Sulfide positive electrode material, preparation method and lithium ion battery

Abstract

The application discloses a sulfide positive electrode material, a preparation method and a lithium ion battery. The sulfide positive electrode material comprises a sulfide base and a structure regulator, and the structure regulator enters the sulfide base material in the form of doping. The application introduces the structure regulator into the crystal structure of the sulfide base, realizes the regulation of the crystallinity of the sulfide base, and the structure regulator participates in the construction of ion conduction paths in the base, so that the ion conductivity of the sulfide base is improved, the electrochemical activity is activated, and the obtained sulfide positive electrode material has higher specific capacity, better rate performance and longer cycle life in a full solid-state lithium ion battery.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium-ion batteries, and particularly relates to a sulfide cathode material, a preparation method thereof, and a lithium-ion battery. Background Art

[0002] The development of advanced cathode materials can promote the practical application of high-energy-density lithium-ion batteries. High-capacity lithium-rich sulfide cathodes, which have better conductivity than pure S or Li2S electrodes, are considered for use in lithium-ion batteries.

[0003] Among them, layered lithium-containing transition metal sulfides such as LiTiS2 and Li2FeS2 mainly provide capacity through the redox of transition metal ions, so the available capacity that can be exerted is very low.

[0004] And rock-salt-structured lithium-containing transition metal sulfides such as Li2TiS3 and Li3NbS4 mainly provide capacity through S2 2- / S 2- and / or the redox of transition metal ions. Although the materials with a rock-salt structure have a relatively high specific capacity, they have large structural changes during charge and discharge, so they have poor rate performance and cycle stability.

[0005] The performance indexes of many lithium-containing transition metal sulfide cathodes including the above cathodes in lithium-ion batteries far cannot meet the requirements of commercial batteries, so technical improvements are still needed in terms of capacity, rate, and cycle performance. Summary of the Invention

[0006] Aiming at the deficiencies existing in the above-mentioned prior art, the present invention provides a sulfide cathode material, a preparation method thereof, and a lithium-ion battery, aiming to increase the charge-discharge capacity of the sulfide cathode material, improve its initial ionic conductivity, and improve the structural stability during the cycle, so that the sulfide cathode material and its lithium-ion battery have better rate performance and cycle stability.

[0007] To achieve the above object, a preparation method of a sulfide cathode material provided by the present invention includes the following steps:

[0008] (1) Mix a sulfide matrix or a raw material of a sulfide matrix with a raw material of a structure regulator to obtain a mixture, wherein the sulfide matrix is Li a M b S c , wherein M includes one or more of the metal elements Ti, Fe, V, Nb, Mo, Ni, Co, Mn, Cu, Mg, and Sn, 0 < a < 5, 0 < b < 5, 0 < c < 10, and the structure regulator is Si 4+ ;

[0009] (2) Ball-mill the mixture to obtain a precursor of the sulfide cathode material;

[0010] (3) Sinter the precursor of the sulfide cathode material under the protection of an inert gas to obtain the sulfide cathode material.

[0011] Preferably, the sulfide cathode material is Li a M b Si d S c , where 0 < d / b < 1 and 0 < b + d < 5.

[0012] Preferably, 0 < d / b < 0.6. d / b is the atomic molar ratio of the structure regulator Si 4+ relative to the doping of the metal element M. Since SiS2 is an insulator, too much Si 4+ doping will be unfavorable to the electronic conductivity of the sulfide matrix.

[0013] Preferably, the raw material of the structure regulator is SiS2.

[0014] Preferably, the process of ball-milling is as follows: the mass ratio of balls to materials is 10 - 500, the ball-milling speed is 200 - 2000 revolutions per minute, and the ball-milling time is 0.5 - 30 hours. Further, the mass ratio of balls to materials is 50 - 300, the ball-milling speed is 300 - 1500 revolutions per minute, and the ball-milling time is 2 - 25 hours. Ball-milling mixes the sulfide matrix and the raw material of the structure regulator in the mixture evenly, and the particles are in full contact with each other.

[0015] Preferably, the process of sintering is as follows: the sintering temperature is 300 - 800 °C, and the sintering time is 2 - 10 hours. Further, the sintering temperature is 400 - 600 °C, and the sintering time is 3 - 8 hours. Too low temperature and too short sintering time are unfavorable to the recrystallization of the sulfide cathode material, and too high temperature and too long time will cause excessive element volatilization, such as S element.

[0016] Preferably, by controlling one or more of the addition amount of the raw material of the structure regulator, the ball-milling parameters and the sintering parameters, the obtained sulfide cathode material is in the form of powder particles, and the particle size of the particles is 0.05 - 10 μm. Further, the particle size of the particles is 0.05 - 6 μm. Too large particle size is unfavorable to improving the lithium-ion percolation network and the electrochemical activity of the sulfide cathode material.

[0017] The present invention also provides a sulfide cathode material prepared by the method according to any one of the above, and the sulfide cathode material includes: a sulfide matrix and a structure regulator, and the structure regulator enters the crystal structure of the sulfide matrix in a doping form.

[0018] The present invention also provides a lithium-ion battery, wherein the positive electrode of the lithium-ion battery includes the above-mentioned sulfide positive electrode material.

[0019] The technical principle of this invention is as follows:

[0020] Through high-temperature sintering, the structure regulator Si 4+ It can be doped into the crystal structure of sulfide matrix materials. Under high temperature, ions in the raw material undergo interdiffusion and structural rearrangement, ultimately achieving the formation of cation mixing and the regulation of crystal structure. For example... Figure 1 As shown, the structure regulator Si 4+ The addition of Si intensifies cation mixing in the lithium-poor layer, activating some blocked lithium ions and connecting them with the 2D lithium-ion diffusion pathways, thus opening up the 3D lithium-ion diffusion channels in the sulfide cathode material. Furthermore, due to the structure modifier Si... 4+ The cation radius of Si is smaller than that of most transition metals, and it has greater electronegativity. 4+ Can react with anion S 2- More stable Si-S bonds are formed. The shorter Si-S bonds and their groups cause distortion of the metal-sulfur groups in the sulfide matrix, thereby widening the diffusion channels of lithium ions in the 2D plane. This not only improves the initial lithium-ion conductivity of the sulfide cathode material and enhances rate performance, but also increases the molar amount of lithium ions that can be intercalated or deintercalated, thus improving the discharge capacity. Furthermore, the Si-S groups play a role in maintaining structural stability during the charge and discharge process of the sulfide cathode, thereby improving its cycle stability.

[0021] Compared with the prior art, the technical solution of the present invention has at least the following beneficial effects:

[0022] (1) The initial ionic conductivity of the sulfide cathode material is σ1, and the initial ionic conductivity of the sulfide matrix is ​​σ2, where σ1 / σ2 = 1-10 5 Through the structure regulator Si 4+ Due to the effect of [the specific chemical process], the ionic conductivity of the proposed sulfide cathode material must be at least higher than that of the sulfide matrix.

[0023] (2) The present invention introduces a structure regulator into the crystal structure of the sulfide matrix, which can regulate the crystallinity and cation mixing degree of the sulfide matrix. This can not only improve the initial lithium-ion conductivity of the material, but also activate the elements in the sulfide matrix that were originally non-electrochemically active to carry out redox reactions, thereby improving the rate performance and discharge specific capacity of the sulfide cathode material.

[0024] (3) The structure regulating agent Si provided by the present invention 4+ and S 2-The formation of stable Si-S bonds can maintain stability during the charge and discharge process of sulfide cathode materials, thus alleviating the structural collapse problem of sulfide cathode materials and improving the cycle stability of sulfide cathode materials. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the principle of optimizing the sulfide matrix using a structure regulating agent in this invention.

[0026] Figure 2 The Li2TiSi obtained in Examples 1 and 2 of this invention 0.01 S 3.02 and Li2Ti 0.90 Si 0.10 XRD patterns of S3 sulfide cathode material and the sulfide matrix Li2TiS3 in Example 1;

[0027] Figure 3 This is a charge-discharge curve diagram of Embodiment 2 in this invention;

[0028] Figure 4 This is a rate performance diagram of Example 2 in this invention;

[0029] Figure 5 This is a cycle performance diagram of Example 2 in this invention. Detailed Implementation

[0030] The present invention will be further described below through several specific embodiments, but is not limited thereto. Unless otherwise specified, the raw materials, reagents or apparatus used in the following embodiments can be obtained from conventional commercial sources or by existing known methods.

[0031] Example 1:

[0032] A Li2TiSi 0.01 S 3.02 Sulfide cathode materials, using Li₂TiS₃ as the sulfide matrix, incorporate a certain stoichiometric ratio of structure modifier Si. 4+ It is incorporated into the lattice of the Li2TiS3 sulfide matrix by lattice doping.

[0033] The Li2TiSi 0.01 S 3.02 A method for preparing sulfide cathode materials includes the following steps: Weigh a total of 10g of Li₂TiS₃ and SiS₂ according to the stoichiometric ratio and place them in a ball mill jar, add 400g of zirconium oxide balls, and then seal the jar. Ball mill at 500 rpm for 5 hours to obtain Li₂TiSiS₃. 0.01 S 3.02 Sulfide cathode material precursor. Then Li2TiSi 0.01 S 3.02The sulfide cathode material precursor was sintered in a muffle furnace under inert gas protection at 450℃ for 5 h to obtain Li₂TiSi. 0.01 S 3.02 Sulfide cathode material precursor. This Li₂TiSi 0.01 S 3.02 The sulfide cathode material (experimental group) and the Li2TiS3 sulfide matrix (control group) were cold-pressed into discs and their ionic conductivity was tested. The test results are shown in Table 1.

[0034] Weigh out Li₂TiSi according to a mass ratio of 60:30:10. 0.01 S 3.02 (Experimental group) or Li₂TiS₃ (control group), Li₆PS₅Cl (sulfide solid electrolyte), and VGCF (carbon fiber) conductive carbon were ground for 5 min to prepare a composite positive electrode. 10 mg of this composite positive electrode and 120 mg of Li₆PS₅Cl were pressed into a battery assembly with a diameter of 10 mm. Li-In was used as the alloy negative electrode to assemble an all-solid-state battery, and its electrochemical performance was tested. Test conditions were: voltage range 1.3-3.6V (vs. Li₂TiS₃) or Li₆PS₅Cl (control group), Li₆PS₅Cl (sulfide solid electrolyte), and VGCF (carbon fiber) conductive carbon. + The test was performed by cycling at 0.1C, 0.3C, 0.5C and 1C for 5 cycles each, and finally at 0.5C for 100 cycles. The test results are shown in Table 1.

[0035] Table 1

[0036]

[0037] Example 2:

[0038] A Li2Ti 0.90 Si 0.10 S3 sulfide cathode material, with Li2Ti 0.90 S3 is a sulfide matrix, with a certain stoichiometric ratio of structure modifier Si. 4+ Incorporating into Li2Ti via lattice doping 0.90 In the lattice of the S3 sulfide matrix.

[0039] The Li2Ti 0.90 Si 0.10 The preparation method of S3 sulfide cathode material includes the following steps: Weigh a total of 10g of Li2S, TiS2, and SiS2 according to the stoichiometric ratio and place them in a ball mill jar. Add 500g of zirconium oxide balls and seal the jar. Mill at 600 rpm for 8 hours to obtain Li2Ti. 0.9 Si 0.1 S3 sulfide cathode material precursor. Then Li2Ti 0.90 Si 0.10The S3 sulfide cathode material precursor was sintered in a muffle furnace under inert gas protection at 400℃ for 6 hours to obtain Li2Ti. 0.9 Si 0.1 S3 sulfide cathode material precursor. This Li2Ti 0.9 Si 0.1 S3 sulfide cathode material (experimental group) and Li2Ti 0.9 S3 sulfide matrix (control group) was cold-pressed into discs for ionic conductivity testing. The results are shown in Table 2. Among them, Li2Ti served as the control group... 0.9 The preparation method of S3 sulfide matrix includes the following steps: Weigh a total of 10g of Li2S, TiS2, and S according to the stoichiometric ratio and place them in a ball mill jar; the other steps are the same as for Li2Ti... 0.9 Si 0.1 The preparation method for S3 material is the same.

[0040] Weigh out Li₂Ti according to a mass ratio of 60:30:10. 0.90 Si 0.10 S3 (experimental group) or Li2Ti 0.9 S3 (control group), Li6PS5Cl (sulfide solid electrolyte), and VGCF (carbon fiber) conductive carbon were ground for 5 min to prepare a composite positive electrode. 10 mg of this composite positive electrode was pressed with 120 mg of Li6PS5Cl to form a battery assembly with a diameter of 10 mm. Using Li-In as the alloy negative electrode, an all-solid-state battery was assembled, and its electrochemical performance was tested. Test conditions were: voltage range 1.3-3.6V (vs. Li). + The test was performed by cycling at 0.1C, 0.3C, 0.5C and 1C for 5 cycles each, and finally at 0.5C for 100 cycles. The test results are shown in Table 2.

[0041] Table 2

[0042]

[0043] Example 3:

[0044] A Li2Fe 0.90 Si 0.05 S2 sulfide cathode material, with Li2Fe 0.90 S2 is a sulfide matrix, with a certain stoichiometric ratio of structure modifier Si. 4+ Incorporating Li2Fe via lattice doping 0.90 In the lattice of the S2 sulfide matrix.

[0045] The Li2Fe 0.90 Si 0.05The preparation method of S2 sulfide cathode material includes the following steps: Weigh a total of 10g of Li2S, FeS, and SiS2 according to the stoichiometric ratio and place them in a ball mill jar. Add 500g of zirconium oxide balls and seal the jar. Mill at 1000rpm for 4 hours to obtain Li2Fe 0.90 Si 0.05 S2 sulfide cathode material precursor. Then Li2Fe 0.90 Si 0.05 The S2 sulfide cathode material precursor was sintered in a muffle furnace under inert gas protection at 600℃ for 4 hours to obtain Li2Fe. 0.90 Si 0.05 S2 sulfide cathode material precursor. This Li2Fe 0.90 Si 0.05 S2 sulfide cathode material (experimental group) and Li2Fe 0.90 S2 sulfide matrix (control group) was cold-pressed into discs for ionic conductivity testing, as shown in Table 3. Li2Fe, used as the control group... 0.90 The preparation method of S2 sulfide matrix includes the following steps: Weigh a total of 10g of Li2S, FeS, and S according to the stoichiometric ratio and place them in a ball mill jar; the other steps are the same as for Li2Fe... 0.90 Si 0.05 The preparation method for S2 material is the same.

[0046] Weigh out Li₂Fe according to a mass ratio of 60:30:10. 0.90 Si 0.05 S2 (experimental group) or Li2Fe 0.90 S2 (control group), Li6PS5Cl (sulfide solid electrolyte), and VGCF (carbon fiber) conductive carbon were ground for 5 min to prepare a composite positive electrode. 10 mg of this composite positive electrode was pressed with 120 mg of Li6PS5Cl to form a battery assembly with a diameter of 10 mm. Using Li-In as the alloy negative electrode, an all-solid-state battery was assembled, and its electrochemical performance was tested. Test conditions were: voltage range 1.0-3.6V (vs. Li). + The test was performed by cycling at 0.1C, 0.3C, 0.5C and 1C for 5 cycles each, and finally at 0.5C for 100 cycles. The test results are shown in Table 3.

[0047] Table 3

[0048]

[0049] Example 4:

[0050] A Li2Ti 0.8 Fe 0.4 Si 0.2 S 3.4Sulfide cathode materials, with Li2Ti 0.8 Fe 0.4 S3 is a sulfide matrix, with a certain stoichiometric ratio of structure modifier Si. 4+ Incorporating into Li2Ti via lattice doping 0.8 Fe 0.4 In the lattice of the S3 sulfide matrix.

[0051] The Li2Ti 0.8 Fe 0.4 Si 0.2 S 3.4 The preparation method of sulfide cathode material includes the following steps: weighing Li₂Ti according to the stoichiometric ratio. 0.8 Fe 0.4 A total of 10g of S3 and SiS2 was placed in a ball mill jar, and 500g of zirconia balls were added before sealing. The jar was milled at 1000 rpm for 5 hours to obtain Li2Ti. 0.8 Fe 0.4 Si 0.2 S 3.4 Sulfide cathode material precursor. Then Li2Ti 0.8 Fe 0.4 Si 0.2 S 3.4 The sulfide cathode material precursor was sintered in a muffle furnace under inert gas protection at 400℃ for 8 hours to obtain Li₂Ti. 0.8 Fe 0.4 Si 0.2 S 3.4 Sulfide cathode material precursor. This Li₂Ti 0.8 Fe 0.4 Si 0.2 S 3.4 Sulfide cathode materials (experimental group) and Li2Ti 0.8 Fe 0.4 S3 sulfide matrix (control group) was cold-pressed into discs and subjected to ionic conductivity testing. The test results are shown in Table 4.

[0052] Weigh out Li₂Ti according to a mass ratio of 60:30:10. 0.8 Fe 0.4 Si 0.2 S 3.4 (Experimental group) or Li2Ti 0.8 Fe 0.4S3 (control group), Li6PS5Cl (sulfide solid electrolyte), and VGCF (carbon fiber) conductive carbon were ground for 5 min to prepare a composite positive electrode. 10 mg of this composite positive electrode was pressed with 120 mg of Li6PS5Cl to form a battery assembly with a diameter of 10 mm. Using Li-In as the alloy negative electrode, an all-solid-state battery was assembled, and its electrochemical performance was tested. Test conditions were: voltage range 1.3-3.6V (vs. Li). + The samples were cycled for 5 cycles each at 0.1C, 0.3C, 0.5C and 1C, and finally 100 cycles at 0.5C. The test results are shown in Table 4.

[0053] Table 4

[0054]

[0055] Example 5:

[0056] A Li3NbSi 0.2 S 4.4 Sulfide cathode materials, using Li3NbS4 as the sulfide matrix, incorporate a certain stoichiometric ratio of structure modifier Si. 4+ It is incorporated into the lattice of the Li3NbS4 sulfide matrix by lattice doping.

[0057] The Li3NbSi 0.2 S 4.4 A method for preparing sulfide cathode materials includes the following steps: Weigh a total of 10g of Li3NbS4 and SiS2 according to the stoichiometric ratio and place them in a ball mill jar, add 400g of zirconium oxide balls, and then seal the jar. Ball mill at 500 rpm for 10 hours to obtain Li3NbSi 0.2 S 4.4 Sulfide cathode material precursor. Then Li3NbSi 0.2 S 4.4 The sulfide cathode material precursor was sintered in a muffle furnace under inert gas protection at 450℃ for 5 h to obtain Li3NbSi. 0.2 S 4.4 Sulfide cathode material precursor. This Li3NbSi... 0.2 S 4.4 The sulfide cathode material was cold-pressed into discs and subjected to ionic conductivity testing. The test comparison structures are shown in Table 5.

[0058] Weigh out Li3NbSi according to a mass ratio of 70:25:5. 0.2 S 4.4(Experimental group) or Li3NbS4 (control group), Li6PS5Cl (sulfide solid electrolyte), and VGCF (carbon fiber) conductive carbon were ground for 5 min to prepare a composite positive electrode. 10 mg of this composite positive electrode and 120 mg of Li6PS5Cl were pressed into a battery assembly with a diameter of 10 mm. Li-In was used as the alloy negative electrode to assemble an all-solid-state battery, and its electrochemical performance was tested. Test conditions were: voltage range 1.0-3.6V (vs. Li + The samples were cycled for 5 cycles each at 0.1C, 0.3C, 0.5C and 1C, and finally 100 cycles at 0.5C. The test results are shown in Table 5.

[0059] Table 5

[0060]

[0061] As shown in Tables 1-5, the lithium-ion conductivity of the sulfide cathode materials prepared in this invention is improved to varying degrees. When used in all-solid-state batteries, the rate performance and capacity retention after 100 cycles are significantly improved. As shown in Tables 1 and 2, with the increase in Si... 4+ The increased doping concentration resulted in a greater increase in the discharge capacity of the prepared sulfide cathode material relative to the original sulfide matrix. This is due to the addition of more structure modifier Si in Example 2. 4+ This results in a higher degree of cation mixing in the structure of the sulfide cathode material, activating a greater molar amount of migratable lithium ions. At the same time, more Si-S groups make the structural framework of the sulfide cathode material more stable after delithiation. Therefore, the all-solid-state batteries corresponding to the sulfide cathode materials shown in Table 2 have better discharge capacity, rate performance and cycle stability.

[0062] Figure 2 The Li2TiSi obtained in Examples 1 and 2 0.01 S 3.02 and Li2Ti 0.90 Si 0.10 The XRD patterns of the S3 sulfide cathode material and the sulfide matrix Li2TiS3 in Example 1 show that as the Si ion doping amount increases, the crystallinity of the obtained sulfide cathode material decreases significantly, and the diffraction peaks at ~50.5° and ~50.1° merge, indicating that Si ion doping causes an increase in the degree of cation mixing.

[0063] Figure 3 The Li2Ti obtained in Example 2 0.90 Si 0.10 S3 and Li2Ti 0.9 A comparison of the charge and discharge curves of the S3 all-solid-state battery shows that Li2Ti 0.90 Si0.10 The S3 all-solid-state battery has a larger discharge specific capacity.

[0064] Figure 4 and Figure 5 The Li2Ti obtained in Example 2 are respectively 0.90 Si 0.10 The rate performance and cycle performance graphs of the S3 all-solid-state battery are shown below. Figure 4 It can be seen that Li2Ti 0.90 Si 0.10 The S3 sulfide cathode material exhibits good rate performance, with a capacity of 349 mAh / g at 1C; from Figure 5 It can be seen that Li2Ti 0.90 Si 0.10 The S3 all-solid-state battery retains 97% of its capacity after 100 cycles at 0.5C, as shown in Table 2.

[0065] This invention is not limited to the examples above. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of this invention, and these improvements and modifications should also be considered within the scope of protection of this invention.

Claims

1. A method for producing a sulfide positive electrode material, characterized by, The method comprises the following steps: (1) mixing a sulfide host and a structure-controlling agent raw material to obtain a mixture, wherein the sulfide host is Li a M b S c wherein M includes Ti or Nb, 0 < a < 5, 0 < b < 5, 0 < c < 10, and the structure-controlling agent is Si 4+ , and the structure-controlling agent enters the crystal structure of the sulfide host in the form of doping; (2) ball-milling the mixture to obtain a sulfide positive electrode material precursor; (3) sintering the sulfide cathode material precursor under inert gas protection to obtain the sulfide cathode material Li a M b Si d S c Wherein, 0 < d / b < 1, 0 < b+d < 5, the sintering process is: sintering temperature 400-600℃, sintering time 3-8 hours.

2. The method of producing a sulfide positive electrode material according to claim 1, characterized by, 0 < d / b < 0.

6.

3. The method of producing a sulfide positive electrode material according to claim 1, characterized by, The structural regulator raw material is SiS2.

4. The method of producing a sulfide positive electrode material according to claim 1, characterized by, The ball-milling process is as follows: the ball-to-material mass ratio is 10-500, the ball-milling rotation speed is 200-2000 rpm, and the ball-milling time is 0.5-30 hours.

5. The method of producing a sulfide positive electrode material according to claim 1, characterized by, According to the control of one or more of the adding amount of the structural regulator raw material, the ball-milling parameters and the sintering parameters, the obtained sulfide positive electrode material is in the form of powder particles, and the particle size of the particles is 0.05-10 μm.

6. A sulfide cathode material produced according to the method of any one of claims 1 to 5, characterized in that, The sulfide positive electrode material comprises a sulfide matrix and a structural regulator which is in the form of doping into the crystal structure of the sulfide matrix.

7. A lithium-ion battery, characterized by The lithium ion battery comprises the sulfide positive electrode material according to claim 6.

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