Lithium-rich layered oxide material with phase structure gradient and its preparation method

Abstract

A lithium-rich layered oxide material with a phase structure gradient and method for making the same are disclosed, used as cathode material for lithium ion battery. The invention has the following technical features: the spherical granule-shaped lithium-rich layered oxide material contains two types of structural units whose ratio gradually changes from the center to the surface of the spherical granule, wherein the monoclinic Li.sub.2MnO.sub.3 structural unit is gradually reduced, and the rhombohedral LiTMO.sub.2 structural unit is gradually increased from the center to the surface of the spherical granule. By controlling the ratio of the monoclinic Li.sub.2MnO.sub.3 structural unit versus the rhombohedral LiTMO.sub.2 structural unit along from the center to the surface the spherical granule, the performance of the Lithium-rich layered oxide materials as cathode for lithium ion battery, such as cyclic stability, specific discharge capacity, safety and other properties, is improved. The preparation process is simple and easy to control, the cost of raw materials is low and the environment is friendly. It can be industrialized on a large scale and has a good prospect of application.

Claims

1. A lithium-rich layered oxide material with a phase structure gradient, comprising: spherical granules comprising material represented by xLi.sub.2MnO.sub.3(1−x)LiTMO.sub.2 (at the core of the spherical granules)-yLi.sub.2MnO.sub.3 (1−y)LiTMO.sub.2 (at the surface of the spherical granules), where the TM is a combination of Ni, Co, and Mn in different molar ratios from one another, wherein 0<y<x<1, wherein a concentration of the monoclinic Li.sub.2MnO.sub.3 structural unit is gradually reduced from the center of the spherical granules to the surface of the spherical granules, and a concentration of the rhombic LiTMO.sub.2 structure unit is gradually increased from the center of the spherical granules to the surface of the spherical granules.

2. A lithium-rich layered oxide material with a phase structure gradient according to claim 1, wherein the lithium-rich layered oxide material is made into a cathode electrode for a lithium-ion battery with a high discharge capacity higher than 250 mAh/g at 25° C.

3. A method for preparing a lithium-rich layered oxide material with a phase structure gradient of claim 1, by a co-precipitation-solid phase synthesis method comprising the steps of: (1) preparing each of a solution A and a solution B from a nickel salt, a cobalt salt and a manganese salt, wherein the total metal concentration of each of the solution A and the solution B is 0.2.sup.˜4 mol/L; wherein the molar ratio of nickel, cobalt, and manganese in the solution A is: 0.05.sup.˜0.3:0.05.sup.˜0.2:0.5.sup.˜0.9; wherein the molar ratio of nickel, cobalt, and manganese in the solution B is: 0.05.sup.˜0.3:0.05.sup.˜0.2:0.5.sup.˜0.9; wherein the molar percentage of manganese in the solution B to nickel, cobalt and manganese is less than the molar percentage of manganese in solution A to nickel, cobalt and manganese; (2) preparing a 0.1.sup.˜6 mol/L alkali solution; (3) preparing a 0.1.sup.˜6 mol/L complexing agent solution; (4) using a co-precipitation method, comprising the steps of: adding solution B to a solution B container, adding solution A to a solution A container, gradually adding the solution B to the solution A container through a constant flow pump with stirring to form a mixed solution, and adding the mixed solution in the solution A container to a reactor through a constant flow pump, thereby the molar percentage concentration of Mn in the mixed solution added to the reactor gradually decreases with the increase of dropping time, whereas the molar percentage concentrations of nickel and cobalt increase gradually; gradually combining and adding into the reactor the alkali solution from step (2) and the complexing agent solution from step (3), controlling the stirring speed in the reactor at 500.sup.˜1500 RPM with the protection of inert gas at 40.sup.˜70° C., keeping pH value between 7.0.sup.˜12.0, to generate a precursor of the lithium-rich layered oxide material with a gradual concentration gradient progression between two structural units by the simultaneous precipitation of multiple elements; (5) the precursor obtained in step (4) is filtered, washed, dried, and mixed with lithium source compounds, wherein the molar ratio of the lithium versus the Ni, Mn, and Co is n:1, with 1<n<5; and (6) in an air atmosphere, the mixture obtained in step (5) is pre-sintered at 400.sup.˜700° C. for 4.sup.˜10 hours, heated at 600.sup.˜1000° C. for 6.sup.˜24 hours, and cooled to room temperature naturally, to obtain the lithium-rich layered oxide material with phase structure gradient.

4. The method according to claim 3, wherein the manganese salt in step (1) is one or more of manganese nitrate, manganese acetate, manganese chloride, and manganese sulfate; wherein the cobalt salt is one or more of cobalt nitrate, cobalt acetate, cobalt chloride, and cobalt sulfate; wherein the nickel salt is one or more of nickel nitrate, nickel acetate, nickel chloride, and nickel sulfate.

5. The method according to claim 3, wherein the alkali solution in step (2) is one or more of sodium bicarbonate, sodium bicarbonate, ammonium bicarbonate, and ammonium carbonate; or one or more of sodium hydroxide, potassium hydroxide, and lithium hydroxide.

6. The method according to claim 3, wherein the complexing agent solution in step (3) is one or more of citric acid, oxalic acid, ammonia, and EDTA.

7. The method according to claim 3, wherein the co-precipitation method from step (4) is carbonate co-precipitation or hydroxide co-precipitation; wherein the inert gas is nitrogen, argon, or carbon dioxide.

8. The method according to claim 3, wherein the lithium source in step (5) is one or more of lithium hydroxide, lithium carbonate, lithium oxalate, and lithium acetate.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram showing a system for making the lithium-rich layered oxide with a phase structure gradient according to an embodiment.

(2) FIG. 2 is an XRD diffraction pattern of a lithium-rich layered oxide with phase structure gradient in embodiment 1.

(3) FIG. 3 is a Scanning Electronic Microscope (SEM) image of a lithium-rich layered oxide with phase structure gradient in embodiment 1.

(4) FIG. 4 is diagram of the phase structure gradient of a lithium-rich layered oxide with phase structure gradient in embodiment 1.

(5) FIG. 5 is a charging and discharging curve of a lithium-rich layered oxide with phase structure gradient in embodiment 1.

(6) FIG. 6 is a cycle performance curve of a lithium-rich layered oxide with phase structure gradient in embodiment 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

(7) The working principle and testing method of the testing device are further described in the following detailed description of embodiments of the invention. Reference is made to the accompanying drawings in which like references indicates similar elements, and in which is shown by way of illustration, specific embodiments in which the invention may be practiced. These embodiments are described in sufficient detail to enable those skilled in the art to practice the invention. In other instances, well-known circuits, structures, and techniques have not been shown in detail in order not to obscure the understanding of this description. The following detailed description is, therefore, not to be taken in a limiting sense, and the scoop of the invention is defined only by the appended claims.

Embodiment 1

(8) (1) Nickel sulfate (NiSO.sub.4.6H.sub.2O), cobalt sulfate (NiSO.sub.4.7H.sub.2O) and manganese sulfate (MnSO.sub.4.H.sub.2O) were dissolved in deionized water, and 2 mol/L solution A and solution B were prepared respectively. In solution A, Ni:Co:Mn (molar ratio)=0.21:0.08:0.71; in solution B, Ni:Co:Mn (molar ratio)=0.343:0.1305:0.5265. 2 mol/L Na.sub.2CO.sub.3 solution and 0.2 mol/L ammonia were also prepared.

(9) (2) The solution B (600 mL) prepared in step (1) was added to the solution A (600 mL) through a constant flow pump while stirring; meanwhile, the mixed solution of A and B was added to a reactor through a constant flow pump, the Na.sub.2CO.sub.3 solution and the ammonia solution are added to the reactor by concurrently flowing through a constant flow pump. The stirring speed was controlled at 1000 RPM and the reaction temperature was 55° C., pH was 8.1, reaction time was 10 hours, a precursor of lithium-rich layered oxide with phase structure gradient was obtained by coprecipitation reaction.

(10) (3) The precursor obtained in step (2) was filtered, washed, dried, and mixed with Li.sub.2CO.sub.3 with the ratio of lithium to combined Ni, Mn and Co being 1.6:1. Pre-sintering at 500° C. for 5 hours under air atmosphere, heating up to 900° C. and maintained for 10 hours, a lithium-rich layered oxide material with phase structure gradient was obtained, with the center of spherical granule being represented by 0.5Li.sub.2MnO.sub.3.0.5Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2, and the surface of the spherical granule being represented by 0.3Li.sub.2MnO.sub.3.0.7Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2.

(11) The above prepared material was mixed with acetylene black and PTFE (aqueous solution) in proportion of 80:15:5 and rolled into film. The film was sliced and pressed onto an aluminum web, assembled into a 2032 button battery and tested for electrochemical performance.

Embodiment 2

(12) (1) Nickel sulfate (NiSO.sub.4.6H.sub.2O), cobalt sulfate (NiSO.sub.4.7H.sub.2O) and manganese sulfate (MnSO.sub.4.H.sub.2O) were dissolved in deionized water, and 2 mol/L solution A and solution B were prepared respectively. In solution A, Ni:Co:Mn (molar ratio)=0.21:0.08:0.71; in solution B, Ni:Co:Mn (molar ratio)=0.2765:0.1055:0.618. 2 mol/L Na.sub.2CO.sub.3 solution and 0.2 mol/L ammonia solution were also prepared.

(13) (2) The solution B (600 mL) prepared in step (1) was added to the solution A (600 mL) through a constant flow pump while stirring; meanwhile, the mixed solution of A and B was added to a reactor through a constant flow pump, the Na.sub.2CO.sub.3 solution and the ammonia solution are added to the reactor by concurrently flowing through a constant flow pump. The stirring speed was controlled at 1000 RPM and the reaction temperature was 55° C., pH was 7.6, reaction time was 18 hours, a precursor of lithium-rich layered oxide with phase structure gradient was obtained by co-precipitation reaction.

(14) (3) The precursor obtained in step (2) was filtered, washed, dried, and mixed with Li.sub.2CO.sub.3 with the ratio of lithium to combined Ni, Mn and Co being 1.6:1. Pre-sintering at 500° C. for 5 hours under air atmosphere, heating up to 900° C. and maintained for 10 hours, a lithium-rich layered oxide material with phase structure gradient was obtained, with the center of spherical granules being represented by 0.5 Li.sub.2MnO.sub.3.0.5Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2, and the surface of the spherical granules being represented by 0.4Li.sub.2MnO.sub.3.0.6Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2.

(15) The above prepared material was mixed with acetylene black and PTFE (aqueous solution) in proportion of 80:15:5 and rolled into film. The film was sliced and pressed onto an aluminum web, assembled into a 2032 button battery and tested for electrochemical performance.

Embodiment 3

(16) (10 Nickel sulfate (NiSO.sub.4.6H.sub.2O), cobalt sulfate (NiSO.sub.4.7H.sub.2O) and manganese sulfate (MnSO.sub.4.H.sub.2O) were dissolved in deionized water. 2 mol/L solution A and solution B were prepared respectively. In solution A, Ni:Co:Mn (molar ratio)=0.21:0.08:0.71; in solution B, Ni:Co:Mn (molar ratio)=0.409:0.156:0.435. 2 mol/L Na.sub.2CO.sub.3 solution and 0.2 mol/L ammonia were also prepared.

(17) (2) The solution B (600 mL) prepared in step (1) was added to the solution A (600 mL) through a constant flow pump while stirring; meanwhile, the mixed solution of A and B was added to a reactor through a constant flow pump, the Na.sub.2CO.sub.3 solution and the ammonia solution are added to the reactor by concurrently flowing through a constant flow pump. The stirring speed was controlled at 1000 RPM and the reaction temperature was 55° C., pH was 7.8, reaction time was 40 hours, a precursor of lithium-rich layered oxide with phase structure gradient was obtained by coprecipitation reaction.

(18) (3) The precursor obtained in step (2) was filtered, washed, dried, and mixed with Li.sub.2CO.sub.3 with the ratio of lithium to combined Ni, Mn and Co being 1.7:1. Pre-sintering at 500° C. for 5 hours under air atmosphere, heating up to 900° C. and maintained for 10 hours, a lithium-rich layered oxide material with phase structure gradient was obtained, with the center of spherical granules being represented by 0.5Li.sub.2MnO.sub.3.0.5Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2, and the surface of the spherical granules being represented by 0.2Li.sub.2MnO.sub.3.0.8Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2.

(19) The above prepared material was mixed with acetylene black and PTFE (aqueous solution) in proportion of 80:15:5 and rolled into film. The film was sliced and pressed onto an aluminum web, assembled into a 2032 button battery and tested for electrochemical performance.

Embodiment 4

(20) (1) Nickel sulfate (NiSO.sub.4.6H.sub.2O), cobalt sulfate (NiSO.sub.4.7H.sub.2O) and manganese sulfate (MnSO.sub.4.H.sub.2O) were dissolved in deionized water. 2 mol/L solution A and solution B were prepared respectively. In solution A, Ni:Co:Mn (molar ratio)=0.21:0.08:0.71; in solution B, Ni:Co:Mn (molar ratio)=0.4755:0.1815:0.343. 2 mol/L Na.sub.2CO.sub.3 solution and 0.2 mol/L ammonia solution were also prepared.

(21) (2) The solution B (600 mL) prepared in step (1) was added to the solution A (600 mL) through a constant flow pump while stirring; meanwhile, the mixed solution of A and B was added to a reactor through a constant flow pump, the Na.sub.2CO.sub.3 solution and the ammonia solution are added to the reactor by concurrently flowing through a constant flow pump. The stirring speed was controlled at 1000 RPM and the reaction temperature was 55° C., pH was 7.8, reaction time was 25 hours, a precursor of lithium-rich layered oxide with phase structure gradient was obtained by coprecipitation reaction.

(22) (3) The precursor obtained in step (2) was filtered, washed, dried, and mixed with Li.sub.2CO.sub.3 with the ratio of lithium to combined Ni, Mn and Co being 1.7:1. Pre-sintering at 500° C. for 5 hours under air atmosphere, heating up to 900° C. and maintained for 10 hours, a lithium-rich layered oxide material with phase structure gradient was obtained, with the center of spherical granules being represented by 0.5Li.sub.2MnO.sub.3.0.5Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2, and the surface of the spherical granules being represented by 0.1Li.sub.2MnO.sub.3.0.9Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2.

(23) The above prepared material was mixed with acetylene black and PTFE (aqueous solution) in proportion of 80:15:5 and rolled into film. The film was sliced and pressed onto an aluminum web, assembled into a 2032 button battery and tested for electrochemical performance.

Embodiment 5

(24) (1) Nickel sulfate (NiSO.sub.4.6H.sub.2O), cobalt sulfate (NiSO.sub.4.7H.sub.2O) and manganese sulfate (MnSO.sub.4.H.sub.2O) were dissolved in deionized water. 3 mol/L solution A and solution B were prepared respectively. In solution A, Ni:Co:Mn (molar ratio)=0.21:0.08:0.71, In solution B, Ni:Co:Mn (molar ratio)=0.4755:0.1815:0.343. 3 mol/L Na.sub.2CO.sub.3 solution and 0.5 mol/L ammonia solution were also prepared.

(25) (2) The solution B (600 mL) prepared in step (1) was added to the solution A (600 mL) through a constant flow pump while stirring; meanwhile, the mixed solution of A and B was added to a reactor through a constant flow pump, the Na.sub.2CO.sub.3 solution and the ammonia solution are added to the reactor by concurrently flowing through a constant flow pump. The stirring speed was controlled at 1000 RPM and the reaction temperature was 55° C., pH was 9.0, reaction time was 15 hours, a precursor of lithium-rich layered oxide with phase structure gradient was obtained by coprecipitation reaction.

(26) (3) The precursor obtained in step (2) was filtered, washed, dried, and mixed with Li.sub.2CO.sub.3 with the ratio of lithium to combined Ni, Mn and Co being 1.6:1. Pre-sintering at 500° C. for 5 hours under air atmosphere, heating up to 900° C. and maintained for 12 hours, a lithium-rich layered oxide material with phase structure gradient was obtained, with the center of spherical granules being represented by 0.5Li.sub.2MnO.sub.3.0.5Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2, and the surface of the spherical granules being represented by 0.1Li.sub.2MnO.sub.3.0.9Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2.

(27) The above prepared material was mixed with acetylene black and PTFE (aqueous solution) in proportion of 80:15:5 and rolled into film. The film was sliced and pressed onto an aluminum web, assembled into a 2032 button battery and tested for electrochemical performance.

Embodiment 6

(28) Nickel sulfate (NiSO.sub.4.6H.sub.2O), cobalt sulfate (NiSO.sub.4.7H.sub.2O) and manganese sulfate (MnSO.sub.4.H.sub.2O) were dissolved in deionized water. 1.5 mol/L solution A and solution B were prepared respectively. In solution A, Ni:Co:Mn (molar ratio)=0.21:0.08:0.71, In solution B, Ni:Co:Mn (molar ratio)=0.409:0.156:0.435. 1.5 mol/L Na.sub.2CO.sub.3 solution and 0.1 mol/L ammonia solution were also prepared.

(29) (2) The solution B (600 mL) prepared in step (1) was added to the solution A (600 mL) through a constant flow pump while stirring; meanwhile, the mixed solution of A and B was added to a reactor through a constant flow pump, the Na.sub.2CO.sub.3 solution and the ammonia solution are added to the reactor by concurrently flowing through a constant flow pump. The stirring speed was controlled at 900 RPM and the reaction temperature was 55° C., pH was 8.2, reaction time was 25 hours, a precursor of lithium-rich layered oxide with phase structure gradient was obtained by coprecipitation reaction.

(30) (3) The precursor obtained in step (2) was filtered, washed, dried, and mixed with Li.sub.2CO.sub.3 with the ratio of lithium to combined Ni, Mn and Co being 1.6:1. Pre-sintering at 500° C. for 5 hours under air atmosphere, heating up to 950° C. and maintained for 12 hours, a lithium-rich layered oxide material with phase structure gradient was obtained, with the center of spherical granules being represented by 0.5Li.sub.2MnO.sub.3.0.5Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2, and the surface of the spherical granules being represented by 0.2Li.sub.2MnO.sub.3.0.81Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2.

(31) The above prepared material was mixed with acetylene black and PTFE (aqueous solution) in proportion of 80:15:5 and rolled into film. The film was sliced and pressed onto an aluminum web, assembled into a 2032 button battery and tested for electrochemical performance.

Embodiment 7

(32) (1) Nickel sulfate (NiSO.sub.4.6H.sub.2O), cobalt sulfate (NiSO.sub.4.7H.sub.2O) and manganese sulfate (MnSO.sub.4.H.sub.2O) were dissolved in deionized water. 2 mol/L solution A and solution B were prepared respectively. In solution A, Ni:Co:Mn (molar ratio)=0.21:0.08:0.71; in solution B, Ni:Co:Mn (molar ratio)=0.343:0.1305:0.5265. 2.5 mol/L Na.sub.2CO.sub.3 solution and 0.3 mol/L ammonia solution were also prepared.

(33) (2) The solution B (600 mL) prepared in step (1) was added to the solution A (600 mL) through a constant flow pump while stirring; meanwhile, the mixed solution of A and B was added to a reactor through a constant flow pump, the Na.sub.2CO.sub.3 solution and the ammonia solution are added to the reactor by concurrently flowing through a constant flow pump. The stirring speed was controlled at 1200 RPM and the reaction temperature was 60° C., pH was 8.2, reaction time was 30 hours, a precursor of lithium-rich layered oxide with phase structure gradient was obtained by coprecipitation reaction.

(34) (3) The precursor obtained in step (2) was filtered, washed, dried, and mixed with Li.sub.2CO.sub.3 with the ratio of lithium to combined Ni, Mn and Co being 1.6:1. Pre-sintering at 500° C. for 5 hours under air atmosphere, heating up to 900° C. and maintained for 10 hours, a lithium-rich layered oxide material with phase structure gradient was obtained, with the center of spherical granules being represented by 0.5Li.sub.2MnO.sub.3.0.5Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2, and the surface of the spherical granules being represented by 0.3Li.sub.2MnO.sub.3.0.7Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2.

(35) The above prepared material was mixed with acetylene black and PTFE (aqueous solution) in proportion of 80:15:5 and rolled into film. The film was sliced and pressed onto an aluminum web, assembled into a 2032 button battery and tested for electrochemical performance.

Embodiment 8

(36) (1) Nickel sulfate (NiSO.sub.4.6H.sub.2O), cobalt sulfate (NiSO.sub.4.7H.sub.2O) and manganese sulfate (MnSO.sub.4.H.sub.2O) were dissolved in deionized water. 2 mol/L solution A and solution B were prepared respectively. In solution A, Ni:Co:Mn (molar ratio)=0.21:0.08:0.71, In solution B, Ni:Co:Mn (molar ratio)=0.409:0.156:0.435. 2 mol/L Na.sub.2CO.sub.3 solution and 0.6 mol/L ammonia solution were also prepared.

(37) (2) The solution B (600 mL) prepared in step (1) was added to the solution A (600 mL) through a constant flow pump while stirring; meanwhile, the mixed solution of A and B was added to a reactor through a constant flow pump, the Na.sub.2CO.sub.3 solution and the ammonia solution are added to the reactor by concurrently flowing through a constant flow pump. The stirring speed was controlled at 1100 RPM and the reaction temperature was 55° C., pH was 8.0, reaction time was 35 hours, a precursor of lithium-rich layered oxide with phase structure gradient was obtained by coprecipitation reaction.

(38) (3) The precursor obtained in step (2) was filtered, washed, dried, and mixed with Li.sub.2CO.sub.3 with the ratio of lithium to combined Ni, Mn and Co being 1.8:1. Pre-sintering at 500° C. for 5 hours under air atmosphere, heating up to 900° C. and maintained for 10 hours, a lithium-rich layered oxide material with phase structure gradient was obtained, with the center of spherical granules being represented by 0.5Li.sub.2MnO.sub.3.0.5Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2, and the surface of the spherical granules being represented by 0.2Li.sub.2MnO.sub.3.0.8Li(Ni.sub.0.42Mn.sub.0.42Co.sub.0.16)O.sub.2.

(39) The above prepared material was mixed with acetylene black and PTFE (aqueous solution) in proportion of 80:15:5 and rolled into film. The film was sliced and pressed onto an aluminum web, assembled into a 2032 button battery and tested for electrochemical performance.