O2-phase lithium cobalt oxide positive electrode material and preparation method thereof

Abstract

The invention discloses an O2-phase lithium cobalt oxide positive electrode material and a preparation method thereof, and belongs to the field of lithium ion battery electrode materials. The preparation method comprises the following steps: uniformly mixing a cobalt precursor containing modified metal M with sodium carbonate by a dry method, pre-sintering after uniformly mixing, and sintering at high temperature to obtain P2-phase NaxCoO2; and carrying out solid-phase ion exchange or liquid-phase ion exchange with a lithium salt, washing, filtering and drying to obtain the O2-phase lithium cobalt oxide positive electrode material. The O2-phase lithium cobalt oxide positive electrode material prepared by the invention has good structural reversibility under high voltage, and the capacity, cycle and other performance of the lithium ion battery positive electrode material under high voltage can be remarkably improved.

Description

Technical Field

[0001] The invention relates to an O2-phase lithium cobalt oxide positive electrode material and a preparation method thereof, and belongs to the field of lithium ion battery electrode materials. Background Art

[0002] Lithium cobalt oxide, a lithium-ion positive electrode material for 3C consumer electronics, has undergone several generations of high-voltage development. Currently, the development of materials for voltage systems such as 4.52V and 4.53V has begun. At 4.55V, an irreversible phase change from O3 phase to H1-3 phase will occur in lithium cobalt oxide positive electrode materials, and at higher voltages, an irreversible phase change from H1-3 phase to O1 phase will also occur. These irreversible phase changes significantly affect the structural stability of O3 phase lithium cobalt oxide, and thus affect a series of electrochemical properties of the material such as cycle, rate, impedance, etc., and have an adverse effect on terminal battery cell applications. Therefore, with the gradual increase in the voltage platform development of lithium cobalt oxide positive electrode materials, the structural phase change problem that exists in it has become imminent. Higher voltage development under the existing O3 phase material system can no longer avoid a series of problems caused by structural phase change.

[0003] Different from the ABCABC stacking method of O3 phase lithium cobalt oxide, O2 phase lithium cobalt oxide is stacked in ABCB mode. The O2 phase lithium cobalt oxide formed by this stacking method will produce a phase transition of O2→T2→O6→O2 during the charging process. Compared with O3 phase lithium cobalt oxide, O2 phase lithium cobalt oxide has higher structural reversibility at >4.55V, and still exists in the form of O2 phase structure, so it has better structural stability. In terms of electrical performance, its cycle performance is significantly better than that of O3 phase lithium cobalt oxide. At the same time, at a high voltage of >4.6V, it also has a higher discharge specific capacity than O3 phase lithium cobalt oxide. Therefore, on a higher voltage development platform such as ≥4.55V, changes in the lithium cobalt oxide material system may be the key to the success of platform development. The improvement and optimization of the O3 phase lithium cobalt oxide material structure can no longer fully meet the irreversible structural change problem caused by the voltage increase at this time. O2 phase lithium cobalt oxide can well solve the basic battery cell requirements such as energy density and cycle performance under the voltage platform of ≥4.55V due to its unique high voltage structural stability characteristics, and is the direction of future high voltage positive electrode material development.

[0004] For example, the invention patent with application number WO 2021 / 248272 A1, “Positive electrode material and electrochemical device of the positive electrode material”, discloses O2-phase lithium cobalt oxide Li x Na z Co 1-y M yO2, but 0.6<x<0.85, the O2 phase lithium cobalt oxide of this component must have the problem of low charging capacity. For example, the Chinese invention patent "A T2 type lithium cobalt oxide collection material with a space group of Cmca and its preparation method" with application number CN 114784269 B discloses T2 type lithium cobalt oxide. The charging and discharging efficiency of lithium cobalt oxide with this structure is generally >100%, which requires that the negative electrode needs to be lithium-rich to ensure the discharge specific capacity, resulting in incompatibility with the current mainstream C negative electrode system, affecting the use of materials. The present invention has overcome the problems of the above-mentioned patents. In the O2 phase lithium cobalt oxide prepared by the present invention, the molar amount of lithium is designed to be in the range of 0.90-0.95, which can ensure the charge and discharge specific capacity. At the same time, the first efficiency is maintained at 99%-100% under the condition of maintaining the O2 phase structure. While maximizing the discharge specific capacity, it has good compatibility and adaptability with the current C negative electrode. Summary of the invention

[0005] The purpose of the present invention is to provide an O2 phase lithium cobalt oxide positive electrode material and a preparation method thereof. The O2 phase lithium cobalt oxide positive electrode material has a 002 crystal plane located at 17.5°-19°, has good structural reversibility under high voltage, and can significantly improve the capacity, cycle and other performances of the lithium ion battery positive electrode material under high voltage.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] An O2 phase lithium cobalt oxide positive electrode material, the structural formula of which is Li x Na y Co 1-z M z O2, wherein 0.90<x<0.95, 0≤y<0.01, 0≤z<0.05, and the modifying element M is selected from one or more of Mg, Al, Ti, La, Y, Zr, Ni, Mn, Ca, Sn, Zn, F, Cr, Nb, and Ce.

[0008] A method for preparing an O2-phase lithium cobalt oxide positive electrode material comprises the following steps:

[0009] (1) Dry-mixing a cobalt precursor containing a modified metal M with sodium carbonate, pre-calcining the mixture, and then sintering at a high temperature to obtain a P2 phase Na x CoO2, where 0.6<x<1;

[0010] (2) P2 phase Na x CoO2 and lithium salt undergo solid phase ion exchange or liquid phase ion exchange to transfer lithium ions to P2 phase Na xThe sodium ions in CoO2 are exchanged for lithium-sodium ions, and after the ion exchange is completed, it is washed, filtered and dried to obtain an O2 phase lithium cobalt oxide positive electrode material.

[0011] Furthermore, in step (1), the modifying element M is selected from one or more of Mg, Al, Ti, La, Y, Zr, Ni, Mn, Ca, Sn, Zn, F, Cr, Nb, and Ce.

[0012] Furthermore, in step (1), the cobalt precursor includes one or more of Co3O4, Co(OH)2, CoO, and Co2O3.

[0013] Furthermore, in step (1), the molar ratio of Na to Co in the cobalt precursor and sodium carbonate is 0.6-1.0.

[0014] Furthermore, the pre-firing condition in step (1) is 400-750° C. for 2-7 hours.

[0015] Furthermore, in step (1), the high temperature sintering condition is 800-1000° C. for 10-30 hours.

[0016] Furthermore, the solid phase ion exchange step in step (2) comprises: reacting the lithium salt with the P2 phase Na x CoO2 is dry mixed evenly, and then the mixture is sintered to complete the lithium-sodium ion exchange.

[0017] Furthermore, in step (2) solid phase ion exchange, the lithium salt is selected from LiNO3, LiNO3 and P2 phase Na x The molar ratio of Li to Na in CoO2 is 1:1-10:1.

[0018] Furthermore, in step (2) solid phase ion exchange, the mixture is sintered at 150-300° C. for 1-7 hours.

[0019] Furthermore, the step of liquid phase ion exchange in step (2) comprises: mixing the mixed lithium salt solution with the P2 phase Na x CoO2 is mixed and stirred in liquid phase in a water bath to complete the lithium and sodium ion exchange.

[0020] Furthermore, in the liquid phase ion exchange of step (2), the mixed lithium salt solution is a LiOH / LiCl solution, and the LiOH / LiCl solution is mixed with the P2 phase Na x The molar ratio of Li to Na of CoO2 is 10:1-40:1.

[0021] Furthermore, in the liquid phase ion exchange of step (2), the water bath temperature is 60-120° C., and the stirring time is 8-50 hours.

[0022] The advantages of the present invention are as follows:

[0023] 1. The present invention proposes an O2 phase lithium cobalt oxide positive electrode material Li x Na y Co 1-z M z O2, the lithium oxygen octahedron and the cobalt oxygen octahedron in the positive electrode material are stacked in a coplanar manner. The lithium cobalt oxide formed by this stacking method has good structural reversibility, and thus has a cycle performance that is significantly better than that of O3 phase lithium cobalt oxide. At the same time, it has a higher discharge specific capacity than O3 phase lithium cobalt oxide at a high voltage of >4.6V.

[0024] 2. Due to the special design of the lithium molar amount in the O2 phase lithium cobalt oxide, the present invention can maximize the discharge specific capacity and the initial efficiency (99%-100%), and also has good compatibility and adaptability with the C negative electrode of the current battery system.

[0025] 3. The present invention utilizes Na element to prepare P2 phase Na x CoO2, then in the P2 phase Na x The preparation of O2 phase lithium cobalt oxide by ion exchange on the basis of CoO2 is obviously different from the trace doping of Na element in O3 phase lithium cobalt oxide in the prior art.

[0026] 4. The present invention has a simple operation process, low raw material cost, and is easy to realize industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] Figure 1A Flow chart for preparing O2-phase lithium cobalt oxide by solid phase ion exchange.

[0028] Figure 1B Flow chart for preparing O2-phase lithium cobalt oxide by liquid phase ion exchange.

[0029] Figures 2A-2F This is the SEM image of the O2 phase lithium cobalt oxide positive electrode material prepared in Example 1-6.

[0030] Figure 3 It is the XRD spectrum of the O2 phase lithium cobalt oxide positive electrode material prepared in the embodiment and the comparative example.

[0031] Figure 4 This is a 4.53V charge and discharge curve of the O2 phase lithium cobalt oxide positive electrode material of Example 1.

[0032] Figure 5 It is a 4.60V cycle performance diagram of the O2 phase lithium cobalt oxide positive electrode material prepared in Examples 1-6 and the comparative example. DETAILED DESCRIPTION

[0033] In order to make the various technical features and advantages or technical effects in the above technical solutions of the present invention more obvious and easy to understand, they are described in detail below in conjunction with embodiments.

[0034] Example 1

[0035] (1) The Co3O4 precursor containing modified metal Mg was dry-mixed with sodium carbonate at a ratio of Na / Co = 0.75, and then pre-sintered at 700°C for 3 hours, and then heated to 850°C for 16 hours to obtain P2 phase Na x CoO2.

[0036] (2) P2 phase Na x CoO2 and lithium salt are exchanged by liquid phase method with Li / Na=20:1. The lithium-sodium ion exchange is completed by stirring in a water bath at 70°C for 24 hours. After the ion exchange is completed, the lithium-sodium ion exchange is carried out by washing, filtering and drying to finally obtain O2 phase lithium cobalt oxide.

[0037] Example 2

[0038] (1) Co3O4 and Co(OH)2 precursors containing modified metal AlTi were mixed with sodium carbonate at a ratio of Na / Co = 0.60 by dry method, pre-sintered at 400°C for 2 hours, and then heated to 800°C for 10 hours to obtain P2 phase Na x CoO2.

[0039] (2) P2 phase Na x CoO2 and lithium salt are exchanged by liquid phase method with Li / Na=10:1. The lithium-sodium ion exchange is completed by stirring in a water bath at 60°C and for 8 hours. After the ion exchange is completed, the ion exchange is washed, filtered and dried to finally obtain O2 phase lithium cobalt oxide.

[0040] Example 3

[0041] (1) The CoO precursor containing the modified metal LaYZr was mixed with sodium carbonate at a ratio of Na / Co=1.0 by dry method, and then pre-sintered at 750°C for 7 hours, and then heated to 1000°C for 30 hours to obtain P2 phase Na x CoO2.

[0042] (2) P2 phase Na x CoO2 and lithium salt are exchanged by liquid phase method with Li / Na=16:1. The lithium-sodium ion exchange is completed by stirring in a water bath at 120°C for 50 hours. After the ion exchange is completed, the ion exchange is washed, filtered and dried to finally obtain O2 phase lithium cobalt oxide.

[0043] Example 4

[0044] (1) Co3O4 and Co(OH)2 precursors containing modified metal NiMn were mixed with sodium carbonate at a ratio of Na / Co=0.60 by dry method, pre-sintered at 400°C for 2 hours, and then heated to 800°C for 10 hours to obtain P2 phase Na x CoO2.

[0045] (2) P2 phase Na x CoO2 and LiNO3 are dry-mixed evenly at a Li / Na molar ratio of 1:1, and then the mixture is sintered at 150°C for 1 hour to complete the lithium-sodium ion exchange. After the ion exchange is completed, it is washed, filtered and dried to finally obtain O2 phase lithium cobalt oxide.

[0046] Example 5

[0047] (1) The CoO precursor containing the modified metal CaSnZn was mixed with sodium carbonate at a ratio of Na / Co=1.0 by dry method, and then pre-sintered at 750°C for 7 hours, and then heated to 1000°C for 30 hours to obtain P2 phase Na x CoO2.

[0048] (2) P2 phase Na x CoO2 and LiNO3 are dry-mixed evenly at a Li / Na molar ratio of 10:1, and then the mixture is sintered at 300°C for 7 hours to complete the lithium-sodium ion exchange. After the ion exchange is completed, it is washed, filtered and dried to finally obtain O2 phase lithium cobalt oxide.

[0049] Example 6

[0050] (1) The Co2O3 precursor containing modified metals F, Cr, Nb, and Ce was mixed with sodium carbonate at a ratio of Na / Co = 0.80 by dry method, and then pre-sintered at 600°C for 5 hours, and then heated to 900°C for 24 hours to obtain P2 phase Na x CoO2.

[0051] (2) P2 phase Na x CoO2 and LiNO3 are dry-mixed evenly at a Li / Na molar ratio of 5:1, and then the mixture is sintered at 240°C for 4 hours to complete the lithium-sodium ion exchange. After the ion exchange is completed, it is washed, filtered and dried to finally obtain O2 phase lithium cobalt oxide.

[0052] Comparative Example

[0053] (1) A Co3O4 precursor containing modified metal Mg is dry-mixed with lithium carbonate at a ratio of Li / Co=1.010, pre-fired at 500°C for 5 hours, and then heated to 1000°C and sintered for 10 hours to obtain an O3 phase LiCoO2 primary product.

[0054] (2) The primary O3-phase LiCoO2 product is evenly mixed with nano-TiO2 and nano-Al2O3 by dry method, and then the mixture is sintered at 800°C for 6 hours to complete the surface coating. After the sintering is completed, it is universally crushed and sieved to finally obtain the finished O3-phase LiCoO2 product.

[0055] Figure 1A The flow chart of preparing O2 phase lithium cobalt oxide by solid phase ion exchange. Figure 1B Flow chart for preparing O2-phase lithium cobalt oxide by liquid phase ion exchange.

[0056] Figures 2A-2F The SEM images of the O2-phase lithium cobalt oxide positive electrode materials prepared in Examples 1 to 6. The O2-phase lithium cobalt oxide and the O3-phase lithium cobalt oxide have similar morphological characteristics, so the compaction density can reach a level comparable to that of the O3-phase lithium cobalt oxide.

[0057] Figure 3 The XRD spectra of the O2 phase lithium cobalt oxide positive electrode materials prepared in Examples 1 to 6 and Comparative Examples are shown in Figure 1. The O2 phase lithium cobalt oxide has a 002 crystal plane of 17.5°-19°, which is obviously different from the O3 phase lithium cobalt oxide, which has a 003 crystal plane of 18.5°-20°.

[0058] The prepared samples were subjected to a button battery test. The test method was as follows: the positive electrode material, carbon black and PVDF were evenly coated on aluminum foil in a ratio of 90:5:5, and a button battery was formed with the lithium negative electrode. The discharge specific capacity was tested at 25°C, 4.53V, and 0.1C, and the cycle performance was tested at 25°C, 4.60V, and 0.2C.

[0059] Table 1 Button battery 4.53V 0.1C charge and discharge specific capacity

[0060]

[0061] The buckling capacity and first efficiency of O2 phase lithium cobalt oxide are significantly higher than those of O3 phase lithium cobalt oxide.

[0062] Figure 4 This is a 4.53V charge and discharge curve of the O2 phase lithium cobalt oxide positive electrode material prepared in Example 1. Compared with O3 phase lithium cobalt oxide, the charge and discharge process of O2 phase lithium cobalt oxide is accompanied by multiple phase changes.

[0063] Figure 5 The 4.60V cycle performance diagram of the O2 phase lithium cobalt oxide positive electrode materials prepared in Examples 1-6 and Comparative Examples. Compared with O3 phase lithium cobalt oxide, the cycle performance of O2 phase lithium cobalt oxide is significantly better than that of O3 phase lithium cobalt oxide.

[0064] Although the present invention has been disclosed as above by way of embodiments, it is not intended to limit the present invention. Appropriate modifications or equivalent substitutions of the technical solutions of the present invention made by ordinary technicians in the field should all be included in the protection scope of the present invention. The protection scope of the present invention shall be based on what is defined in the claims.

Claims

1. An O2 phase lithium cobalt oxide positive electrode material, characterized in that: The structural formula is Li x Na y Co 1-z M z O2, wherein 0.90<x<0.95, 0≤y<0.01, 0≤z<0.05, and the modifying element M is selected from one or more of Mg, Al, Ti, La, Y, Zr, Ni, Mn, Ca, Sn, Zn, F, Cr, Nb, and Ce.

2. A method for preparing an O2-phase lithium cobalt oxide positive electrode material, characterized in that: The following steps are involved: (1) Dry-mixing a cobalt precursor containing a modified metal M with sodium carbonate, pre-calcining the mixture, and then sintering at a high temperature to obtain a P2 phase Na x CoO2, where 0.6<x<1; (2) P2 phase Na x CoO2 and lithium salt undergo solid phase ion exchange or liquid phase ion exchange to transfer lithium ions to P2 phase Na x The sodium ions in CoO2 are exchanged for lithium-sodium ions, and after the ion exchange is completed, it is washed, filtered and dried to obtain an O2 phase lithium cobalt oxide positive electrode material.

3. The preparation method according to claim 2, characterized in that: In step (1), the modifying element M is selected from one or more of Mg, Al, Ti, La, Y, Zr, Ni, Mn, Ca, Sn, Zn, F, Cr, Nb, and Ce.

4. The preparation method according to claim 2, characterized in that: In step (1), the cobalt precursor includes one or more of Co3O4, Co(OH)2, CoO, and Co2O3; and the molar ratio of Na to Co of the cobalt precursor and sodium carbonate is 0.6-1.

0.

5. The preparation method according to claim 2, characterized in that: The pre-firing condition in step (1) is 400-750° C. for 2-7 hours.

6. The preparation method according to claim 2, characterized in that: In step (1), the high temperature sintering condition is 800-1000° C. for 10-30 hours.

7. The preparation method according to claim 2, characterized in that: The solid phase ion exchange step in step (2) comprises: reacting a lithium salt with a P2 phase Na x CoO2 is dry mixed evenly, and then the mixture is sintered to complete the lithium-sodium ion exchange; the lithium salt is LiNO3, LiNO3 and P2 phase Na x The molar ratio of Li to Na in CoO2 is 1:1-10:

1.

8. The preparation method according to claim 2, characterized in that: In step (2) of solid phase ion exchange, the mixture is sintered at 150-300° C. for 1-7 hours.

9. The preparation method according to claim 2, characterized in that: The step of liquid phase ion exchange in step (2) comprises: mixing the mixed lithium salt solution with the P2 phase Na x CoO2 is mixed and stirred in liquid phase in a water bath to complete lithium-sodium ion exchange; the mixed lithium salt solution is LiOH / LiCl solution, and the LiOH / LiCl solution is mixed with P2 phase Na x The molar ratio of Li to Na of CoO2 is 10:1-40:

1.

10. The preparation method according to claim 2, characterized in that: In step (2) of liquid phase ion exchange, the water bath temperature is 60-120° C. and the stirring time is 8-50 hours.

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