A lithium battery cathode active material, a lithium battery cathode, a preparation method thereof, and a lithium battery

Abstract

The present invention discloses a lithium battery positive electrode active material, a lithium battery positive electrode, and a preparation method thereof, and a lithium battery. The lithium battery positive electrode active material includes defective-rich 1T combined with 2H mixed-phase MoS2 and an organic selenium-sulfur compound PhSeS x SePh, where x ≤ 6. The lithium battery positive electrode includes CNTs and the above-mentioned lithium battery positive electrode active material uniformly dispersed in the CNTs. It is prepared by starting with a MoS3 nanoparticle / CNTs composite as the positive electrode, using a lithium battery electrolyte containing a PDSe additive as the electrolyte, and a lithium metal as the negative electrode, and then charging after assembling the battery. The present invention provides a lithium battery positive electrode active material constructed at the molecular level, which has excellent electrochemical performance in the lithium battery electrode, has a high specific capacity, excellent rate performance, and long cycle stability. After 500 cycles, the capacity decay rate per cycle is only 0.04%.

Description

Technical Field

[0001] The present invention belongs to the technical field of lithium battery electrode materials, and particularly relates to a lithium battery positive electrode active material, a lithium battery positive electrode, a preparation method thereof, and a lithium battery. Background Art

[0002] Currently, the commercial lithium-ion battery positive electrode materials based on insertion / extraction reactions have reached their capacity limit (<300 mAh g -1 ). Therefore, electrode materials based on multi-electron conversion reactions have attracted much attention. For example, sulfur can provide a higher specific capacity. However, such materials currently also face problems of slow kinetics and irreversible structural changes brought about by multi-electron conversion and multi-step reactions. For example, the volume expansion of the sulfur positive electrode and the shuttle effect of soluble intermediates polysulfides (LiPSs). This makes it difficult for such materials to achieve an ideal reversible capacity. For these problems, the most commonly used solutions are: (1) Physical confinement; mainly confining the positive electrode active material into a porous conductive nanocomposite material, such as a carbon material, which can not only improve the conductivity but also achieve the effect of capturing LiPSs; (2) Chemical adsorption and catalytic conversion; mainly using some metal-based catalysts, especially transition metal sulfides (TMSs), to anchor soluble LiPSs and accelerate their conversion, thereby improving the utilization rate of sulfur. As a typical TMS, MoS2 is a panacea for improving battery performance and has attracted more and more attention. However, the biggest challenge currently lies in the difficulty of perfectly mixing sulfur with these introduced functional materials at the same molecular level.

[0003] Amorphous molybdenum trisulfide (MoS3) has a high sulfur content, and the theoretical specific capacity can be as high as ~837 mAh g -1 , in which divalent sulfur anions S 2- and disulfide anions S2 2- are covalently grafted around molybdenum atoms. This structure is beneficial to avoiding some adverse factors caused by the simple physical composite of sulfur and the TMS host material, such as: discontinuous electron conduction paths, uncontrollable physical confinement, and poor interfacial catalytic effects. In addition, compared with sulfur and lithium disulfide, MoS3 has higher conductivity. MoS3 presents a one-dimensional chain-like structure, which can also provide more storage sites for lithium ions, and the diffusion rate of lithium ions is also faster than that of common crystalline MoS2. Therefore, MoS3 has the potential to become a positive electrode material comparable to sulfur. However, due to the disorder and instability of the MoS3 itself, the battery performance cannot be accurately controlled. Summary of the Invention

[0004] The object of the present invention is to provide a lithium battery cathode active material, a lithium battery cathode, and a preparation method thereof and a lithium battery. This cathode active material is used in the lithium battery cathode, showing fast reduction reaction kinetics, weak shuttle effect of polysulfides (LiPSs), and having more excellent rate performance and cycle stability.

[0005] To solve the above technical problems, the present invention provides the following technical solutions:

[0006] Provide a lithium battery cathode active material, including defective-rich 1T combined with 2H mixed-phase MoS2 (1T / 2H-MoS2) and organic selenium sulfide compound PhSeS x SePh, where x ≤ 6 and x is an integer.

[0007] Among them, 1T combined with 2H mixed-phase MoS2 means it contains both 1T-MoS2 and 2H-MoS2. 1T-MoS2 means MoS2 in which Mo atoms and S atoms present octahedral coordination; 2H-MoS2 means MoS2 in which Mo atoms and S atoms present trigonal prism coordination.

[0008] Provide a lithium battery cathode, including CNTs and the above lithium battery cathode active material, and the lithium battery cathode active material is uniformly dispersed in the CNTs.

[0009] According to the above scheme, the lithium battery cathode is prepared by using a MoS3 nanoparticle / CNTs composite material as the starting cathode, using a lithium battery electrolyte containing a PDSe additive as the electrolyte, using lithium metal as the anode, assembling the battery and then charging, and in-situ generating defective-rich 1T / 2H mixed-phase MoS2 and organic selenium sulfide compound PhSeS x SePh, where x ≤ 6.

[0010] Among them, the MoS3 nanoparticle / CNTs composite material is sheet-shaped and can be directly used as the positive electrode sheet.

[0011] Preferably, in the MoS3 nanoparticle / CNTs composite material, the mass ratio of CNTs to MoS3 nanoparticles is (0.5 - 2.5):1.

[0012] Preferably, the concentration of the PDSe additive in the lithium battery electrolyte is 0.05 - 0.3 mol L -1 .

[0013] Preferably, the particle size of the MoS3 nanoparticles is 20 - 50 nm; the diameter of the CNTs is 8 - 10 nm.

[0014] Preferably, the MoS3 nanoparticles are uniformly distributed in the CNT network structure.

[0015] Preferably, the recharging voltage is up to 2.8 - 3.0 V.

[0016] Provide a preparation method of the above lithium battery cathode, and the specific steps are as follows:

[0017] 1) Disperse MoS3 nanoparticles and CNTs evenly in a polar solvent, and after treatment, obtain a MoS3 nanoparticle / CNT composite material. Then, use the obtained MoS3 nanoparticle / CNT composite material as the initial cathode, use a lithium battery electrolyte containing a PDSe additive as the electrolyte, and use lithium metal as the anode to assemble a Li|MoS3-PDSe battery;

[0018] 2) Recharge the Li|MoS3-PDSe battery obtained in step 1), and electrochemically in-situ generate defective-rich 1T / 2H-MoS2 and PhSeS x SePh (x ≤ 6) on the initial cathode, and then the lithium battery cathode is obtained.

[0019] According to the above scheme, in step 1), the polar solvent is absolute ethanol.

[0020] According to the above scheme, in step 1), the dispersion method of MoS3 nanoparticles and CNTs in the solvent is ultrasonic dispersion, the power is 600 - 800 W, and the working time is 10 - 15 min.

[0021] According to the above scheme, in step 1), the preparation method of MoS3 nanoparticles is as follows: add ammonium tetrathiomolybdate to deionized water, stir and dissolve it, and then slowly drop 1.2 - 1.5 mol L -1 of hydrochloric acid until the pH value of the mixed solution reaches 3, react and stir at room temperature for 2 - 3 h to obtain a MoS3 nanoparticle precursor, and finally sinter it at 200 - 250 °C in an argon atmosphere for 2 - 3 h.

[0022] According to the above scheme, in step 1), the post-treatment is: suction filtration, washing with absolute ethanol, vacuum drying, and slicing according to requirements.

[0023] According to the above scheme, in step 1), in the lithium battery electrolyte, the concentration of the PDSe additive is 0.05 - 0.3 molL -1 .

[0024] According to the above scheme, in step 1), the mass ratio of CNTs to MoS3 nanoparticles is (0.5 - 2.5):1.

[0025] According to the above scheme, in step 1), the diameter of MoS3 nanoparticles is 20 - 50 nm; the diameter of CNTs is 8 - 10 nm.

[0026] According to the above solution, in step 1), in the lithium battery electrolyte, the lithium salt is lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) and lithium nitrate (LiNO3), and the solvent is a mixed solvent of ethylene glycol dimethyl ether (DME) and 1,3-dioxolane (DOL).

[0027] Preferably, the volume ratio of DME to DOL is (0.8 - 1.2):1, and the molar concentration of lithium salt LiTFSI in the mixed solvent is 0.8 - 1.2 mol / L -1 , and the molar concentration of LiNO3 in the mixed solvent is 0.2 - 0.3 mol / L -1 .

[0028] Provided is a lithium battery, including a lithium battery electrolyte, a separator, and a lithium negative electrode, and further including a positive electrode, and the positive electrode is a MoS3 nanoparticle / CNTs composite material; the lithium battery electrolyte contains a PDSe additive.

[0029] According to the above solution, when the lithium battery is a button battery, the concentration of the PDSe additive in the lithium battery electrolyte is 0.15 - 0.3 mol / L -1 ; when the lithium battery is a soft-pack battery, the concentration of the PDSe additive in the lithium battery electrolyte is 0.05 - 0.15 mol / L -1 .

[0030] According to the above solution, after the lithium battery is assembled, it is recharged, and a defective-rich 1T / 2H mixed-phase MoS2 and an organic selenium sulfide compound PhSeS x SePh (x ≤ 6) are in-situ generated at the positive electrode.

[0031] Provided is a method for using the above lithium battery. After the battery is assembled, it is first recharged and then continues to be used.

[0032] According to the above solution, the recharging voltage is up to 2.8 - 3.0 V.

[0033] In the present invention, a MoS3 nanoparticle / CNTs composite material is used as the starting positive electrode, a lithium battery electrolyte containing a PDSe additive is used as the electrolyte, and lithium metal is used as the negative electrode. After the battery is assembled, it is recharged. Specifically: during the first discharge process, the starting active material MoS3 is converted into defective-rich 1T / 2H-MoS2 and Li2S, and the Se-Se bond in PDSe is broken to form PhSe·, and these free radicals react with Li + and e - to form PhSeLi. During the further discharge process, due to the ultra-high electrochemical activity of the defective-rich 1T / 2H-MoS2, it will be lithiated to form Li y MoS2. Next, during the de-lithiation charging process, Li yDuring the delithiation of MoS2, Li2S, and PhSeLi, defective-rich 1T / 2H-MoS2, S·, and PhSe· free radicals are formed respectively. Among them, S· will covalently bond with PhSe· free radicals to form a series of transformed charging products PhSeS x SePh (x ≤ 6). The formation of PhSeS x SePh (x ≤ 6) changes the redox reaction path of sulfur removed from the starting active material MoS3, realizes sulfur fixation at the atomic level, reduces the generation of LiPSs, and reduces the shuttle effect. In addition, the introduction of PDSe can also reduce the activation energy during the sulfur reduction reaction, thereby accelerating the sulfur reduction reaction kinetics. The present invention is based on the insertion-type defective-rich 1T / 2H-MoS2 combined with the transformed PhSeS x SePh (x ≤ 6) to form a stable lithium-ion battery cathode active material, which is further uniformly dispersed in CNTs to form a lithium-ion battery cathode, showing fast reduction reaction kinetics, weak shuttle effect of polysulfides (LiPSs), and excellent rate performance and cycle stability.

[0034] The beneficial effects of the present invention are as follows:

[0035] 1. The present invention provides a lithium-ion battery cathode active material constructed at the molecular level, which has excellent electrochemical performance in lithium-ion batteries, high specific capacity, excellent rate performance, and long cycle stability. After 500 cycles, the capacity attenuation rate per cycle is only 0.04%.

[0036] 2. The present invention provides a preparation method of a lithium-ion battery cathode. Using the MoS3 nanoparticle / CNTs composite material as the initial cathode, adding a lithium battery electrolyte containing PDSe, with the anode being lithium metal, assembling to obtain a Li|MoS3-PDSe battery. After recharging, an intercalation-type defective-rich 1T / 2H-MoS2 and a transformed PhSeS x SePh (x ≤ 6) can be obtained to form the lithium-ion battery cathode. During the recharging process, the sulfur atoms removed from the starting active substance MoS3 form new charging products with PDSe during the charge and discharge process, reducing the dissolution loss of LiPSs during the charging process, realizing sulfur fixation at the atomic level, reducing the loss of active substances, reducing the shuttle effect, and effectively improving the cycle performance of the lithium battery; the steps are simple, the operation is convenient and easy to control, green and safe, and convenient for industrial production, with popularization significance.

[0037] 3. The present invention provides a lithium battery and its usage method. Using MoS3 nanoparticle / CNTs composite material as the initial positive electrode, and adding a lithium battery electrolyte containing PDSe, a high-performance intercalation-conversion positive electrode can be obtained through simple recharge activation, achieving a significant improvement in the electrochemical performance of the lithium battery. When it is cycled 500 times in a button battery, the reversible capacity is 589.9 mAh g -1 , and the capacity decay rate is 0.04% / cycle, which has important industrial application value; furthermore, it can be assembled into a soft-pack battery. After being cycled 75 times under the condition of 1 mA cm -2 , its reversible capacity can be maintained at 70.6 mAh, having potential application prospects. Description of the Drawings

[0038] Figure 1 This is the structure of MoS3 synthesized in Example 1 of the present invention.

[0039] Figure 2 This is the transmission electron microscope image (TEM) of the starting active material MoS3 / CNTs synthesized in Example 1 of the present invention.

[0040] Figure 3 This is the X-ray diffraction pattern (XRD) of the starting active material MoS3 / CNTs synthesized in Example 1 of the present invention.

[0041] Figure 4 This is the X-ray photoelectron spectroscopy (XPS) of the starting active material MoS3 / CNTs synthesized in Example 1 of the present invention.

[0042] Figure 5 This is the Raman spectrum (Raman) of the starting active material MoS3 / CNTs synthesized in Example 1 of the present invention.

[0043] Figure 6 This is the Raman spectrum of the first charge-discharge product of the Li|MoS3 battery assembled with the starting active material MoS3 / CNTs prepared in Example 2 of the present invention.

[0044] Figure 7 This is the cryogenic transmission electron microscope image (Cryo-TEM) of the discharge product of the Li|MoS3 battery assembled with the starting active material MoS3 / CNTs prepared in Example 2 of the present invention.

[0045] Figure 8 This is the electron paramagnetic resonance spectrum (EPR) of the charge-discharge product of the Li|MoS3 battery in Example 2 of the present invention.

[0046] Figure 9 This is the ultraviolet-visible absorption spectrum (UV-vis) of the discharge intermediate of the Li|MoS3 and Li|MoS3-PDSe batteries assembled in Example 2 of the present invention.

[0047] Figure 10 Mass spectrometry (MS) of the discharge intermediate of the Li|MoS3-PDSe battery assembled in Example 2 of the present invention.

[0048] Figure 11 Mass spectrometry (MS) of the charging product PhSeS5SePh of the Li|MoS3-PDSe battery assembled in Example 2 of the present invention.

[0049] Figure 12 Mass spectrometry (MS) of the charging product PhSeS6SePh of the Li|MoS3-PDSe battery assembled in Example 2 of the present invention.

[0050] Figure 13 Discharge mechanism in a lithium battery of the intercalation-conversion type cathode material (insertion-type defect-rich 1T / 2H-MoS2 combined with conversion-type PhSeS x SePh) prepared in Example 2 of the present invention.

[0051] Figure 14 Activation energy (E a ) during the discharge process in a lithium battery of the MoS3 / CNTs electrode and the intercalation-conversion type electrode prepared in Example 2 of the present invention.

[0052] Figure 15 Comparison chart of charge-discharge voltage curves of the Li|MoS3 and Li|MoS3-PDSe batteries assembled in Example 2 of the present invention.

[0053] Figure 16 Comparison chart of rate performance of the Li|MoS3 and Li|MoS3-PDSe batteries assembled in Example 2 of the present invention.

[0054] Figure 17 Comparison chart of long cycle performance of the Li|MoS3 and Li|MoS3-PDSe batteries assembled in Example 2 of the present invention.

[0055] Figure 18 Cycle performance of the Li|MoS3-PDSe soft-pack battery assembled in Example 3 of the present invention. Detailed implementation manners

[0056] To enable those skilled in the art to better understand the technical solutions of the present invention, the present invention will be further described in detail below with reference to the accompanying drawings.

[0057] Example 1

[0058] A preparation method of a nano MoS3 / CNTs composite material specifically includes the following steps:

[0059] 1) Preparation of MoS3 nanoparticles: Add 1 mmol of ammonium tetrathiomolybdate to 40 mL of deionized water, stir to dissolve, and then slowly add 1.0 mol L -1 of hydrochloric acid until the pH value of the mixed solution reaches 3. React and stir at room temperature for 2 h to obtain a MoS3 nanoparticle precursor, and finally sinter it at 200 °C for 2 h under an argon atmosphere.

[0060] 2) Preparation of nano-MoS3 / CNTs composite: Add 60 mg of CNTs (with a diameter of 8 - 10 nm) and 35 mg of the MoS3 nanoparticles obtained in step 1) to beakers containing 300 mL of absolute ethanol respectively, ultrasonically disperse for 10 min respectively, then mix the above two solutions together and ultrasonically disperse for another 10 min. Filter by suction and wash several times with absolute ethanol. Dry at 80 °C for 24 hours under vacuum conditions. Cut the dried substrate material into circular small pieces with an area of about 1.13 cm 2 in diameter, 12 mm in diameter, and the MoS3 loading mass in the circular small pieces is 1.2 - 1.4 mg, thus obtaining the nano-MoS3 / CNTs composite (MoS3 / CNTs).

[0061] Figure 2 This is the TEM image of MoS3 / CNTs prepared in Example 1 of the present invention. The figure shows that MoS3 nanoparticles are evenly distributed in the CNT network structure, and the particle size of MoS3 particles ranges from 20 to 50 nm.

[0062] Figure 3 This is the XRD pattern of MoS3 / CNTs prepared in Example 1 of the present invention. The figure shows that MoS3 has an amorphous characteristic, manifested as a large broad peak appearing at about 14°, which is consistent with the literature results, indicating that the prepared MoS3 is relatively pure. The two crystallization peaks appearing at 25° and 45° belong to the characteristic peaks of CNTs.

[0063] Figure 4 This is the XPS Mo 3d spectrum of MoS3 / CNTs prepared in Example 1 of the present invention. As shown in the figure: The two peaks appearing at 229.3 eV and 232.4 eV respectively belong to the characteristic peaks of Mo 4+ 3d 5 / 2 and Mo 4+ 3d 3 / 2 , which is consistent with the literature results.

[0064] Figure 5 This is the Raman spectrum of MoS3 / CNTs prepared in Example 1 of the present invention. As shown in the figure: The peak signals appearing in the range of 200 - 400 cm -1 belong to the vibration of the Mo - S bond in MoS3; 1344 cm -1and 1580 cm -1 The peak signals that appear at -1 and 1580 cm are respectively attributed to the D peak and G peak of CNTs.

[0065] Example 2

[0066] Provide a preparation of a Li|MoS3-PDSe button battery, including the following steps:

[0067] Using the MoS3 / CNTs obtained in Example 1 as the positive electrode, adding a PDSe additive to the lithium battery electrolyte, using lithium metal as the negative electrode, and adding a separator to assemble a Li|MoS3-PDSe battery.

[0068] Among them: the electrolyte is 1 mol L -1 LiTFSI and 0.3 mol L -1 LiNO3 dissolved in a DME / DOL solvent with a volume ratio of 1:1. The concentration of the PDSe additive in the lithium battery electrolyte is 0.25 mol L -1 , the thickness of the lithium metal negative electrode is 450 μm, the diameter is 15.6 mm, the separator is Celgard 2400, and the diameter is 19 mm.

[0069] Recharge the Li|MoS3-PDSe battery obtained in this example. First, discharge it to 1.8 V, and then normally charge it to 3.0 V. During the charging process, sulfur will be removed from MoS3 to generate the intercalated 1T / 2H mixed-phase MoS2. Then sulfur enters the PDSe molecular structure to generate a transformed organoselenium sulfide compound. After recharging, intercalated defective-rich 1T / 2H-MoS2 and transformed PhSeS x SePh (x≤6) are formed in situ at the initial positive electrode, that is, the positive electrode of the lithium battery is obtained, and then subsequent cycles are carried out.

[0070] Comparative Example 1

[0071] Assemble a Li|MoS3 button battery. The battery structure includes: using the MoS3 / CNTs composite material obtained in Example 1 as the positive electrode, lithium metal as the negative electrode, a separator and an electrolyte. The electrolyte is 1 mol L -1 LiTFSI and 0.3 mol L -1 LiNO3 dissolved in a DME / DOL solvent with a volume ratio of 1:1. The thickness of the lithium metal negative electrode is 450 μm, the diameter is 15.6 mm, the separator is Celgard 2400, and the diameter is 19 mm.

[0072] By means of a series of experimental characterization methods (Raman, Cryo-TEM, EPR), the charge-discharge mechanisms of the Li|MoS3 button battery obtained in Comparative Example 1 of the present invention and the Li|MoS3-PDSe battery obtained in Example 2 were deeply explored.

[0073] Figure 6 This is the Raman image during the first charge-discharge process of the Li|MoS3 button battery assembled in Comparative Example 1 of the present invention. From the figure, we can draw the following conclusions: a. During discharge, MoS3 is converted into a mixed phase of 1T and 2H MoS2 (1T / 2H-MoS2); b. When MoS3 is recharged, its structure is irreversible and it is converted into 1T / 2H-MoS2 during charging.

[0074] Figure 7 This is the Cryo-TEM image of the discharge product of the Li|MoS3 button battery assembled in Comparative Example 1 of the present invention. As shown in the figure, there is Li y MoS2 formed, and the lattice fringe spacing at MoS2(002) changes from 0.62 nm to 0.88 nm, indicating that when discharged to 1.8 V, 1T / 2H-MoS2 has electrochemical activity and the lithium insertion reaction is realized.

[0075] Figure 8 This is the EPR spectrum of the charge-discharge products of the Li|MoS3 battery assembled in Comparative Example 1 of the present invention. As shown in the figure, the products of MoS3 in different charge-discharge states all have sulfur vacancies, manifested as peak signals at g = 2.00. This shows that the 1T / 2H-MoS2 generated by the conversion of MoS3 is rich in defects.

[0076] Figure 9 This is the UV-vis of the discharge intermediates of the Li|MoS3 assembled in Comparative Example 1 and the Li|MoS3-PDSe battery assembled in Example 2 of the present invention. The figure shows that polysulfides S6 2- / S8 2- (285 nm, 260 nm) signal peaks are detected in the discharge intermediates of the Li|MoS3 battery, indicating the generation of polysulfides during the discharge process of MoS3. However, the characteristic peaks of polysulfides are not detected in the discharge intermediates of the Li|MoS3-PDSe battery, proving that the PDSe additive changes the charge-discharge process of MoS3 and inhibits the generation of LiPSs.

[0077] Figure 10The MS of the discharge intermediate of the Li|MoS3-PDSe battery assembled in Example 2 of the present invention detected the discharge intermediate product PhSeS4Li. Since lithium ions will be replaced by hydrogen protons during the detection process, the actually detected form is PhSeS4H, and its mass-to-charge ratio is 285.867, which indicates that PDSe can capture S· free radicals, eliminating the conversion of sulfur to LiPSs at the source and greatly reducing the formation of LiPSs.

[0078] Figure 11 The mass spectrometry (MS) of the charging product PhSeS5SePh of the Li|MoS3-PDSe battery assembled in Example 2 of the present invention, and its mass-to-charge ratio is 468.867.

[0079] Figure 12 The mass spectrometry (MS) of the charging product PhSeS6SePh of the Li|MoS3-PDSe battery assembled in Example 2 of the present invention, and its mass-to-charge ratio is 506.714.

[0080] Figure 13 Analysis of the discharge mechanism of the lithium battery cathode active material (insertion-type defective-rich 1T / 2H-MoS2 combined with conversion-type PhSeS x SePh) prepared in Example 2 of the present invention in the lithium battery. As shown in the figure, the intercalation-type defective-rich 1T / 2H MoS2 and conversion-type PhSeS x SePh (x≤6) in-situ generated from MoS3 will discharge respectively. The defective-rich 1T / 2HMoS2 mainly undergoes lithium intercalation / deintercalation reactions in the voltage range of 1.8V - 3.0V. For the conversion-type PhSeS x SePh, taking PhSeS5SePh as an example, Li + and e - first attack two sulfur atoms in the middle to form intermediate 2. Due to the unstable elongation of the S-S bond, intermediate 2 reacts with another Li + and e - to dissociate into two PhSeS3Li (intermediate 3), then intermediate 3 is rapidly lithiated to form intermediate PhSeS2Li (intermediate 4), and then PhSeSLi (intermediate 5) is formed. Finally, intermediate 5 is reduced to form PhSeLi (product 6) and Li2S. The discharge mechanism of PhSeS x SePh when x takes other values is similar to that of PhSeS5SePh and will not be elaborated here.

[0081] Figure 14 The MoS3 / CNTs electrode prepared in Comparative Example 1 of the present invention and the intercalation-conversion type electrode (defective-rich 1T / 2H-MoS2-PhSeS obtained in Example 2x Activation energy (E a ) during the discharge process in a lithium battery. The figure shows the overall E a value of this electrode during the discharge process is lower than that of the MoS3 electrode. This indicates that the sulfur reduction reaction (SRR) kinetics of this electrode is faster than that of the MoS3 electrode. The improvement of SRR kinetics is related to the formation of PhSeS n Li(n≥1) intermediates during the discharge process. These PhSeS n Li(n≥1) molecules can shorten the reaction steps and reduce the formation of long-chain LiPSs. In addition, they have different highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies from LiPSs molecules, which may lead to different reduction abilities of PhSeS n Li(n≥1), thus improving its reduction reaction kinetics.

[0082] Figure 15 Comparison chart of charge-discharge voltage curves of Li|MoS3 assembled in Comparative Example 1 of the present invention and Li|MoS3-PDSe battery assembled in Example 2. The figure shows that the polarization voltage difference (160 mV) of the Li|MoS3-PDSe battery is less than that of the Li|MoS3 battery (250 mV). In addition, the discharge capacity (1.04 mAh) of the Li|MoS3-PDSe battery is much higher than that of the Li|MoS3 battery (0.61 mAh) electrode, which can be attributed to the excellent SRR kinetics of the in-situ generated intercalation-conversion type electrode (rich in deficient 1T / 2H-MoS2-PhSeS x SePh).

[0083] Figure 16 Comparison chart of rate performance of Li|MoS3 assembled in Comparative Example 1 of the present invention and Li|MoS3-PDSe battery assembled in Example 2. As shown in the figure: at 0.1 A g -1 , 0.15 A g -1 , 0.4 A g -1 , 0.8 A g -1 and 1.6 A g -1 , the discharge specific capacities of the Li|MoS3-PDSe battery are 806.1, 735.7, 683.3, 644.3 and 603.8 mAh g -1 respectively. When the current density returns to 0.1 A g -1 , it can retain a reversible capacity of 755.7 mAh g -1 . In contrast, the discharge specific capacities of the Li|MoS3 battery at all current densities are lower than those of the Li|MoS3-PDSe battery.

[0084] Figure 17 Cycling performance comparison chart of the Li|MoS3 assembled in Comparative Example 1 and the Li|MoS3-PDSe battery assembled in Example 2 of the present invention. As shown in the figure: The reversible capacity of the Li|MoS3-PDSe battery is 589.9 mAh g after 500 cycles -1 , and the capacity decay rate is 0.04% / cycle, which is much lower than that of the Li|MoS3 battery (0.16%). These results further prove that the in-situ generated intercalation-conversion type electrode (defect-rich 1T / 2H-MoS2-PhSeS x SePh) has good cycling stability and fast redox reaction kinetics.

[0085] Example 3

[0086] The preparation of the Li|MoS3-PDSe soft-pack battery is as follows:

[0087] 1) Preparation of MoS3 nanoparticles: The same as in Example 1.

[0088] 2) Preparation of the starting active substrate material MoS3 / CNTs: Add 200 mg of CNTs (with a diameter of 8-10 nm) and 300 mg of the MoS3 nanoparticles obtained in step 1) into beakers containing 300 mL of absolute ethanol respectively, ultrasonically disperse for 15 min respectively, then mix the above two solutions together and ultrasonically disperse for another 15 min. Filter by suction and wash several times with absolute ethanol. Dry at 80 °C for 24 hours under vacuum conditions. Cut the dried substrate material into a 6 cm × 6 cm square electrode sheet, and the loading mass of MoS3 in the electrode sheet is 180 mg.

[0089] 4) Preparation of the Li|MoS3-PDSe soft-pack battery: Using the active substrate material MoS3 / CNTs as the initial positive electrode, adding a PDSe additive to the lithium battery electrolyte, the negative electrode is lithium metal, and the separator is Celgard 2400 to obtain a Li|MoS3-PDSe battery. The electrolyte is 1 mol L -1 LiTFSI and 0.3 mol L -1 LiNO3 are dissolved in a DME / DOL solvent with a volume ratio of 1:1. The concentration of the PDSe additive in the lithium battery electrolyte is 0.1 mol L -1 .

[0090] Figure 18 Cycling performance of the Li|MoS3-PDSe soft-pack battery prepared in Example 3 of the present invention. Through simple recharge activation, the soft-pack battery can maintain a high reversible capacity of 70.6 mAh after 75 stable cycles.

[0091] In practical applications, the optimal concentration of PDSe can be screened according to the battery performance. For example, in a soft-pack battery, the applicable concentration of PDSe is 0.05 - 0.15 mol L -1 , and an appropriate PDSe concentration is beneficial to improving the long-cycle performance of the soft-pack battery; when the PDSe concentration in the soft-pack battery is too high, it is to some extent not conducive to the formation of the SEI layer on the lithium negative electrode of the soft-pack battery.

[0092] Obviously, the above embodiments are only examples clearly described and not limitations on the implementation manners. For those of ordinary skill in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to enumerate all implementation manners here. And the obvious changes or modifications thus extended are still within the protection scope of the present invention.

Claims

1. A lithium battery positive electrode, characterized in that, It includes CNTs and lithium-ion cathode active materials, and the lithium-ion cathode active materials are uniformly dispersed in the CNTs; wherein: The lithium-ion cathode active material includes defective-rich 1T combined with 2H mixed-phase MoS2 and organic selenium sulfide compound PhSeS x SePh, where x ≤ 6; The lithium-ion cathode is prepared by using a MoS3 nanoparticle / CNTs composite as the starting cathode, a lithium battery electrolyte containing a PDSe additive as the electrolyte, and lithium metal as the anode. After assembling the battery and charging it, a defective-rich 1T combined with 2H mixed-phase MoS2 and an organic selenium sulfide compound PhSeS x SePh, where x ≤ 6, are in-situ generated on the starting cathode.

2. The lithium battery positive electrode according to claim 1, wherein The particle size of the MoS3 nanoparticles is 20 - 50 nm; the diameter of the CNTs is 8 - 10 nm.

3. The lithium-ion battery positive electrode according to claim 1, wherein The recharge voltage is up to 2.8 - 3.0 V.

4. The preparation method of the lithium battery positive electrode according to claim 1, characterized in that, The specific steps are as follows: 1) Disperse the MoS3 nanoparticles and CNTs uniformly in a polar solvent, and post-treat to obtain a MoS3 nanoparticle / CNT composite material. Then, use the obtained MoS3 nanoparticle / CNT composite material as the initial cathode, use a lithium battery electrolyte containing a PDSe additive as the electrolyte, and use lithium metal as the anode to assemble a Li|MoS3-PDSe battery; 2) After recharging the Li|MoS3-PDSe battery obtained in step 1), a lithium-ion battery positive electrode rich in defective 1T combined with 2H mixed-phase MoS2 and PhSeS is electrochemically in-situ generated at the initial positive electrode. x SePh, where x ≤ 6, thus obtaining the lithium-ion battery positive electrode.

5. The preparation method according to claim 4, characterized in that, In the step 1), the mass ratio of CNTs to MoS3 nanoparticles is (0.5~2.5):1; the concentration of PDSe additive in the lithium battery electrolyte is 0.05~0.3 mol L -1 .

6. A lithium battery, characterized in that, It includes a lithium battery electrolyte, a separator, a positive electrode, and a lithium negative electrode. The positive electrode is a MoS3 nanoparticle / CNTs composite material. The lithium battery electrolyte contains a PDSe additive. After the lithium battery is assembled, it is recharged, and a defective-rich 1T combined with 2H mixed-phase MoS2 and an organic selenium sulfide compound PhSeS are in-situ generated on the positive electrode. x SePh, where x ≤ 6.

7. The lithium battery according to claim 6, wherein, When the lithium battery is a button battery, the concentration of the PDSe additive in the lithium battery electrolyte is 0.15 - 0.3 mol L -1 ; When the lithium battery is a soft-pack battery, the concentration of the PDSe additive in the lithium battery electrolyte is 0.05 - 0.15 mol L -1 .

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