CN116598477A - Lithium supplementing material, preparation method thereof, positive electrode plate and secondary battery - Google Patents

Lithium supplementing material, preparation method thereof, positive electrode plate and secondary battery Download PDF

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Publication number
CN116598477A
CN116598477A CN202310101017.5A CN202310101017A CN116598477A CN 116598477 A CN116598477 A CN 116598477A CN 202310101017 A CN202310101017 A CN 202310101017A CN 116598477 A CN116598477 A CN 116598477A
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lithium
carbon fiber
core
supplementing material
positive electrode
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谢友森
万远鑫
孔令涌
裴现一男
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Foshan Defang Chuangjie New Energy Technology Co ltd
Qujing Defang Chuangjie New Energy Technology Co ltd
Shenzhen Dynanonic Innovazone New Energy Technology Co Ltd
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Foshan Defang Chuangjie New Energy Technology Co ltd
Qujing Defang Chuangjie New Energy Technology Co ltd
Shenzhen Dynanonic Innovazone New Energy Technology Co Ltd
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Priority to CN202310101017.5A priority Critical patent/CN116598477A/en
Publication of CN116598477A publication Critical patent/CN116598477A/en
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    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/581—Chalcogenides or intercalation compounds thereof
    • H01M4/5815—Sulfides
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/628—Inhibitors, e.g. gassing inhibitors, corrosion inhibitors
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/021—Physical characteristics, e.g. porosity, surface area
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

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  • Chemical & Material Sciences (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Materials Engineering (AREA)
  • Inorganic Chemistry (AREA)
  • Manufacturing & Machinery (AREA)
  • Battery Electrode And Active Subsutance (AREA)

Abstract

The lithium supplementing material comprises a core and carbon fibers, wherein the core consists of lithium-containing sulfide; the carbon fiber is formed with a hole extending inward from the surface, and the core is embedded in the carbon fiber and accommodated in the hole. The lithium supplementing material provided by the application has higher lithium supplementing specific capacity and excellent electronic conductivity.

Description

Lithium supplementing material, preparation method thereof, positive electrode plate and secondary battery
Technical Field
The application relates to the technical field of secondary batteries, in particular to a lithium supplementing material and a preparation method thereof, an anode plate and a secondary battery.
Background
Lithium ion batteries are one of the energy storage and power battery technologies with the best comprehensive performance at present. However, at the time of the initial charging process, lithium ions are stored by the positive electrode to the negative electrode, accompanied by formation of a Solid Electrolyte (SEI) on the surface of the negative electrode. This process irreversibly consumes a portion of the active lithium and reduces the capacity and energy density of the battery. Pre-lithiation can introduce additional active lithium into the battery system and is very promising in compensating for initial lithium loss and increasing the energy density of lithium ion batteries.
Nano lithium sulfide is an electrode material with high theoretical capacity and low charge barrier, which is lower than the cut-off charge potential of many existing cathode materials, so that lithium sulfide can be completely delithiated. However, existing commercial lithium sulfide powders are all micron-sized in particle size, with internal volumes impeding sulfur conversion, resulting in lower micron-sized lithium sulfide capacities and higher potential barriers. And the electron conductivity of lithium sulfide is poor due to the insulating property of lithium sulfide. It becomes a key issue how to provide a lithium supplementing material having nano-sized lithium sulfide and excellent electron conductivity.
Disclosure of Invention
The application aims to provide a lithium supplementing material, a preparation method thereof, a positive electrode plate and a secondary battery.
The application provides the following technical scheme:
in a first aspect, the present application provides a lithium supplementing material, the lithium supplementing material comprising a core and carbon fibers, the core being composed of a lithium-containing sulfide; the carbon fiber is provided with holes extending inwards from the surface, and the inner core is embedded in the carbon fiber and is accommodated in the holes. In particular, the core may be a lithium-containing sulfide having a nano-size, and is a lithium source core for lithium supplementation. The carbon fiber may be a fiber having a micro-nano size obtained by carbonization. The carbon fiber can be provided with holes with the size corresponding to the size of the inner core, the holes extend from the surface of the carbon fiber to the inside, and the inner core is embedded in the carbon fiber, so that the carbon fiber can partially coat the inner core. The reason for forming the holes of the carbon fibers can be that in the preparation process of the lithium supplementing material, the lithium source reacts with the precursor of the carbon fibers, so that the lithium source can simultaneously etch the surfaces of the carbon fibers when reducing the lithium source into lithium-containing sulfide, thereby embedding the carbon fibers. Alternatively, the specific process of carbon fiber intercalation in the core may be to uniformly mix the polymer solution, lithium sulfate and micro-nano sized fibers, and then sinter the above mixture, so that the polymer and micro-nano sized fibers may be carbonized, and then carbothermic reduction of lithium sulfate and both to produce lithium sulfide. In the above process, the carbon source formed by the polymer may react with lithium sulfate first to be consumed, and then the remaining lithium sulfate reacts with the carbon fiber, so that carbon on the surface of the carbon fiber is consumed by the reaction, and the generated lithium sulfide can be intercalated therein. It will be appreciated that a plurality of uniformly dispersed cores may be embedded in any one carbon fiber such that the plurality of cores form a beaded structure on the carbon fiber.
According to the lithium supplementing material provided by the application, the lithium-containing sulfide is used as the inner core, the inner core is embedded into the carbon fiber by regulating and controlling etching, and the inner core is partially coated by the carbon fiber, so that on one hand, the capability of the lithium supplementing material for transmitting lithium ions outwards can be enhanced by utilizing the strong electric conductivity of the carbon fiber, the defect of poor electric conductivity of the lithium-containing sulfide is overcome, and meanwhile, the carbon fiber also has a larger specific surface area, so that the lithium ion transmission efficiency of the lithium supplementing material can be further improved; on the other hand, the carbon fiber has larger specific surface area, so that the precursor containing lithium sulfide can have more attachment points in the sintering process, the finally obtained core is not easy to agglomerate, the dispersibility of the core is improved, and the size of the core is reduced; furthermore, the structure of the carbon fiber coated inner core can reduce the inner core to the nanoscale size, the structural advantage of the nanoscale inner core is utilized, so that the polarization of the lithium-containing sulfide is smaller, and the voltage platform is lower during charging, so that the lithium-supplementing material can have a lower activation barrier, the deintercalation efficiency of lithium ions can be remarkably improved, and the higher lithium-supplementing specific capacity of the lithium-supplementing material is realized.
In one possible embodiment, the inner core is partially embedded in the carbon fiber, and at least partially protrudes from the surface of the carbon fiber; and/or the inner core is fully embedded into the carbon fiber and is fully arranged in the hole. Specifically, in the specific process of embedding the core into the carbon fiber provided in the above embodiment, the content of the remaining lithium sulfate reacted with the carbon fiber may be different due to the different content of each core reacted with the carbon source formed by the polymer during the formation process. It can be understood that when the content of the residual lithium sulfate reacting with the carbon fiber is low, that is, the etching degree of the carbon fiber is low, the inner core is mostly partially embedded into the carbon fiber, and the inner core is partially exposed out of the carbon fiber and protrudes out of the surface of the carbon fiber; when the content of the residual lithium sulfate reacted with the carbon fiber is high, namely the etching degree of the carbon fiber is high, the inner core is mostly embedded into the holes, and the inner core is completely accommodated in the holes. The inner core is partially embedded into the carbon fiber, so that the consumption of a precursor in preparation can be reduced, and the preparation cost is reduced; meanwhile, the preparation difficulty of embedding the carbon fiber into the inner core part is low, and the formability is easy to control. The inner core is arranged to be fully embedded with the carbon fiber, so that the contact area between the inner core and the carbon fiber can be maximized, and higher electronic conductivity is provided.
In one possible embodiment, the lithium supplementing material further comprises a coating layer, wherein the coating layer coats the outer surface of the inner core exposed to the external environment. It can be appreciated that, since the core is embedded in the carbon fiber by etching, either the half-embedded holes or the full-embedded holes or at least a part of the core is exposed to the external environment, the core exposed to the external environment is extremely reactive with water in the environment, thereby reducing the electrochemical performance of the lithium-supplementing material. A cladding layer may be provided on the exposed portion of the core to isolate the core from the external environment. Of course, in other embodiments, the coating layer may also cover the portion of the core embedded in the carbon fiber. The material of the coating layer may be graphite or other small-sized carbon source, and is not particularly limited. The coating layer is arranged, so that the electronic and ion conduction performance of the lithium supplementing material in the inner core can be effectively improved, and the lithium release in the charging process is improved; can also play a certain role in isolating moisture, improve the stability of the lithium supplementing material and realize a stable lithium supplementing effect. In addition, the stability, the dispersion uniformity and the good processing performance of the lithium supplementing material in the electrode active slurry and the active layer can be ensured.
In one possible embodiment, the distribution density of the inner core on the single carbon fiber is 10g/cm 3 ～15g/cm 3 . By controlling the distribution density of the cores on the carbon fibers within the range, too dense distribution of the cores on the carbon fibers can be avoided, aggregation of the cores on the carbon fibers can be reduced, occurrence of the condition that the cores are not embedded into the carbon fibers can be reduced, and each carbon fiber can be ensured to be provided for a proper conductive environment of the cores.
In one possible embodiment, the carbon fiber accounts for 1% -5% of the mass of the lithium supplementing material. By controlling the distribution density of the cores on the carbon fibers within the range, too dense distribution of the cores on the carbon fibers can be avoided, aggregation of the cores on the carbon fibers can be reduced, occurrence of the condition that the cores are not embedded into the carbon fibers can be reduced, and each carbon fiber can be ensured to be provided for a proper conductive environment of the cores.
In one possible embodiment, the particle size D50 of the inner core is from 5nm to 80nm. The particle size of the lithium sulphide powder in the current commercial is typically 10 μm to 30 μm. Due to the insulating properties, the internal volume of most particles impedes the conversion of sulfur, thus showing a higher barrier and lower capacity. The particle size of the inner core in the embodiment of the application can be controlled at the nanometer level through the high polymer solution, and the inner core containing lithium sulfide reaching the nanometer level can shorten the diffusion length and enlarge the active specific surface area by greatly reducing the particle size, thereby being beneficial to the intercalation and deintercalation of lithium ions and further increasing the capacity of the lithium supplementing material. When the particle size of the inner core is smaller than the above range, the difficulty of preparation increases, and the particles form relatively serious agglomeration; when the particle diameter of the core is larger than the above range, the specific surface area of the core is reduced, and the intercalation and deintercalation efficiency of lithium ions is lowered, thereby resulting in poor lithium supplementing effect of the lithium supplementing material.
In one possible embodiment, the carbon fibers have a diameter of 20nm to 100nm. The diameter of the carbon fiber is controlled within the above range in order to enable the carbon fiber to be adapted to the size of the core, thereby facilitating the embedding of the core; meanwhile, the carbon fiber is ensured to have proper specific surface area, and excellent lithium ion extraction environment can be provided. When the diameter of the carbon fiber is smaller than the range, the diameter of the carbon fiber is too small, so that the core is easy to penetrate through the carbon fiber, and the coating area of the carbon fiber on the core is reduced; when the diameter of the carbon fiber is larger than the above range, the specific surface area of the carbon fiber is reduced, which is unfavorable for the removal of lithium ions.
In one possible embodiment, the carbon fibers have a length of 1 μm to 20 μm. The length of the carbon fiber is controlled within the range, so that the fiber can be fully dispersed in the preparation process, and the fiber is prevented from being excessively long to generate winding; and the contact area between the carbon fiber and the inner core is increased, so that the inner core is uniformly distributed on the carbon fiber, and the density distribution of the inner core on the carbon fiber is controlled.
In a possible embodiment, the outline of the hole is spherical, hemispherical or ellipsoidal. It is understood that the size of the core is controlled to the nano-scale by the high molecular polymer solution so that the shape of the core is mostly spherical or spheroid. The holes are etched from the inner shell, so the outline shape of the holes should match the shape of the inner shell. When the inner core is fully embedded in the carbon fiber, the shape of the hole can be spherical or ellipsoidal; when the inner core is partially embedded in the carbon fiber, the shape of the holes may be hemispherical.
In one possible embodiment, the pores have a pore diameter of 5nm to 80nm. It is understood that the pore diameter of the pores may refer to the particle diameter of the core in the above embodiment, and will not be described herein.
In one possible embodiment, the volume of the holes is 40% -70% of the volume of the carbon fibers. It is understood that the volume of the holes is the size of the space occupied by the holes on the encapsulation layer. From the above embodiments, it is known that the volume ratio of the holes should be related to the distribution density of the core on the carbon fiber, and the volume ratio of the holes is controlled within the above range, which means that the distribution density of the core on the carbon fiber is moderate, and the depth of the core embedded in the carbon fiber is appropriate. When the volume of the holes is too small, the distribution of the inner cores on the carbon fiber is less, and the inner cores are free outside the carbon fiber, so that the carbon fiber is easy to not exert the conductive effect; it is also possible that the core is embedded deeper and shallower, resulting in the core being prone to fall off, thereby affecting electrochemical performance.
In one possible embodiment, the thickness of the coating layer is 10nm to 100nm. It will be appreciated that the thickness of the coating ensures both the specific capacity of the lithium-compensating material and the electronically conductive environment. When the thickness of the coating layer is smaller than the range, the coating layer does not completely coat the inner core, so that a good electronic conductive environment is not constructed; when the coating layer thickness is larger than the above range, since the coating layer does not contribute lithium ions, the overall gram capacity of the additive is reduced.
In one possible embodiment, the mass ratio of the coating layer in the lithium supplementing material is 2% -5%. The ratio of the coating layer in the lithium supplementing material is controlled, so that the coating layer can fully coat the exposed part of the inner core and the part in the external environment, and the influence of water and carbon dioxide in the external environment on the inner core is avoided; but also provides the core with excellent specific capacity and electronically conductive environment. If the coating layer mass ratio is too high, the added overall gram capacity is reduced because the coating layer does not contribute lithium ions; if the coating layer has too low mass ratio, the coating layer with complete coating and uniform thickness is not formed on the outer surface of the core, and the coating is incomplete, so that a good electronic conductive environment is not constructed.
In one possible embodiment, the chemical formula of the lithium-containing sulfide includes Li x S y Wherein x is more than or equal to 1 and less than or equal to 2, and y is more than or equal to 1 and less than or equal to 6.
In a second aspect, the present application also provides a method for preparing a lithium supplementing material, including: mixing a lithium-containing sulfide precursor, a polymer precursor and a carbon fiber precursor, and shaping to obtain a precursor mixture; and sintering the precursor mixture to obtain the lithium supplementing material, wherein the lithium supplementing material comprises a core and carbon fibers, the carbon fibers are formed with holes extending inwards from the surface, and the core is embedded into the holes of the carbon fibers.
In one possible embodiment, the method further comprises the steps of: and after the lithium supplementing material and the carbon source are mixed and sintered, the carbon source forms a coating layer to cover the outer surface of the inner core exposed to the external environment.
In a third aspect, the present application further provides a positive electrode sheet, where the positive electrode sheet includes a current collector and an active material layer disposed on the current collector, where the active material layer includes a positive electrode material and a lithium supplementing material according to any one of the first aspect of embodiments, or where the active material layer includes a positive electrode material and a lithium supplementing material obtained by a method for preparing a lithium supplementing material according to any one of the second aspect of embodiments.
In a fourth aspect, the present application further provides a secondary battery, including the positive electrode sheet according to the third aspect, or the battery includes the lithium-supplementing material according to any one of the embodiments of the first aspect, or the battery includes the lithium-supplementing material obtained by the method for preparing the lithium-supplementing material according to any one of the embodiments of the second aspect.
Drawings
In order to more clearly illustrate the embodiments of the application or the technical solutions in the prior art, the drawings which are used in the description of the embodiments or the prior art will be briefly described, it being obvious that the drawings in the description below are only some embodiments of the application, and that other drawings can be obtained from them without inventive effort for a person skilled in the art.
FIG. 1 is a schematic view showing the appearance of a lithium supplementing material according to an embodiment;
FIG. 2 is a schematic cross-sectional view of a core partially embedded carbon fiber in one embodiment;
FIG. 3 is a schematic cross-sectional view of a core with fully embedded carbon fibers in one embodiment;
FIG. 4 is a schematic cross-sectional view of a lithium-compensating material in one embodiment;
fig. 5 is a flowchart of a method for preparing a lithium-supplementing material according to an embodiment.
Detailed Description
The following description of the embodiments of the present application will be made clearly and fully with reference to the accompanying drawings, in which it is evident that the embodiments described are only some, but not all embodiments of the application. All other embodiments, which can be made by those skilled in the art based on the embodiments of the present application without making any inventive effort, are intended to fall within the scope of the present application.
It will be understood that when an element is referred to as being "fixed to" another element, it can be directly on the other element or intervening elements may also be present. When a component is considered to be "connected" to another component, it can be directly connected to the other component or intervening components may also be present.
Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used in the description of the application herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application. The term "and/or" as used herein includes any and all combinations of one or more of the associated listed items.
Some embodiments of the present application are described in detail below with reference to the accompanying drawings. The following embodiments and features of the embodiments may be combined with each other without conflict.
In a first aspect, referring to fig. 1, 2 and 4, the present application provides a lithium supplementing material 100, where the lithium supplementing material 100 includes a core 10 and a carbon fiber 20, the core 10 is composed of a lithium-containing sulfide, and the core 10 has a nanoscale size; the carbon fiber 20 is formed with holes 21 extending inward from the surface, and the core 10 is embedded in the carbon fiber 20 and is accommodated in the holes 21.
In particular, the core 10 may be a nano-sized lithium-containing sulfide, a lithium source core for lithium replenishment. Alternatively, the lithium-containing sulfide may be lithium sulfide and the precursor may be lithium sulfate. The lithium-containing sulfide is added to the electrode as the lithium-supplementing material 100 of the inner core 10, so that the lithium-containing sulfide is used as a sacrificial agent in the first-cycle charging process, and all lithium ions contained in the lithium-containing sulfide are released as soon as possible to supplement irreversible lithium ions consumed by the negative electrode forming an SEI film, thereby maintaining the abundance of lithium ions in the battery system and improving the first effect and the overall electrochemical performance of the battery. Compared with other lithium supplementing materials 100, the lithium supplementing material 100 made of the lithium-containing sulfur compound has weaker binding force between lithium ions and sulfur ions, smaller polarization of the lithium-containing sulfur compound and lower voltage platform required during charging, so that the activation potential barrier of the lithium-containing sulfur compound can be effectively reduced, the deintercalation efficiency of lithium ions is obviously improved, and the lithium supplementing material 100 can have higher lithium supplementing specific capacity. In addition, the lithium-containing sulfur compound can not generate oxygen in the lithium supplementing process, so that the risk of the occurrence of the gas expansion phenomenon of the lithium battery can be reduced. Meanwhile, lithium polysulfide formed after lithium-containing sulfur compound is removed can be diffused to the negative electrode, so that the problem of lithium precipitation of the negative electrode is relieved.
The carbon fiber 20 may be a fiber having a micro-nano size obtained by carbonization. The carbon fiber 20 may have holes 21 corresponding to the size of the core 10, the holes 21 extending inward from the surface of the carbon fiber 20, and the core 10 being embedded in the carbon fiber 20, so that the carbon fiber 20 may partially encapsulate the core 10. The reason why the pores 21 of the carbon fiber 20 are formed may be that the lithium source reacts with the precursor of the carbon fiber 20 in the preparation process of the lithium supplementing material 100, so that the lithium source can simultaneously etch the surface of the carbon fiber 20 when being reduced to a sulfide containing lithium, thereby filling and embedding the carbon fiber 20.
Alternatively, the core 10 may be embedded in the carbon fiber 20 by uniformly mixing a polymer solution, lithium sulfate and micro-nano sized fibers, and then sintering the mixture so that the polymer and micro-nano sized fibers may be carbonized, and then carbothermic reduction of lithium sulfate and the two to produce lithium sulfide. In the above process, the carbon source formed by the polymer may be firstly reacted with lithium sulfate to be consumed, and then the remaining lithium sulfate reacts with the carbon fiber 20, so that carbon on the surface of the carbon fiber 20 is consumed by the reaction, and the generated lithium sulfide can be intercalated therein. It will be appreciated that any one of the carbon fibers 20 may have a plurality of uniformly dispersed cores 10 embedded therein such that the plurality of cores 10 form a beaded structure on the carbon fibers 20.
According to the lithium-ion-supplementing material 100 provided by the application, the lithium-containing sulfide is used as the inner core 10, the inner core 10 is embedded into the carbon fiber 20 by regulating and controlling etching, and the carbon fiber 20 is used for partially coating the inner core 10, so that on one hand, the strong electric conductivity of the carbon fiber 20 can be utilized to enhance the capability of the lithium-ion-supplementing material 100 for transmitting lithium ions outwards, the defect of poor electric conductivity of the lithium-containing sulfide is overcome, and meanwhile, the carbon fiber 20 also has a larger specific surface area, so that the lithium ion transmission efficiency of the lithium-ion-supplementing material 100 can be further improved; on the other hand, the carbon fiber 20 has larger specific surface area, so that the precursor containing lithium sulfide can have more attachment points in the sintering process, the finally obtained core 10 is not easy to agglomerate, the dispersibility of the core 10 is improved, and the size of the core 10 is reduced; further, the structure of the core 10 coated by the carbon fiber 20 can reduce the size from the core 10 to the nanoscale, and the advantage of the structure of the core 10 with the nanoscale is utilized to make the polarization of the lithium-containing sulfide smaller, and the voltage platform lower during charging, so that the lithium-supplementing material 100 can have a lower activation barrier, and the deintercalation efficiency of lithium ions can be remarkably improved, thereby realizing a higher lithium-supplementing specific capacity of the lithium-supplementing material 100.
In one possible embodiment, referring to fig. 1 to 3, the inner core 10 is partially embedded in the carbon fiber 20, and at least partially protrudes from the surface of the carbon fiber 20; and/or the core 10 is fully embedded with the carbon fiber 20 and fully disposed in the hole 21. Specifically, in the specific process of embedding the core 10 into the carbon fiber 20 provided in the above embodiment, the content of the remaining lithium sulfate reacted with the carbon fiber 20 may be different due to the different content of each core 10 reacted with the carbon source formed by the polymer during the formation process. It can be understood that when the content of the remaining lithium sulfate reacting with the carbon fiber 20 is small, that is, the etching degree of the carbon fiber 20 is low, the core 10 is mostly partially embedded in the carbon fiber 20, and also partially exposed outside the carbon fiber 20 and protrudes out of the surface of the carbon fiber 20; when the content of the remaining lithium sulfate reacting with the carbon fiber 20 is large, that is, the etching degree of the carbon fiber 20 is high, the core 10 is mostly embedded into the hole 21, and the core 10 is completely accommodated in the hole 21.
Alternatively, controlling the core 10 to be a half-embedded hole 21 or a full-embedded hole 21 may be achieved by adjusting the concentration of the polymer solution. When the polymer solution concentration is low, the core 10 is mostly fully embedded in the cavity 21, and when the polymer solution concentration is high, the core 10 is mostly semi-embedded in the cavity 21.
By setting the inner core 10 to be partially embedded with the carbon fiber 20, the use amount of the precursor during preparation can be reduced, so that the preparation cost is reduced; meanwhile, the preparation difficulty of partially embedding the carbon fiber 20 into the inner core 10 is low, and the formability is easy to control. The inner core 10 is configured to fully embed the carbon fibers 20, so that the contact area between the inner core 10 and the carbon fibers 20 can be maximized, thereby providing higher electronic conductivity.
In one possible embodiment, referring to fig. 2 and 3, the lithium supplementing material 100 further includes a coating layer 30, where the coating layer 30 covers an outer surface of the core 10 exposed to the external environment. It will be appreciated that since the core 10 is embedded in the carbon fiber 20 by etching, either the half-embedded holes 21 or the full-embedded holes 21 or at least a portion of the core is exposed to the external environment, the core 10 exposed to the external environment is extremely reactive with water and carbon dioxide in the environment, thereby reducing the electrochemical performance of the lithium-supplementing material 100. The cladding 30 may be provided on the exposed portion of the core 10 to isolate the core 10 from the external environment. Of course, in other embodiments, the cladding 30 may also cover the portion of the core 10 embedded in the carbon fiber. The material of the coating layer 30 may be graphite or other small-sized carbon source, and is not particularly limited. The coating layer 30 can effectively improve the electronic and ionic conductivity of the lithium supplementing material 100 in the core 10 and improve the lithium release in the charging process; can also play a certain role in isolating moisture, improve the stability of the lithium supplementing material 100 and realize a stable lithium supplementing effect. In addition, the stability of lithium supplementing in the electrode active paste and the active layer, the uniformity of dispersion and good processability of the lithium supplementing material 100 can be ensured.
In one possible embodiment, the core has a distribution density of 10g/cm on the individual carbon fibers 3 ～15g/cm 3 . In particular, the distribution density of the inner core on the single carbon fiber may be, but is not limited to, 10g/cm 3 、11g/cm 3 、12g/cm 3 、13g/cm 3 、14g/cm 3 、15g/cm 3 . By controlling the distribution density of the cores on the carbon fibers within the range, too dense distribution of the cores on the carbon fibers can be avoided, aggregation of the cores on the carbon fibers can be reduced, occurrence of the condition that the cores are not embedded into the carbon fibers can be reduced, and each carbon fiber can be ensured to be provided for a proper conductive environment of the cores.
In one possible embodiment, the carbon fiber accounts for 1-5% of the lithium supplementing material by mass. By controlling the distribution density of the cores on the carbon fibers within the range, too dense distribution of the cores on the carbon fibers can be avoided, aggregation of the cores on the carbon fibers can be reduced, occurrence of the condition that the cores are not embedded into the carbon fibers can be reduced, and each carbon fiber can be ensured to be provided for a proper conductive environment of the cores.
In one possible embodiment, the particle size D50 of the inner core is from 5nm to 80nm. In particular, the particle size of the core may be, but is not limited to, 5nm, 10nm, 15nm, 20nm, 30nm, 50nm, 80nm. The particle size of the lithium sulphide powder in the current commercial is typically 10 μm to 30 μm. Due to the insulating properties, the internal volume of most particles impedes the conversion of sulfur, thus showing a higher barrier and lower capacity. The particle size of the inner core in the embodiment of the application can be controlled at the nanometer level through the high polymer solution, and the inner core containing lithium sulfide reaching the nanometer level can shorten the diffusion length and enlarge the active specific surface area by greatly reducing the particle size, thereby being beneficial to the intercalation and deintercalation of lithium ions and further increasing the capacity of the lithium supplementing material. When the particle size of the inner core is smaller than the above range, the difficulty of preparation increases, and the particles form relatively serious agglomeration; when the particle diameter of the core is larger than the above range, the specific surface area of the core is reduced, and the intercalation and deintercalation efficiency of lithium ions is lowered, thereby resulting in poor lithium supplementing effect of the lithium supplementing material.
In one possible embodiment, the carbon fibers have a diameter of 20nm to 100nm. In particular, the diameter of the carbon fibers may be, but is not limited to, 20nm, 25nm, 30nm, 40nm, 60nm, 80nm, 100nm. The diameter of the carbon fiber is controlled within the above range in order to enable the carbon fiber to be adapted to the size of the core, thereby facilitating the embedding of the core; meanwhile, the carbon fiber is ensured to have proper specific surface area, and excellent lithium ion extraction environment can be provided. When the diameter of the carbon fiber is smaller than the range, the diameter of the carbon fiber is too small, so that the core is easy to penetrate through the carbon fiber, and the coating area of the carbon fiber on the core is reduced; when the diameter of the carbon fiber is larger than the above range, the specific surface area of the carbon fiber is reduced, which is unfavorable for the removal of lithium ions.
In one possible embodiment, the carbon fibers have a length of 1 μm to 20 μm. Specifically, the length of the carbon fiber may be, but is not limited to, 1 μm, 3 μm, 5 μm, 10 μm, 15 μm, 20 μm. The length of the carbon fiber is controlled within the range, so that the fiber can be fully dispersed in the preparation process, and the fiber is prevented from being excessively long to generate winding; and the contact area between the carbon fiber and the inner core is increased, so that the inner core is uniformly distributed on the carbon fiber, and the density distribution of the inner core on the carbon fiber is controlled.
In one possible embodiment, the outline of the hole is spherical, hemispherical or ellipsoidal. It is understood that the size of the core is controlled to the nano-scale by the high molecular polymer solution so that the shape of the core is mostly spherical or spheroid. The holes are etched from the inner shell, so the outline shape of the holes should match the shape of the inner shell. When the inner core is fully embedded in the carbon fiber, the shape of the hole can be spherical or ellipsoidal; when the inner core is partially embedded in the carbon fiber, the shape of the holes may be hemispherical.
In one possible embodiment, the pores have a pore diameter of 5nm to 80nm. In particular, the pore size of the pores may be, but is not limited to, 5nm, 10nm, 15nm, 20nm, 30nm, 50nm, 80nm. It is understood that the pore diameter of the pores may refer to the particle diameter of the core in the above embodiment, and will not be described herein.
In one possible embodiment, the volume of the pores is 40% -70% of the volume of the carbon fiber. It is understood that the volume of the holes is the size of the space occupied by the holes on the encapsulation layer. From the above embodiments, it is known that the volume ratio of the holes should be related to the distribution density of the core on the carbon fiber, and the volume ratio of the holes is controlled within the above range, which means that the distribution density of the core on the carbon fiber is moderate, and the depth of the core embedded in the carbon fiber is appropriate. When the volume of the holes is too small, the distribution of the inner cores on the carbon fiber is less, and the inner cores are free outside the carbon fiber, so that the carbon fiber is easy to not exert the conductive effect; it is also possible that the core is embedded deeper and shallower, resulting in the core being prone to fall off, thereby affecting electrochemical performance.
In one possible embodiment, the thickness of the coating is between 10nm and 100nm. In particular, the thickness of the cladding layer may be, but is not limited to, 10nm, 15nm, 20nm, 40nm, 60nm, 80nm, 100nm. It will be appreciated that the thickness of the coating ensures both the specific capacity of the lithium-compensating material and the electronically conductive environment. When the thickness of the coating layer is smaller than the range, the coating layer does not completely coat the inner core, so that a good electronic conductive environment is not constructed; when the coating layer thickness is larger than the above range, since the coating layer does not contribute lithium ions, the overall gram capacity of the additive is reduced.
In one possible embodiment, the coating layer accounts for 2-5% of the mass of the lithium supplementing material. The ratio of the coating layer in the lithium supplementing material is controlled, so that the coating layer can fully coat the exposed part of the inner core and the part in the external environment, and the influence of water and carbon dioxide in the external environment on the inner core is avoided; but also provides the core with excellent specific capacity and electronically conductive environment. If the coating layer mass ratio is too high, the added overall gram capacity is reduced because the coating layer does not contribute lithium ions; if the coating layer has too low mass ratio, the coating layer with complete coating and uniform thickness is not formed on the outer surface of the core, and the coating is incomplete, so that a good electronic conductive environment is not constructed.
In one possible embodiment, the chemical formula of the lithium-containing sulfide includes Li x S y Wherein x is more than or equal to 1 and less than or equal to 2, and y is more than or equal to 1 and less than or equal to 6. In particular, the chemical formula of the lithium-containing sulfide may be, but is not limited to, li 2 S、Li 2 S 2 、Li 2 S 4 、Li 2 S 6 。
In a second aspect, the present application further provides a method for preparing a lithium-supplementing material, please refer to fig. 5, which is specifically used for preparing the lithium-supplementing material in the first aspect. The preparation method comprises the following steps:
and step S10, mixing the lithium-containing sulfide precursor, the polymer precursor and the carbon fiber precursor, and shaping to obtain a precursor mixture.
And S20, sintering the precursor mixture to obtain a lithium supplementing material, wherein the lithium supplementing material comprises an inner core and carbon fibers, the carbon fibers are provided with holes extending inwards from the surface, and the inner core is embedded into the holes of the carbon fibers.
And step S30, mixing and sintering the lithium supplementing material and the carbon source, and coating the outer surface of the inner core exposed in the external environment by the carbon source forming coating layer.
In particular, the principle and specific process of preparing lithium sulfide by the polymer precursor and the carbon fiber precursor can be referred to the above embodiments.
In a possible embodiment, in the step S10, the lithium-containing sulfide precursor may be a lithium sulfate solution; the concentration of the lithium sulfate solution is 0.5mol/L to 5mol/L.
In a possible embodiment, in the step S10, the polymer precursor may be polyethylene oxide (Polyethylene oxide, PEO), polyvinylpyrrolidone (polyvinyl pyrrolidone, PVP), polyacrylamide (PAM), or the like. Preferably, the polymer precursor is a water-soluble polymer. The reason for choosing the water-soluble polymer is that it can be mixed directly with the lithium sulphate solution without the addition of further organic solvents. In addition, the water-soluble polymers have a strong dispersing effect, and most of the water-soluble polymers contain hydrophilic groups and a certain number of hydrophobic groups, so that the water-soluble polymers are easily adsorbed on the outer surfaces of the particles to form shells, and the particles are shielded from aggregation. Therefore, it is easier to obtain a core having nano-sized lithium-containing sulfide using a water-soluble polymer as a precursor.
In one possible embodiment, the polymer precursor is added in an amount of 0.5g to 5g.
In a possible embodiment, in the step S10, the carbon fiber precursor may be a natural fiber or an artificial fiber. Wherein the natural fiber can be bacterial cellulose, and the artificial fiber can be polyacrylonitrile fiber. The preparation method of the artificial fiber comprises, but is not limited to, a stretching method, template synthesis, self-assembly, microphase separation and electrostatic spinning. It will be appreciated that the diameter of the carbon fiber precursor selected may be slightly larger than that provided in the above embodiments, since the carbon fiber precursor is thermally separated during carbonization, and the final carbon fiber diameter is shrunk, so that a precursor having a slightly larger diameter may be selected in order to ensure control of the final carbon fiber diameter within the above range. Meanwhile, the length of the carbon fiber precursor may be slightly longer than that of the carbon fiber provided in the above embodiment.
In one possible embodiment, the carbon fiber precursor is added in an amount of 1g to 5g.
In a possible embodiment, in the step S10, the shaping may be freeze-drying or extrusion drying.
In a possible embodiment, in the step S20, the sintering temperature of the precursor mixture may be 600 to 800 ℃ and the sintering time may be 5 to 10 hours.
In a possible embodiment, in the step S20, the sintering environment of the precursor mixture may be an atmosphere formed by any one of a nitrogen gas, an argon gas, and a nitrogen-argon gas mixture.
In a possible embodiment, in the step S30, the method further includes crushing and grinding the lithium supplementing material obtained in the step S20; then the mixing ratio of the carbon source and the carbon source can be 50:1-20:1, the carbon source and the carbon source are fully mixed in a solid phase mixing ball milling mode, and the carbon source can be firmly coated on the surface of the inner core in a secondary sintering mode.
In a third aspect, the present application also provides a positive electrode sheet, where the positive electrode sheet includes a current collector and an active material layer disposed on the current collector, the active material layer includes a positive electrode material and the lithium supplementing material of the first aspect, or the active material layer includes the positive electrode material and the lithium supplementing material obtained by the preparation method of the lithium supplementing material of the second aspect. The positive electrode plate provided by the application contains the lithium supplementing material, and the lithium supplementing material can provide active lithium ions consumed by the formation of an SEI film when a battery is charged for the first time, so that the gram capacity of the positive electrode plate is effectively maintained, and the capacity retention rate of the positive electrode plate is improved; meanwhile, the lithium supplementing material can release lithium polysulfide to eliminate lithium precipitation, so that the performance of the positive electrode plate can be maintained, and the service life of the positive electrode plate can be prolonged.
In a possible implementation manner, the positive electrode plate comprises a positive current collector, the positive current collector is provided with a positive electrode active layer, the positive electrode active layer comprises positive electrode materials, a conductive agent, a binder and the like, the materials are not particularly limited, and proper materials can be selected according to practical application requirements. The positive electrode current collector includes, but is not limited to, any one of copper foil and aluminum foil. The positive electrode active material may be a phosphate positive electrode active material or a ternary positive electrode active material, and in specific embodiments, the positive electrode active material includes one or more of lithium cobaltate, lithium manganate, lithium iron phosphate, lithium iron manganese phosphate, lithium vanadium phosphate, lithium vanadyl phosphate, lithium vanadium fluorophosphate, lithium titanate, lithium nickel cobalt manganate, and lithium nickel cobalt aluminate. The conductive agent comprises one or more of graphite, carbon black, acetylene black, graphene, carbon fiber, C60 and carbon nano tube, and the content of the conductive agent in the positive electrode active layer is 3-5 wt%. The binder comprises one or more of polyvinylidene chloride, soluble polytetrafluoroethylene, styrene-butadiene rubber, hydroxypropyl methyl cellulose, carboxymethyl cellulose, polyvinyl alcohol, acrylonitrile copolymer, sodium alginate, chitosan and chitosan derivative, and the content of the binder in the positive electrode active layer is 2-4wt%.
In one possible embodiment, the content of the lithium supplementing material in the positive electrode material may be controlled to be 1% -6% of the mass of the positive electrode active material. The ratio can exactly compensate the loss of active lithium in the first charging process of the battery. If the addition amount of the lithium supplementing material in the positive electrode plate is too low, the lost active lithium in the positive electrode material cannot be fully supplemented, and the energy density, the capacity retention rate and the like of the battery are not improved. If the addition amount of the lithium supplementing material in the positive electrode material is too high, lithium may be severely separated from the negative electrode, and the cost may be increased. In some embodiments, the mass percentage of the lithium supplementing material in the positive electrode material may be 1%, 2%, 4%, 6%, etc.
In a fourth aspect, the present application also provides a secondary battery, where the secondary battery includes the positive electrode sheet. The positive electrode plate is added with the lithium supplementing material, so that active lithium ions consumed by formation of an SEI film when the battery is charged for the first time can be effectively compensated, gram capacity of the positive electrode plate is effectively maintained, and capacity retention rate of the positive electrode plate is improved. Meanwhile, the shape of the secondary battery can be maintained, the service life of the secondary battery is prolonged, the charging capacity of the secondary battery can be increased due to elimination of lithium precipitation, and the possibility of spontaneous combustion of the secondary battery is reduced.
The technical scheme of the invention is described in detail by specific examples.
Example 1
The embodiment provides a lithium supplementing material and a preparation method thereof, the lithium supplementing material comprises a core, carbon fibers and a coating layer, wherein the core is embedded in the carbon fibers, the coating layer is coated on the exposed outer surface of the core, and the core is Li 2 S。
The preparation method of the lithium supplementing material comprises the following steps:
(1) Adding polyethylene oxide and bacterial cellulose into lithium sulfate solution, and freeze-drying to obtain a precursor mixture; wherein the concentration of the lithium sulfate solution is 2mol/L, the volume is 200mL, the mass of polyethylene oxide is 12g, and the mass of bacterial cellulose is 0.5g.
(2) Placing the precursor mixture in a tube furnace, and sintering for 3 hours in an argon environment at 700 ℃ to obtain carbon fibers and Li embedded in the carbon fibers 2 S kernel.
(3) Placing the sintered material in a glove box for crushing and grinding, mixing with conductive carbon black solid phase, ball milling for 2 hours, and then placing in a tube furnace for secondary sintering to finally obtain a lithium supplementing material; wherein, the mixing proportion is 30:1, sintering for 2 hours in an argon atmosphere at 500 ℃.
In the lithium supplementing material, the particle diameter D50 of the inner core is 30nm, the diameter of the carbon fiber is 60nm, the length of the carbon fiber is 1 mu m, and the thickness of the coating layer is 60nm.
Example 2
The embodiment provides a lithium supplementing material and a preparation method thereof, the lithium supplementing material comprises a core, carbon fibers and a coating layer, wherein the core is embedded in the carbon fibers, the coating layer is coated on the exposed outer surface of the core, and the core is Li 2 S。
The preparation method of the positive electrode material comprises the following steps:
(1) The same as in step (1) in example 1;
(2) The difference from step (2) in example 1 is that the sintering temperature is 650 ℃;
(3) The same as in step (3) of example 1.
In the lithium supplementing material, the particle diameter D50 of the inner core is 10nm, the diameter of the carbon fiber is 60nm, the length of the carbon fiber is 1 mu m, and the thickness of the coating layer is 60nm.
Example 3
The embodiment provides a lithium supplementing material and a preparation method thereof, the lithium supplementing material comprises a core, carbon fibers and a coating layer, wherein the core is embedded in the carbon fibers, the coating layer is coated on the exposed outer surface of the core, and the core is Li 2 S。
The preparation method of the positive electrode material comprises the following steps:
(1) The same as in step (1) in example 1;
(2) The difference from step (2) in example 1 is that the sintering temperature is 750 ℃;
(3) The same as in step (3) of example 1.
In the lithium supplementing material, the particle diameter D50 of the inner core is 80nm, the diameter of the carbon fiber is 60nm, the length of the carbon fiber is 1 mu m, and the thickness of the coating layer is 60nm.
Example 4
The embodiment provides a lithium supplementing material and a preparation method thereof, the lithium supplementing material comprises a core, carbon fibers and a coating layer, wherein the core is embedded in the carbon fibers, the coating layer is coated on the exposed outer surface of the core, and the core is Li 2 S。
The preparation method of the positive electrode material comprises the following steps:
(1) The same as in step (1) in example 1;
(2) Unlike step (2) in example 1, the sintering temperature was 800 ℃;
(3) The same as in step (3) of example 1.
In the lithium supplementing material, the particle diameter D50 of the inner core is 200nm, the diameter of the carbon fiber is 60nm, the length of the carbon fiber is 1 mu m, and the thickness of the coating layer is 60nm.
Example 5
The embodiment provides a lithium supplementing material and a preparation method thereof, the lithium supplementing material comprises a core, carbon fibers and a coating layer, wherein the core is embedded in the carbon fibers, the coating layer is coated on the exposed outer surface of the core, and the core is Li 2 S。
The preparation method of the positive electrode material comprises the following steps:
(1) The same as in step (1) in example 1;
(2) The same as in step (2) in example 1;
(3) The difference from step (3) in example 1 is that only grinding and sieving, solid phase mixing ball milling with conductive carbon black and secondary sintering are not performed.
In the lithium supplementing material, the particle diameter D50 of the inner core is 30nm, the diameter of the carbon fiber is 60nm, the length of the carbon fiber is 1 mu m, and the thickness of the coating layer is 0nm.
Comparative example 1
The positive electrode lithium supplementing material of this comparative example is different from example 1 in that:
unlike step (1) and step (2) of example 1, the precursor is not prepared by carbothermal reduction, and the core directly adopts commercial micron-sized lithium sulfide;
the same as in step (3) of example 1.
In the lithium supplementing material, the particle diameter D50 of the core is 2um, and the thickness of the coating layer is 60nm.
The lithium supplementing materials provided in examples 1 to 5 and the lithium supplementing material provided in comparative example 1 described above were assembled into a lithium sulfide positive electrode, an inter-working positive electrode, and a lithium ion battery, respectively, according to the following methods:
lithium sulfide positive electrode: mixing the lithium supplementing material with polyvinylidene fluoride and SP-Li in a mass ratio of 80:8:12, ball milling and stirring to obtain positive electrode slurry, coating the positive electrode slurry on the surface of an aluminum foil, vacuum drying overnight at 110 ℃, and rolling to obtain a positive electrode plate;
and (3) an interworking positive electrode: mixing a lithium supplementing material and lithium iron phosphate according to the mass ratio of 4:96 to obtain a mixture, mixing the mixture, polyvinylidene fluoride and SP-Li according to the mass ratio of 93:3:4, ball-milling and stirring to obtain positive electrode slurry, coating the positive electrode slurry on the surface of an aluminum foil, vacuum-drying at 110 ℃ for overnight, and rolling to obtain a positive electrode plate;
And (3) a negative electrode: graphite with carboxymethylcellulose (CMC), SBR and SP according to 95.8: mixing, ball milling and stirring in a mass ratio of 1.2:2:1 to obtain negative electrode slurry, coating the negative electrode slurry on the surface of a copper foil, and vacuum drying overnight at 110 ℃ to obtain a negative electrode plate;
electrolyte solution: mixing ethylene carbonate and ethylmethyl carbonate in a volume ratio of 3:7, and adding LiPF 6 Electrolyte is formed, liPF 6 The concentration of (2) is 1mol/L;
a diaphragm: a polypropylene microporous separator;
and (3) assembling a lithium ion battery: and assembling the button type lithium ion full battery in an inert atmosphere glove box according to the assembling sequence of the graphite negative electrode plate, the diaphragm, the electrolyte and the positive electrode plate.
The electrochemical properties of each lithium ion battery assembled in the above lithium ion battery examples were respectively subjected to the performance test as in table 1, and the test results are shown in table 1 below:
TABLE 1
As can be seen from the test results of examples 1-5 and comparative example 1 in table 1, the method provided by the application can not only obviously reduce the grain size of the core, but also increase the electrochemical performance of the assembled lithium ion battery by introducing carbon fiber when the core of lithium sulfide is treated and coated; the charge gram capacity of the lithium ion battery is obviously improved, and the diffusion coefficient of lithium ions is obviously increased under the introduction of carbon fibers. From the test results of examples 1-4 of table 1, it can be seen that the grain size of the lithium sulfide core also has a significant effect on the electrochemical performance of the lithium ion battery, and the smaller the grain size, the better the chemical performance of the lithium ion battery assembled from the core; the smaller particle size is beneficial to the release of internal lithium ions and is also more beneficial to the intercalation of the internal lithium ions into carbon fibers with nano-sized diameters. This greatly enhances the electron and ion conductance of the positive electrode, and thus the positive electrode capacity is also sufficiently released. The proper carbon coating layer not only can improve the conductivity, but also can inhibit the trace moisture reaction in the positive electrode and the electrolyte, and can maintain the capacity. Meanwhile, the grain size of the inner core is also influenced by the sintering temperature, and the lower the sintering temperature is, the smaller the grain size of the inner core is; also, since the sintering temperature affects carbonization of the polymer precursor and the micro-nano fiber, thereby affecting the degree of carbothermic reaction of the polymer precursor and lithium sulfate, the grain size of the core can be controlled by controlling the sintering temperature.
In conclusion, the size of the lithium sulfide core can be greatly reduced by utilizing the polymer precursor to mix lithium sulfate for realizing the pre-coating, so that the nano-scale is achieved, and the high theoretical capacity is realized; meanwhile, compared with the commercial lithium sulfide with high price, the method can reduce the cost greatly by carbothermic reduction of the lithium sulfate into the lithium sulfide, and is favorable for large-scale industrialization. Secondly, carbon fibers are embedded by regulating and controlling the etching of the inner core, so that the defect of poor electric conductivity of lithium sulfide electrons is overcome, and the dispersibility of the inner core is improved. Finally, the carbon coating layer prevents the inner core which is not embedded with the carbon fiber from being directly exposed in the air, isolates moisture, reduces the generation of hydrogen sulfide and is beneficial to keeping high capacity.
In the description of the embodiments of the present application, it should be noted that, the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," and the like refer to the orientation or positional relationship described based on the drawings, which are merely for convenience of description and simplification of the description, and do not indicate or imply that the apparatus or elements referred to must have a specific orientation, be configured and operated in a specific orientation, and therefore should not be construed as limiting the present application.
The above disclosure is only a preferred embodiment of the present application, and it should be understood that the scope of the application is not limited thereto, but all or part of the procedures for implementing the above embodiments can be modified by one skilled in the art according to the scope of the appended claims.

Claims (12)

1. A lithium supplementing material, comprising:
a core composed of lithium-containing sulfide;
and the carbon fiber is provided with holes extending inwards from the surface, and the inner core is embedded in the carbon fiber and is accommodated in the holes.
2. The lithium-supplementing material according to claim 1, wherein the core is partially embedded in the carbon fiber and at least partially protrudes from the surface of the carbon fiber; and/or the inner core is fully embedded into the carbon fiber and is fully arranged in the hole.
3. The lithium-compensating material of claim 1, further comprising a cladding layer that covers an outer surface of the core that is exposed to an external environment.
4. The lithium supplementing material according to claim 1, wherein a distribution density of the core on the single carbon fiber is 10g/cm 3 ～15g/cm 3 The method comprises the steps of carrying out a first treatment on the surface of the And/or the mass ratio of the carbon fiber in the lithium supplementing material is 1-5%.
5. The lithium supplementing material according to claim 1, wherein the particle diameter D50 of the core is 5nm to 80nm; and/or the diameter of the carbon fiber is 20 nm-100 nm; and/or the length of the carbon fiber is 1-20 μm.
6. The lithium-supplementing material according to claim 1, wherein the outline of the hole is spherical, hemispherical or ellipsoidal; and/or the aperture of the hole is 5 nm-80 nm; and/or the volume of the holes accounts for 40-70% of the volume of the carbon fiber.
7. The lithium supplementing material according to claim 3, wherein a thickness of the coating layer is 10nm to 100nm; and/or the mass ratio of the coating layer in the lithium supplementing material is 2-5%.
8. The lithium supplementing material according to claim 1, wherein a chemical formula of the lithium-containing sulfide includes Li x S y Wherein x is more than or equal to 1 and less than or equal to 2, and y is more than or equal to 1 and less than or equal to 6.
9. The preparation method of the lithium supplementing material is characterized by comprising the following steps:
mixing a lithium-containing sulfide precursor, a polymer precursor and a carbon fiber precursor, and shaping to obtain a precursor mixture;
And sintering the precursor mixture to obtain the lithium supplementing material, wherein the lithium supplementing material comprises a core and carbon fibers, the carbon fibers are formed with holes extending inwards from the surface, and the core is embedded into the holes of the carbon fibers.
10. The method for preparing a lithium supplementing material according to claim 9, wherein the step of sintering the precursor mixture to obtain the lithium supplementing material further comprises the steps of:
and after the lithium supplementing material and the carbon source are mixed and sintered, the carbon source forms a coating layer to cover the outer surface of the inner core exposed to the external environment.
11. A positive electrode sheet, characterized in that the positive electrode sheet comprises a current collector and an active material layer provided on the current collector, the active material layer comprising a positive electrode material and the lithium supplementing material according to any one of claims 1 to 8, or the active material layer comprising a positive electrode material and the lithium supplementing material obtained by the preparation method of the lithium supplementing material according to claim 9 or 10.
12. A secondary battery comprising the positive electrode sheet according to claim 11, or comprising the lithium-supplementing material according to any one of claims 1 to 8, or comprising the lithium-supplementing material obtained by the method for producing the lithium-supplementing material according to claim 9 or 10.
CN202310101017.5A 2023-01-19 2023-01-19 Lithium supplementing material, preparation method thereof, positive electrode plate and secondary battery Pending CN116598477A (en)

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