CN102420323B - Electrode composite material of lithium secondary battery and preparation method thereof - Google Patents

Abstract

The embodiment of the invention discloses an electrode composite material for a lithium secondary battery and a preparation method thereof. The electrode composite material includes: an electrode active material for a lithium secondary battery, graphene and a conductive material. Since graphene has better electronic conductivity, the electronic conductivity of the electrode composite material is improved. In addition, the electrode composite material provided by the present invention also includes a conductive material with higher conductivity, thereby further improving the conductivity of the electrode composite material. The electrode composite material of the lithium secondary battery provided by the invention adopts the composite form of the electrode active material of the lithium secondary battery, graphene and conductive material, and has good conductivity. Experimental results prove that the electronic conductivity of the electrode composite material provided by the invention can be as high as 0.87S/cm, and the ion diffusion coefficient can be as high as 8.4×10 ^-8 cm ² /S.

Description

Electrode composite material for lithium secondary battery and preparation method thereof

technical field

The invention relates to the technical field of energy storage materials, and more specifically, relates to an electrode composite material for a lithium secondary battery and a preparation method thereof.

Background technique

In recent years, with the increasing depletion of resources and the emergence of issues such as global warming, green and low-carbon lifestyles have been advocated. Among them, the development of electric vehicles and hybrid electric vehicles to partially replace internal combustion engine vehicles that consume fossil fuels is one of the main methods to solve the energy crisis and environmental degradation. Driving power is a key component that affects the popularization and use of electric vehicles. Today, widely used driving power includes lead-acid batteries, nickel metal hydride/nickel cadmium, and lithium secondary batteries. Among various driving power sources, lithium secondary batteries have been extensively studied due to their advantages such as high energy density, good cycle performance, low self-discharge rate, long service life and low environmental burden.

Electrode materials for lithium secondary batteries include positive electrode materials and negative electrode materials. The negative electrode materials of lithium secondary batteries include graphite, simple metals, alloys, semimetals, metal oxides, metal nitrides, and metal sulfides. Graphite is currently the most common negative electrode material in lithium secondary batteries; metals and their alloys, such as Li metal and its alloys, Ni-based materials, and Zn-based materials, are the earliest negative electrode materials used in lithium secondary batteries; semi-metals Compared with graphite, the specific capacity of the material has been greatly improved, which has important strategic significance for improving the specific energy of the secondary battery; metal oxides, metal nitrides, and metal sulfides can be expressed as M _m X _n , where X is O , S, or N, M selected from Li, Na, K, Mg, Ca, AL, Ti, Sc, Ge, V, Cr, Zr, Co, Ni, Zn, Cu, Mn, Hf, Nb, Ta, Mo , W, Ru, Ag, Sn, Si, Pb, In, Y, P, one or more of them, 0<m<10, 0<n<10, and choose among M, X, m, n combination to ensure that M _m X _n is electrically neutral. However, the conductivity of the above negative electrode materials is not ideal.

Cathode materials for lithium secondary batteries include lithium-containing metal oxides and polyanion materials. Commonly used lithium-containing metal oxides include lithium cobaltate, lithium manganate, lithium-rich layered ^nickel The electrical conductivity of lithium manganese oxide is 10 ^-4 S/cm, and the electrical conductivity of lithium nickelate is 10 ^-3 S/cm. However, lithium-containing metal oxides are prone to safety problems during high-current charging and discharging. At this time, some materials with high conductivity but electrochemical inertness need to be used for compounding to improve performance.

The general formula of the polyanion material is A _a M'_b' M _b (X _c Y _d ) _e Z _f , wherein, A is Li, and 0<a<8; M is one or more metals, wherein at least A metal that can be oxidized to a higher valence state, including at least one of iron, aluminum, titanium, cobalt, boron, chromium, nickel, magnesium, zirconium, gallium, vanadium, manganese and zinc, and 0<b≤5;M' can occupy the position of A or M or both positions at the same time, including 1 to 4 valent metal ions, such as alkali metal ions, Ti, Sc, Ge, V, Cr, Zr, Co, Ni, Zn, Cu, One or more of Mn, Hf, Nb, Ta, Mo, W, Ru, Ag, Sn and Pb, 0≤b'≤5; in X _c Y _d , X is selected from P, As, Sb, One or more of Si, Ge, V, S, Y selected from one or more of S, O, N, 0<c≤5, 0<d≤10; Z is optional, including OH , one or more of halogen, N, S, 0<f≤10; among them, for A, M, M', X, Y, Z, a, b, b', c, d, e, f Selection is made to keep the compound electrically neutral. Since the polyanion material contains polyanions, it has strong structural stability and high safety performance, and is suitable as an electrode material for a power battery. But on the other hand, the strong chemical bonding between polyanions and transition metal ions and lithium metal ions leads to poor electrical conductivity of the material, making it difficult to charge and discharge large currents. materials and/or ionically conductive materials to improve the rate capability of the material.

In the Chinese patent literature with the publication number CN101453020A, M. Almon of the Canadian Hydro-Quebec Company proposed to use pyrolytic carbon to coat the polyanion material so that the electrical conductivity of the material can reach 10 ^-8 S/cm; in the patent CN1652999A, Wei Jeremy Barker of Lens Technology Co., Ltd. proposed to use carbothermal reduction to prepare polyanion materials, which improved the conductivity of polyanion materials to a certain extent. However, the conductivity of the polyanion materials was not ideal because of When preparing polyanion materials, in order to avoid phase transition of polyanion materials, the heat treatment temperature used is usually 600-750°C, but when the heat treatment temperature is below 750°C, the Sp that determines the electrical conductivity of pyrolytic carbon materials The degree of graphitization of ² hybrids is usually lower. In the patent CN101345099A, Liao Benjie of Taiwan Likai Power Technology Co., Ltd. proposed to use the eutectic of oxides to improve the conductivity of polyanion materials, but the conductivity of a single oxide material is still low.

Graphene material is a kind of hexagonal carbon material with a single layer or a few layers of sp ² hybridization. In the multilayer structure, the layers are combined in the form of π bonds. Since the electrons of this type are Dirac electrons near the Fermi energy, the effective mass It is zero, so the conductivity reaches 10 ⁶ S/cm, which is the material with the highest conductivity found by human beings. In the Chinese patent documents with application number 200910155316.7 and application number 201010226062.6, Liu Zhaoping from the Ningbo Institute of Materials Technology and Engineering, Chinese Academy of Sciences proposed to use graphene and polyanion materials to composite, which improved the electrical conductivity of the composite material.

The present inventor considers to provide an electrode composite material for a lithium secondary battery, which can further improve the conductivity of the lithium secondary battery material compared with the above-mentioned positive electrode material and negative electrode material for the lithium secondary battery.

Contents of the invention

In view of this, the technical problem to be solved by the present invention is to provide an electrode composite material for a lithium secondary battery, and the composite material has relatively high electrical conductivity.

The invention provides an electrode composite material for a lithium secondary battery, comprising:

Lithium secondary battery electrode active materials, graphene and conductive materials,

The conductive material is graphite, expanded graphite, carbon nanotube, carbon fiber, activated carbon, amorphous carbon, conductive carbon black, conductive carbon material produced by pyrolysis of organic matter, Ag, Cu, Pt, Au, transition metal, semi-metal , M _m X _n , conductive polymers with conjugated structures, and ion-conductive materials with conductivity greater than 10 ^-10 S/cm,

Among them, X is O, S or N, M is Li, Na, K, Mg, Ca, AL, Ti, Sc, Ge, V, Cr, Zr, Co, Ni, Zn, Cu, Mn, Hf, Nb, One or more of Ta, Mo, W, Ru, Ag, Sn, Si, Pb, In, Y, P, 0<m<10, 0<n<10.

Preferably, the ion-conducting material is:

Lithium-containing VI main group compounds, lithium-containing VII main group compounds, LiTi ₂ (PO ₄ ) ₃ , LiGe ₂ (PO ₄ ) ₃ , Li _p M _r X _q , derivatives of lithium-containing VI main group compounds, One or more of lithium-containing VII main group compound derivatives, LiTi ₂ (PO ₄ ) ₃ derivatives, LiGe ₂ (PO ₄ ) ₃ derivatives and _Lip M _r X _q derivatives, M is one or more of P, C, and S, X is O and/or S, and p, q, and r are positive numbers.

Preferably, the conductive polymer with conjugated structure is polyaniline, polyacetylene, polypyrrole, polythiophene or polyphenylene sulfide.

Preferably, the mass ratio of the lithium secondary battery electrode active material, graphene and conductive material is 80-99:0.01-10:0.01-10.

Preferably, the electrode active material of the lithium secondary battery is a positive electrode active material and/or a negative electrode active material, the positive electrode active material includes a polyanion material and a lithium-containing metal oxide, and the negative electrode active material is The active material whose potential difference with respect to lithium metal is less than 2V.

Preferably, the negative electrode active material is one or more of graphite, simple metal, alloy, semi-metal, metal oxide, metal nitride and metal sulfide.

Preferably, the polyanion material is lithium iron phosphate, the metal oxide is manganese-based metal oxide, and the negative electrode material is silicon, tin, silicon oxide and/or tin oxide.

Preferably, the graphene is a single layer or the number of layers is between 1 and 20 layers, the carbon atoms in the layer form a hexagonal honeycomb lattice with ^sp2 hybrid orbitals, and the carbon atoms in the layer are bonded by π bonds flaky carbon material; graphene material and/or intercalated graphene containing one or more of fluorine, nitrogen, oxygen, carbonyl, carboxyl and hydroxyl.

Preferably, the lithium secondary battery electrode active material, graphene and conductive material coexist in the form of mixing, composite, eutectic and/or physical contact.

The present invention also provides a preparation method of an electrode composite material for a lithium secondary battery, comprising:

The lithium secondary battery electrode active material or its precursor, graphene, conductive material or its precursor are mixed, and then heat-treated at 200-900 ° C in a non-oxidizing atmosphere to obtain an electrode composite material for a lithium secondary battery,

The conductive material is graphite, expanded graphite, carbon nanotube, carbon fiber, activated carbon, amorphous carbon, conductive carbon black, conductive carbon material produced by pyrolysis of organic matter, Ag, Cu, Pt, Au, transition metal, semi-metal , M _m X _n , conductive polymers with conjugated structures, and ion-conductive materials with conductivity greater than 10 ^-10 S/cm,

Among them, X is O, S or N, M is Li, Na, K, Mg, Ca, AL, Ti, Sc, Ge, V, Cr, Zr, Co, Ni, Zn, Cu, Mn, Hf, Nb, One or more of Ta, Mo, W, Ru, Ag, Sn, Si, Pb, In, Y, P, 0<m<10, 0<n<10.

Preferably, the ion-conducting material is:

Lithium-containing VI main group compounds, lithium-containing VII main group compounds, LiTi ₂ (PO ₄ ) ₃ , LiGe ₂ (PO ₄ ) ₃ , Li _p M _r X _q , derivatives of lithium-containing VI main group compounds, One or more of lithium-containing VII main group compound derivatives, LiTi ₂ (PO ₄ ) ₃ derivatives, LiGe ₂ (PO ₄ ) ₃ derivatives and _Lip M _r X _q derivatives, M is one or more of P, C, and S, X is O and/or S, and p, q, and r are positive numbers.

Preferably, the mass ratio of the lithium secondary battery electrode active material, graphene and conductive material is 80-99:0.01-10:0.01:10.

Preferably, the electrode active material of the lithium secondary battery includes a positive electrode active material and/or a negative electrode active material, the positive electrode active material includes a polyanion material and a lithium-containing metal oxide, and the negative electrode material has a median charge and discharge potential An active material with a potential difference of less than 2V relative to metallic lithium.

Preferably, the graphene is a single layer or the number of layers is between 1 and 20 layers, and the carbon atoms in the layer form a hexagonal honeycomb lattice with ^sp2 hybrid orbitals, and the carbon atoms between the layers are bonded by π bonds flaky carbon material; graphene material and/or intercalated graphene containing one or more of fluorine, nitrogen, oxygen, carbonyl, carboxyl and hydroxyl.

Preferably, the heat treatment time is 0.2-50 hours.

It can be seen from the above technical solutions that the present invention provides an electrode composite material for a lithium secondary battery and a preparation method thereof. The electrode composite material includes: an electrode active material for a lithium secondary battery, graphene and a conductive material. Graphene and conductive material are distributed on the surface of the active material and between the particles of the active material to form the electrode composite material of the lithium secondary battery. Since graphene has better electronic conductivity, the electronic conductivity of the electrode composite material is improved. In addition, the electrode composite material provided by the present invention also includes a conductive material with higher conductivity, thereby further improving the conductivity of the electrode composite material. Therefore, the electrode composite material of the lithium secondary battery provided by the present invention adopts the composite form of the electrode active material of the lithium secondary battery, graphene and conductive material, and has good conductivity. Experimental results prove that the electronic conductivity of the electrode composite material provided by the invention can be as high as 0.87S/cm, and the ion diffusion coefficient can be as high as 8.4×10 ^-8 cm ² /S.

Description of drawings

In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings that need to be used in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only These are some embodiments of the present invention. Those skilled in the art can also obtain other drawings based on these drawings without creative work.

Figure 1 is the XRD patterns of LiFePO ₄ , LiFePO ₄ /graphene/C and LiFe _0.99 Mg _0.01 PO ₄ /graphene/C/Li ₃ PO ₄ prepared in Example 2 of the present invention;

Fig. 2 is the SEM photo of LiFePO ₄ /graphene/C prepared in Example 2 of the present invention;

Fig. 3 is the SEM photo of LiFePO ₄ /graphene/C prepared in Example 2 of the present invention;

Fig. 4 is the TEM photo of LiFe _0.99 Mg _0.01 PO ₄ /graphene/C/Li ₃ PO ₄ prepared in the embodiment of the present invention;

Fig. 5 is LiFePO ₄ and the LiFePO ₄ /graphene/C IV characteristic figure prepared by the embodiment 2 of the present invention;

Fig. 6 is LiFePO ₄ , LiFePO ₄ /graphene, LiFePO ₄ /graphene/C prepared in Example 2 of the present invention and LiFe _0.99 Mg _0.01 PO ₄ /graphene/C/Li ₃ PO ₄ prepared in Example 2 of the present invention Charge and discharge performance curve;

Figure 7 is the XRD pattern of LiMn ₂ O ₄ and LiMn ₂ O ₄ /graphene;

Fig. 8 is the SEM photo of LiMn ₂ O ₄ and LiAl _0.02 Mn _1.98 O ₄ /graphene/Li ₃ PO ₄ prepared by the embodiment of the present invention;

Fig. 9 is the SEM photo of LiMn ₂ O ₄ and LiAl _0.02 Mn _1.98 O ₄ /graphene/Li ₃ PO ₄ prepared by the embodiment of the present invention;

Figure 10 is the charge and discharge curves of LiMn ₂ O ₄ and LiAl _0.02 Mn _1.98 O ₄ /graphene/Li ₃ PO ₄ prepared by the embodiment of the present invention;

Fig. 11 is the SEM photo of Si/graphene/C prepared by the embodiment of the present invention 20;

Fig. 12 is the SEM photo of the Si/graphene/C prepared by the embodiment of the present invention 20;

Fig. 13 is the SEM photo of the Si/graphene/C prepared by the embodiment of the present invention 20;

Fig. 14 is the SEM photo of Si/graphene/C prepared by the embodiment of the present invention 20;

Figure 15 is the charge and discharge curves of Si/C and Si/graphene/C prepared in Example 20 of the present invention.

Detailed ways

The following clearly and completely describes the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only some of the embodiments of the present invention, but not all of them. Based on the embodiments of the present invention, all other embodiments obtained by persons of ordinary skill in the art without creative efforts fall within the protection scope of the present invention.

The embodiment of the present invention discloses an electrode composite material for a lithium secondary battery, comprising:

Lithium secondary battery electrode active materials, graphene and conductive materials,

The conductive material is graphite, expanded graphite, carbon nanotube, carbon fiber, activated carbon, amorphous carbon, conductive carbon black, conductive carbon material, Ag, Cu, Pt, Au, Ag oxide, Cu oxide, Pt Oxides of Au, oxides of Au, sulfides of Ag, sulfides of Cu, sulfides of Pt, sulfides of Au, nitrides of Ag, nitrides of Cu, nitrides of Pt, nitrides of Au, organic One or more of conductive materials and ion-conductive materials with conductivity greater than 10 ^-8 S/cm.

The electrode active material of the lithium secondary battery preferably includes a positive electrode active material and/or a negative electrode active material, the positive electrode active material includes a polyanion material and a lithium-containing metal oxide, and the negative electrode active material preferably has a median charge and discharge potential An active material with a potential difference of less than 2V relative to metallic lithium.

In the present invention, the polyanion material is an electrochemically active material, the general formula is A _a M'_b' M _b (X _c Y _d ) _e Z _f , wherein, A is Li, and 0<a<8; M Preferably one or more metals, at least one of which can be oxidized to a higher valence state, including iron, aluminum, titanium, cobalt, boron, chromium, nickel, magnesium, zirconium, gallium, vanadium, manganese and zinc At least one of, 0<b≤5;M' can occupy the position of A or M or both positions, preferably including 1 to 4 valent metal ions, such as alkali metal ions, Ti, Sc, Ge, V, One or more of Cr, Zr, Co, Ni, Zn, Cu, Mn, Hf, Nb, Ta, Mo, W, Ru, Ag, Sn, Pb, 0≤b'≤5; X _c Y _d , wherein X is selected from one or more of P, As, Sb, Si, Ge, V, S, Y is selected from one or more of S, O, N, 0<c≤5,0 <d≤10; Z is optional, including one or more of OH, halogen, N, S, 0<f≤10; among them, for A, M, M', X, Y, Z, a, b, b', c, d, e, f are selected to keep the compound electrically neutral.

The above lithium-containing metal oxides have the general formula A _a M _b M′ _c O _d Z _f ,

Where a, b, c, d are not zero, and are values between 1 and 10, A preferably includes one or more of alkali metals such as Li, Na, K, Mg, Ca, Al, etc.; M preferably includes transition Metal, more preferably one or more of manganese, iron, cobalt, nickel, vanadium, molybdenum, titanium, zirconium; M' can occupy the A or M position or both positions, preferably 1 to 4 valence Metal ions, more preferably alkali metal ions, Ti, Sc, Ge, V, Cr, Zr, Co, Ni, Zn, Cu, Mn, Hf, Nb, Ta, Mo, W, Ru, Ag, Sn, Pb, etc. One or more of Z, 0≤b'≤5; Z is preferably OH, one or more of halogen, N, and S, and the metal oxide of lithium is electrically neutral.

The metal oxide of lithium described in the present invention is more preferably lithiated molybdenum oxide, lithiated vanadium oxide, lithiated manganese oxide, lithiated cobalt oxide, lithiated titanium oxide, lithiated Nickel oxide and its doped and modified derivatives.

The above-mentioned negative electrode active material is preferably an active material with a median charge-discharge potential relative to metal lithium with a potential difference less than 2V, preferably one of graphite, metal element, alloy, semimetal, metal oxide, metal nitride and metal sulfide And several kinds, specifically including metal lithium, carbon materials, materials that can form alloys with lithium, metal oxides, metal sulfides, etc. The carbon material can be graphite, pyrolytic carbon, coke, activated carbon, carbon fiber, high-temperature sintered organic polymer compound, and the like. The material capable of forming an alloy with lithium can be a metal element, such as Mg, B, Al, Ga, In, Si, Sn, Pb, Sb, Bi, Cd, Ag, Zn, Hf, Zr, Y, etc., containing Alloys of Si and Sn, such as SiB ₄ , SiB ₆ , Mg ₂ Si, Mg ₂ Sn, Ni ₂ Si, TiSi 2 , MoSi ₂ , CoSi ₂ , NiSi ₂ , CaSi ₂ , CrSi _{2 ,} Cu ₅ Si, FeSi ₂ , MnSi ₂ , NbSi ₂ , TaSi ₂ , VSi ₂ , WSi ₂ and ZnSi ₂ ; and other active materials such as SiC, Si ₃ N ₄ , Si ₂ N ₂ O, Ge ₂ N ₂ O, SiO _x (0<x ≤2), SnO _x (0<x≤2), LiSiO and LiSnO, etc. The metal oxide and metal sulfide can be expressed as M _m X _n (X=O, S, or N), including M _m X _n (X=O, S, or N), wherein M is selected from Li, Na, K, Mg, Ca, AL, Ti, Sc, Ge, V, Cr, Zr, Co, Ni, Zn, Cu, Mn, Hf, Nb, Ta, Mo, W, Ru, Ag, Sn, One or more of Si, Pb, In, Y, P, 0<m<10, 0<n<10, and select and combine M, X, m, n to ensure that M _m X _n is electrically Neutral, especially including SnO, SnO ₂ , SiO ₂ -based materials, composites of oxides and metals, such as Si/SiO ₂ composites, Sn/SnO, Sn/SnO ₂ .

Graphene is a kind of hexagonal carbon material with a single layer or a few layers of sp ² hybridization. In the multilayer structure, the interlayers are combined in the form of π bonds. Since the electrons of this type are Dirac electrons near the Fermi energy, the effective mass is Zero, so the conductivity reaches 10 ⁶ S/cm, which is the material with the highest conductivity found by human beings. The graphene is a single layer or between 1 and 20 layers, in which carbon atoms form a hexagonal honeycomb lattice with Sp ² hybrid orbitals in the layer, and a flaky carbon material bonded by π bonds between layers. In addition, the present invention also includes graphene materials and intercalated graphene containing one or more of fluorine, nitrogen, oxygen, carbonyl, carboxyl, and hydroxyl groups, as well as graphene materials containing inevitable defects.

The conductive material in the present invention is preferably an electron-conductive or ion-conductive material other than graphene, and a material with good electronic conductivity and ion conductivity. The electronically conductive material is specifically graphite, expanded graphite, carbon nanotubes, carbon fibers, activated carbon, amorphous carbon, conductive carbon black, conductive carbon materials produced by pyrolysis of organic matter, Ag, Cu, Pt, Au, transition metals, One or more of semi-metals, M _m X _n , conductive polymers with conjugated structures, and ion-conductive materials with conductivity greater than 10 ^-10 S/cm, where X is O, S or N, and M is Li, Na, K, Mg, Ca, AL, Ti, Sc, Ge, V, Cr, Zr, Co, Ni, Zn, Cu, Mn, Hf, Nb, Ta, Mo, W, Ru, Ag, Sn, One or more of Si, Pb, In, Y, P, 0<m<10, 0<n<10, and select and combine M, X, m, n to ensure that M _m X _n is electrically neutral. The semimetal is preferably Si or Ge, and the conductive polymer with a conjugated structure is preferably one or more of polyaniline, polyacetylene, polypyrrole, polythiophene and polyphenylene sulfide.

The ion-conductive material is lithium-containing VI main group compound, lithium-containing VII main group compound, LiTi ₂ (PO ₄ ) ₃ , LiGe ₂ (PO ₄ ) ₃ , Li _p M _r X _q , lithium-containing VI Among the derivatives of main group compounds, derivatives of lithium-containing VII main group compounds, derivatives of LiTi ₂ (PO ₄ ) ₃ , derivatives of LiGe ₂ (PO ₄ ) ₃ and derivatives of _Lip M _r X _q One or more of them, M is one or more of P, C, and S, X is O and/or S, and p, q, and r are positive numbers.

The mass ratio of the lithium secondary battery electrode active material, graphene and conductive material is preferably 80-99: 0.01-10: 0.01-10, more preferably 85-99: 0.1-5: 0.1-10, most preferably 90-99: 1-3: 1-5.

In the present invention, the graphene and the conductive material are distributed on the surface of the active material and among the particles of the active material through one or more contact modes of uniform mixing, compounding, encapsulation, eutectic, and physical contact. Since graphene has better electronic conductivity, the electronic conductivity of the electrode composite material is improved. In addition, the electrode composite material provided by the present invention also includes a conductive material with higher conductivity, thereby further improving the conductivity of the electrode composite material.

The present invention also provides a preparation method of an electrode composite material for a lithium secondary battery, comprising:

The lithium secondary battery electrode active material or its precursor, graphene, conductive material or its precursor are mixed, and then heat-treated at 200-900 ° C in a non-oxidizing atmosphere to obtain an electrode composite material for a lithium secondary battery,

The conductive material is graphite, expanded graphite, carbon nanotube, carbon fiber, activated carbon, amorphous carbon, conductive carbon black, conductive carbon material produced by pyrolysis of organic matter, Ag, Cu, Pt, Au, transition metal, semi-metal , M _m X _n , conductive polymers with conjugated structures, and ion-conductive materials with conductivity greater than 10 ^-10 S/cm,

Among them, X is O, S or N, M is Li, Na, K, Mg, Ca, AL, Ti, Sc, Ge, V, Cr, Zr, Co, Ni, Zn, Cu, Mn, Hf, Nb, One or more of Ta, Mo, W, Ru, Ag, Sn, Si, Pb, In, Y, P, 0<m<10, 0<n<10.

The lithium secondary battery electrode active material precursor compound and the conductive material precursor compound described in the present invention are precursor compounds known in the art.

The electrode active material of the lithium secondary battery includes a positive electrode active material and/or a negative electrode active material, the positive electrode active material includes a polyanion material and a lithium-containing metal oxide, and the negative electrode material is a metal lithium with a median charge and discharge potential Active material with a potential difference of less than 2V.

The ion-conductive material is lithium-containing VI main group compound, lithium-containing VII main group compound, LiTi ₂ (PO ₄ ) ₃ , LiGe ₂ (PO ₄ ) ₃ , Li _p M _r X _q , lithium-containing VI Among the derivatives of main group compounds, derivatives of lithium-containing VII main group compounds, derivatives of LiTi ₂ (PO ₄ ) ₃ , derivatives of LiGe ₂ (PO ₄ ) ₃ and derivatives of _Lip M _r X _q One or more of them, M is one or more of P, C, and S, X is O and/or S, and p, q, and r are positive numbers.

The mass ratio of the lithium secondary battery electrode active material, graphene and conductive material is preferably 80-99: 0.01-10: 0.01-10, more preferably 85-99: 0.1-5: 0.1-10, most preferably 90-99: 1-3: 1-5.

The non-oxygen atmosphere is preferably one or more of argon, nitrogen, hydrogen, carbon monoxide and carbon dioxide. The heat treatment temperature is preferably 300-800°C, more preferably 400-700°C. The heat treatment time is preferably 0.2-50 hours, more preferably 5-40 hours, more preferably 10-30 hours.

The mixing method described in the present invention includes simple physical mixing, such as ball milling, grinding, ultrafine grinding, stirring and mixing, etc., and preferably also includes molecular level mixing, such as mixing after dissolution.

The preparation method of the electrode composite material of the lithium secondary battery provided by the present invention can control the shape of the electrode composite material of the prepared battery, for example, it is preferably prepared by spray drying, precipitation, co-precipitation, agglomeration and/or granulation. When spray drying is adopted, the shape of the electrode composite material of the prepared lithium secondary battery is a spherical aggregate with a size of 0.5-50 microns, and each aggregate is composed of smaller particles.

In the process of preparing the electrode composite material of the lithium secondary battery, it is preferably carried out in a reactor that promotes the balance of solid powder, for example, selected from the following reactors: fluidized bed, converter, pusher furnace, belt-driven converter, so The reactor is capable of controlling the composition and flow of the gas atmosphere.

The conductive material of the present invention is a carbon material, especially a carbon material uniformly distributed on the particle surface, preferably a carbon material produced in situ on the surface of the active material by pyrolysis of organic matter. Among them, the pyrolytic carbon material generated in situ can improve the conductivity of the surface of the active material particles, and graphene is used to improve the conductivity between the particles. Therefore, two conductive materials, graphene and pyrolytic carbon material, are used. Superior to any of the conductive materials.

In another embodiment, the conductive material of the present invention is an ion-conductive material with a conductivity greater than 10 ⁻¹⁰ S/cm. Since the ion-conductive material has the effect of improving the ion conductivity of the active material interface, and graphene is used to improve the conductivity between the particles, the lithium secondary battery electrode active material, graphene and ion-conductive material formed lithium The electrode composite material of the secondary battery has good electrical conductivity.

The lithium secondary battery electrode active materials and conductive materials described in the present invention are purchased from the market, or can be prepared by themselves. The preparation of electrode active materials and conductive materials can be carried out by methods well known to those skilled in the art.

The preparation method of the polyanion compound in the lithium secondary battery electrode active material of the present invention preferably adopts the following method:

(1) Select transition metal ion compound, lithium salt and polyanion salt raw material containing variable price, place in acetone dispersant after taking by stoichiometric ratio, make solid content reach 10%-70%;

(2) Mix in a high-energy ball mill for 1 to 20 hours until uniform, then dry;

(3) Put the mixture in (2) in an atmosphere sintering furnace, treat it at 200-800°C for 1h-48 hours under the protection of a non-oxidizing atmosphere, and then cool it to room temperature to obtain the required polyanion material;

(4) Test the electrochemical performance and conductivity of the material.

The lithium salt preferably includes one or more combinations of lithium hydroxide, lithium carbonate, lithium acetate, lithium nitrate, lithium sulfate, lithium chloride, lithium bromide, lithium fluoride, lithium nitride, lithium salts containing polyanions . The transition metal ion compound includes one or a combination of transition metal oxides, sulfates, phosphates, nitrates, oxalates, acetates, citrates, and metal salts containing polyanions. The polyanion salt preferably includes one or a combination of polyanion-containing acids, ammonium salts, esters, hydrocarbons, and polyanion-containing metal salts. Wherein the molar ratio of lithium, the metal ion M containing variable valence, and the polyanion is the content demarcated in the chemical formula, and the floating range is 80% to 120% of the stoichiometric ratio;

The dispersant used in the present invention can also be one or more of water, alcohols, ketones, ethers, acids, polymer solutions, etc., and the solvent quality is 0.3 to 10 times the sum of other reactant precursors, The solid content is 5-60%, preferably 20%-40%. Spray drying is carried out by means of direct heating drying or vacuum filtration. The above heat treatment time can be between 200-1000°C, the heating time is preferably 1-48 hours, the preferred temperature is 600-800°C, and the preferred heating time is 3-15 hours.

The preparation method of the metal oxide in the electrode active material of the lithium secondary battery described in the present invention, taking LiMn ₂ O ₄ as an example is as follows:

(1) choose manganese dioxide, Lithium Retard raw material, take by weighing by molar ratio Mn: Li is the ratio of 2: 1.05;

(2) Mix the mixture obtained in step (1) in a high-energy ball mill for 7 hours until uniform, add a dispersant during the grinding process, and dry;

(3) The product obtained in step (2) was heat-treated at 850° C. for 5 h and then cooled to room temperature to obtain the desired lithium manganate material, which was pure phase LiMn ₂ O ₄ .

Electrochemical tests show that the capacity of the material is 110mAh/g when charging and discharging at a current density of 20mA/g, and the conductivity of the material is 5.1X10 ^-4 S/cm.

When the lithium secondary battery electrode active material of the present invention is a negative electrode active material, taking silicon oxide/graphene/carbon material as an example, the preparation method is preferably:

Step (1) Fully mix silicon compounds, carbon-containing compounds and graphene in a ball mill, and add 30wt% grinding aid acetone at the same time, wherein graphene is 1% to 5% of the mass of the composition, and silicon oxide is the composition 50% to 90% of the mass, and the sum of the mass of the carbon material is 3% to 50% of the mass of the composition;

Step (2) The mixture obtained in step (1) is heat-treated in a vacuum furnace at 200° C. to 1000° C. for 1 to 20 hours under the protection of nitrogen atmosphere, so as to obtain the final product silicon oxide/graphene/carbon material composition.

The carbon material can improve the nanometerization degree of the electrode composite material of the lithium secondary battery, suppress the volume change in the electrochemical process, and improve the electrical conductivity. Graphene can further improve the electronic conductivity of silicon oxide, and has a better effect of "inhibiting volume change" than ordinary carbon materials. The use of graphene and pyrolytic carbon materials as a composite silicon anode material can increase the conductivity of the anode active material and suppress the volume change during charge and discharge, thereby achieving the effect of increasing the specific capacity and improving the cycle life. Therefore, the cost of the prepared electrode composite material of the lithium secondary battery is reduced.

Using the electrode composite material of the lithium secondary battery provided by the present invention as an electrode, a lithium secondary battery is prepared, and the battery will include a positive electrode, a negative electrode, an electrolyte and a diaphragm, at least one of which electrodes is selected from the lithium secondary battery provided by the present invention electrode composite materials.

The separator is preferably a porous polymer film, such as a microporous polypropylene film. The non-aqueous electrolytic solution is composed of non-aqueous solvent and electrolyte. The non-aqueous solvent (non-proton-donating solvent) is preferably dimethyl carbonate, dipropyl carbonate, propylene carbonate, ethylene carbonate, butylene carbonate, gamma butyrolactone, sulfolane, methyl sulfolane, 1,2 -Dimethoxyethane, 1,2-diethoxyethane, tetrahydrofuran, 2-methyltetrahydrofuran, methylpropionic acid, methylbutyric acid, acetonitrile, propionitrile, anisole, acetate, milk One or more mixtures of esters and propionates. The electrolyte is preferably lithium-containing salts such as LiCl, LiBr, LiPF ₆ , LiClO ₄ , LiAsF ₆ , LiBF ₄ , LiCH ₃ SO ₃ , LiCF ₃ SO ₃ , LiN(CF ₃ SO ₂ ) ₂ and LiB(C ₆ H ₅ ) ₄ etc.

The present invention preferably adopts the following method to test the electrochemical performance and conductivity of the electrode composite material of the lithium secondary battery prepared in the present invention.

Test electrochemical performance

The electrode composite material of the lithium secondary battery prepared by the present invention, polyvinylidene fluoride (PVDF), and conductive acetylene black are added to N-methylpyrrolidone in a mass ratio of 80:5:15, and after magnetic stirring is uniform, oven dry The positive electrode sheet was made and assembled into a 2032 button battery in a glove box, wherein the negative electrode was a lithium sheet, the separator was polypropylene, the electrolyte was 1M LiPF6, and the mass ratio of the electrolyte was EC:DMC:EMC=1:1:1.

The test temperature is 25°C, the voltage range is 2.0-4.2V, and the test equipment is ArbinBT2000, Autolab electrochemical workstation.

Determination of conductivity

The electrode composite material 1g of the lithium secondary battery prepared by the present invention is placed in a kind of cylindrical mold with a diameter of 1.3 centimeters, and is pressed between two stainless steel pistons with a press, and the pressure is 14MPa, and the sheet After taking it out, plate a silver electrode, and ensure that the resistance between any two points on the same electrode sheet after silver plating is less than 10 ^-2 ohms. The conductivity is measured by the AC composite impedance method known to those skilled in the art, and the conductivity is obtained from the resistance using the formula ρ=RS/L, where R is the measured resistance, S is the surface area of 1.33 cm ² , and L is the sheet thickness of. The ionic conductivity is also measured by the AC complex impedance test method, wherein the ion diffusion coefficient D=R ² T ² /2A ² n ⁴ F ⁴ C ² V ² , Z _real =Vω ^−1/2 .

In order to further illustrate the technical solution of the present invention, the preferred embodiments of the present invention are described below in conjunction with examples, but it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, rather than limiting the claims of the present invention.

The graphene powder that the present invention adopts can be purchased on the market.

Example 1

Preparation of LiFePO4/graphene/Li ₃ PO ₄

(1) take ferrous oxalate, lithium carbonate and ammonium dihydrogen phosphate as raw materials, place in acetone solution after taking by weighing the mol ratio of Fe: Li: P 1.15: 1: 1.05, and add 5wt% graphene, Make the solid content reach 20%;

(2) Mix the material obtained in step (1) in a high-energy ball mill for 20 hours until uniform, the ball mill rotating speed is 500r/min, and the mass ratio of the ball to the ground material is 2:1;

(3) The material obtained in step (2) is dried by spray drying, the air inlet temperature of the spray dryer is 220°C, and the air outlet temperature is 100°C;

(4) Place the mixture obtained in step (3) in a sintering furnace, treat it at 650° C. for 10 hours under the protection of nitrogen atmosphere, and then cool to room temperature to obtain the required LiFePO4/graphene/Li ₃ PO ₄ material, LiFePO4 , The mass ratio of graphene to Li ₃ PO ₄ is 90:5:5. The properties of the electrode composite material of the lithium secondary battery prepared in this embodiment are shown in Table 1.

Example 2

Preparation of LiFePO ₄ /graphene/C

LiFePO ₄ , graphene and phenolic resin are mixed, and then heat-treated at 400° C. under nitrogen protection to obtain an electrode composite material for a lithium secondary battery. The mass ratio of LiFePO ₄ /graphene/C is 97:1:2. The properties of the electrode composite material of the lithium secondary battery prepared in this embodiment are shown in Table 1.

Embodiment 3-10

Using the same preparation method as in Example 1, an electrode composite material for a lithium secondary battery was prepared. The raw materials and properties of the electrode composite material for a lithium secondary battery are shown in Table 1.

The properties of the lithium secondary battery electrode composite material, LiFePO ₄ , LiFePO ₄ /C electrode composite material, and LiFePO ₄ /graphene electrode composite material prepared in Examples 1-10 were measured respectively, and the results are shown in Table 1.

Preparation raw materials and properties of table 1 polyanion material/graphene/conductive material

In the drawings of the present invention, G represents graphene, C represents carbon, and LFP represents lithium iron phosphate. As shown in Figure 1, the XRD patterns of LiFePO ₄ , LiFePO ₄ /graphene/C and LiFe _0.99 Mg _0.01 PO ₄ /graphene/C/Li ₃ PO ₄ prepared in Example 2 are shown from top to bottom.

Fig. 2 and Fig. 3 are SEM photos of LiFePO ₄ /graphene/C prepared in Example 2.

FIG. 4 is a TEM photo of LiFe _0.99 Mg _0.01 PO ₄ /graphene/C/Li ₃ PO ₄ in Table 1.

Fig. 5 is the IV characteristic diagram of LiFePO ₄ and LiFePO ₄ /graphene/C prepared in Example 2.

6 is the charge and discharge performance curves of LiFePO ₄ , LiFePO ₄ /graphene, LiFePO ₄ /graphene/C prepared in Example 2, and LiFe _0.99 Mg _0.01 PO ₄ /graphene/C/Li ₃ PO ₄ .

From the above results, it can be concluded that the electrode composite material of the lithium secondary battery prepared in the above examples has good electrical conductivity. ,

Example 11

Preparation of LiMn ₂ O ₄ /Graphene/Li ₃ PO ₄

(1) take manganese dioxide and lithium carbonate raw materials in a molar ratio of Mn: Li=2: 1.05 by weighing;

(2) Mix the mixture obtained in step (1) in a high-energy ball mill for 7 hours until uniform, the ball mill rotating speed is 500r/min, and the mass ratio of the ball to the substance to be ground is 2:1;

(3) Heating in a resistance heating oven at 100°C for 10 hours to dryness;

(4) cooling to room temperature after heat treatment at 850° C. for 5 hours to obtain LiMn ₂ O ₄ ;

(5) Mix LiMn ₂ O ₄ obtained in step (4) with graphene, LiOH and H ₃ PO ₄ , wherein graphene is 6% of the mass of LiMn ₂ O ₄ , and the molar ratio of LiOH and H ₃ PO ₄ is 3 : 1, the sum of the quality of LiOH and H ₃ PO ₄ is 7.5% of the LiMn ₂ O ₄ quality, grinding and mixing;

(6) The mixture obtained in step 5 was heat-treated at 400° C. for 1 hour under a nitrogen atmosphere to obtain LiMn ₂ O ₄ /graphene/Li ₃ PO ₄ .

The properties of the electrode composite material of the lithium secondary battery prepared in this embodiment are shown in Table 2.

Example 12

Preparation of LiAl _0.02 Mn _1.98 O ₄ /Graphene/Al ₂ O ₃

Mix LiAl _0.02 Mn _1.98 O ₄ , graphene and aluminum nitrate, and then heat-treat at 400°C under nitrogen protection to obtain an electrode composite material for a lithium secondary battery. The LiAl _0.02 Mn _1.98 O ₄ /graphene/Al ₂ O The mass ratio of ₃ is 97:1:2. The properties of the electrode composite material of the lithium secondary battery prepared in this embodiment are shown in Table 2.

Examples 13-18

Using the same preparation method as in Example 12, an electrode composite material for a lithium secondary battery was prepared. The raw materials and properties of the electrode composite material for a lithium secondary battery are shown in Table 2.

The properties of the lithium secondary battery electrode composite materials, LiMn ₂ O ₄₄ , and LiMn ₂ O ₄ /graphene electrode composite materials prepared in Examples 11-18 were measured respectively, and the results are shown in Table 1.

Preparation raw materials and performance of metal oxide/graphene/conductive material containing lithium in table 2

As shown in Fig. 7, it is the XRD pattern of LiMn ₂ O ₄ and LiMn ₂ O ₄ /graphene.

As shown in Fig. 8 and Fig. 9, they are SEM photos of LiMn ₂ O ₄ and LiAl _0.02 Mn _1.98 O ₄ /graphene/Li ₃ PO ₄ in Table 2.

Figure 10 is the charge and discharge curves of LiMn ₂ O ₄ and LiAl _0.02 Mn _1.98 O ₄ /graphene/Li ₃ PO ₄ in Table 2.

From the above results, it can be concluded that the electrode composite materials for lithium secondary batteries prepared in Examples 11-18 have good electrical conductivity.

Example 19

Preparation of silicon/graphene/pyrolytic carbon materials

(1) With the mass ratio of 10:0.08:0.1 orthosilicate, graphene, and glucose as raw materials, it is dissolved in water, and the mass concentration is 30%;

(2) Mix the mixture obtained in step (1) in a high-energy ball mill for 5 hours, the ball mill rotating speed is 500r/min, and the mass ratio of the ball to the ground substance is 2:1;

(3) The above-mentioned materials are dried by spray drying, the air inlet temperature of the spray dryer is 220°C, and the air outlet temperature is 100°C;

(4) the mixture that step (3) obtains is placed in the atmosphere sintering furnace, under the protection of nitrogen atmosphere

After being treated at 900° C. for 10 hours, it was cooled to room temperature to obtain silicon/graphene/pyrolytic carbon material, and the mass ratio of silicon/graphene/pyrolytic carbon material was 90:5:5. The properties of the electrode composite material of the lithium secondary battery prepared in this embodiment are shown in Table 3.

Example 20

Preparation of Si/graphene/C

Si, graphene and glucose are mixed, and then heat-treated at 400° C. under nitrogen protection to obtain an electrode composite material for a lithium secondary battery. The mass ratio of LSi/graphene/C is 90:2:8. The properties of the electrode composite material of the lithium secondary battery prepared in this embodiment are shown in Table 3.

Examples 21-25

Using the same preparation method as in Example 20, an electrode composite material for a lithium secondary battery was prepared. The raw materials and properties of the electrode composite material for the lithium secondary battery are shown in Table 3.

The properties of the lithium secondary battery electrode composite materials, LiMn ₂ O ₄₄ , and LiMn ₂ O ₄ /graphene electrode composite materials prepared in Examples 19-25 were measured respectively, and the results are shown in Table 1.

Preparation raw materials and properties of table 3 negative electrode active material/graphene/conductive material

As shown in FIG. 11 , FIG. 12 , FIG. 13 and FIG. 14 , they are SEM photos of Si/graphene/C prepared in Example 20.

Figure 15 is the charge and discharge curves of Si/C and Si/graphene/C prepared in Example 20.

From the above results, it can be concluded that the electrode composite materials for lithium secondary batteries prepared in Examples 19-25 have good electrical conductivity.

The invention provides an electrode composite material of a lithium secondary battery and a preparation method thereof. The electrode composite material comprises: an electrode active material of a lithium secondary battery, graphene and a conductive material. Graphene and conductive material are distributed on the surface of the active material and between the particles of the active material to form the electrode composite material of the lithium secondary battery. Since graphene has better electronic conductivity, the electronic conductivity of the electrode composite material is improved. In addition, the electrode composite material provided by the present invention also includes a conductive material with higher conductivity, thereby further improving the conductivity of the electrode composite material. Experimental results prove that the electronic conductivity of the electrode composite material provided by the invention reaches 0.87S/cm, and the ion diffusion coefficient reaches 8.4×10 ^-8 cm ² /S.

The above description of the disclosed embodiments is provided to enable any person skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the present invention will not be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims (1)

1. an electrode composite material for a lithium secondary battery, characterized in that, it is prepared according to the following method: Iron oxide, vanadium oxide, lithium carbonate, ammonium dihydrogen phosphate, PEG, LiOH, H ₃ PO ₄ are used as raw materials, weighed and placed in acetone solution, and 5wt% graphene is added to make the solid content reach 20%; Mix the material obtained in the above steps in a high-energy ball mill for 20 hours until uniform, the ball mill speed is 500r/min, and the mass ratio of the ball to the ground material is 2:1; The material obtained in the above steps is dried by spray drying, the air inlet temperature of the spray dryer is 220°C, and the air outlet temperature is 100°C; The mixture obtained in the above steps was placed in a sintering furnace, treated at 650°C for 10 hours under the protection of nitrogen atmosphere, and then cooled to room temperature to obtain the desired LiFe _0.99 V _0.01 PO ₄ /graphene/C/Li ₃ PO ₄ , The mass ratio of LiFe _0.99 V _0.01 PO ₄ , graphene, C and Li ₃ PO ₄ is 95:1:1:3; Or prepare as follows: Use iron oxide, vanadium oxide, magnesium oxide, lithium carbonate, phosphoric acid, PEG, PVA, LiOH, H ₃ PO ₄ as raw materials, weigh and place in acetone solution, and add 5wt% graphene to make the solid content reach 20 %; Mix the material obtained in the above steps in a high-energy ball mill for 20 hours until uniform, the ball mill speed is 500r/min, and the mass ratio of the ball to the ground material is 2:1; The material obtained in the above steps is dried by spray drying, the air inlet temperature of the spray dryer is 220°C, and the air outlet temperature is 100°C; The mixture obtained in the above steps was placed in a sintering furnace, treated at 650°C for 10 hours under the protection of nitrogen atmosphere, and then cooled to room temperature to obtain the desired LiFe _0.98 V _0.01 Mg _0.01 PO ₄ /graphene/C/Li ₃ PO ₄ , the mass ratio of LiFe _0.98 V _0.01 Mg _0.01 PO ₄ , graphene, C and Li ₃ PO ₄ is 95:1:1:3; Or prepare as follows: Manganese nitrate, chromium nitrate, lithium carbonate, phosphoric acid, AgNO ₃ , PVA, tetrabutyl titanate, H ₃ PO ₄ were used as raw materials, weighed and placed in acetone solution, and 5wt% graphene was added to make the solid content Up to 20%; Mix the material obtained in the above steps in a high-energy ball mill for 20 hours until uniform, the ball mill speed is 500r/min, and the mass ratio of the ball to the ground material is 2:1; The material obtained in the above steps is dried by spray drying, the air inlet temperature of the spray dryer is 220°C, and the air outlet temperature is 100°C; The mixture obtained in the above steps was placed in a sintering furnace, treated at 650°C for 10 hours under the protection of nitrogen atmosphere, and then cooled to room temperature to obtain the desired LiMn _0.99 Cr _0.01 PO ₄ /graphene/Ag/C/LiTi ₂ ( The mass ratio of PO ₄ ) ₃ , LiMn _0.99 Cr _0.01 PO ₄ , graphene, Ag and C/LiTi ₂ (PO ₄ ) ₃ is 95:1:1:2.

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