CN112216818A - Lithium ion battery cathode, preparation method thereof, lithium ion battery and battery module - Google Patents

Lithium ion battery cathode, preparation method thereof, lithium ion battery and battery module Download PDF

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CN112216818A
CN112216818A CN201910625701.7A CN201910625701A CN112216818A CN 112216818 A CN112216818 A CN 112216818A CN 201910625701 A CN201910625701 A CN 201910625701A CN 112216818 A CN112216818 A CN 112216818A
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polymer layer
lithium
polymer
negative electrode
solvent
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CN112216818B (en
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谢静
郭姿珠
张露露
陈嵩
任建新
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BYD Co Ltd
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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
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • 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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H—ELECTRICITY
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    • 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
    • H01M4/131—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H01M4/1315—Electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx containing halogen atoms, e.g. LiCoOxFy
    • 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
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
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    • 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
    • H01M4/139—Processes of manufacture
    • H01M4/1391—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx
    • H01M4/13915—Processes of manufacture of electrodes based on mixed oxides or hydroxides, or on mixtures of oxides or hydroxides, e.g. LiCoOx containing halogen atoms, e.g. LiCoOxFy
    • 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
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    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • 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
    • H01M2004/027—Negative electrodes
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Abstract

The lithium ion battery negative electrode comprises a current collector, a first polymer layer attached to the current collector and a second polymer layer attached to the first polymer layer, wherein the diameter D of a hole in the first polymer layer50Greater than 1 μm, second polymer layerDiameter D of the mesopores50Is the diameter D of the pores in the first polymer layer500.001-1 times of the total amount of the active ingredient. The ion battery containing the lithium ion battery cathode has good cycle performance and rate capability.

Description

Lithium ion battery cathode, preparation method thereof, lithium ion battery and battery module
Technical Field
The disclosure relates to the field of lithium ion batteries, in particular to a lithium ion battery cathode and a preparation method thereof, a lithium ion battery and a battery module.
Background
Lithium metal is the most ideal negative electrode material of the next generation of high-capacity lithium ion battery, but the lithium metal has the characteristics of high reactivity, infinite volume expansion and nonuniform deposition and extraction, which can cause problems of low coulombic efficiency and safety, and prevent the lithium metal from being commercially applied. The existing electrolyte adopts organic electrolyte as a main body for lithium ion transmission, and the organic liquid electrolyte has higher ionic conductivity, can effectively infiltrate electrode particles, and has lower internal resistance and cycling stability of the battery. When the organic electrolyte is matched with a metal lithium negative electrode, the metal lithium is directly contacted with the electrolyte to generate a Solid Electrolyte Interface (SEI), and the SEI is aggregated to cause the lithium ion transmission to be blocked, so that the capacity of the battery is attenuated. The deposition of the metal lithium has infinite volume expansion and non-uniform phenomena in the process, the deposition and dissolution behavior of the metal lithium can cause the fracture of a surface SEI film, the surface of the exposed fresh metal lithium can react with an electrolyte to cause further reaction, meanwhile, the non-uniformly deposited dendritic lithium can cause short circuit and even thermal runaway in the battery, and finally cause safety problems, and furthermore, dendritic lithium can form dead lithium in the process of extraction to cause capacity loss and low coulombic efficiency.
For the problem of the metallic lithium negative electrode, researchers respectively carry out related researches on the aspects of developing a new electrolyte formula, a metallic lithium electrode structure design, a metallic lithium alloy, a solid electrolyte and composite electrolyte design, a Li-C composite electrode, a metallic lithium protective layer and the like. Nae-Lih Wu et al are prepared by depositing a protective layer of β -PVDF of about 4um thickness on the surface of a metallic lithium or copper foil. The high 'F' environment at the interface can guide the uniform deposition of the metal lithium, and a good effect of inhibiting the lithium dendrites is achieved. The 3D porous PVDF prepared by Donghai Wang and the like through NaCl pore forming is used as a deposition 'host' of lithium, and due to the porous structure of the PVDF porous PVDF metallic lithium deposition can.
However, the existing lithium ion battery still has the defects of poor cycle performance and rate capability.
Disclosure of Invention
The invention aims to overcome the problems of poor cycle performance and rate performance of the conventional lithium ion battery, and provides a lithium ion battery cathode, a preparation method thereof, a lithium ion battery and a battery module.
In order to achieve the above object, a first aspect of the present disclosure provides a lithium ion battery negative electrode including a current collector, a first polymer layer attached on the current collector, and a second polymer layer attached on the first polymer layer, a diameter D of a hole in the first polymer layer50Greater than 1 μm, diameter D of the pores in the second polymer layer50Is the diameter D of the pores in the first polymer layer500.001-1 times of the total amount of the active ingredient.
Optionally, the diameter D of the pores in the second polymer layer50Is 1nm-1 μm.
Optionally, the diameter D of the pores in the first polymer layer50Greater than 1 μm and at most 10 μm, the diameter D of the pores in the second polymer layer50Is 1nm-100 nm.
Optionally, the first polymer layer has a porosity of 80-98% and the second polymer layer has a porosity of 7-30%.
Optionally, the first polymer layer has a thickness of 4 μm to 20 μm and the second polymer layer has a thickness of 10nm to 5 μm.
Optionally, the second polymer layer contains a lithium salt; the lithium salt is contained in an amount of 0.5 to 20 wt% based on the total weight of the second polymer layer; the lithium salt is LiPF6、LiAsF6、LiClO4、LiBF6、LiN(CF3SO3)2、LiCF3SO3、LiC(CF3SO3)2、LiN(C4F9SO2)(CF3SO3)、LiF、One or more of LiCl, LiBr and LiI.
Optionally, the pores in the second polymer layer have a diameter of 500nm to 1 μm.
Optionally, the current collector and/or the first polymer layer contain metallic lithium; the current collector and/or the first polymer layer have a lithium insertion capacity of 0.001mAh/cm2The above.
Optionally, the first polymer layer contains a conductive agent therein; the content of the conductive agent is 0.1-5 wt% based on the total weight of the first polymer layer; the conductive agent is one or more selected from nano gold powder, silver powder, acetylene black, carbon nano tubes, graphene and nano carbon fibers.
Optionally, the current collector has a thickness of 5-8 μm; the main material of the current collector is selected from one or more of copper, aluminum, stainless steel, nickel, lithium-boron alloy, lithium-silicon alloy, carbon nano tube and graphene.
Optionally, the first polymer layer comprises a first polymer, and the second polymer layer comprises a second polymer, wherein the first polymer and the second polymer are independently selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polyethylene terephthalate, perfluorosulfonic acid polymer, polyimide and styrene butadiene rubber.
A second aspect of the present disclosure provides a method of preparing the anode provided by the first aspect of the present disclosure, the method comprising the steps of:
s1, coating slurry containing a first polymer and a pore-forming agent on a current collector, and removing a first solvent to form a first polymer layer to obtain a first negative plate;
s2, coating the slurry containing the second polymer on the first polymer layer, and removing the second solvent to form a second polymer layer to obtain a second negative plate;
s3, removing the pore-forming agent in the second negative electrode sheet to form pores in the first polymer layer, so as to obtain the negative electrode;
alternatively, the method comprises:
A. coating the slurry containing the first polymer and the reactive pore-forming agent on a current collector, and removing the third solvent to form a first polymer layer to obtain a first negative plate; the reactive porogen is reactive with the third solvent to generate a gas or a soluble compound to form pores in the first polymer layer;
B. and coating the slurry containing the second polymer on the first polymer layer, and removing the fourth solvent to obtain the negative electrode coated with the second polymer layer.
Optionally, the step S1 further includes: coating a slurry containing the first polymer, the pore-forming agent and a conductive agent on the current collector, and drying at 50-60 ℃ to remove the third solvent; alternatively, the first and second electrodes may be,
the step A further comprises the following steps: coating the slurry containing the first polymer, the reactive pore-forming agent and the conductive agent on a current collector, and drying at 80-120 ℃ to remove the third solvent.
Optionally, the reactive pore former is selected from one or more of polyethylene oxide, alkali metal halide, alkali metal hydroxide, alkali metal nitrate, alkali metal carbonate, alkaline earth metal carbonate, alkali metal hydroxide, magnesium hydroxide, calcium hydroxide, copper oxide, iron oxide and aluminum oxide.
Optionally, the method further comprises: introducing metallic lithium into the current collector and/or said first polymer layer.
Optionally, the method of introducing lithium metal into the first polymer layer comprises: at a current density of 0.5-1mA/cm2Under the condition of (2), carrying out lithium intercalation treatment on the first negative plate; the lithium intercalation capacity of the first negative plate after the lithium intercalation treatment is 0.1-0.001mAh/cm2。
Optionally, the step S2 further includes: coating a slurry containing the second polymer and the lithium salt on the first polymer layer, and drying at 60-80 ℃ to remove the second solvent;
the step B further comprises the following steps: coating the slurry containing the second polymer and the lithium salt on the first polymer layer, and drying at 60-80 ℃ to remove the fourth solvent.
A third aspect of the present disclosure provides a lithium ion battery including the negative electrode provided in the first aspect of the present disclosure.
A fourth aspect of the present disclosure provides a battery module including the lithium ion battery provided by the third aspect of the present disclosure.
Through above-mentioned technical scheme, this disclosure has following beneficial effect: the lithium ion battery negative electrode has a double-layer polymer protective layer with a specific aperture ratio, and lithium ions can be deposited on a current collector after sequentially passing through a second polymer layer with a smaller aperture and a first polymer layer with a larger aperture. The first polymer layer can avoid being separated from a current collector due to volume expansion in the metal lithium deposition and dissolution process, the second polymer layer can avoid being deposited on metal lithium in the first polymer layer to be contacted with electrolyte, so that the metal lithium loss caused by side reaction between the metal lithium and the electrolyte is reduced, and the first polymer layer and the second polymer layer of the negative electrode of the lithium ion battery are matched, so that the lithium ion battery has excellent cycle performance and rate capability.
Additional features and advantages of the disclosure will be set forth in the detailed description which follows.
Drawings
The accompanying drawings, which are included to provide a further understanding of the disclosure and are incorporated in and constitute a part of this specification, illustrate embodiments of the disclosure and together with the description serve to explain the disclosure without limiting the disclosure. In the drawings:
fig. 1 is a schematic structural diagram of one embodiment of a negative electrode of a lithium ion battery according to the present disclosure;
fig. 2 is an SEM image (2000 x magnification) of the surface of the lithium ion battery negative electrode tab a1 of example 1 of the present disclosure;
fig. 3 is an SEM image (magnification 5000 times) of the surface of the lithium ion battery negative electrode sheet C1 of example 1 of the present disclosure.
Reference numerals
1 second polymer layer 2 first polymer layer 3 current collector
Detailed Description
The following detailed description of specific embodiments of the present disclosure is provided in connection with the accompanying drawings. It should be understood that the detailed description and specific examples, while indicating the present disclosure, are given by way of illustration and explanation only, not limitation.
A first aspect of the present disclosure provides a lithium ion battery negative electrode including a current collector, a first polymer layer attached to the current collector, and a second polymer layer attached to the first polymer layer, a diameter D of a hole in the first polymer layer50Greater than 1 μm, diameter D of the pores in the second polymer layer50Is the diameter D of the pores in the first polymer layer500.001-1 times of the total amount of the active ingredient.
The lithium ion battery negative electrode disclosed by the invention has a first polymer layer and a second polymer layer with specific aperture ratio, and the first polymer layer and the second polymer layer have good synergistic effect. Specifically, the second polymer layer and the first polymer layer have matched pore structures, the two layers form a channel with the diameter gradually increasing along the lithium ion deposition direction, and lithium ions in the electrolyte of the lithium ion battery can pass through the second polymer layer with relatively small pore diameter and then are deposited in the first polymer layer with relatively large pore diameter. The second polymer layer with smaller pore diameter can avoid or reduce the contact of the metal lithium deposited in the first polymer layer with the electrolyte, thereby reducing the loss of the metal lithium caused by the side reaction of the metal lithium and the electrolyte; the first polymer layer with larger aperture can provide space for the deposition of the metal lithium, and guide the metal lithium to deposit in the pores of the porous layer, thereby ensuring uniform deposition and avoiding the problem that the polymer layer is separated from the current collector due to volume deformation generated in the process of depositing and dissolving the metal lithium. The lithium ion battery cathode disclosed by the invention can reduce the consumption of lithium ions to the maximum extent, and has the advantage of well maintaining the structural integrity of the cathode, so that the lithium ion battery has excellent cycle performance and rate capability.
In one embodiment, the diameter D of the pores in the second polymer layer50May be 1nm to 1 μm. Preferably, the diameter D of the pores in the first polymer layer50May be greater than 1 μm and may be up toUp to 10 μm, diameter D of the pores in the second polymer layer50Can be 1nm-100 nm; more preferably, the diameter D of the pores in the first polymer layer508 μm to 10 μm, diameter D of the pores in the second polymer layer50Is 500nm-1 μm. Within the preferable pore diameter range, the transmission of lithium ions can be further ensured, and the lithium ions are prevented from being deposited above the first polymer layer; and reduces the metallic lithium directly exposed to the electrolyte system, the generation of SEI and the consumption of metallic lithium. Within the range, the pore diameter of the first polymer layer and the pore diameter of the second polymer layer are proper in size, the first polymer layer and the second polymer layer have good matching performance, higher pore volume is obtained under the condition of relatively thinner thickness, and the cycle performance and the rate capability of the lithium ion battery can be further improved.
According to the present disclosure, the porosity of the first polymer layer may be 80-98%, and the porosity of the second polymer layer may be 7-30%, preferably, the porosity of the first polymer layer is 90-96%, and the porosity of the second polymer layer may be 10-15%. Within the range, the higher porosity in the first polymer layer can provide space for the deposition of the metal lithium as much as possible, so that the metal lithium is ensured to be deposited only in the porous layer without penetrating through the whole polymer layer to react with the electrolyte, the relatively lower porosity in the second polymer layer can ensure the transmission performance of lithium ions in the second polymer layer, and simultaneously, the contact of solvent components in the electrolyte penetrating through the second layer and the metal lithium deposited on the first polymer layer is reduced, the side reaction of the metal lithium and the electrolyte is reduced in two aspects, the utilization rate of the metal lithium is high, the interface impedance is small, and the cycle performance and the rate performance of the lithium ion battery can be further improved. The porosity can be determined by a weighing method.
According to the present disclosure, the thickness of the first polymer layer and the thickness of the second polymer layer may vary within a wide range, and preferably, the thickness of the first polymer layer may be 4 μm to 20 μm; the thickness of the second polymer layer may be 10nm to 5 μm; more preferably, the first polymer layer has a thickness of 10 μm to 17 μm and the second polymer layer has a thickness of 30nm to 1 μm. Within the above range, the first polymer layer and the second polymer layer have appropriate thicknesses, so that the side reaction of the metal lithium and the electrolyte can be reduced, the lithium ion battery can maintain good structural stability, and the cycle performance and the rate performance of the lithium ion battery can be further improved. Within the above-described preferable thickness range, the energy density of the lithium ion battery can be further improved.
According to the present disclosure, the second polymer layer may contain a lithium salt therein; the content of the lithium salt may vary within a wide range, and preferably, the content of the lithium salt may be 0.5 to 20% by weight, more preferably 10 to 15% by weight, based on the total weight of the second polymer layer. The lithium salt may be one conventionally employed by those skilled in the art, and is, for example, LiPF6、LiAsF6、LiClO4、LiBF6、LiN(CF3SO3)2、LiCF3SO3、LiC(CF3SO3)2、LiN(C4F9SO2)(CF3SO3) One or more of LiF, LiCl, LiBr and LiI. The lithium salt in the second polymer layer may create a microporous structure in situ upon dissolution, e.g., pores in the second polymer layer having a diameter of 500nm to 1 μm. On one hand, micropores generated by the lithium salt can provide a transmission channel of lithium ions, on the other hand, the lithium salt dissolved in the second polymer layer can improve the concentration of the lithium ions at the negative electrode side to generate a local super-concentration effect, the lithium ions in the polymer layer can preferentially and timely supplement the concentration of the lithium in a lithium deposition area, the transmission path of the lithium ions is shortened, the diffusion process of the lithium ions is enhanced, the metal lithium can be ensured to obtain a relatively high deposition speed, and the rate capability of the battery is further improved.
According to the present disclosure, the current collector and/or the first polymer layer may contain metallic lithium; the current collector and/or the first polymer layer may have a lithium insertion capacity of 0.001mAh/cm2Above, for example, the lithium intercalation capacity is 0.1 to 0.001mAh/cm2. The lithium intercalated in the current collector and/or the first polymer layer can be used as a lithium source to supplement the loss of lithium ions, and the cycle performance and rate performance of the lithium ion battery are further improved.
According to the present disclosure, the first polymer layer may contain a conductive agent to provide a good electron transport channel, enhance the transport process of lithium ions, and facilitate uniform deposition of metal lithium into the first polymer layer. The content of the conductive agent may vary within a wide range, and preferably, the content of the conductive agent may be 0.1 to 5% by weight, preferably 0.2 to 1% by weight, based on the total weight of the first polymer layer. The conductive agent may be conventionally used by those skilled in the art, and may be, for example, one or more selected from nano gold powder, silver powder, acetylene black, carbon nanotubes, graphene, and carbon nanofibers.
According to the present disclosure, the thickness of the current collector may vary within a wide range, and preferably, the thickness of the current collector may be 5-8 μm; the host material of the current collector may be conventionally used by those skilled in the art, and may be, for example, one or more selected from copper, aluminum, stainless steel, nickel, lithium-boron alloy, lithium-silicon alloy, carbon nanotube, and graphene. The current collector made of the material can be a copper net, an aluminum net, a stainless steel net and a nickel net.
According to the present disclosure, the first polymer layer comprises a first polymer, the second polymer layer comprises a second polymer, the first polymer and the second polymer may be the same or different, and each of the first polymer and the second polymer may be independently selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polyethylene terephthalate, perfluorosulfonic acid polymer, polyimide, and styrene-butadiene rubber. The polymer has the advantages of high dielectric constant, lithium affinity, strong bonding capability and flexibility.
The second aspect of the present disclosure provides a method for preparing the negative electrode of the lithium ion battery provided by the first aspect of the present disclosure. In one embodiment, the method comprises: s1, coating slurry containing a first polymer and a pore-forming agent on a current collector, and removing a first solvent to form a first polymer layer to obtain a first negative plate; s2, coating the slurry containing the second polymer on the first polymer layer, and removing the second solvent to form a second polymer layer to obtain a second negative plate; and S3, removing the pore-forming agent in the second negative electrode sheet to obtain the negative electrode.
Wherein, the first polymer and the second polymer can be the same or different, and the two polymers can be respectively and independently selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polyethylene terephthalate, perfluorinated sulfonic acid polymer, polyimide and styrene butadiene rubber. The amount ratio of the first polymer to the first solvent and the amount ratio of the second polymer to the second solvent are not particularly limited as long as the polymers can be uniformly dispersed.
In another embodiment, the method comprises:
A. coating the slurry containing the first polymer and the reactive pore-forming agent on a current collector, and removing the third solvent to form a first polymer layer to obtain a first negative plate; the reactive porogen may react with the third solvent to generate a gas or a soluble compound to form pores in the first polymer layer;
B. and coating the slurry containing the second polymer on the first polymer layer, and removing the fourth solvent to obtain the negative electrode coated with the second polymer layer.
Wherein, the ratio of the second polymer to the fourth solvent is not particularly limited as long as the polymer can be uniformly dispersed; the ratio of the amount of the first polymer to the third solvent is not particularly limited as long as the reactive pore-forming agent can sufficiently react with the third solvent and the polymer can be well dispersed. The selection of the specific type of the third solvent is not limited as long as it can react with the reactive pore-forming agent to produce a gas or a soluble compound; the type of reaction of the reactive pore-forming agent with the third solvent to produce a gas or soluble compound is not limited, and may be, for example, a dissolution reaction, a decomposition reaction, or a metathesis reaction. In one embodiment, the third solvent is subjected to a dissolution reaction with a reactive pore former, for example, the third solvent may be selected from at least one of acetone, deionized water, and alcohol, and the reactive pore former may be selected from at least one of polyethylene oxide, alkali metal halide, alkali metal hydroxide, and alkali metal nitrate; in another embodiment, the third solvent undergoes a decomposition reaction with a reactive pore-forming agent, for example, the third solvent may be selected from at least one of dilute hydrochloric acid, dilute acetic acid, citric acid, and dilute sulfuric acid, and the reactive pore-forming agent may be selected from at least one of alkali metal carbonate, alkaline earth metal carbonate, alkali metal hydroxide, magnesium hydroxide, calcium hydroxide, copper oxide, iron oxide, and aluminum oxide. The first polymer layer of the lithium ion battery cathode can have a pore diameter with a proper size under the action of the reactive pore-forming agent, so that the lithium ion battery cathode has better electrochemical performance.
The kind of the fourth solvent is not particularly limited, and preferably, the fourth solvent may be selected from at least one of anhydrous N-methylpyrrolidone, anhydrous dimethylacetamide, cyclohexanone, and toluene. The method disclosed by the invention can be used for simply and efficiently preparing the lithium ion battery cathode with good cycle performance and rate capability.
According to the present disclosure, in the embodiment in which the pore-forming agent is used to form the pores in the first polymer layer, the type of the pore-forming agent and the specific method of removing the pore-forming agent are not limited in step S3 as long as the pore-forming agent can be removed to form the pores.
In a specific embodiment, the pore-forming agent may be one or more selected from alumina, alkali metal carbonate, alkaline earth metal carbonate, alkali metal hydroxide and alkaline earth metal hydroxide, wherein the alkali metal carbonate may be sodium carbonate and potassium carbonate, and the alkaline earth metal carbonate may be calcium carbonate and magnesium carbonate. When the pore-forming agent is selected from the above-mentioned materials, the first solvent and the second solvent may each be a material which does not react with the pore-forming agent and does not dissolve the pore-forming agent, and may be at least one of acetone, anhydrous N-methylpyrrolidone, anhydrous dimethylacetamide, N-methylformamide, cyclohexanone, and toluene, for example. Step S3 may further include: and (3) carrying out contact reaction on the second negative plate and an acid solution to remove the pore-forming agent, and drying at the temperature of 80-120 ℃ to obtain the negative electrode. For example, the second negative electrode plate can be soaked in an acid solution with the concentration of 0.001-0.5mol/L for 1-24h to remove the pore-forming agent. The acid solution can be one or more of dilute acetic acid, dilute hydrochloric acid, dilute sulfuric acid and citric acid. The second negative plate can contact and react with the acid solution to form a pore structure with a certain porosity and a proper pore diameter, so that the lithium ion battery disclosed by the invention is negativeHas excellent electrochemical performance. More preferably, the step 3 may further include, after the second negative electrode sheet is subjected to a contact reaction with an acid solution and dried, coating a layer of solution containing lithium salt on the second polymer layer, and performing drying treatment to obtain the negative electrode of the lithium ion battery, so as to compensate for lithium salt loss caused by acid washing, and further improve cycle performance and rate performance of the lithium ion battery. The solution of lithium salt may be a conventional lithium salt solution, for example, a solution containing LiCF3SO3The glycol dimethyl ether solution of (1).
In another embodiment, the pore-forming agent may be a water soluble salt or polymer, and may be, for example, at least one of polyethylene oxide, sodium chloride, lithium chloride, potassium chloride, lithium nitrate, and potassium nitrate. When the pore-forming agent is selected from the above-mentioned materials, the first solvent and the second solvent may be materials that do not react with the pore-forming agent and do not dissolve the pore-forming agent, and may be at least one of ethanol and deionized water, for example. Step S3 may further include: and (3) placing the second negative plate in water to remove the pore-forming agent, and drying at the temperature of 80-120 ℃ to obtain the negative electrode. The amount of water used is not particularly limited as long as the pore-forming agent can be dissolved and removed.
In a method according to the present disclosure, in a specific embodiment, a conductive agent may be introduced into the first polymer layer, for example, in an embodiment using a pore former, step S1 may further include: and coating the slurry containing the first polymer, the pore-forming agent and the conductive agent on a current collector, and drying at 50-60 ℃ to remove the first solvent. In embodiments where a reactive porogen is used, step a may further comprise: and coating the slurry containing the first polymer, the reactive pore-forming agent and the conductive agent on a current collector, and drying at the temperature of 80-120 ℃ to remove the third solvent. The slurry may be applied on the current collector by using equipment and methods conventionally used by those skilled in the art, such as spin coating, spray coating or drop coating, and the specific operating conditions may also be selected according to the needs, and will not be described herein again.
According to the present disclosure, the method may further comprise: and introducing metallic lithium into the current collector and/or the first polymer layer, preferably, introducing the metallic lithium into the first polymer layer to more effectively supplement lithium ion consumption and further improve the cycle performance and rate performance of the lithium ion battery.
In one embodiment, a method of introducing lithium metal into a first polymer layer may comprise: at a current density of 0.5-1mA/cm2Under the condition of (3), carrying out lithium intercalation treatment on the first negative plate; the lithium intercalation capacity of the first negative plate after lithium intercalation treatment can be 0.001mAh/cm2Above, preferably 0.1-0.001mAh/cm2More preferably 0.08 to 0.05mAh/cm2. The lithium intercalation may be carried out in an apparatus conventionally used by those skilled in the art, using conventional methods, for example using an electrochemical test cell apparatus at a current density of 0.5-1mA/cm2The first negative electrode sheet and the lithium sheet are placed in an electrolyte to perform lithium intercalation treatment. Wherein the electrolyte may contain an electrolyte lithium salt and a fifth solvent, and the electrolyte lithium salt may be selected from LiCF3SO3、LiPF6、LiAsF6、LiClO4、LiBF6、LiN(CF3SO3)2、LiC(CF3SO3)2And LiN (C)4F9SO2)(CF3SO3) And the fifth solvent may be at least one selected from the group consisting of 1, 3-dioxolane, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether and dioxane. Under the conditions, the embedding amount of lithium ions in the negative plate can be effectively controlled, so that the negative electrode of the lithium ion battery prepared by the method disclosed by the invention has good electrochemical performance. The current collector containing lithium metal may be commercially available as needed, or may be prepared according to methods well known in the art, and the specific methods will not be described herein.
In the method according to the present disclosure, in one embodiment, a lithium salt may be introduced into the second polymer layer to provide a transport channel for lithium ions; specifically, in the embodiment using the pore-forming agent, step S2 may further include: and coating the slurry containing the second polymer and the lithium salt on the first polymer layer, and drying at 60-80 ℃ to remove the second solvent. In useIn embodiments of the reactive porogen, step B further comprises: and coating the slurry containing the second polymer and the lithium salt on the first polymer layer, and drying at 60-80 ℃ to remove the fourth solvent. The lithium salt may be LiCF3SO3、LiPF6、LiAsF6、LiClO4、LiBF6、LiN(CF3SO3)2、LiC(CF3SO3)2And LiN (C)4F9SO2)(CF3SO3) One or more of them. The coating may be performed in a manner conventionally employed by those skilled in the art, and preferably, the coating may be performed by spin coating, spray coating or drop coating. In this embodiment, on one hand, the dissolved lithium salt can generate a local super-concentration effect, so as to enhance the diffusion process of lithium ions, and further improve the rate capability of the battery.
In a third aspect of the present disclosure, a lithium ion battery is provided, which is the negative electrode provided in the first aspect of the present disclosure, and the lithium ion battery of the present disclosure has good cycle performance and rate capability.
The lithium ion battery of the present disclosure further includes a positive electrode, an electrolyte, and a separator. The positive electrode comprises a positive electrode current collector and a positive electrode active material, and the positive electrode active material can be selected from LiFexMnyMzPO4(x is more than or equal to 0 and less than or equal to 1, y is more than or equal to 0 and less than or equal to 1, z is more than or equal to 0 and less than or equal to 1, and x + y + z is 1, wherein M is at least one of Al, Mg, Ga, Ti, Cr, Cu, Zn and Mo), Li3V2(PO4)3、Li3V3(PO4)3、LiNi0.5-xMn1.5- yMx+yO4X is more than or equal to 0.1 and less than or equal to 0.5, y is more than or equal to 0 and less than or equal to 1.5, M is at least one of Li, Co, Fe, Al, Mg, Ca, Ti, Mo, Cr, Cu and Zn), and LiVPO4F、Li1+xL1－y－zMyNzO2(L, M, N is at least one of Li, Co, Mn, Ni, Fe, Al, Mg, Ga, Ti, Cr, Cu, Zn, Mo, F, I, S and B-0.1-0.2 x, 0-1 y, 0-1 z, 0-1 + z 1.0), Li2CuO2And Li5FeO4One or more of (a). Superior foodOptionally, the positive active material is selected from LiAl0.05Co0.15Ni0.80O2、LiNi0.80Co0.10Mn0.10O2、LiNi0.60Co0.20Mn0.20O2、LiCoO2、LiMn2O4、LiFePO4、LiMnPO4、LiNiPO4、LiCoPO4、LiNi0.5Mn1.5O4And Li3V3(PO4)3One or more of (a). More preferably, the positive active material is selected from sulfur, lithium sulfide, V2O5、MnO2、TiS2And FeS2To have better matching with the lithium ion battery negative electrode of the present disclosure.
The electrolyte solution contains a solvent and a lithium salt, wherein the compound contained in the solvent may have one or more of an ether group, a nitrile group, a cyanide group, a fluorine ester group, a tetrazolyl group, a fluorine sulfonyl group, a chlorosulfonyl group, a nitro group, a carbonate group, a dicarbonate group, a nitrate group, a fluorine amide group, a diketone group, an azole group, and a triazine group. For example, the solvent may be one or more of ethylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, 1, 3-dioxolane, ethylene glycol dimethyl ether, tetraethylene glycol dimethyl ether, and dioxane. The lithium salt may be one conventionally employed by those skilled in the art, and is, for example, LiPF6、LiAsF6、LiClO4、LiBF6、LiN(CF3SO3)2、LiCF3SO3、LiC(CF3SO3)2And LiN (C)4F9SO2)(CF3SO3) One or more of (a).
The membrane may be conventionally employed by those skilled in the art and will not be described in detail herein.
In the present invention, the method for preparing the lithium ion battery is not particularly limited, and the lithium ion battery provided by the first aspect of the present disclosure is made into a pole core according to a method known in the art, and then the pole core is placed in a battery case, and the electrolyte is added and sealed to obtain the lithium ion battery. The sealing method and the amount of the electrolyte are known to those skilled in the art.
A fourth aspect of the present disclosure provides a battery module including the lithium ion battery provided by the third aspect of the present disclosure. The lithium ion battery module disclosed by the invention has good cycle performance and rate capability.
The present disclosure is further illustrated by the following examples, but is not to be construed as being limited thereby.
Example 1
(1) Preparing a lithium ion battery cathode C1:
4.95g of polyvinylidene fluoride (PVDF), 0.05g of acetylene black and 0.50g of lithium nitrate are added into acetone, then stirred in a vacuum stirrer to form stable and uniform slurry, the slurry is uniformly and intermittently coated on a copper foil with the thickness of 8 mu m, dried at 80 ℃, and cut into a pole piece A1 with the diameter of 15mm, and FIG. 1 is an SEM topography of the pole piece A1.
Pre-embedding lithium into the pole piece A1 in a blue test cabinet, specifically, pre-embedding lithium with a capacity of 0.17mAh into an electrolyte by the pole piece A1 and a metal lithium piece, wherein the electrolyte contains a lithium salt and a solvent, and the lithium salt is LiCF with 1mol/L3SO3The solvent is a solvent with the volume ratio of 1:1, 3-dioxolane and ethylene glycol dimethyl ether (DOL/DME) at a current density of 0.5mA/cm2And then taking out the A1 and drying at 60 ℃ to obtain a pole piece B1.
4.95g of styrene-butadiene rubber and 0.05g of LiCF3SO3Adding the mixture into anhydrous methylbenzene, and stirring the mixture in a vacuum stirrer to form stable and uniform slurry; the slurry is uniformly spin-coated on a B1 pole piece at the rotation speed of 500rpm for 1min, and then dried at 80 ℃ to obtain a lithium ion battery cathode pole piece C1, wherein FIG. 2 is an SEM morphology diagram of a lithium ion battery cathode C1.
Wherein the diameter D of the hole in the first polymer layer in negative electrode C1509.5 μm, a porosity of 93% and a thickness of 16 μm; diameter D of the pores in the second Polymer layer500.8 μm, a porosity of 13% and a thickness of 0.8. mu.m.
(2) Preparing a lithium ion battery anode Z1:
stirring by adopting vacuumMixing the positive active material (LiFePO)4)4.90mg, 0.05mg of a conductive agent (acetylene black) and 0.05mg of a binder (polyvinylidene fluoride, PVDF) were uniformly mixed in N-methylpyrrolidone (NMP) to form a stable and uniform slurry, wherein the stirring speed was 1000rpm and the stirring time was 12 hours; coating the obtained slurry on a current collector aluminum sheet, drying at 80 ℃, and cutting into a wafer with the diameter of 13.0 mm; and drying at 80 ℃, and tabletting by a roller press to obtain the positive electrode Z1.
(3) Assembled battery
The positive plate Z1, the separator and the metallic lithium negative electrode C1 were stacked one by one in a button cell, and 50. mu.L of electrolyte (4mol/L LiCF) was added dropwise3SO3And the solvent is DME), and then packaging is carried out, so that the lithium metal negative electrode battery S1 is obtained.
Example 2
Preparing a lithium ion battery cathode C2:
4.98g of polyvinylidene fluoride and 1.00g of calcium carbonate particles (particle diameter D)502 μm), 0.05g of acetylene black was added to acetone and then stirred in a vacuum stirrer to form a stable and uniform slurry; this slurry was uniformly coated on a copper foil having a thickness of 8 μm in a batch manner, and dried at 80 ℃ to obtain a pole piece A2.
4.95g of polyethylene terephthalate and 0.05g of LiCF3SO3Adding the mixture into anhydrous N-methylacetamide, and stirring in a vacuum stirrer to form stable and uniform slurry; the slurry was uniformly spin coated on A2 and dried at 80 ℃ to give pole piece B2.
Soaking the pole piece B3 in 0.45mol/L dilute hydrochloric acid for 12h, then washing with deionized water for 3 times, drying at 80 ℃, and then uniformly spin-coating 26.7mL of 0.01mol/L LiCF on the surface3SO3And drying the solvent which is DME solution at the temperature of 80 ℃ to obtain the lithium ion battery negative pole piece C2.
A positive electrode for a lithium ion battery was prepared and assembled by the same method as in example 1, and battery S2 was assembled.
Wherein the diameter D of the hole in the first polymer layer in negative electrode C2509.5 μm, a porosity of 93% and a thickness of 16 μm; diameter D of the pores in the second Polymer layer50Is 08 μm, a porosity of 13% and a thickness of 0.8. mu.m.
Example 3
Preparing a lithium ion battery cathode C3:
adding 4.95g of polyvinylidene fluoride, 0.05g of acetylene black and 1.0g of lithium nitrate into acetone, and then stirring in a vacuum stirrer to form stable and uniform slurry; this slurry was uniformly coated on a copper foil having a thickness of 8 μm in a batch manner, and dried at 60 ℃ to obtain a pole piece A3.
Pre-embedding lithium into the pole piece A1 in a blue test cabinet device, specifically, pre-embedding lithium with a capacity of 0.17mAh into an electrolyte by the pole piece A3 and a metal lithium piece, wherein the electrolyte contains a lithium salt and a solvent, and the lithium salt is LiCF with a lithium salt of 1mol/L3SO3The solvent is a solvent with the volume ratio of 1:1, 3-dioxolane and ethylene glycol dimethyl ether (DOL/DME) at a current density of 0.5mA/cm2And then taking out the A3 and drying at 60 ℃ to obtain a pole piece B3.
4.8g of polyvinylidene fluoride-hexafluoropropylene and 0.2g of LiCF were mixed3SO3Adding the mixture into cyclohexanone, and stirring in a vacuum stirrer to form stable and uniform slurry; uniformly spin-coating the slurry on a B3 pole piece at the rotation speed of 500rpm for 1 min; and uniformly spin-coating the slurry on A3, and drying at 80 ℃ to obtain the lithium ion battery negative electrode sheet C3.
A positive electrode for a lithium ion battery was prepared and assembled by the same method as in example 1, and battery S3 was assembled.
Wherein the diameter D of the hole in the first polymer layer in negative electrode C35025 μm, a porosity of 93% and a thickness of 16 μm; diameter D of the pores in the second Polymer layer505 μm, a porosity of 13% and a thickness of 0.8. mu.m.
Example 4
Preparing a lithium ion battery cathode C4:
adding 4.95g of polytetrafluoroethylene, 0.02g of acetylene black and 0.01g of lithium nitrate into acetone, and then stirring in a vacuum stirrer to form stable and uniform slurry; this slurry was uniformly coated on a copper foil having a thickness of 8 μm in a batch manner, and dried at 60 ℃ to obtain a pole piece A4.
Placing pole piece A4 in bluePre-embedding lithium in a test cabinet device, specifically, pre-embedding 0.17mAh lithium in an electrolyte by using a pole piece A4 and a metal lithium piece, wherein the electrolyte contains a lithium salt and a solvent, and the lithium salt is LiCF (lithium ion fluoride) with 1mol/L3SO3The solvent is a solvent with the volume ratio of 1:1, 3-dioxolane and ethylene glycol dimethyl ether (DOL/DME) at a current density of 0.5mA/cm2And then taking out the A4 and drying at 60 ℃ to obtain a pole piece B4.
4.8g of polyvinylidene fluoride-hexafluoropropylene and 0.2g of LiCF were mixed3SO3Adding the mixture into cyclohexanone, and stirring in a vacuum stirrer to form stable and uniform slurry; uniformly spin-coating the slurry on a B4 pole piece at the rotation speed of 500rpm for 1 min; and uniformly spin-coating the slurry on A4, and drying at 80 ℃ to obtain the lithium ion battery negative electrode sheet C4.
A positive electrode for a lithium ion battery was prepared and assembled by the same method as in example 1, and battery S4 was assembled.
Wherein the diameter D of the hole in the first polymer layer in negative electrode C4509.5 μm, a porosity of 50% and a thickness of 16 μm; diameter D of the pores in the second Polymer layer500.8 μm, a porosity of 50% and a thickness of 0.8. mu.m.
Example 5
Preparing a lithium ion battery cathode C5:
4.95g of polyvinylidene fluoride (PVDF), 0.05g of acetylene black and 0.50g of lithium nitrate were added to acetone, and then stirred in a vacuum stirrer to form a stable and uniform slurry, which was uniformly coated intermittently on a copper foil having a thickness of 8 μm, dried at 80 ℃ and cut into a 15 mm-diameter pole piece A5.
Pre-embedding lithium into the pole piece A5 in a blue test cabinet, specifically, pre-embedding lithium with a capacity of 0.17mAh into an electrolyte by the pole piece A5 and a metal lithium piece, wherein the electrolyte contains a lithium salt and a solvent, and the lithium salt is LiCF with 1mol/L3SO3The solvent is a solvent with the volume ratio of 1:1, 3-dioxolane and ethylene glycol dimethyl ether (DOL/DME) at a current density of 0.5mA/cm2And then taking out the A1 and drying at 60 ℃ to obtain a pole piece B5.
4.95g of styrene-butadiene rubber and 0.05g of LiCF3SO3Is added toStirring in water toluene in a vacuum stirrer to form stable and uniform slurry; and uniformly spin-coating the slurry on a B5 pole piece at the rotation speed of 500rpm for 5min, and drying at 80 ℃ to obtain the lithium ion battery negative pole piece C5.
A positive electrode for a lithium ion battery was prepared and assembled by the same method as in example 1, and battery S5 was assembled.
Wherein the diameter D of the hole in the first polymer layer in negative electrode C5509.5 μm, a porosity of 93% and a thickness of 1 μm; diameter D of the pores in the second Polymer layer500.8 μm, a porosity of 13% and a thickness of 10 μm.
Example 6
Pole pieces A6 and B6 were prepared in the same manner as pole piece A1 and pole piece B1 in example 1, except that 4.99g of styrene-butadiene rubber and 0.01g of LiCF were added3SO3Adding the mixture into toluene, and stirring the mixture in a vacuum stirrer to form stable and uniform slurry; and uniformly spin-coating the slurry on B6, and drying at 80 ℃ to prepare the lithium ion battery negative electrode sheet C6.
A positive electrode for a lithium ion battery was prepared and assembled by the same method as in example 1, and battery S6 was assembled.
Wherein the diameter D of the hole in the first polymer layer in negative electrode C6509.5 μm, a porosity of 93% and a thickness of 16 μm; diameter D of the pores in the second Polymer layer500.5 μm, 3% porosity and 0.8 μm thickness.
Example 7
Preparing a pole piece A7 by the same method as the pole piece A1 prepared in the example 1, except that the pole piece A7 is not pre-embedded with lithium, 5.0g of styrene butadiene rubber is added into toluene, and then the mixture is stirred in a vacuum stirrer to form stable and uniform slurry; and uniformly spin-coating the slurry on A7, and drying at 80 ℃ to prepare the lithium ion battery negative electrode sheet C7.
A positive electrode for a lithium ion battery was prepared and assembled by the same method as in example 1, and battery S7 was assembled.
Wherein the diameter D of the hole in the first polymer layer in negative electrode C7509.5 μm, a porosity of 93% and a thickness of 16 μm; diameter D of the pores in the second Polymer layer500.05 μm, 3% porosity and 0.8 μm thickness.
Comparative example 1
Preparing a lithium ion battery negative electrode D1:
adding 4.99g of polytetrafluoroethylene, 0.01g of acetylene black and 0.001g of lithium nitrate into acetone, and then stirring in a vacuum stirrer to form stable and uniform slurry; this slurry was uniformly coated on a copper foil having a thickness of 8 μm in a batch manner, and dried at 80 ℃ to obtain a pole piece E1.
Pre-embedding lithium into the pole piece E1 in a blue test cabinet, specifically, pre-embedding lithium with the capacity of 0.17mAh into the electrolyte by the pole piece E1 and a metal lithium piece, wherein the electrolyte contains lithium salt and a solvent, and the lithium salt is LiCF with the lithium salt of 1.0mol/L3SO3The solvent is a solvent with the volume ratio of 1:1, 3-dioxolane and ethylene glycol dimethyl ether (DOL/DME) at a current density of 0.5mA/cm2And then taking out the E1 and drying at 60 ℃ to obtain a pole piece F1.
4.95g of styrene-butadiene rubber and 0.05g of LiCF were mixed3SO3Adding the mixture into toluene, and stirring the mixture in a vacuum stirrer to form stable and uniform slurry; uniformly spin-coating the slurry on an F1 pole piece at the rotation speed of 500rpm for 1 min; and uniformly spin-coating the slurry on F1, and drying at 60 ℃ to obtain the lithium ion battery negative electrode sheet D1.
A lithium ion battery positive electrode was prepared and assembled with cell DS1 using the same method as in example 1.
Wherein the diameter D of the pores in the first polymer layer in negative electrode D1500.8 μm, a porosity of 65% and a thickness of 16 μm; diameter D of the pores in the second Polymer layer500.01 μm, a porosity of 13% and a thickness of 0.8. mu.m.
Comparative example 2
Preparing a lithium ion battery negative electrode D2:
adding 4.95g of styrene-butadiene rubber, 0.01g of acetylene black and 0.05g of lithium nitrate into acetone, and then stirring in a vacuum stirrer to form stable and uniform slurry; this slurry was uniformly coated on a copper foil having a thickness of 8 μm in a batch manner, and dried at 80 ℃ to obtain a pole piece E2.
Pre-embedding lithium into the pole piece E2 in a blue test cabinet, specifically, pre-embedding lithium with the capacity of 0.17mAh into the electrolyte by the pole piece E1 and a metal lithium piece, wherein the electrolyte contains lithium salt and a solvent, and the lithium salt is LiCF with the lithium salt of 1.0mol/L3SO3The solvent is a solvent with the volume ratio of 1:1, 3-dioxolane and ethylene glycol dimethyl ether (DOL/DME) at a current density of 0.5mA/cm2And then taking out the E2 and drying at 60 ℃ to obtain a pole piece F2.
4.98g of polyvinylidene fluoride and 0.02g of LiCF were added3SO3Adding the mixture into toluene, and stirring the mixture in a vacuum stirrer to form stable and uniform slurry; uniformly spin-coating the slurry on an F2 pole piece at the rotation speed of 500rpm for 1 min; and uniformly spin-coating the slurry on F2, and drying at 60 ℃ to obtain the lithium ion battery negative electrode sheet D2.
A lithium ion battery positive electrode was prepared and assembled with cell DS2 using the same method as in example 1.
Wherein, the diameter D of the hole in the 2 nd polymer layer in the negative electrode D2500.8 μm, a porosity of 13% and a thickness of 16 μm; diameter D of pores in layer 1 Polymer509.5 μm, a porosity of 93% and a thickness of 0.8. mu.m.
Comparative example 3
Preparing a lithium ion battery negative electrode D3:
adding 4.95g of PVDF, 0.05g of acetylene black and 0.50g of lithium nitrate into acetone, and stirring in a vacuum stirrer to form stable and uniform slurry; the slurry is evenly and intermittently coated on a copper foil with the thickness of 8 mu m, dried at the temperature of 80 ℃ and cut into a pole piece E3 with the diameter of 15 mm;
the pole piece E3 and a metal lithium piece are put into an electrolyte of 1mol/L LiCF3SO3Pre-embedding 0.17mAh capacity of lithium in DOL/DME with the volume ratio of 1:1, and the current density of 1mA/cm2Then taking out E3 and drying to obtain the cathode D3, the diameter D of the hole in the polymer layer of the pole piece D3509.5 μm, a porosity of 93% and a thickness of 16.8. mu.m.
A lithium ion battery positive electrode was prepared and assembled with cell DS3 using the same method as in example 1.
Comparative example 4
Preparing a lithium ion battery negative electrode D4:
weighing 4.95g of styrene butadiene rubber and 0.05g of LiCF3SO3Adding the mixture into NMP, and stirring the mixture in a vacuum stirrer to form stable and uniform slurry; the slurry is evenly and intermittently coated on a copper foil with the diameter of 8 mu m, dried at the temperature of 80 ℃ below zero, and cut into a pole piece E4 with the diameter of 15 mm;
the pole piece E4 and a metal lithium piece are put into an electrolyte of 1mol/L LiCF3SO3Pre-embedding 0.17mAh capacity of lithium in DOL/DME with the volume ratio of 1:1, and the current density of 1mA/cm2Then taking out E4 and drying to obtain a pole piece D4, the diameter D of a hole in a polymer layer in the pole piece D4500.8 μm, a porosity of 13% and a thickness of 16.8. mu.m.
A lithium ion battery positive electrode was prepared and assembled with cell DS4 using the same method as in example 1.
Test example
(1) The negative electrode sheets of C1-C7 and D1-D4 prepared in the examples and comparative examples were combined with a lithium foil (thickness 25um) with a diameter of 16mm and an electrolyte of 4mol/L LiCF3SO3Wherein DME is used as solvent, assembling half cell at 25 deg.C and 1mA/cm2And 2 hours of charge/2 hours of discharge, testing, and evaluating the stability of the metal lithium negative electrode through four aspects of the lithium deposition overpotential of the first cycle, the efficiency, the cycle times and the thickness expansion rate of the pole piece after the cycle, wherein the test result is shown in table 1.
(2) The batteries prepared in examples and comparative examples were 5 batteries each, and the batteries were subjected to charge-discharge cycle test at 2C under 298 ± 1K on a LAND CT 2001C secondary battery performance testing apparatus. The method comprises the following steps: standing for 10 min; constant voltage charging to 3.8V/2C cut-off; standing for 10 min; constant current discharge to 2.7V, i.e. 1 cycle. Repeating the steps, when the battery capacity is lower than 80% of the first discharge capacity in the circulation process, ending the circulation, wherein the circulation times are the circulation service life of the battery, disassembling the battery, measuring the volume expansion rate of the battery core before and after the test, averaging each group, and obtaining the test result shown in table 2.
TABLE 1
Figure BDA0002127011120000211
TABLE 2
Battery with a battery cell Capacity retention/% at 200 cycles Battery thickness swelling rate/%)
S1 95 32
S2 90 53
S3 87 60
S4 86 75
S5 83 83
S6 83 86
S7 80 87
DS1 72 113
DS2 73 124
DS3 75 108
DS4 70 129
As can be seen from table 1, the lithium negative electrodes of the first polymer layer and the second polymer layer with specific pore size distribution have very low over-potential and high coulombic efficiency, and the comparison of examples 1 and 2 shows that the performance of the lithium negative electrode can be further improved by performing the pre-deposition of lithium.
As can be seen from table 2, the capacity retention rate of the battery after 200 cycles at 2C rate still has good electrochemical performance under a higher rate condition, and the rate performance is greatly improved, which may be because the special pore size distribution can provide a transmission channel for lithium ions. Meanwhile, the first polymer layer and the second polymer layer are proper in thickness, the first polymer layer can provide a metal lithium deposition space, uniform deposition of metal lithium is guaranteed, side reaction of the metal lithium and electrolyte can be reduced through the second polymer layer, and the lithium ion battery can keep good structural stability, so that the problem of volume expansion of the metal lithium can be effectively solved, and the volume expansion rate of the negative electrode plate and the volume expansion rate of an assembled battery cell are small.
Preferably, the second polymer layer contains lithium salt, and the lithium salt can generate local super-concentration effect, enhance the diffusion process of lithium ions and further improve the rate performance of the battery.
The preferred embodiments of the present disclosure are described in detail with reference to the accompanying drawings, however, the present disclosure is not limited to the specific details of the above embodiments, and various simple modifications may be made to the technical solution of the present disclosure within the technical idea of the present disclosure, and these simple modifications all belong to the protection scope of the present disclosure.
It should be noted that, in the foregoing embodiments, various features described in the above embodiments may be combined in any suitable manner, and in order to avoid unnecessary repetition, various combinations that are possible in the present disclosure are not described again.
In addition, any combination of various embodiments of the present disclosure may be made, and the same should be considered as the disclosure of the present disclosure, as long as it does not depart from the spirit of the present disclosure.

Claims (19)

1. A lithium ion battery negative electrode is characterized by comprising a current collector, a first polymer layer attached to the current collector and a second polymer layer attached to the first polymer layer, wherein the diameter D of a hole in the first polymer layer50Greater than 1 μm, diameter D of the pores in the second polymer layer50Is the diameter D of the pores in the first polymer layer500.001-1 times of the total amount of the active ingredient.
2. The negative electrode of claim 1, wherein the diameter D of the pores in the second polymer layer50Is 1nm-1 μm.
3. The negative electrode of claim 1, wherein the diameter D of the pores in the first polymer layer50Greater than 1 μm and at most 10 μm, the diameter D of the pores in the second polymer layer50Is 1nm-100 nm.
4. The negative electrode of claim 1, wherein the first polymer layer has a porosity of 80-98% and the second polymer layer has a porosity of 7-30%.
5. The anode of claim 1, wherein the first polymer layer has a thickness of 4 μ ι η to 20 μ ι η and the second polymer layer has a thickness of 10nm to 5 μ ι η.
6. The negative electrode of claim 1, wherein the second polymer layer comprises a lithium salt; the lithium salt is contained in an amount of 0.5 to 20 wt% based on the total weight of the second polymer layer; the lithium salt is LiPF6、LiAsF6、LiClO4、LiBF6、LiN(CF3SO3)2、LiCF3SO3、LiC(CF3SO3)2、LiN(C4F9SO2)(CF3SO3) One or more of LiF, LiCl, LiBr and LiI.
7. The anode of claim 6, wherein the pores in the second polymer layer have a diameter of 500nm to 1 μm.
8. The negative electrode of claim 1, wherein the current collector and/or the first polymer layer comprises metallic lithium; the current collector and/or the first polymer layer have a lithium insertion capacity of 0.001mAh/cm2The above.
9. The negative electrode according to claim 1, wherein the first polymer layer contains a conductive agent; the content of the conductive agent is 0.1-5 wt% based on the total weight of the first polymer layer; the conductive agent is one or more selected from nano gold powder, silver powder, acetylene black, carbon nano tubes, graphene and nano carbon fibers.
10. The negative electrode of claim 1, wherein the current collector has a thickness of 5-8 μ ι η; the main material of the current collector is selected from one or more of copper, aluminum, stainless steel, nickel, lithium-boron alloy, lithium-silicon alloy, carbon nano tube and graphene.
11. The negative electrode of claim 1, wherein the first polymer layer comprises a first polymer, and the second polymer layer comprises a second polymer, and the first polymer and the second polymer are each independently selected from one or more of polyvinylidene fluoride, polyvinylidene fluoride-hexafluoropropylene, polytetrafluoroethylene, polyethylene terephthalate, perfluorosulfonic acid polymer, polyimide, and styrene-butadiene rubber.
12. A method of preparing the anode of any of claims 1-11, comprising:
s1, coating slurry containing a first polymer and a pore-forming agent on a current collector, and removing a first solvent to form a first polymer layer to obtain a first negative plate;
s2, coating the slurry containing the second polymer on the first polymer layer, and removing the second solvent to form a second polymer layer to obtain a second negative plate;
s3, removing the pore-forming agent in the second negative electrode sheet to form pores in the first polymer layer, so as to obtain the negative electrode;
alternatively, the method comprises:
A. coating the slurry containing the first polymer and the reactive pore-forming agent on a current collector, and removing the third solvent to form a first polymer layer to obtain a first negative plate; the reactive porogen is reactive with the third solvent to generate a gas or a soluble compound to form pores in the first polymer layer;
B. and coating the slurry containing the second polymer on the first polymer layer, and removing the fourth solvent to obtain the negative electrode coated with the second polymer layer.
13. The method according to claim 12, wherein the step S1 further comprises: coating a slurry containing the first polymer, the pore-forming agent and a conductive agent on the current collector, and drying at 50-60 ℃ to remove the first solvent; alternatively, the first and second electrodes may be,
the step A further comprises the following steps: coating the slurry containing the first polymer, the reactive pore-forming agent and the conductive agent on the current collector, and drying at 80-120 ℃ to remove the third solvent.
14. The method of claim 12 or 13, wherein the reactive pore former is selected from one or more of polyethylene oxide, alkali metal halides, alkali metal hydroxides, alkali metal nitrates, alkali metal carbonates, alkaline earth metal carbonates, alkali metal hydroxides, magnesium hydroxide, calcium hydroxide, copper oxide, iron oxide and aluminum oxide.
15. The method of claim 12, further comprising: introducing metallic lithium into the current collector and/or said first polymer layer.
16. The method of claim 15, wherein introducing lithium metal into the first polymer layer comprises: at a current density of 0.5-1mA/cm2Under the condition of (2), carrying out lithium intercalation treatment on the first negative plate; the lithium intercalation capacity of the first negative plate after the lithium intercalation treatment is 0.001mAh/cm2The above.
17. The method according to claim 12, wherein the step S2 further comprises: coating a slurry containing the second polymer and the lithium salt on the first polymer layer, and drying at 60-80 ℃ to remove the second solvent;
the step B further comprises the following steps: coating the slurry containing the second polymer and the lithium salt on the first polymer layer, and drying at 60-80 ℃ to remove the fourth solvent.
18. A lithium ion battery comprising the negative electrode according to any one of claims 1 to 11.
19. A battery module characterized by comprising the lithium ion battery according to claim 18.
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