COBALT-FREE SINGLE CRYSTAL COMPOSITE MATERIAL, AND PREPARATION METHOD THEREFOR AND USE THEREOF

Abstract

A cobalt-free single crystal composite material, and a preparation method therefor and a use thereof. The cobalt-free single crystal material is of a core-shell structure, the core layer is the cobalt-free single crystal material, and the shell layer is prepared from TiNb.sub.2O.sub.7 and conductive lithium salt. The TiNb.sub.2O.sub.7 and the conductive lithium salt are selected as materials of the shell layer to coat the cobalt-free single crystal material, thereby improving the lithium ion conductivity of the cobalt-free single crystal material, and further improving the capacity and the first effect of the material.

Claims

1. A cobalt-free single crystal composite material having a core-shell structure, wherein the core layer is of a cobalt-free single crystal material, and the shell layer is of a material formulation comprises TiNb2O7 and a conductive lithium salt.

2. The cobalt-free single crystal composite material according to claim 1, wherein the cobalt-free single crystal material has a chemical formula of LimNixMnyMnO2, wherein 0.4≤x≤0.95, 0.05≤y≤0.6, and m is 1.05 to 1.5.

3. The cobalt-free single crystal composite material according to claim 1, wherein the conductive lithium salt comprises at least one of LiH2PO4, CaF2, TiN, TiC, LiAlO2 and BiO—YO.

4. (canceled)

5. The cobalt-free single crystal composite material according to claim 1, wherein in the shell layer, a molar ratio of TiNb2O7 to the conductive lithium salt is (0.1-10): 1.

6. The cobalt-free single crystal composite material according to claim 1, wherein the shell layer accounts for a ratio of 0.1-0.5 wt % in the cobalt-free single crystal composite material and/or the core layer accounts for a ratio of 99.5-99.9 wt % in the cobalt-free single crystal composite material.

7. (canceled)

8. The cobalt-free single crystal composite material according to claim 1, wherein the cobalt-free single crystal composite material has a particle size D50 of 1-5 μm.

9. The cobalt-free single crystal composite material according to claim 1, wherein the cobalt-free single crystal composite material has a specific surface area of 0.3-1.5 m2/g.

10. The cobalt-free single crystal composite material according to claim 1, wherein the cobalt-free single crystal composite material has a surface pH of 11.8 or below and 3500 ppm or below of total alkalis.

11. A method for preparing the cobalt-free single crystal composite material according to claim 1, comprising: mixing a cobalt-free single crystal material, TiNb2O7 and a conductive lithium salt, and carrying out sintering to obtain the cobalt-free single crystal composite material.

12. The method according to claim 11, wherein a method for preparing the cobalt-free single crystal material comprises: mixing a lithium salt and a precursor of the cobalt-free single crystal material, and carrying out calcination to obtain the cobalt-free single crystal material.

13. The method according to claim 12, wherein the precursor of the cobalt-free single crystal material has a chemical formula of NiaMnb(OH)2, wherein 0.4≤a≤0.95 and 0.05≤b≤0.6.

14. The method according to claim 12, wherein the lithium salt comprises lithium hydroxide and/or lithium carbonate.

15. The method according to claim 12, wherein a ratio of a molar amount of lithium in the lithium salt to a molar amount of total metal elements in the precursor of the cobalt-free single crystal material is 1.05-1.5.

16. The method according to claim 12, wherein the lithium salt and the precursor of the cobalt-free single crystal material are mixed under stirring.

17-26. (canceled)

27. The method according to claim 11, wherein a ratio of a total mass of TiNb2O7 and the conductive lithium salt to a weight of the cobalt-free single crystal material is 1000-3000 pmm.

28. The method according to claim 11, wherein a molar ratio of TiNb2O7 to the conductive lithium salt is (0.1-10):1.

29. The method according to claim 11, wherein a process of mixing the cobalt-free single crystal material, TiNb2O7 and the conductive lithium salt comprises: mixing and dissolving TiNb2O7 and the conductive lithium salt in deionized water, drying the mixture, and mixing the mixture and the cobalt-free single crystal material.

30-38. (canceled)

39. The method according to any claim 11, comprising the following steps: (1) mixing a lithium salt and a precursor of the cobalt-free single crystal material under stirring at a rotational speed of 1500-2500 rpm for 5-15 min, wherein a ratio of a molar amount of lithium in the lithium salt to a molar amount of total metal elements in the precursor of the cobalt-free single crystal material is 1.05-1.5; carrying out calcination for 8-20 h at a temperature of 850-1000° C. and in an oxygen atmosphere with a flowrate of 5-10 L/min, wherein the calcination is carried out at a temperature ramp rate of 3-5° C./min; and cooling, crushing and sieving with a 300-400 mesh sieve to obtain the cobalt-free single crystal material; and (2) mixing and dissolving TiNb2O7 and LiH2PO4 at a molar ratio of (0.1-10):1 in deionized water, drying the mixture, and mixing the mixture and the cobalt-free single crystal material for 10-20 min in a handheld stirrer, wherein a ratio of a total mass of TiNb2O7 and LiH2PO4 to a weight of the cobalt-free single crystal material is 1000-3000 pmm; carrying out sintering for 6-12 h at a temperature of 300-700° C. and in an oxygen atmosphere with a flowrate of 5-10 L/min, wherein the sintering is carried out at a temperature ramp rate of 3-5° C./min; and cooling, crushing and sieving to obtain the cobalt-free single crystal composite material.

40. A cathode sheet, comprising the cobalt-free single crystal composite material according to claim 1.

41. A lithium-ion battery, comprising the cathode sheet according to claim 40.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0058] The drawings are used to provide a further understanding of technical solutions of the present disclosure, constitute a part of the description, explain the technical solutions of the present disclosure in conjunction with embodiments of the present application and do not limit the technical solutions of the present disclosure.

[0059] FIGS. 1 and 2 are scanning electron microscopic (SEM) images of a cobalt-free single crystal composite material prepared in an example of the present disclosure.

[0060] FIGS. 3 and 4 are SEM images of a cobalt-free single crystal material prepared in Comparative Example 1 of the present disclosure.

DETAILED DESCRIPTION

[0061] Technical solutions of the present disclosure are further described below through embodiments in conjunction with drawings.

Example 1

[0062] A method for preparing a cobalt-free single crystal composite material includes steps described below.

[0063] (1) LiOH powder and a precursor Ni.sub.0.75Mn.sub.0.25(OH).sub.2 of a cobalt-free single crystal material were mixed under stirring at a rotational speed of 2000 rpm for 10 min, where a ratio of a molar amount of lithium in LiOH to a molar amount of total metal elements in the precursor Ni.sub.0.75Mn.sub.0.25(OH).sub.2 of the cobalt-free single crystal material was 1.1; calcination was carried out for 10 h at a temperature of 900° C. and in an oxygen atmosphere with a flowrate of 8 L/min, where the calcination was carried out at a temperature ramp rate of 4° C./min; and the calcined substance was cooled, crushed and sieved with a 300 mesh sieve to obtain a cobalt-free single crystal material.

[0064] (2) TiNb.sub.2O.sub.7 and LiH.sub.2PO.sub.4 were mixed and dissolved in deionized water at a molar ratio of 1:1, dried, and mixed with the cobalt-free single crystal material for 15 min in a handheld stirrer, where a ratio of a total mass of TiNb.sub.2O.sub.7 and LiH.sub.2PO.sub.4 to a weight of the cobalt-free single crystal material was 1000 pmm; sintering was carried out for 8 h at a temperature of 500° C. and in an oxygen atmosphere with a flowrate of 8 L/min, where the sintering was carried out at a temperature ramp rate of 4° C./min; and the sintered substance was cooled, crushed and sieved to obtain a cobalt-free single crystal composite material.

[0065] FIGS. 1 and 2 are SEM images of the cobalt-free single crystal composite material provided in this example. It can be seen from the figures that the single crystal materials synthesized in this example have good morphology, uniform particle distribution and a particle size of 1-5 μm.

Example 2

[0066] This example differs from Example 1 in that in step (2), the ratio of the total mass of TiNb.sub.2O.sub.7 and LiH.sub.2PO.sub.4 to the weight of the cobalt-free single crystal material was 2000 pmm.

Example 3

[0067] This example differs from Example 1 in that in step (2), the ratio of the total mass of TiNb.sub.2O.sub.7 and LiH.sub.2PO.sub.4 to the weight of the cobalt-free single crystal material was 3000 pmm.

Example 4

[0068] This example differs from Example 1 in that in step (2), the ratio of the total mass of TiNb.sub.2O.sub.7 and LiH.sub.2PO.sub.4 to the weight of the cobalt-free single crystal material was 500 pmm.

Example 5

[0069] This example differs from Example 1 in that in step (2), the molar ratio of TiNb.sub.2O.sub.7 and LiH.sub.2PO.sub.4 was 0.1:1.

Example 6

[0070] This example differs from Example 1 in that in step (2), the molar ratio of TiNb.sub.2O.sub.7 and LiH.sub.2PO.sub.4 was 0.05:1.

Example 7

[0071] This example differs from Example 1 in that in step (2), the molar ratio of TiNb.sub.2O.sub.7 and LiH.sub.2PO.sub.4 was 12:1.

Example 8

[0072] A method for preparing a cobalt-free single crystal composite material includes steps described below.

[0073] (1) LiOH powder and a precursor Ni.sub.0.75Mn.sub.0.25(OH).sub.2 of a cobalt-free single crystal material were mixed under stirring at a rotational speed of 2500 rpm for 5 min, where a ratio of a molar amount of lithium in LiOH to a molar amount of total metal elements in the precursor Ni.sub.0.75Mn.sub.0.25(OH).sub.2 of the cobalt-free single crystal material was 1.3; calcination was carried out for 20 h at a temperature of 850° C. and in an oxygen atmosphere with a flowrate of 10 L/min, where the calcination was carried out at a temperature ramp rate of 3° C./min; and the calcined substance was cooled, crushed and sieved with a 400 mesh sieve so that the cobalt-free single crystal material was obtained.

[0074] (2) TiNb.sub.2O.sub.7 and LiH.sub.2PO.sub.4 were mixed and dissolved in deionized water at a molar ratio of 8:1, dried, and mixed with the cobalt-free single crystal material for 20 min in a handheld stirrer, where a ratio of a total mass of TiNb.sub.2O.sub.7 and LiH.sub.2PO.sub.4 to a weight of the cobalt-free single crystal material was 1500 pmm; sintering was carried out for 6 h at a temperature of 700° C. and in an oxygen atmosphere with a flowrate of 10 L/min, where the sintering was carried out at a temperature ramp rate of 5° C./min; and the sintered substance was cooled, crushed and sieved so that the cobalt-free single crystal composite material was obtained.

[0075] The cobalt-free single crystal composite material obtained in this example has electrochemical performance similar to that of Example 1.

Comparative Example 1

[0076] The cobalt-free single crystal material obtained in step (1) of Example 1 was used.

[0077] FIGS. 3 and 4 are SEM images of the cobalt-free single crystal material provided in this comparative example. It can be seen from the figures that a particle size of the cobalt-free single crystal material is not significantly different from that of Example 1, indicating that coating in Example 1 has no effect on the particle size of the material.

Performance Test

[0078] The cobalt-free single crystal composite materials (the cobalt-free single crystal material in Comparative Example 1) obtained in examples and comparative examples were assembled as a cathode active material into batteries.

[0079] A cathode slurry was prepared according to a ratio 92:4:4 of the cathode active material:conductive carbon black SP: a polyvinylidene fluoride (PVDF) glue solution (with a solid content of 6.05%), and coated on an aluminum foil so that a cathode sheet was obtained.

[0080] Then, an anode sheet (lithium sheet), the cathode sheet, an electrolyte (lithium hexafluorophosphate (LiPF.sub.6) of 1 mol/L and ethylene carbonate (EC):ethyl methyl carbonate (EMC)=1:1) and a separator were assembled into the battery.

[0081] (1) Test of electrochemical performance: The obtained battery was charged and discharged in an environment of 25±2° C. at a charge/discharge voltage of 3-4.4 V in order to measure the initial charge specific capacity at 0.1C, the initial discharge specific capacity at 0.1C, the initial discharge specific capacity at 1C, the initial efficiency (0.1C) and the capacity retention rate after 50 cycles (1C). The results are shown in Table 1.

[0082] (2) Test of powder resistance: Three samples were taken in parallel for each group of the cobalt-free single crystal composite materials (the cobalt-free single crystal material in Comparative Example 1) obtained in Examples 1 to 3 and Comparative Example 1, where 3.5 g were weighed for each group. The cobalt-free single crystal composite materials (the cobalt-free single crystal material in Comparative Example 1) were loaded into molds (drained with a funnel to prevent the material from being hung on the wall) and flattened. The molds were mounted on a device and started to be tested. Equal pressure was applied until 4KN, 8KN, 12KN and 16KN, separately. After the pressure was stabilized, values of resistivity were measured (an average value was obtained for each group). The results are shown in Table 2.

[0083] (3) Galvanostatic intermittent titration technique (GITT) test: The batteries obtained in Examples 1 to 3 and Comparative Example 1 were charged and discharged (three batteries were used for each group and named 1, 2 and 3 respectively). After the test, a lithium ion diffusion coefficient was calculated by using the formula

[00001]$D=\frac{4}{\mathrm{\pi \Delta \tau }}{\left(\frac{m_B{V}_M}{M_{B}S}\right)}^2{\left(\frac{\Delta E_S}{\Delta E_{\tau }}\right)}^2,$

where m.sub.B denotes a mass (g) of an active material, M.sub.B denotes a molar mass (g/mol), V.sub.M denotes a molar volume (cm.sup.3/mol), S denotes a sheet area (cm.sup.2), ΔE.sub.S=E.sub.0−E.sub.s, and Δt=300 s. The results are shown in Table 3.

TABLE-US-00001 TABLE 1 Initial Initial Charge Discharge Initial Capacity Specific Specific Discharge Retention Capacity Capacity at Specific Initial Rate after at 0.1 C 0.1 C Capacity at Efficiency 50 Cycles (mAh/g) (mAh/g) 1 C (mAh/g) (%) (%) Example 1 222.5 193.7 175 87.06 97.1 Example 2 223.1 196.2 177.2 87.94 98.1 Example 3 221.4 194.1 173.2 87.67 97.3 Example 4 218.0 189.2 172.0 86.78 97.1 Example 5 218.1 188.0 172.2 86.20 96.6 Example 6 217.2 188.5 170.1 86.79 95.2 Example 7 218.5 188.1 170.2 86.09 95.5 Comparative 219 190.2 172.4 86.85 96.2 Example 1

TABLE-US-00002 TABLE 2 4KN (Q .Math. cm) 8KN (Q .Math. cm) 12KN (Q .Math. cm) 16KN (Q .Math. cm) Example 1 2.69 × 10.sup.5 1.31 × 10.sup.4 8.07 × 10.sup.4 5.80 × 10.sup.4 Example 2 3.08 × 10.sup.5 9.39 × 10.sup.4 4.04 × 10.sup.4 2.57 × 10.sup.3 Example 3 3.16 × 10.sup.5 1.20 × 10.sup.4 5.68 × 10.sup.3 3.33 × 10.sup.3 Comparative 3.15 × 10.sup.5 9.01 × 10.sup.4 4.24 × 10.sup.4 2.59 × 10.sup.4 Example 1

[0084] The values of the lithium ion diffusion coefficients D in Example 1, Example 2, Example 3 and Comparative Example 1 are listed in Table 3. Parameters during calculation of the lithium ion diffusion coefficients D (P in Table 4 denotes a density of the active material) are listed in Table 4.

TABLE-US-00003 TABLE 3 D (cm.sup.2/s) Average Value of D 1 2 3 (cm.sup.2/s) Example 1 1.90 × 10.sup.−8 1.71 × 10.sup.−8 1.35 × 10.sup.−8 1.65 × 10.sup.−8 Example 2 1.52 × 10.sup.−8 1.95 × 10.sup.−8 1.14 × 10.sup.−8 1.54 × 10.sup.−8 Example 3 1.62 × 10.sup.−8 1.90 × 10.sup.−8 1.32 × 10.sup.−8 1.62 × 10.sup.−8 Comparative 3.37 × 10.sup.−9 4.40 × 10.sup.−9 9.90 × 10.sup.−9 5.89 × 10.sup.−9 Example 1

TABLE-US-00004 TABLE 4 M.sub.B(g/ P(g/ m.sub.B(g) mol) cm.sup.3) S(cm.sup.2) E.sub.0 E.sub.S ΔE.sub.S Δt(.sub.S) ΔE.sub.τ Example 1 0.009384 97 4.66 1.1304 4.4 4.349 0.051 300 0.043 1 2 0.009384 97 4.66 1.1304 4.349 4.331 0.018 300 0.016 3 0.009384 97 4.66 1.1304 4.331 4.316 0.015 300 0.015 Example 1 0.009292 97 4.66 1.1304 4.4 4.356 0.044 300 0.041 2 2 0.009292 97 4.66 1.1304 4.356 4.339 0.017 300 0.014 3 0.009292 97 4.66 1.1304 4.339 4.326 0.013 300 0.014 Example 1 0.009292 97 4.66 1.1304 4.4 4.359 0.041 300 0.037 3 2 0.009292 97 4.66 1.1304 4.359 4.341 0.018 300 0.015 3 0.009292 97 4.66 1.1304 4.341 4.329 0.012 300 0.012 Comparative 1 0.009384 97 4.66 1.1304 3.855 3.851 0.004 300 0.008 Example 2 0.009384 97 4.66 1.1304 3.851 3.847 0.004 300 0.007 1 3 0.009384 97 4.66 1.1304 3.847 3.841 0.006 300 0.007

[0085] As can be seen from Table 1, the coated material has an improved capacity and an improved cycle performance relative to the uncoated material (Comparative Example 1), where coating has optimal effects in the case of 2000 ppm.

[0086] As can be seen from Table 2, the materials obtained in the examples and the comparative example vary in the order of magnitude of resistivity under different pressure, and the coating structure of the present disclosure improves electron conductivity of the cobalt-free single crystal material.

[0087] As can be seen from Table 3, the lithium ion diffusion coefficient of the uncoated material (Comparative Example 1) has a power of −9 and has a power of −8 after coating, which is improved by one order of magnitude. It indicates that coating agents, TiNb.sub.2O.sub.7 and the conductive lithium salt, are conducive to improving the ion conductivity of the material, thereby improving the electrochemical performance of the material.

[0088] As can be seen from the comparison between Example 1 and Example 4, the capacity of the material cannot function well in the case of a small amount of coating.

[0089] As can be seen from the comparison of Example 1 with Examples 6 and 7, too large a molar ratio or too small a molar ratio both result in poor electrochemical performance of the obtained product, and TiNb.sub.2O.sub.7 and the conductive lithium salt can better exert a synergistic effect to improve the electrochemical performance of the cobalt-free single crystal material only when the molar ratio of TiNb.sub.2O.sub.7 and conductive lithium salt is (0.1-10): 1.

[0090] The cobalt-free single crystal composite material obtained in Example 8 of the present disclosure has electrochemical performance similar to that of Example 1.

[0091] As can be seen from the comparison of Example 1 with Comparative Example 1, the use of the coating structure of the present disclosure for coating the cobalt-free single crystal material can effectively improve the specific capacity, initial efficiency and cycle performance of the cobalt-free single crystal material.