number of Ni, Mn and Co, and the mixture is pre-sintered at 500°C for 5 h in an air atmosphere, and then heated to 900°C and kept for 10 h to obtain the gradient lithium-rich manganese-based positive electrode material.

[0097] Comparative Example 1

[0098] A gradient lithium-rich manganese-based positive electrode material, wherein the phase structure of the gradient lithium-rich manganese-based positive electrode material is a gradient gradual structure, and the center of the particle is 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 )O2, the outer layer of the particle is 0.3Li2MnO3·0.7Li(Ni 0.42 Mn 0.42 Co 0.16 )O2.

[0099] The preparation method is the same as that of Example 1, except that no yttrium sulfate solution is added.

[0100] Comparative Example 2

[0101] A gradient lithium-rich manganese-based positive electrode material, the gradient lithium-rich manganese-based positive electrode material is a core-shell structure, the core center is 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co0.16 Y 0.28 )O2, the outer core is 0.3Li2MnO3·0.7Li(Ni 0.42 Mn 0.42 Co 0.16 Y 0.28 )O2, a coating layer is provided on the surface of the core, the coating layer is LiYO2 and Y2O3, and the average thickness of the coating layer is 12nm.

[0102] The preparation method is the same as that in Example 1, except that the yttrium sulfate solution is directly fed into the reactor.

[0103] Comparative Example 3

[0104] A gradient lithium-rich manganese-based positive electrode material, wherein the phase structure of the gradient lithium-rich manganese-based positive electrode material is a gradient gradual structure, and the center of the particle is 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 Y 0.01 )O2, the outer layer of the particle is 0.3Li2MnO3·0.7Li(Ni 0.42 Mn 0.42 Co 0.16 Y 0.01 )O2.

[0105] The preparation method is the same as that of Example 1, except that the concentration of the yttrium sulfate solution is 0.01 mol / L.

[0106] Comparative Example 4

[0107] A gradient lithium-rich manganese-based positive electrode material, the gradient lithium-rich manganese-based positive electrode material is a core-shell structure, the core center is 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 Y 0.01 )O2, the outer core is 0.3Li2MnO3·0.7Li(Ni 0.42 Mn 0.42 Co 0.16 Y8)O2, a coating layer is arranged on the surface of the core, the coating layer is LiYO2 and Y2O3, and the average thickness of the coating layer is 12nm.

[0108] The preparation method is the same as that of Example 1, except that the concentration of the yttrium sulfate solution is 10 mol / L.

[0109] Comparative Example 5

[0110] A lithium-rich manganese-based positive electrode material, wherein the lithium-rich manganese-based positive electrode material is a core-shell structure, wherein the core center is 0.5Li2MnO3·0.5Li(Ni0.42 Mn 0.42 Co 0.16 Y 0.28 )O2, the outer core layer is 0.5Li2MnO3·0.5Li(Ni 0.42 Mn 0.42 Co 0.16 Y 0.28 )O2, a coating layer is provided on the surface of the core, the coating layer is LiYO2 and Y2O3, and the average thickness of the coating layer is 12nm.

[0111] The preparation method is the same as that in Example 1, except that solution A and solution B are not prepared separately, but 1200 mL of a 2 mol / L mixed solution of nickel, cobalt and manganese in a molar ratio of 0.553:0.2105:1.2365 is directly prepared and added to the reactor in parallel, and the yttrium sulfate solution is also directly added to the reactor in parallel.

[0112] Application Examples 1 to 3 and Comparative Application Examples 1 to 5

[0113] The positive electrode materials prepared in Examples 1 to 3 and Comparative Examples 1 to 5, acetylene black and binder PVDF were mixed in a mass ratio of 8:1:1 to prepare positive electrode slurry, and the positive electrode slurry was evenly coated on an aluminum foil current collector, and after drying, punched and rolled to obtain a positive electrode sheet.

[0114] The negative electrode of the battery is made of lithium sheet, and the electrolyte is LiPF6 / EC+DEC (Colodex). The positive electrode, lithium sheet, separator and electrolyte are assembled into a 2032 button cell in a battery shell. After the battery is prepared, it is left to stand for 12 hours.

[0115] The positive electrode materials prepared in Examples 1 to 3 and Comparative Examples 1 to 5 were tested for ion migration rate, and the batteries of Examples 1 to 3 and Comparative Application Examples 1 to 5 were tested for constant current charge and discharge and rate performance. The test results are shown in Table 1.

[0116] Among them, the test method of ion migration rate is: testing through EIS, testing the ion migration resistance between the electrode and the electrolyte at the 5th cycle.

[0117] The test method for constant current charge and discharge cycle is: at room temperature (25°C), the battery is activated for 3 cycles at a voltage range of 2.0 to 4.8V and a current density of 0.1C, and then the charge and discharge cycle test is carried out at a voltage range of 2.0 to 4.8V and a current density of 0.1C, and the capacity retention rate is tested for 100 cycles.

[0118] The test method for rate performance is: testing the first discharge specific capacity at 2.0-4.8V, 0.1C and 2C.

[0119] Table 1 Electrochemical performance test record

[0120] Ion migration resistance Capacity retention rate 2C first discharge specific capacity 0.1C first discharge specific capacity Example 1 20Ω 99.8％ 210mAh / g 286mAh / g Example 2 22Ω 99.5％ 208mAh / g 284mAh / g Example 3 24Ω 99.2％ 209mAh / g 283mAh / g Comparative Example 1 46Ω 98.1％ 165mAh / g 275mAh / g Comparative Example 2 36Ω 98.4％ 168mAh / g 276mAh / g Comparative Example 3 40Ω 98.2％ 165mAh / g 273mAh / g Comparative Example 4 56Ω 97.5％ 156mAh / g 266mAh / g Comparative Example 5 42Ω 96.2％ 150mAh / g 254mAh / g

[0121] It can be seen from the data in Table 1 that the gradient lithium-rich manganese-based positive electrode material provided by the present invention has good ion mobility, and has a high capacity retention rate and excellent rate performance after being assembled into a battery.

[0122] In Comparative Example 1, yttrium sulfate solution is not added, and the ion migration performance, capacity retention rate and rate performance of the positive electrode material are reduced; in Comparative Example 2, yttrium sulfate is used for uniform doping, and the overall ion migration performance, capacity retention rate and rate performance of the positive electrode material are reduced; It can be seen from Comparative Examples 3 and 4 that if too much or too little yttrium sulfate solution is added, the ion migration performance, capacity retention rate and rate performance of the positive electrode material are reduced; It can be seen from Comparative Example 5 that the phase structure gradient lithium manganese-rich positive electrode material is changed to an ordinary lithium manganese-rich positive electrode material without phase structure change, and the overall ion migration performance, capacity retention rate and rate performance are reduced.

[0123] It can be seen from the above embodiments and comparative examples that the gradient lithium-rich manganese-based positive electrode material provided by the present invention has good ion mobility, and has a high capacity retention rate and excellent rate performance after being assembled into a battery.

[0124] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A gradient lithium-rich manganese-based cathode material having a core-shell structure, including a core center, a core surface layer and a coating layer arranged in sequence from the inside to the outside; The composition of the core center is shown in Formula I xLi2MnO3·(1-x)LiTMM a O2 of formula I The composition of the core surface layer is shown in Formula II yLi2MnO3·(1-y)LiTMM b Formula II of O2 In the formula I and formula II, 0<y<x<1, 0.01<a<b<4, TM is Ni, Co and Mn, and M is a rare earth element; The coating layer is an oxide containing rare earth elements.

2. The gradient lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The molar ratio of Ni, Co and Mn in the gradient lithium-rich manganese-based positive electrode material is (14-30):(5-11):(50-90).

3. The gradient lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The rare earth element includes one or more of lanthanum, cerium, praseodymium, neodymium or yttrium.

4. The gradient lithium-rich manganese-based positive electrode material according to claim 1, characterized in that: The coating layer has a thickness of 2 to 50 nm.

5. The method for preparing the gradient lithium-rich manganese-based positive electrode material according to any one of claims 1 to 4, characterized in that: The steps include: 1) mixing a metal source solution with an alkali solution, a complexing agent solution and a rare earth salt solution in parallel to perform a coprecipitation reaction to obtain a layered oxide precursor; the metal source solution is a solution containing nickel ions, cobalt ions and manganese ions; during the coprecipitation reaction, adjusting the ratio of nickel ions, cobalt ions and manganese ions in the reaction system and the concentration of rare earth ions as the reaction progresses; 2) The layered oxide precursor obtained in step 1) is mixed with a lithium source and then sintered to obtain a gradient lithium-rich manganese-based positive electrode material.

6. The preparation method according to claim 5, characterized in that: In the step 1), the total concentration of nickel ions, cobalt ions and manganese ions in the metal source solution is 0.2-4 mol / L.

7. The preparation method according to claim 5, characterized in that: The pH value of the co-precipitation reaction in step 1) is 7-12, and the temperature is 40-70°C.

8. The preparation method according to claim 5, characterized in that: The sintering in step 2) includes a first sintering and a second sintering performed sequentially, wherein the first sintering temperature is 400-700° C. and the holding time is 4-10 hours; the second sintering temperature is 600-1000° C. and the holding time is 6-24 hours.

9. Use of the gradient lithium-rich manganese-based positive electrode material according to any one of claims 1 to 4 or the gradient lithium-rich manganese-based positive electrode material prepared by the preparation method according to any one of claims 5 to 8 in lithium-containing energy storage devices.

10. A positive electrode sheet for a lithium-ion battery, comprising a current collector and a conductive agent, a binder and an active material coated on the current collector, characterized in that: The active material is the gradient lithium-rich manganese-based positive electrode material described in any one of claims 1 to 4 or the gradient lithium-rich manganese-based positive electrode material prepared by the preparation method described in any one of claims 5 to 8.

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