CN111816856B - Composite material, preparation method thereof and negative electrode - Google Patents
Composite material, preparation method thereof and negative electrode Download PDFInfo
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- 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
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- H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
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- Y02E60/10—Energy storage using batteries
Abstract
The invention belongs to the technical field of battery materials, and particularly relates to a composite material, a preparation method thereof and a negative electrode. The composite material comprises a carbon active substance core, and an alloying active substance layer and a shell layer which are coated on the surface of the carbon active substance core, wherein the alloying active substance layer is positioned between the carbon active substance core and the shell layer. The composite material can realize highly uniform dispersion of different active substance phases, thereby effectively relieving stress concentration, isolating electrolyte and reducing side reaction, so that the composite material with a special structure can be used for the cathode active material of the lithium ion battery to obviously improve the cycling stability of the cathode active material.
Description
Technical Field
The invention belongs to the technical field of battery materials, and particularly relates to a composite material, a preparation method thereof and a negative electrode.
Background
Lithium ion batteries have been widely used in various fields such as consumer electronics, electric tools, electric vehicles, energy storage, etc. due to their good electrochemical properties. However, graphite is mostly adopted as a negative electrode material in the current commercial lithium ion battery, and the theoretical capacity of the graphite is limited (372mAh g) -1 ) And the performance requirements of high energy density and long endurance time are difficult to meet. Therefore, the development of a novel anode material having a high capacity is an important research direction for lithium ion batteries. Alloying negative electrode materials, e.g. siliconGermanium, aluminum, tin, antimony, zinc and the like have high theoretical capacity, and have good application prospect when being used as a high-capacity flexible negative electrode material. However, pure alloyed cathodes suffer from large volume expansion during the alloying reaction (e.g., silicon cathodes-300%), which severely affects the cycling stability of the battery. The composite cathode material is prepared by adding a proper amount of alloying cathode material into the graphite cathode material, so that on one hand, the capacity of the graphite cathode can be improved, and meanwhile, the volume expansion of the alloying cathode can be reduced to a certain degree, and the composite cathode material has a good development prospect.
However, the alloying negative electrode material particles with micron and nanometer dimensions are easy to agglomerate in the process of mixing with carbon particles such as graphite and the like, and uniform dispersion is difficult to realize, so that the alloying negative electrode material particles are locally accumulated, and in the alloying reaction process, the volume of the locally accumulated region of the alloying particles is seriously expanded, so that stress concentration is caused, active materials are peeled off, even a current collector is cracked, and the cycle performance of the battery is seriously influenced.
Therefore, the prior art is in need of improvement.
Disclosure of Invention
The invention aims to provide a composite material and a preparation method thereof, and aims to solve the technical problem that the existing carbon active substance and alloying active substance are poor in mixing dispersibility.
In order to realize the purpose of the invention, the technical scheme adopted by the invention is as follows:
the invention provides a composite material, which comprises a carbon active substance core, and an alloying active substance layer and an outer shell layer which are coated on the surface of the carbon active substance core, wherein the alloying active substance layer is positioned between the carbon active substance core and the outer shell layer.
The invention also provides a preparation method of the composite material, which comprises the following steps:
providing a carbon-based active material core;
preparing the alloying active material layer on the surface of the carbon active material core;
preparing the outer shell layer on the surface of the alloying active material layer.
The composite material provided by the invention comprises three layers of materials, namely a carbon active material core positioned at the core, an alloying active material layer positioned in the middle and an outer shell layer positioned on the outer surface, so that the composite material with a specific structure can be used as a negative active material; the materials of the carbon active material core and the alloying active material layer belong to active materials, the alloying active material layer is coated on the surface of the carbon active material core, the active properties of the carbon active material core and the alloying active material layer can be utilized, and meanwhile, the high uniform dispersion of different active material phases can be realized, so that the stress concentration is effectively relieved, the shell layer not only plays a role in mechanical protection of the alloying active material layer and the carbon active material core, but also can isolate electrolyte and reduce side reactions, and therefore, the composite material with a specific structure can be used for the negative active material of the lithium ion battery to obviously improve the circulation stability.
The invention also aims to provide a negative electrode, aiming at solving the technical problem that the cycle performance is influenced due to poor mixing dispersibility of the carbon active material and the alloying active material in the conventional negative electrode.
In order to achieve the purpose, the invention adopts the following technical scheme:
the invention provides a negative electrode, which comprises a current collector and a negative active layer coated on the current collector, wherein the negative active layer comprises a negative active material, a conductive agent and a binder, and the negative active material is the composite material or the composite material prepared by the preparation method of the composite material.
The cathode active material in the cathode provided by the invention is the special composite material or the special composite material obtained by the preparation method of the composite material, the composite material can realize highly uniform dispersion of different active substance phases, so that stress concentration is effectively relieved, electrolyte can be isolated, and side reactions are reduced, so that the circulation stability of the lithium ion battery can be remarkably improved by preparing the composite material with the special structure into the electrode.
Drawings
FIG. 1 is a schematic structural view of a composite material according to an embodiment of the present invention;
FIG. 2 is a SEM comparison of a negative electrode made of the composite material of the embodiment of the invention and a negative electrode prepared by mixing natural graphite and aluminum powder particles through a traditional mechanical mixing process;
fig. 3 is a comparison graph of cycle performance of the negative electrode made of the composite material of the embodiment of the present invention and the negative electrode prepared by mixing natural graphite and aluminum powder particles according to the conventional mechanical mixing process.
Detailed Description
In order to make the technical problems, technical solutions and advantageous effects to be solved by the present invention more clearly apparent, the present invention is further described in detail below with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not limit the invention.
In one aspect, an embodiment of the present invention provides a composite material, as shown in fig. 1, including a carbon-based active material core 1, and an alloying-based active material layer 2 and an outer shell layer 3 coated on a surface of the carbon-based active material core 1, where the alloying-based active material layer 2 is located between the carbon-based active material core 1 and the outer shell layer 3.
The composite material provided by the embodiment of the invention comprises three layers of materials, namely a carbon active material core positioned at the core, an alloying active material layer positioned in the middle and a shell layer positioned on the outer surface, so that the composite material with a specific structure can be used as a negative active material; the materials of the carbon active material core and the alloying active material layer belong to active materials, the alloying active material layer is coated on the surface of the carbon active material core, the active properties of the carbon active material core and the alloying active material layer can be utilized, and meanwhile, the high uniform dispersion of different active material phases can be realized, so that the stress concentration is effectively relieved, the shell layer not only plays a role in mechanical protection of the alloying active material layer and the carbon active material core, but also can isolate electrolyte and reduce side reactions, and therefore, the composite material with a specific structure can be used for the negative active material of the lithium ion battery to obviously improve the circulation stability.
In one embodiment, the carbon-based active material of the carbon-based active material core includes at least one of a graphite-based active material and a non-graphite-based active material. Wherein the graphite-based active material includes, but is not limited to, one or more combinations of natural graphite, artificial graphite, and the like, and the non-graphite-based active material includes, but is not limited to, one or more combinations of soft carbon, hard carbon, coke, mesocarbon microbeads (MCMB), carbon nanotubes, graphene, and activated carbon, and the like. Specifically, the particle size of the carbon-based active material core composed of the above carbon-based active material is in the micro-scale or nano-scale, such as 10-100nm, or 0.1-100 μm, etc.
In an embodiment, the alloying active material of the alloying active material layer comprises a simple substance element and/or an alloy of at least two elements, such as at least one of aluminum, silicon, germanium, tin, lead, antimony, bismuth, zinc, aluminum copper alloy, copper tin alloy, aluminum silicon alloy, aluminum magnesium alloy, tin nickel alloy and tin cobalt nickel alloy. Specifically, the thickness of the alloying active material layer composed of the above alloying active material is 50nm to 10 μm.
The composite material comprises two active materials, namely a carbon active material and an alloying active material, wherein the core is the carbon active material, the middle alloying active material layer is the alloying active material, and the alloying active material is coated on the surface of the carbon active material, so that the capacity of the composite material used as a negative electrode can be improved, the volume expansion of the alloying negative electrode can be reduced, and more importantly, the alloying active material and the carbon active material can be highly uniformly distributed, so that the defect of stress concentration caused by uneven dispersion is avoided, and the cycle stability of the composite material used as the negative electrode material can be effectively improved.
In one embodiment, the shell material of the shell layer comprises carbon, zirconium dioxide (ZrO) 2 ) Titanium nitride (TiN), titanium aluminum nitride (TiAlN), lithium phosphorus oxynitride (LiPON), tantalum-doped lithium lanthanum zirconium oxide (LLZTO), Lithium Aluminum Germanium Phosphorus (LAGP), lithium phosphate-phosphorus pentasulfide (Li) 3 PO 4 -P 2 S 5 ) And lithium sulfide-phosphorus pentasulfide (Li) 2 S-P 2 S 5 ) At least one of; or the shell layer is at least one of a carbon material coating layer, an oxide coating layer, a nitride coating layer and a solid electrolyte coating layer. The material of the oxide coating layer can be zirconium dioxide, the material of the nitride coating layer can be titanium nitride or titanium aluminum nitride, and the material of the solid electrolyte coating layer can be lithium phosphorus oxynitride, tantalum-doped lithium lanthanum zirconium oxide, lithium aluminum germanium phosphorus, lithium phosphate-phosphorus pentasulfide and lithium sulfide-phosphorus pentasulfide. The outer shell layer is used as a surface protection layer, on one hand, the outer shell layer plays a mechanical protection role for active substances in the composite material, and on the other hand, the outer shell layer can isolate electrolyte and reduce side reactions. Specifically, the thickness of the outer shell layer is 10nm to 200 nm.
On the other hand, the embodiment of the invention also provides a preparation method of the composite material, which comprises the following steps:
s01: providing a carbon-based active material core;
s02: preparing the alloying active material layer on the surface of the carbon active material core;
s03: preparing the outer shell layer on the surface of the alloying active material layer.
According to the preparation method of the composite material provided by the embodiment of the invention, the composite material consisting of three layers of materials is prepared, namely the carbon active material core positioned at the core, the alloying active material layer positioned in the middle and the shell layer positioned on the outer surface, so that the composite material with a special structure can be used as a negative active material; the composite material obtained by the preparation method can realize highly uniform dispersion of different active material phases, so that stress concentration is effectively relieved, and the shell layer can play a role in mechanical protection of the alloying active material layer and the carbon active material core, so that the composite material can isolate electrolyte and reduce side reactions, and therefore, the composite material with a special structure can be used as a negative electrode active material of a lithium ion battery, and the circulation stability of the composite material can be remarkably improved.
In step S01, the carbon-based active material core may be a granular carbon-based active material, which may be in a nanometer or micrometer scale, and the specific types are as described above.
In step S02, the step of preparing the alloying active material layer on the surface of the carbon-based active material core includes: and coating an alloying active substance material on the surface of the carbon active substance core by using any one of a vapor deposition method, an electroplating method, a chemical plating method, a hydrothermal synthesis method, a microwave synthesis method, an electrophoretic deposition method and a ball milling method. Wherein the vapor deposition method may be physical vapor deposition, chemical vapor deposition, or the like. And the species of alloying-type active material are as set forth above.
In step S03, the step of preparing the outer shell layer on the surface of the alloying active material layer includes: forming the outer shell layer on the surface of the alloying active material layer by using a vapor deposition method or a sintering method. The envelope material of the envelope layer is as described above.
Finally, an embodiment of the present invention further provides a negative electrode, including a current collector and a negative active layer covering the current collector, where the negative active layer includes a negative active material, a conductive agent, and a binder, and the negative active material is the composite material described in the embodiment of the present invention or the composite material obtained by the preparation method of the composite material described in the embodiment of the present invention.
The negative active material in the negative electrode provided by the embodiment of the invention is a special composite material in the embodiment of the invention or a special composite material obtained by the preparation method of the composite material in the embodiment of the invention, and the composite material can realize highly uniform dispersion of different active substance phases, so that stress concentration is effectively relieved, electrolyte can be isolated, and side reactions are reduced, therefore, the circulation stability of the lithium ion battery can be remarkably improved when the electrode is prepared from the composite material with a special structure.
The negative electrode comprises a current collector and a negative active layer arranged on the surface of the current collector, wherein the current collector can be a copper foil, an aluminum foil, an alloy foil and the like. The negative electrode active layer includes a negative electrode active material, a conductive agent, and a binder. The negative electrode sheet can be obtained by preparing negative electrode active slurry containing the negative electrode active material, a conductive agent and a binder, then uniformly coating the negative electrode active slurry on the current collector, uniformly coating the surface of the current collector through the procedures of mixing, pulping, coating, rolling and the like, and drying. Wherein, the binder can be carboxylic styrene butadiene latex (SBR), sodium carboxymethylcellulose (CMC), Polytetrafluoroethylene (PTFE) and polyacrylic acid (PAA), the conductive agent can be carbon black, carbon nano tube and SP, and the solvent of the cathode active slurry can be deionized water or N-methyl pyrrolidone.
The invention is described in further detail with reference to a part of the test results, which are described in detail below with reference to specific examples.
Example 1
The present embodiment provides a composite material: the method comprises the following steps of (1) adopting natural graphite as a carbon active substance core, aluminum as an alloying active substance layer and a carbon material as a shell layer, wherein D50 of the natural graphite is 12 micrometers, the thickness of the alloying active substance layer is 1 micrometer, the thickness of the shell layer is 100nm, and the mass percent of the aluminum is 40%; the composite material is used as a negative active material to prepare a negative electrode, and the specific preparation process comprises the following steps:
(1) the method comprises the steps of taking natural graphite particles as a substrate material, taking pure aluminum as a sputtering target material, depositing an aluminum active substance on the surfaces of the graphite particles by adopting a magnetron sputtering technology to obtain an alloying active substance layer, and controlling the thickness of a film layer to be about 3 mu m.
(2) And (2) taking a sucrose solution as a precursor, coating a carbon layer on the surface of the graphite particle of the prepared alloying active material layer deposited with the aluminum active material by adopting a high-temperature carbonization technology to obtain a shell layer, and controlling the thickness of the shell layer to be 100nm by controlling the concentration of the precursor solution and the carbonization treatment time to obtain the natural graphite/silicon/carbon composite material, namely the negative active material.
(3) Adding a conductive agent and a binder into the negative electrode material obtained in the step (2), wherein the mass ratio of the negative electrode material: conductive agent: and (2) uniformly mixing a conductive agent which is conductive carbon black and a binder which is PVDF, adding an N-methylpyrrolidone (NMP) solvent, fully stirring to obtain a slurry, uniformly coating the slurry on the surface of the copper foil, and then putting the copper foil into a vacuum oven for drying treatment at the baking temperature of 80 ℃ for 48 hours to obtain the cathode.
The natural graphite and the aluminum powder particles are mixed by adopting a traditional mechanical mixing process to prepare the composite electrode, wherein the mass percent of the aluminum active substance is consistent with that of the three-layer structure design of the embodiment 1 and is controlled to be 40%. The mixing uniformity and electrochemical properties of the composite cathode of the traditional process and the cathode with the three-layer structure design of the embodiment are compared: the scanning electron microscopic morphology images of the two cathodes are shown in fig. 2, wherein the composite cathode in the traditional process has uneven dispersion and the agglomeration phenomenon of aluminum powder particles (shown in fig. 2 a), while the cathode in the embodiment has a three-layer structure design, and the two phases of natural graphite and aluminum exhibit the characteristic of highly uniform dispersion (shown in fig. 2 b).
The lithium metal sheet is used as a counter electrode, EC: DEC (volume ratio 1:1) is used as an electrolyte to assemble a half cell, and an electrochemical performance test is performed, and a test result is shown in fig. 3, the negative electrode made of the negative electrode active material with the three-layer structure design in the embodiment circulates 2000 circles under the multiplying factor condition of 0.2C, the capacity retention rate reaches 97%, while the negative electrode adopting the traditional process circulates 500 circles under the same multiplying factor condition, and the capacity retention rate is lower than 80%.
Negative electrode based on different carbon active material materials
Examples 2 to 7
Examples 2 to 7 differ from example 1 in that different carbon-based active materials were used, and the same were used, and the carbon-based active materials used were: artificial graphite, soft carbon, hard carbon, MCMB, coke, graphene, half-cell electrochemical performance tests were performed on the cathodes of examples 2-7 at 0.2C rate and compared to example 1, with the test results shown in table 1 below.
TABLE 1
From table 1, it can be seen that: the negative electrodes prepared from different carbon active substances have good cycle stability and capacity retention rate, and the capacity retention rate of the negative electrode prepared from MCMB is the highest.
Negative electrode based on alloyed active material layers of different thicknesses
Examples 8 to 16 differ from example 1 in that the aluminum active material as an alloying active material layer had a different thickness, and the thicknesses of the aluminum active material as an alloying active material layer were the same: the anodes of examples 8 to 16 were subjected to half-cell electrochemical performance tests at 50nm, 200nm, 500nm, 700nm, 2 μm, 3 μm, 5 μm, and 6 μm under a rate condition of 0.2C, and compared with example 1, and the test results are shown in Table 2 below.
TABLE 2
From table 2, it can be seen that: the alloying active substance layer is 50nm-2 μm, and the cycle stability is better.
Negative electrode based on different alloying active substances
Examples 17 to 30 are different from example 1 in the alloying type active material, and the others are the same. The alloying active material materials were silicon, germanium, tin, lead, aluminum, antimony, bismuth, zinc, aluminum-copper alloy, copper-tin alloy, aluminum-silicon alloy, aluminum-magnesium alloy, tin-nickel alloy, tin-cobalt-nickel alloy, tin-nickel-carbon alloy, respectively, and the negative electrodes of examples 17 to 30 were subjected to the half-cell electrochemical performance test under the test rate condition of 0.2C and compared with example 1, and the test results are shown in table 3 below.
TABLE 3
From table 3, it can be seen that: the negative electrodes prepared from different alloying active material materials have good cycle stability and capacity retention rate.
Negative electrode based on different outer shell layers
Examples 31-36 differ from example 1 in that different skin layers were used, all other things being equal, and the skin layer materials used were: ZrO (zirconium oxide) 2 、TiN、TiAlN、LiPON、LLZTO、LAGP、Li 3 PO 4 -P 2 S 5 、Li 2 S-P 2 S 5 The preparation technique of the outer shell layer was carried out by vapor deposition, and the cathodes of examples 31-36 were tested for half-cell electrochemical performance at 0.2C rate and compared to example 1, with the results shown in table 4 below.
TABLE 4
From table 4, it can be seen that: the negative electrodes prepared by different shell layers have good cycling stability and capacity retention rate.
Full battery based on negative active material having three-layer structure
The cathode prepared by the embodiment of the invention is used for constructing the full battery, wherein the cathode active materials are respectively as follows: lithium iron phosphate, lithium cobaltate, ternary positive electrode (111, 532, 622, 811). The preparation method comprises the following specific steps:
(1) preparing a negative electrode by using a composite material with a three-layer structure: see examples 1-38 above for specific procedures.
(2) Electrolyte preparation: the specific steps are the same as those in example 1 of the present invention.
(3) Preparing a positive electrode: uniformly mixing a positive electrode active material, conductive carbon black and polyvinylidene fluoride (PVDF) according to a mass ratio of 8:1:1, adding an N-methylpyrrolidone (NMP) solvent, fully stirring to obtain a slurry, uniformly coating the slurry on the surface of a carbon-coated aluminum foil, and then putting the carbon-coated aluminum foil into a vacuum oven for drying treatment, wherein the baking temperature is 80 ℃, and the baking time is 48 hours.
(4) And (6) assembling the whole battery.
The full cell based on the negative electrode having the three-layer structure composite material prepared in this example was subjected to cycle and rate performance tests, and the test results are shown in table 5.
TABLE 5
From table 5 above, it can be seen that: the full battery based on the negative active material with the three-layer structure in the embodiment of the invention has good cycle stability and capacity retention rate.
The above description is only for the purpose of illustrating the preferred embodiments of the present invention and is not to be construed as limiting the invention, and any modifications, equivalents and improvements made within the spirit and principle of the present invention are intended to be included within the scope of the present invention.
Claims (5)
1. A composite material is characterized by comprising a carbon active material core, and an alloying active material layer and an outer shell layer which are coated on the surface of the carbon active material core, wherein the alloying active material layer is positioned between the carbon active material core and the outer shell layer; the material of the alloying active material layer is selected from tin-cobalt-nickel alloy; the carbon active material of the carbon active material core is graphene, the thickness of the alloying active material layer is 50nm-2 μm, the material of the shell layer is selected from lithium phosphorus oxygen nitrogen, and the thickness of the shell layer is 10nm-200 nm.
2. A method of preparing a composite material according to claim 1, comprising the steps of:
providing a carbon-based active material core;
preparing the alloying active material layer on the surface of the carbon-based active material core;
preparing the outer shell layer on the surface of the alloying active material layer.
3. The method of producing a composite material according to claim 2, wherein the step of producing the alloying type active material layer on the surface of the carbon type active material core includes: and coating the surface of the carbon active substance core with an alloying active substance material by adopting any one of a vapor deposition method, an electroplating method, a chemical plating method, a hydrothermal synthesis method, a microwave synthesis method, an electrophoretic deposition method and a ball milling method to obtain the alloying active substance layer.
4. The method of preparing a composite material according to claim 2, wherein the step of preparing the outer shell layer on the surface of the alloying-type active material layer comprises: and forming the shell layer on the surface of the alloying active material layer by adopting a vapor deposition method or a sintering method.
5. A negative electrode, comprising a current collector and a negative active layer coated on the current collector, wherein the negative active layer comprises a negative active material, a conductive agent and a binder, and is characterized in that the negative active material is the composite material of claim 1 or the composite material obtained by the preparation method of the composite material of any one of claims 2 to 4.
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| CN112467116A (en) * | 2020-11-30 | 2021-03-09 | 湖南中科星城石墨有限公司 | Graphite coating material, preparation method thereof and battery cathode |
| CN112467118B (en) * | 2020-11-30 | 2022-07-05 | 湖南中科星城石墨有限公司 | Graphite composite material, preparation method thereof and lithium battery cathode |
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