CN111816856A - Composite material and preparation method thereof and negative electrode - Google Patents

Abstract

The invention belongs to the technical field of battery materials, and in particular relates to a composite material, a preparation method thereof, and a negative electrode. The composite material includes a carbon-based active material core, an alloyed-based active material layer and a shell layer coated on the surface of the carbon-based active material core, and the alloyed-based active material layer is located on the carbon-based active material core and the outer shell layer. between the outer shell layers. The composite material can achieve highly uniform dispersion of different active material phases, thereby effectively alleviating stress concentration, and can isolate the electrolyte and reduce side reactions. Therefore, the composite material with such a unique structure can be used as a negative electrode active material for lithium-ion batteries. Cyclic stability performance.

Description

Composite material and preparation method thereof and negative electrode

technical field

The invention belongs to the technical field of battery materials, and in particular relates to a composite material, a preparation method thereof, and a negative electrode.

Background technique

Lithium-ion batteries have been widely used in various consumer electronic devices, power tools, electric vehicles, energy storage and other fields due to their good electrochemical properties. However, most of the current commercial lithium-ion batteries use graphite as the negative electrode material, and the theoretical capacity of graphite is limited (372mAh g ^-1 ), which makes it difficult to meet the performance requirements of high energy density and long battery life. Therefore, the development of new anode materials with high capacity has become an important research direction for lithium-ion batteries. Alloyed anode materials, such as silicon, germanium, aluminum, tin, antimony, zinc, etc., have high theoretical capacity and have good application prospects as high-capacity flexible anode materials. However, pure alloyed anodes have large volume expansion (eg, silicon anodes ~300%) during the alloying reaction, which seriously affects the cycling stability of the batteries. The composite negative electrode material is prepared by adding an appropriate amount of alloyed negative electrode material to the graphite negative electrode material. On the one hand, the capacity of the graphite negative electrode can be improved, and at the same time, the volume expansion of the alloyed negative electrode can be reduced to a certain extent, which has a good development prospect.

However, the alloyed anode material particles with micron and nanometer scales are prone to agglomeration during the mixing process with carbon particles such as graphite, and it is difficult to achieve uniform dispersion, so that the alloyed anode material particles have local accumulation, while in the alloying During the reaction process, the area where the alloyed particles are locally accumulated has serious volume expansion, resulting in stress concentration, which causes the active material to peel off, and even causes the current collector to crack, which seriously affects the battery cycle performance.

Therefore, the existing technology needs to be improved.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a composite material and a preparation method thereof, aiming at solving the technical problem of poor mixing and dispersibility of the existing carbon-based active materials and alloyed active materials.

For realizing the above-mentioned purpose of the invention, the technical scheme adopted in the present invention is as follows:

One aspect of the present invention provides a composite material, comprising a carbon-based active material core, an alloyed active material layer and a shell layer coated on the surface of the carbon-based active material core, and the alloyed active material layer is located on the surface of the carbon-based active material core. between the carbon-based active material core and the outer shell layer.

Another aspect of the present invention provides a method for preparing a composite material, comprising the steps of:

Provide carbon-based active material core;

preparing the alloyed active material layer on the surface of the carbon-based active material core;

The outer shell layer is prepared on the surface of the alloyed active material layer.

The composite material provided by the present invention includes three-layer materials, namely a carbon-based active material core located in the core, an alloyed active material layer located in the middle, and an outer shell layer located on the outer surface, so that the composite material with a unique structure can be used for negative electrode active materials. ; The materials of the carbon-based active material core and the alloyed active material layer are both active materials, and the alloyed active material layer is coated on the surface of the carbon-based active material core, not only can use the active properties of the two, but also can The highly uniform dispersion of different active material phases is achieved, thereby effectively alleviating stress concentration, and the outer shell layer not only acts as a mechanical protection for the alloyed active material layer and the carbon-based active material core, but also enables it to isolate the electrolyte and reduce Therefore, the composite material with such a unique structure can be used as the negative electrode active material of lithium ion battery to significantly improve its cycle stability performance.

Another object of the present invention is to provide a negative electrode, which aims to solve the technical problem that the carbon-based active material and the alloyed active material in the existing negative electrode have poor mixing and dispersibility, thereby affecting the cycle performance.

For realizing the above-mentioned purpose of the invention, the technical scheme adopted in the present invention is as follows:

The present invention provides a negative electrode, comprising a current collector and a negative electrode active layer covering the current collector, the negative electrode active layer comprising a negative electrode active material, a conductive agent and a binder, and the negative electrode active material is described in the present invention The composite material or the composite material obtained by the preparation method of the composite material of the present invention.

The negative electrode active material in the negative electrode provided by the present invention is the unique composite material of the present invention or the unique composite material obtained by the preparation method of the composite material of the present invention, and the composite material can realize highly uniform dispersion of different active material phases, thereby effectively alleviating stress concentration , and can isolate the electrolyte and reduce side reactions, so the preparation of such a composite material with a unique structure into an electrode can significantly improve the cycle stability of lithium-ion batteries.

Description of drawings

Fig. 1 is the structural representation of the composite material of the embodiment of the present invention;

2 is a SEM comparison diagram of a negative electrode made of a composite material according to an embodiment of the present invention and a negative electrode prepared by mixing natural graphite and aluminum powder particles in a traditional mechanical mixing process;

3 is a comparison diagram of the cycle performance of a negative electrode made of a composite material according to an embodiment of the present invention and a negative electrode prepared by mixing natural graphite and aluminum powder particles in a traditional mechanical mixing process.

Detailed ways

In order to make the technical problems, technical solutions and beneficial effects to be solved by the present invention clearer, the present invention will be further described in detail below with reference to the embodiments. It should be understood that the specific embodiments described herein are only used to explain the present invention, but not to limit the present invention.

In one aspect, an embodiment of the present invention provides a composite material, as shown in FIG. 1 , the composite material includes a carbon-based active material core 1 and an alloyed active material layer coated on the surface of the carbon-based active material core 1 2 and an outer shell layer 3 , the alloyed 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 present invention includes three layers of materials, namely a carbon-based active material core located in the core, an alloyed active material layer located in the middle, and an outer shell layer located on the outer surface, so that the composite material with a unique structure can be used for negative electrodes Active materials; the materials of the carbon-based active material core and the alloyed active material layer belong to active materials, and the alloyed active material layer is coated on the surface of the carbon-based active material core, which can not only utilize the active properties of the two, but also It can also achieve highly uniform dispersion of different active material phases, thereby effectively alleviating stress concentration, and the outer shell layer not only acts as a mechanical protection for the alloyed active material layer and the carbon-based active material core, but also can isolate the electrolyte. , reducing side reactions, so the composite material with such a unique structure can be used as the negative electrode active material of lithium ion battery to significantly improve its cycle stability performance.

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. Graphite active materials include but are not limited to one or more combinations of natural graphite and artificial graphite, and non-graphite active materials include but are not limited to soft carbon, hard carbon, coke, mesocarbon microbeads (MCMB), One or more combinations of carbon nanotubes, graphene and activated carbon, etc. Specifically, the particle size of the carbon-based active material core composed of the above-mentioned carbon-based active material material is micro-scale or nano-scale, such as 10-100 nm, or 0.1-100 μm.

In one embodiment, the alloying active material of the alloying active material layer includes a single element and/or an alloy of at least two elements, such as aluminum, silicon, germanium, tin, lead, antimony, bismuth, zinc , at least one of aluminum-copper alloy, copper-tin alloy, aluminum-tin alloy, aluminum-silicon alloy, aluminum-magnesium alloy, tin-nickel alloy and tin-cobalt-nickel alloy. Specifically, the thickness of the alloyed active material layer composed of the above alloyed active material material is 50 nm-10 μm.

The composite material described in the embodiment of the present invention includes two active materials, a carbon-based active material material and an alloyed-based active material material, wherein the core is a carbon-based active material material, and the intermediate layer of an alloyed-based active material layer is an alloyed-based active material. Material, the above alloyed active material is coated on the surface of the carbon active material, on the one hand, the capacity of the composite material can be improved when used as a negative electrode, and at the same time, the volume expansion of the alloyed negative electrode can be reduced, and more importantly, The alloyed active material and the carbon active material can be highly uniformly distributed, thereby avoiding stress concentration defects caused by uneven dispersion, which can effectively improve the cycle stability of the composite material used as a negative electrode material.

In one embodiment, the shell material of the shell layer includes carbon, zirconium dioxide (ZrO ₂ ), titanium nitride (TiN), titanium aluminum nitride (TiAlN), lithium phosphorus oxynitride (LiPON), tantalum doped at least one of lithium lanthanum zirconium oxygen (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 SP ₂ S ₅ ); Alternatively, the outer shell layer is at least one of a carbon-based 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 Oxygen, Lithium Aluminum Germanium Phosphorus, Lithium Phosphate-Phosphorus Pentasulfide and Lithium Sulfide-Phosphorus Pentasulfide. As a surface protective layer, the outer shell layer can mechanically protect the active substances inside the composite material on the one hand, and can isolate the electrolyte and reduce side reactions on the other hand. Specifically, the thickness of the outer shell layer is 10 nm-200 nm.

On the other hand, an embodiment of the present invention also provides a method for preparing a composite material, comprising the following steps:

S01: Provide carbon-based active material core;

S02: preparing the alloyed active material layer on the surface of the carbon-based active material core;

S03: Prepare the outer shell layer on the surface of the alloyed active material layer.

The preparation method of the composite material provided in the embodiment of the present invention is to prepare a composite material composed of three layers of materials, that is, a carbon-based active material core located in the core, an alloyed active material layer located in the middle, and an outer shell layer located on the outer surface, so that The composite material with the unique structure can be used for the negative electrode active material; the composite material obtained by the preparation method can not only achieve a highly uniform dispersion of different active material phases, thereby effectively alleviating stress concentration, and the outer shell layer can play a role in the alloying active material layer. The mechanical protection of carbon-based active material cores can isolate the electrolyte and reduce side reactions. Therefore, the composite material with such a unique structure can be used as the negative electrode active material of lithium-ion batteries to significantly improve its cycle stability.

In step S01 , the carbon-based active material core may be a granular carbon-based active material material, which may be nano-scale or micro-scale. For specific types, please refer to the above description.

In step S02, the step of preparing the alloyed active material layer on the surface of the carbon-based active material core includes: adopting methods including but not limited to vapor deposition, electroplating, chemical plating, hydrothermal synthesis, and microwave synthesis. , any one of the electrophoretic deposition method and the ball milling method, the alloyed active material is coated on the surface of the carbon-based active material core to obtain the alloyed active material layer. The vapor deposition method may be physical vapor deposition, chemical vapor deposition, and the like. For the types of alloyed active material materials, please refer to the above description.

In step S03, the step of preparing the outer shell layer on the surface of the alloyed active material layer includes: forming the outer shell layer on the surface of the alloyed active material layer by a method including but not limited to vapor deposition or sintering. The shell material of the shell layer is described above.

Finally, an embodiment of the present invention also provides a negative electrode, comprising a current collector and a negative electrode active layer covering the current collector, the negative electrode active layer comprising a negative electrode active material, a conductive agent and a binder, the negative electrode active material It 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 electrode active material in the negative electrode provided by the embodiment of the present invention is the unique composite material of the embodiment of the present invention or the unique composite material obtained by the preparation method of the composite material of the embodiment of the present invention, and the composite material can realize highly uniform dispersion of different active material phases. , thereby effectively alleviating stress concentration, and isolating the electrolyte, reducing side reactions, so the preparation of such a composite material with a unique structure into an electrode can significantly improve the cycle stability of lithium-ion batteries.

The negative electrode includes a current collector and a negative electrode active layer disposed on the surface of the current collector, and the current collector can be copper foil, aluminum foil, alloy foil, or the like. The negative electrode active layer includes a negative electrode active material, a conductive agent and a binder. The negative electrode active slurry containing the above-mentioned negative electrode active material, conductive agent and binder can be prepared, and then uniformly coated on the above-mentioned current collector, and uniform on the surface of the current collector through processes such as mixing, beating, coating, and rolling. coating, and drying to obtain a negative electrode sheet. Wherein, the binder can be carboxylated styrene-butadiene latex (SBR), sodium carboxymethyl cellulose (CMC), polytetrafluoroethylene (PTFE), polyacrylic acid (PAA), and the conductive agent can be carbon black, carbon nanotubes, SP, the solvent of the negative electrode active slurry can be deionized water or N-methylpyrrolidone.

The present invention has been tested for many times, and now some test results are used as a reference to further describe the invention, and the following is a detailed description in conjunction with specific embodiments.

Example 1

This embodiment provides a composite material: natural graphite is used as the carbon active material core, aluminum is used as the alloyed active material layer, and carbon material is used as the outer shell layer, wherein the D50 of natural graphite is 12 μm, and the alloyed active material layer is The thickness is 1 μm, the thickness of the outer shell is 100 nm, and the mass percentage of aluminum is 40%; the composite material is used as a negative electrode active material to prepare a negative electrode, and the specific preparation process is as follows:

(1) Using natural graphite particles as the base material and pure aluminum as the sputtering target, using magnetron sputtering technology to deposit aluminum active material on the surface of the graphite particles to obtain an alloyed active material layer, and the thickness of the control film layer is about 3 μm .

(2) Using sucrose solution as the precursor, using high temperature carbonization technology to coat the carbon layer on the surface of the graphite particles deposited with the aluminum active material alloyed active material layer prepared above is the outer shell layer. By controlling the concentration of the precursor solution and Carbonization treatment time, the thickness of the outer shell layer is controlled to be 100 nm, and the obtained natural graphite/silicon/carbon composite material is the negative electrode active material.

(3) A conductive agent and a binder are added to the negative electrode material obtained in step (2), and the mass ratio is negative electrode material: conductive agent: binder=8:1:1, wherein the conductive agent is conductive carbon black, adhesive The binder is PVDF, and after mixing evenly, N-methylpyrrolidone (NMP) solvent is added to fully stir to obtain a slurry, and then the slurry is uniformly coated on the surface of the copper foil, and then placed in a vacuum oven for drying and baking. The temperature was 80°C and the baking time was 48h to obtain a negative electrode.

The composite electrode is prepared by mixing natural graphite and aluminum powder particles by a traditional mechanical mixing process, wherein the mass percentage of aluminum active material is consistent with the three-layer structure design of the above-mentioned Example 1, and is controlled to 40%. The mixing uniformity and electrochemical performance of the traditional composite negative electrode and the negative electrode with a three-layer structure design in this example are compared: the scanning electron micrographs of the two negative electrodes are shown in Figure 2, in which the traditional composite negative electrode is dispersed Inhomogeneity, the phenomenon of agglomeration of aluminum powder particles appears (as shown in Figure 2a), while this example has a negative electrode with a three-layer structure design, and the two phases of natural graphite and aluminum show highly uniform dispersion characteristics (as shown in Figure 2b). ).

The lithium metal sheet was used as the counter electrode, and the half-cell was assembled with EC:DEC (volume ratio 1:1) as the electrolyte, and the electrochemical performance was tested. The test results are shown in Figure 3. This embodiment has a three-layer structure designed The negative electrode made of the negative electrode active material was cycled for 2000 cycles at a rate of 0.2C, and the capacity retention rate reached 97%, while the negative electrode using the traditional process was cycled for 500 cycles at the same rate, and the capacity retention rate was lower than 80%.

Anodes based on different carbon-based active materials

Example 2-7

The difference between Examples 2-7 and Example 1 is that different carbon-based active materials are used, and others are the same. The carbon-based active materials used are respectively: artificial graphite, soft carbon, hard carbon, MCMB, coke, and graphene. , the half-cell electrochemical performance test was carried out on the negative electrodes of Examples 2-7 under the condition of 0.2C rate, and compared with Example 1. The test results are shown in Table 1 below.

Table 1

It can be seen from Table 1 that the anodes prepared with different carbon active materials have good cycle stability and capacity retention rate, and the anode prepared by MCMB has the highest capacity retention rate.

Anodes based on alloyed active material layers with different thicknesses

The difference between Examples 8-16 and Example 1 is that the thickness of the aluminum active material as the alloying active material layer is different, and the others are the same. The thicknesses of the aluminum active material as the alloying active material layer are: 50nm, 200nm, 500nm, 700nm, 2μm, 3μm, 3μm, 5μm, 6μm, half-cell electrochemical performance test was performed on the negative electrodes of Examples 8-16, the rate condition was 0.2C, and compared with Example 1, the test results are shown in Table 2 below.

Table 2

It can be seen from Table 2 that the alloyed active material layer is 50 nm-2 μm, and the cycle stability is better.

Anodes based on different alloyed active materials

The difference between Examples 17-30 and Example 1 is that the alloyed active material materials are different, and the others are the same. Alloying active material materials are silicon, germanium, tin, lead, aluminum, antimony, bismuth, zinc, aluminum-copper alloy, copper-tin alloy, aluminum-tin alloy, aluminum-silicon alloy, aluminum-magnesium alloy, tin -Nickel alloy, tin-cobalt-nickel alloy, tin-nickel-carbon alloy, half-cell electrochemical performance test is carried out on the negative electrode of Example 17-30, the test rate condition is 0.2C, and compared with Example 1, the test The results are shown in Table 3 below.

table 3

It can be seen from Table 3 that the anodes prepared from different alloyed active materials have good cycle stability and capacity retention.

Anodes based on different shell layers

The difference between Examples 31-36 and Example 1 is that different shell layers are used, and others are the same. The shell layer materials used are: ZrO ₂ , TiN, TiAlN, LiPON, LLZTO, LAGP, Li ₃ PO ₄ -P ₂ S ₅ , Li ₂ SP ₂ S ₅ , the preparation technology of the outer shell layer is prepared by vapor deposition technology, and the half-cell electrochemical performance test is carried out on the negative electrodes of Examples 31-36 under the condition of 0.2C rate, and the same as that of Example 1. For comparison, the test results are shown in Table 4 below.

Table 4

It can be seen from Table 4 that the anodes prepared with different shell layers have good cycle stability and capacity retention.

Full cell based on anode active material with three-layer structure

Various types of negative electrodes prepared in the embodiments of the present invention are used to construct a full battery, wherein the positive electrode active materials are: lithium iron phosphate, lithium cobalt oxide, and ternary positive electrodes (111, 532, 622, 811). The specific preparation steps are as follows:

(1) Preparation of a negative electrode with a composite material with a three-layer structure: refer to the above-mentioned Examples 1-38 for the specific steps.

(2) Electrolyte configuration: the specific steps are the same as those in Embodiment 1 of the present invention.

(3) Positive electrode preparation: The positive electrode active material, conductive carbon black and polyvinylidene fluoride (PVDF) are mixed uniformly according to the mass ratio of 8:1:1, and then N-methylpyrrolidone (NMP) solvent is added for thorough stirring to obtain Then, the slurry was uniformly coated on the surface of the carbon-coated aluminum foil, and then placed in a vacuum oven for drying treatment, the baking temperature was 80°C, and the baking time was 48h.

(4) Full battery assembly.

The cycle and rate performance tests were performed on the full battery based on the negative electrode with the three-layer structure composite material prepared in this example, and the test results are shown in Table 5.

table 5

It can be seen from the above Table 5 that the full battery based on the negative active material having the three-layer structure in the embodiment of the present invention has good cycle stability and capacity retention rate.

The above descriptions are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements and improvements made within the spirit and principles of the present invention shall be included in the protection of the present invention. within the range.

Claims (10)

1. A composite material, characterized in that it comprises a carbon-based active material core and an alloyed active material layer and an outer shell layer coated on the surface of the carbon-based active material core, wherein the alloyed active material layer is located at the between the carbon-based active material core and the outer shell layer. 2 . The composite material according to claim 1 , wherein the carbon-based active material of the carbon-based active material core comprises at least one of a graphite-based active material and a non-graphite-based active material. 3 . 3. The composite material according to claim 2, wherein the graphite-based active material comprises at least one of natural graphite and artificial graphite; and/or, The non-graphite active material includes at least one of soft carbon, hard carbon, coke, mesophase carbon microbeads, carbon nanotubes, graphene and activated carbon. 4. The composite material according to claim 1, wherein the alloyed active material of the alloyed active material layer comprises aluminum, silicon, germanium, tin, lead, antimony, bismuth, zinc, aluminum-copper At least one of alloys, copper-tin alloys, aluminum-tin alloys, aluminum-silicon alloys, aluminum-magnesium alloys, tin-nickel alloys, and tin-cobalt-nickel alloys. 5. The composite material according to claim 1, wherein the shell material of the shell layer comprises carbon, zirconium dioxide, titanium nitride, aluminum titanium nitride, lithium phosphorus oxynitride, tantalum doped lithium lanthanum zirconium At least one of oxygen, lithium aluminum germanium phosphorus, lithium phosphate-phosphorus pentasulfide, and lithium sulfide-phosphorus pentasulfide; or, The outer shell layer is at least one of a carbon-based material coating layer, an oxide coating layer, a nitride coating layer and a solid electrolyte coating layer. 6. The composite material according to any one of claims 1-5, wherein the particle size of the carbon-based active material core is microscale or nanoscale; and/or, The thickness of the alloyed active material layer is 50nm-10μm; and/or, The thickness of the outer shell layer is 10nm-200nm. 7. the preparation method of composite material as described in any one of claim 1-6, is characterized in that, comprises the steps: Provide carbon-based active material core; preparing the alloyed active material layer on the surface of the carbon-based active material core; The outer shell layer is prepared on the surface of the alloyed active material layer. 8. The method for preparing a composite material according to claim 7, wherein the step of preparing the alloyed active material layer on the surface of the carbon-based active material core comprises: adopting vapor deposition, electroplating, chemical Any one of plating method, hydrothermal synthesis method, microwave synthesis method, electrophoretic deposition method and ball milling method, and the alloyed active material is coated on the surface of the carbon-based active material core to obtain the alloyed active material Floor. 9 . The method for preparing a composite material according to claim 7 , wherein the step of preparing the outer shell layer on the surface of the alloyed active material layer comprises: adopting a vapor deposition method or a sintering method on the alloyed active material layer. 10 . The outer shell layer is formed on the surface of the active material-like layer. 10. A negative electrode comprising a current collector and a negative electrode active layer covered on the current collector, the negative electrode active layer comprising a negative electrode active material, a conductive agent and a binder, wherein the negative electrode active material is the right active material. The composite material according to any one of claims 1-6 or the composite material obtained by the preparation method for the composite material according to any one of claims 7-9.

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