Preparation method and application of solid-liquid two-phase positive electrode material

Abstract

The application discloses a preparation method and application of a solid-liquid two-phase positive electrode material and belongs to the technical field of battery materials. The application prepares a solid-liquid two-phase positive electrode system applied to a lithium battery by taking an organic sulfur polymer as a solid-phase active substance and taking an organic small-molecule ether dissolved in an electrolyte as a liquid-phase active substance. The prepared positive electrode material enables the organic sulfur polymer to play a higher surface capacity of the lithium battery of the positive electrode and has an ultralong cycle life. The preparation process of the application is simple, the battery performance is effectively improved, and the application of the organic sulfur group positive electrode material in the lithium battery is provided with a broad prospect.

Description

Technical Field

[0001] This invention belongs to the field of battery materials technology, specifically relating to a method for preparing a solid-liquid dual-phase cathode material and its application. Background Technology

[0002] Sulfur, due to its abundant reserves, environmental friendliness, and high theoretical capacity (1675 mAh / g), has become an ideal material for novel electrochemical energy storage devices. Lithium-sulfur batteries, constructed with sulfur as the positive electrode and lithium metal as the negative electrode, exhibit a much higher theoretical energy density than lithium-ion batteries (2600 Wh / kg). However, sulfur has poor intrinsic conductivity, leading to a shuttle effect during discharge. Furthermore, the significant volume change during charge and discharge results in reduced utilization of active materials, decreased cycle stability, and low coulombic efficiency, severely hindering the development of lithium-sulfur batteries. Current methods primarily employ physical confinement, chemical adsorption, and catalytic effects to improve reaction kinetics and suppress the shuttle effect. However, the introduction of inactive materials can negatively impact the battery's energy density.

[0003] Organosulfur materials, composed of carbon, hydrogen, and chalcogens, offer mild preparation conditions and controllable structures, making them highly promising cathode materials. By modulating the carbon skeleton, sulfur chains, and functional groups, the structure, voltage plateau, and reaction pathway of organosulfur materials can be altered. Simultaneously, tunable sulfur chains can suppress the shuttle effect. The relatively high sulfur content of sulfur-containing polymers gives them a higher theoretical capacity than smaller molecular structures; however, due to the intrinsic properties of sulfur-containing polymers (poor electronic conductivity, poor kinetics, etc.), rapid reaction kinetics cannot be achieved. Compared to organosulfur polymers, organoselenium and organtellurium polymers, which belong to the same group as sulfur, exhibit higher ionic and electronic conductivity, but their preparation conditions are demanding, making large-scale applications difficult.

[0004] Therefore, by combining organosulfur compounds with molecules of the same group in the same system, and utilizing their interactions during the electrochemical process to in-situ crosslink sulfur with its group-related atoms such as selenium and tellurium, selenium- and tellurium-containing organosulfur polymers can be constructed. This effectively increases the electronic conductivity of organosulfur compounds, enhances the capacity of electrode materials, and achieves long-cycle performance. Furthermore, this method is simple, feasible, and easy to scale up. Therefore, constructing suitable organosulfur cathode systems helps to promote electrochemical reaction kinetics and improve the electrochemical performance of lithium batteries. Summary of the Invention

[0005] The purpose of this invention is to provide a solid-liquid dual-phase cathode material for use in lithium batteries. During charge and discharge, the solid-phase cathode active material and the liquid-phase active material undergo cross-linking of active segments, forming in-situ SX bonds (where X is a chalcogenide element such as selenium or tellurium). Through the formation of SX bonds, elements with high electronic conductivity are introduced into the organosulfur polymer backbone, improving the electronic conductivity of the organosulfur polymer while providing electrochemical capacity. Simultaneously, highly soluble small organic ether molecules in the liquid phase are anchored to the cathode side due to the formation of SX bonds, reducing the dissolution and loss of the active material and improving utilization. Furthermore, the introduction of inactive functional groups also helps to improve the conversion capability of the active material.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A method for preparing a solid-liquid dual-phase cathode material includes the following steps:

[0008] Step (1): Use organic sulfur polymer as the solid-phase sulfur cathode material and organic small molecule ether as the liquid-phase cathode material.

[0009] Step (2): In the battery structure, the positive electrode side is a solid sulfur positive electrode, and the electrolyte part is a liquid positive electrode, thus obtaining a solid-liquid dual-phase positive electrode material.

[0010] Furthermore, in the above-mentioned method for preparing a solid-liquid dual-phase cathode material, the organic sulfur polymer in step (1) is a sulfur-rich polymer with a "solid-liquid-solid" or "solid-solid" electrochemical reaction, including poly(sulfide-indole-1,3-diisopropenebenzene), polysulfide propane, or sulfurized polyacrylonitrile.

[0011] Furthermore, in the above-mentioned method for preparing a solid-liquid dual-phase cathode material, the organic small molecule ether in step (1) is one or more of diphenyl diselenide, dimethyl diselenide, dibenzyl diselenide, diethyl diselenide, bis(aminophenyl)diselenide, biphenyl distelluride, or diphenyl distelluride.

[0012] Furthermore, in the above-mentioned method for preparing a solid-liquid dual-phase cathode material, in step (1), the organic small molecule ether is soluble in ether electrolyte and exists stably. During the charging and discharging process, the ether bond exerts its electrochemical capacity through the bond breaking / bonding process.

[0013] Furthermore, in the above-mentioned method for preparing a solid-liquid dual-phase cathode material, the organic small molecule ether in step (1) contains a conjugated structure, including but not limited to phenyl.

[0014] Furthermore, in the above-mentioned method for preparing a solid-liquid dual-phase cathode material, in step (2), the sulfur / X atomic ratio of the organic sulfur polymer to the organic small molecule ether is (1-10):1, where X is a Se or Te element; the organic sulfur polymer and the organic small molecule ether cross-link during the electrochemical reaction, thereby changing the structure and electrochemical performance of the active material.

[0015] Furthermore, in the above-mentioned method for preparing a solid-liquid dual-phase cathode material, the concentration of the small organic molecule ether in the electrolyte in step (2) is (10-1000) mmol / L.

[0016] Furthermore, in the above-mentioned method for preparing a solid-liquid dual-phase cathode material, in step (2), the organic small molecule ether is added to the cathode sheet during the battery assembly process.

[0017] Furthermore, in the above-mentioned method for preparing a solid-liquid dual-phase cathode material, in step (1), the solid sulfur cathode is attached to the cathode current collector, and the current collector includes, but is not limited to, carbon-coated aluminum foil or self-supporting current collector.

[0018] The solid-liquid dual-phase cathode material prepared by the above-mentioned method is used in lithium batteries.

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

[0020] First, a solid-phase organic sulfur polymer is synthesized and attached to the positive electrode current collector to serve as the solid-phase positive electrode in the solid-liquid dual-phase positive electrode system. Second, a certain concentration of small organic molecule ether is dissolved in a commercial ether electrolyte or added dropwise to the positive electrode during battery assembly to serve as the liquid-phase positive electrode in the solid-liquid dual-phase positive electrode system. Combining the two results in the solid-liquid dual-phase positive electrode system.

[0021] During electrochemical processes, cross-linking of active segments occurs in the two-phase active materials, forming SX bonds in situ on the cathode side. The formation of SX bonds introduces other elements from the same group into the organosulfur framework of the solid-phase cathode, improving electronic conductivity, reducing ohmic impedance, and promoting reaction kinetics. Simultaneously, other active segments contribute to capacity utilization. SX bonds can anchor small organic ether molecules dissolved in the electrolyte to the cathode side, promoting the reaction and improving their utilization. Functional groups or conjugated structures in the solid-liquid two-phase active materials also promote reaction kinetics and accelerate electrochemical conversion. Therefore, the solid-liquid two-phase cathode system exhibits high reaction kinetics, high capacity, and stable long-cycle characteristics.

[0022] Advantages and beneficial effects of the present invention:

[0023] 1. The solid-liquid dual-phase cathode material prepared by the present invention improves the conductivity and reaction kinetics of the solid organic sulfur polymer through the cross-linking effect of the active segments, and promotes the reactivity of small molecules and the utilization rate of active substances in the liquid phase.

[0024] 2. The solid-liquid dual-phase cathode material prepared by this invention promotes cycle stability and capacity through the interaction of the two active phases.

[0025] 3. The present invention contains functional groups or conjugated structures in the solid and liquid phase active materials, which can reduce the lowest unoccupied molecular orbital (LUMO) energy level of the active materials and promote the conversion reaction of the active materials in the positive electrode.

[0026] 4. The preparation process of this invention is simple, the raw materials required for preparation are widely available, and it can be used for large-scale production.

[0027] 5. The cathode system of the present invention has wide applicability. Different types of organic sulfur polymers and small organic molecules soluble in electrolytes can be used to realize diverse biphase cathode systems. Attached Figure Description

[0028] Figure 1 The electrochemical performance diagram of the benzoquinone-based polytetrasulfide (BTP) solid-phase cathode is shown.

[0029] In the figure: (a) at 1mA cm -2 (a) First charge-discharge curve at current density; (b) at 1 mA cm -2 Areal capacity versus number of cycles and coulombic efficiency versus number of cycles at current density;

[0030] Figure 2 Electrochemical performance diagram of diphenyldiselelenide (DPhDSe) liquid-phase cathode;

[0031] In the figure: (a) at 1mA cm -2 (a) First charge-discharge curve at current density; (b) 1 mA cm -2 Areal capacity versus number of cycles and coulombic efficiency versus number of cycles at current density;

[0032] Figure 3 The diagram shows the electrochemical performance of the solid-liquid dual-phase cathode.

[0033] In the figure: (a) at 1mA cm -2 (a) First charge-discharge curve at current density; (b) at 1 mA cm -2 Areal capacity versus number of cycles and coulombic efficiency versus number of cycles at current density;

[0034] Figure 4This is a comparison between the solid-liquid dual-phase cathode and the sum of the electrochemical capacities of the two active materials in the system.

[0035] The black curve in the figure represents the distance at 1 mA cm. -2 The areal capacity-cycle count curve of a solid-liquid dual-phase cathode cell at current density; the blue curve represents the areal capacity at 1 mA cm⁻¹. -2 Curves showing the sum of areal capacity per cycle and the number of cycles for BTP and DPhDSe batteries at current density;

[0036] Figure 5 For 2mA cm -2 Areal capacity-cycle count and coulombic efficiency-cycle count curves of solid-liquid dual-phase cathode cells at current density;

[0037] Figure 6 The graph shows the electrochemical performance of a solid-liquid dual-phase cathode cell under high BTP loading conditions.

[0038] In the figure: (a) at 10mg BTP cm -2 At load capacity, 2mA cm -2 (a) Battery first charge-discharge curve at current density; (b) at 2mA cm -2 Areal capacity-cycle count and coulombic efficiency-cycle count curves of the battery at current density;

[0039] Figure 7 When the solid-liquid dual-phase positive electrode reaches the charging state (2.8V) after 10 cycles, the BTP solid-phase positive electrode at 200-800cm⁻¹ -1 Raman characterization within the range. Detailed Implementation

[0040] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings, examples, and comparative examples. Example 1

[0041] This embodiment discloses a solid-liquid dual-phase cathode material. Benzoquinone-based polytetrasulfide (BTP) prepared by interfacial polymerization in aqueous phase is used as the solid phase cathode part in the solid-liquid dual-phase cathode, and lithium-sulfur battery electrolyte containing DPhDSe is used as the liquid phase cathode in the solid-liquid dual-phase cathode system.

[0042] The preparation of BTP involves three steps: First, sodium sulfide nonahydrate (Na₂S·9H₂O) and sulfur powder are mixed and reacted in an aqueous phase at a molar ratio of 1:3 to generate a sodium tetrasulfide solution. Second, trichloropropane (TCP) and dichlorobenzoquinone (DCBQ) are mixed at a molar ratio of 0.01 to prepare a TCP solution containing DCBQ. Third, the resulting sodium tetrasulfide aqueous solution and the DCBQ TCP solution are added at a molar ratio of 0.5 to an aqueous solution containing 20 mmol / L CTAB and stirred continuously. After reacting for more than 12 hours, BTP is finally obtained. The sulfur content in BTP is approximately 60%. The cleaned and dried BTP is mixed with conductive additives and binders at a ratio of 7:2:1, uniformly coated onto the surface of a carbon-containing aluminum foil current collector, and dried to obtain a BTP electrode with a BTP loading of approximately 2 mg / cm³. 2 .

[0043] 500 mmol / L DPhDSe was dissolved in the lithium-sulfur battery electrolyte to obtain the positive electrode solution. The lithium-sulfur battery electrolyte was a mixed solution of DOL and DME (volume ratio 1:1) containing 1 M LiTFSI electrolyte and 0.2 M LiNO3 additive.

[0044] The positive electrode described in this example was subjected to electrochemical performance testing in a lithium battery. A 2025 coin cell was used for the electrode material electrochemical performance testing: a 10mm diameter circle of BTP positive electrode was cut as the working electrode, a 16mm diameter, 0.45mm thick lithium sheet was used as the counter electrode, and a 19mm diameter Celgard 2400 polypropylene film coated with rGO was used as the separator. The electrolyte was the DPhDSe positive electrode solution prepared above, with an addition amount of 30μl. The sulfur / selenium atomic ratio of the organic sulfur polymer and the organic small molecule ether was 1:1. During the discharge test, the potential range was 1.7-2.8V (vs. Li / Li). + ).like Figure 3 As shown in (a), the solid-liquid dual-phase cathode at 1 mA cm⁻¹ -2 The initial discharge capacity at the current density is 1.38 mAh / cm³. -2 The difference between the polarization voltage, i.e., the charging voltage plateau and the discharging voltage plateau, is small, approximately 0.15V. For example... Figure 3 As shown in (b), the solid-liquid dual-phase cathode maintained a capacity of 1.07 mAh / cm² after 400 cycles. -2 The areal capacity was [value missing]. The average capacity decay rate per cycle was 0.024%. This indicates that the synergistic effect of the solid-liquid dual-phase cathode system helps to improve the reaction kinetics of the lithium battery, thereby improving the actual capacity and promoting the overall cycle stability of the battery. Furthermore, to further demonstrate the synergistic promoting effect in the solid-liquid dual-phase cathode system, the electrochemical performance of this example was compared with that of two comparative examples. Figure 4As shown, during 400 cycles, the areal capacity of the solid-liquid biphase cathode was consistently higher than the sum of the areal capacities of the cathodes in both ratios. Therefore, the capacity increase is a result of the interaction between the solid-phase organic sulfur polymer and the liquid-phase small organic molecule ether during the electrochemical process, rather than the sum of the electrochemical capacities exerted by the two active materials themselves.

[0045] Furthermore, a long-cycle test was conducted on the battery in this embodiment. For example... Figure 5 As shown, the solid-liquid dual-phase cathode at 2 mA cm⁻¹ -2 The initial discharge capacity at the current density is 0.82 mAh / cm³. -2 It maintained 0.46 mAh / cm³ after 1700 cycles. -2 The areal capacity was [value missing]. The average capacity decay rate per cycle was 0.026%. This indicates that the synergistic effect of the solid-liquid dual-phase cathode system helps improve the reaction kinetics of the lithium battery and promotes the overall cycle stability of the battery.

[0046] The solid-phase cathode in this embodiment was prepared with a diameter of 10 mm and a BTP loading of approximately 10 mg / cm³. 2 A circular positive electrode was used, and the amount of positive electrode liquid added in this embodiment was changed to 90 μl for electrochemical testing. The sulfur / selenium atomic ratio of the organic sulfur polymer and the organic small molecule ether was 10:3. Figure 6 As shown in (a), the solid-liquid dual-phase cathode is at 2 mA cm⁻¹ -2 The initial discharge capacity at the current density is 11.39 mAh / cm³. -2 The difference between the polarization voltage, i.e., the charging voltage plateau and the discharging voltage plateau, is small, approximately 0.2V. For example... Figure 6 As shown in (b), the high-load solid-liquid dual-phase cathode maintained 7.69 mAh / cm² after 25 cycles. -2 The areal capacity indicates that the synergistic effect of the solid-liquid dual-phase cathode system helps to improve the reaction kinetics of lithium batteries and enhance their actual capacity.

[0047] Comparative Example 1

[0048] This comparative example uses benzoquinone-based polytetrasulfide (BTP) prepared by interfacial polymerization in the aqueous phase as the cathode material for lithium batteries.

[0049] The preparation of BTP involves three steps: First, sodium sulfide nonahydrate (Na₂S·9H₂O) and sulfur powder are mixed and reacted in an aqueous phase at a molar ratio of 1:3 to generate a sodium tetrasulfide solution. Second, trichloropropane (TCP) and dichlorobenzoquinone (DCBQ) are mixed at a molar ratio of 0.01 to prepare a TCP solution containing DCBQ. Third, the resulting sodium tetrasulfide aqueous solution and the DCBQ TCP solution are added at a molar ratio of 0.5 to an aqueous solution containing 20 mmol / L CTAB and stirred continuously. After reacting for more than 12 hours, BTP is finally obtained. The cleaned and dried BTP is mixed with conductive additives and binders at a ratio of 7:2:1, uniformly coated onto the surface of a carbon-containing aluminum foil current collector, and dried to obtain a BTP electrode with a BTP loading of approximately 2 mg / cm³. 2 .

[0050] The solid-phase organic sulfur polymer of this comparative example was used to conduct electrochemical performance tests in a lithium-sulfur battery. A 2025 coin cell battery case was used to assemble the electrode materials for electrochemical performance testing. A 10 mm diameter disc of BTP positive electrode was cut as the working electrode, a lithium sheet (16 mm diameter, 0.45 mm thickness) was used as the counter electrode, and a Celgard 2400 polypropylene film (19 mm diameter) coated with reduced graphene oxide (rGO) was used as the separator. The electrolyte was a mixed solution (volume ratio 1:1) of 1,3-dioxane (DOL) and dimethyl ethylene glycol (DME) containing 1 M lithium bis(trifluoromethanesulfonyl)imide (LiTFSI) electrolyte and 0.2 M lithium nitrate (LiNO3) additive. During discharge testing, the potential range was 1.7–2.8 V (vs. Li / Li). + ).like Figure 1 As shown in (a), the BTP positive electrode is at 1 mA cm⁻¹ -2 The initial discharge capacity at the current density is 0.74 mAh / cm³. -2 The polarization voltage, i.e., the difference between the charging voltage plateau and the discharging voltage plateau, is relatively large, approximately 0.3V. For example... Figure 1 As shown in (b), the BTP cathode maintained a capacity of 0.57 mAh / cm² after 400 cycles. -2 The surface capacity has an average capacity decay rate of 0.058% per cycle.

[0051] Comparative Example 2

[0052] This comparative example uses DPhDSe added to the electrolyte of a lithium-sulfur battery as the positive electrode solution.

[0053] 500 mmol / L DPhDSe was dissolved in the lithium-sulfur battery electrolyte to obtain the positive electrode solution. The lithium-sulfur battery electrolyte was a mixed solution of DOL and DME (volume ratio 1:1) containing 1 M LiTFSI electrolyte and 0.2 M LiNO3 additive. Conductive additives and binders were mixed in a 9:1 ratio and uniformly coated on the surface of a carbon-containing aluminum foil current collector. After drying, a pure carbon electrode sheet was obtained.

[0054] The electrochemical performance of the liquid-phase organic small molecule ether in this comparative example was tested in a lithium battery using a 2025 coin cell as the positive electrode. A 10mm diameter circle of pure carbon electrode was used as the current collector, a 16mm diameter, 0.45mm thick lithium sheet was used as the counter electrode, and a 19mm diameter Celgard 2400 polypropylene film coated with rGO was used as the separator. The electrolyte was the DPhDSe positive electrode solution prepared above. During discharge testing, the potential range was 1.7-2.8V (vs. Li / Li). + ).like Figure 2 As shown in (a), the DPhDSe positive electrode is at 1 mA cm⁻¹ -2 The initial discharge capacity at the current density is 0.33 mAh / cm³. -2 The difference between the polarization voltage, i.e., the charging voltage plateau and the discharging voltage plateau, is small, approximately 0.1V. For example... Figure 2 As shown in (b), DPhDSe maintained a capacity of 0.24 mAh / cm³ after 400 cycles. -2 The surface capacity has an average capacity decay rate of 0.069% per cycle.

[0055] Therefore, based on the above description, this invention provides a method for preparing a solid-liquid dual-phase cathode material, which can effectively improve the electrochemical kinetics and cycle stability of lithium battery cathodes. Through the cross-linking of active segments in both phases, a capacity synergy of "1+1>2" is achieved, exhibiting high capacity utilization and cycle performance under long-cycle conditions and high solid-phase active material loading. This patented preparation method is simple, highly reproducible, offers high flexibility in material selection, is easy to control, and has broad application prospects.

[0056] The above description is only a preferred embodiment of the present invention. It should be noted that the above embodiments are exemplary and should not be construed as limiting the present invention. Several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for preparing a solid-liquid dual-phase cathode material, characterized in that, Includes the following steps: Step (1): Use organic sulfur polymer as the solid-phase sulfur cathode material and organic small molecule ether as the liquid-phase cathode material. Step (2): In the battery structure, the positive electrode side is a solid sulfur positive electrode, and the electrolyte part is a liquid positive electrode, thus obtaining a solid-liquid dual-phase positive electrode material.

2. The method for preparing a solid-liquid dual-phase cathode material according to claim 1, characterized in that, In step (1), the organic sulfur polymer is a sulfur-rich polymer with a "solid-liquid-solid" or "solid-solid" electrochemical reaction, including poly(sulfide-indole-1,3-diisopropenebenzene), polysulfide propane, or sulfurized polyacrylonitrile.

3. The method for preparing a solid-liquid dual-phase cathode material according to claim 1, characterized in that, In step (1), the organic small molecule ether is one or more of diphenyl diselenide, dimethyl diselenide, dibenzyl diselenide, diethyl diselenide, bis(aminophenyl)diselenide, biphenyl distelluride, or diphenyl distelluride.

4. The method for preparing a solid-liquid dual-phase cathode material according to claim 3, characterized in that, In step (1), the small organic molecule ether is soluble in ether electrolyte and exists stably. During the charging and discharging process, the ether bond exerts its electrochemical capacity through the bond breaking / bonding process.

5. The method for preparing a solid-liquid dual-phase cathode material according to claim 3, characterized in that, In step (1), the small organic ether contains a conjugated structure, including phenyl.

6. The method for preparing a solid-liquid dual-phase cathode material according to claim 1, characterized in that, In step (2), the sulfur / X atomic ratio of the organic sulfur polymer and the organic small molecule ether is (1-10):1, where X is Se or Te. During the electrochemical reaction, the active segments of the organic sulfur polymer and the organic small molecule ether crosslink, thereby changing the structure and electrochemical performance of the active substances.

7. The method for preparing a solid-liquid dual-phase cathode material according to claim 1, characterized in that, In step (2), the concentration of the small organic molecule ether in the electrolyte is (10-1000) mmol / L.

8. The method for preparing a solid-liquid dual-phase cathode material according to claim 1, characterized in that, In step (2), the small organic molecule ether is added to the positive electrode during the battery assembly process.

9. The method for preparing a solid-liquid dual-phase cathode material according to claim 1, characterized in that, In step (1), the solid sulfur cathode is attached to the cathode current collector, which includes carbon-coated aluminum foil or a self-supporting current collector.

10. The application of the solid-liquid dual-phase cathode material prepared by the method of any one of claims 1-9 in lithium batteries.

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