WO2018153386A1 - 一种锂离子电池硅酸盐正极材料及其制备和应用 - Google Patents

一种锂离子电池硅酸盐正极材料及其制备和应用 Download PDF

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WO2018153386A1
WO2018153386A1 PCT/CN2018/083524 CN2018083524W WO2018153386A1 WO 2018153386 A1 WO2018153386 A1 WO 2018153386A1 CN 2018083524 W CN2018083524 W CN 2018083524W WO 2018153386 A1 WO2018153386 A1 WO 2018153386A1
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positive electrode
silicate
electrode material
group
ion battery
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PCT/CN2018/083524
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French (fr)
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张志峰
陈珍莲
黎军
张贤惠
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中国科学院宁波材料技术与工程研究所
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Priority to US16/488,545 priority Critical patent/US20200006804A1/en
Publication of WO2018153386A1 publication Critical patent/WO2018153386A1/zh

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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B33/00—Silicon; Compounds thereof
    • C01B33/20—Silicates
    • C01B33/32—Alkali metal silicates
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/04—Processes of manufacture in general
    • H01M4/0471—Processes of manufacture in general involving thermal treatment, e.g. firing, sintering, backing particulate active material, thermal decomposition, pyrolysis
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/133—Electrodes based on carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/136—Electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/13—Electrodes for accumulators with non-aqueous electrolyte, e.g. for lithium-accumulators; Processes of manufacture thereof
    • H01M4/139—Processes of manufacture
    • H01M4/1397—Processes of manufacture of electrodes based on inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/362—Composites
    • H01M4/366—Composites as layered products
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/5825—Oxygenated metallic salts or polyanionic structures, e.g. borates, phosphates, silicates, olivines
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/36—Selection of substances as active materials, active masses, active liquids
    • H01M4/58—Selection of substances as active materials, active masses, active liquids of inorganic compounds other than oxides or hydroxides, e.g. sulfides, selenides, tellurides, halogenides or LiCoFy; of polyanionic structures, e.g. phosphates, silicates or borates
    • H01M4/583—Carbonaceous material, e.g. graphite-intercalation compounds or CFx
    • H01M4/587—Carbonaceous material, e.g. graphite-intercalation compounds or CFx for inserting or intercalating light metals
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M4/62—Selection of inactive substances as ingredients for active masses, e.g. binders, fillers
    • H01M4/624—Electric conductive fillers
    • H01M4/625—Carbon or graphite
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M10/00—Secondary cells; Manufacture thereof
    • H01M10/05—Accumulators with non-aqueous electrolyte
    • H01M10/052—Li-accumulators
    • H01M10/0525—Rocking-chair batteries, i.e. batteries with lithium insertion or intercalation in both electrodes; Lithium-ion batteries
    • H—ELECTRICITY
    • H01—ELECTRIC ELEMENTS
    • H01M—PROCESSES OR MEANS, e.g. BATTERIES, FOR THE DIRECT CONVERSION OF CHEMICAL ENERGY INTO ELECTRICAL ENERGY
    • H01M4/00—Electrodes
    • H01M4/02—Electrodes composed of, or comprising, active material
    • H01M2004/026—Electrodes composed of, or comprising, active material characterised by the polarity
    • H01M2004/028—Positive electrodes
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02E—REDUCTION OF GREENHOUSE GAS [GHG] EMISSIONS, RELATED TO ENERGY GENERATION, TRANSMISSION OR DISTRIBUTION
    • Y02E60/00—Enabling technologies; Technologies with a potential or indirect contribution to GHG emissions mitigation
    • Y02E60/10—Energy storage using batteries

Definitions

  • the invention relates to the field of materials, in particular to a lithium ion battery silicate positive electrode material and its preparation and application.
  • lithium-ion battery As an alkali metal ion secondary battery, a lithium ion battery is considered to be the most promising energy storage system due to its high capacity and is widely used in various portable devices. Compared with traditional nickel-metal hydride batteries, nickel-cadmium batteries, and lead-acid batteries, lithium-ion batteries not only provide 2-3 times higher energy density and 5-6 times higher power density than they, but also have long cycle life. The average output voltage is high, the output power is large, there is no memory effect, and the self-discharge is small. However, with the development of lithium-ion batteries from small portable devices to high-power energy storage devices, especially power supplies, the requirements for energy density are getting higher and higher. However, the limitation of cathode materials hinders the lithium-ion battery. Further development.
  • cathode materials are mainly lithium cobaltate (LiCoO 2 ), lithium manganate (LiMn 2 O 4 ), lithium iron phosphate (LiFePO 4 ), lithium nickel cobalt manganese oxide ternary material (LiNi 1/3 Co 1/3 Mn 1/3 O 2 ) and the like.
  • These positive electrode materials are all composed of metal or non-metal oxygen ion hexahedron group, which can only provide one lithium ion insertion and extraction, which limits the theoretical range of the reversible capacity of the positive electrode material.
  • its low embedding potential (CV peak ⁇ 4V) limits the space for increasing its discharge energy density, which greatly restricts their development potential in new 5V battery technology and industry in large energy storage equipment and power supply.
  • CV peak ⁇ 4V limits the space for increasing its discharge energy density, which greatly restricts their development potential in new 5V battery technology and industry in large energy storage equipment and power supply.
  • Application therefore, there is an urgent need in the field of electrochemical energy storage to develop a
  • orthosilicates are composed of metal or non-metal oxygen ion tetrahedral groups, which theoretically allow the insertion and extraction of two lithium ions (T 2+ /T 3+ , T 3+ /T 4 + redox pair) and thus may have twice the theoretical capacity of the hexahedral oxygen ion group positive electrode material.
  • Li 2 FeSiO 4 and Li 2 MnSiO 4 are less than 3 V, and during the electrochemical cycle, the charging voltage between the first and subsequent cycles undergoes a structural voltage drop phenomenon; and Li 2 MnSiO 4 The micro/nano structure of the material is converted to an amorphous structure during the electrochemical cycle.
  • the experimentally prepared Li 2 CoSiO 4 has a charge and discharge voltage platform greater than 4 V, and the three polymorphic materials having symmetry Pmn 2 1 , Pbn 2 1 and P 2 1 /n show no signs of structural voltage drop during charge and discharge.
  • the object of the present invention is to provide a lithium ion battery cobalt-based silicate positive electrode material and its preparation and application.
  • a silicate positive electrode material comprising a core Li a Co x T 1-x Si y M 1-y O 4 and coated outside the core a carbon coating of the surface, and the silicate positive electrode material has the composition shown in Formula I:
  • T is a metal ion selected from the group consisting of metal elements: Mn, Fe, Ni, Ca, Mg, Al, La, Y, Sc, Zn, Cu, V, Mo, Tc, Ru, Rh, Pd, Cr Or a combination thereof; and the valence of T is the same as the valence of Co in formula I;
  • M is an ion selected from the group consisting of P, V, Ti, Ge, Ga, N, F, S, or a combination thereof;
  • the value of a is such that the valence of the core Li a Co x T 1-x Si y M 1-y O 4 is 0 as a whole.
  • a is selected from the group consisting of: 2, 1.9.
  • the silicate positive electrode material is a solid solution material.
  • the silicate positive electrode material is a solid solution material, which means that when the valence of T is the same as the valence of Co in formula I, the T moiety replaces Co in the Co oxygen tetrahedron to form a T oxygen tetrahedral anion. group.
  • T and Co are both solid solution components in the silicate positive electrode material.
  • the valence of Co and T in Formula I is selected from the group consisting of +2, +3, or a combination thereof.
  • M is a doping element in the silicate positive electrode material.
  • M is a doping element in the silicate positive electrode material
  • M is a doping element in the Si oxytetrahedral anion group
  • the silicate positive electrode material is a polymorphic material.
  • the silicate positive electrode material is a polymorphic material means that the silicate positive electrode material comprises a Pmn 2 1 phase and a phase optionally selected from the group consisting of Pbn 2 1 phase, P 2 1 / n phase, or a combination thereof.
  • the silicate positive electrode material has a bimodal group characteristic, and preferably, the bimodal group characteristic is stably present during a charge and discharge cycle.
  • the silicate positive electrode material simultaneously comprises two types of tetrahedral oxygen ion groups: a T-substituted or unsubstituted Co oxygen tetrahedral oxygen ion group, M-doped or undoped Si. Oxygen tetrahedral oxygen ion group.
  • the silicate positive electrode material has a particle diameter of 5 to 500 nm.
  • the silicate positive electrode material has a particle diameter of 10 to 300 nm, preferably 15 to 200 nm, more preferably 20 to 100 nm.
  • the core Li 2 Co x T 1-x Si y M 1-y O 4 has a diameter of 15 to 100 nm, preferably 20 to 100 nm.
  • the carbon coating layer has a thickness of 10 to 100 nm, preferably 20 to 50 nm.
  • the silicate positive electrode material is in the form of particles.
  • the silicate positive electrode material has one or more characteristics selected from the group consisting of:
  • the discharge voltage platform of the lithium ion battery prepared by using the silicate positive electrode material as the positive electrode active material is higher than 4V;
  • a lithium ion battery prepared by using the silicate positive electrode material as a positive electrode active material does not exhibit a structural voltage drop in the cycle.
  • a silicate positive electrode material according to the first aspect of the invention, the method comprising the steps of:
  • the first solution comprises a first solvent, a lithium source material, and a silicon source material;
  • the second solution comprises a second solvent, a cobalt source material, a T source material, and/or an M source material;
  • step 5) mixing the product obtained in step 4) with the carbon source material, and calcining the resulting mixture at a second temperature T2 for t2 to obtain the silicate positive electrode material of the first aspect of the invention.
  • the first solvent is selected from the group consisting of water, ethanol, ethylene glycol, aqueous ammonia, or a combination thereof, preferably deionized water.
  • the second solvent is selected from the group consisting of ethylene glycol, water, ethanol, or a combination thereof.
  • the lithium source material is selected from the group consisting of lithium hydroxide, lithium oxide, or a combination thereof;
  • the silicon source material is selected from the group consisting of silicon oxide, tetraethyl orthosilicate, methyl orthosilicate, silicate, silicone, or a combination thereof;
  • the cobalt source material is a cobalt salt selected from the group consisting of acetate, hydrochloride, sulfate, nitrate, carbonate, hydrogencarbonate, citrate, halogenated salt, or a combination thereof;
  • the T source material is a T salt selected from the group consisting of acetate, hydrochloride, sulfate, nitrate, carbonate, bicarbonate, citrate, halogenated salt, or a combination thereof;
  • the M source material is a substance selected from the group consisting of an M element: an acid, an ammonium salt, an oxide, a lipid substance;
  • the carbon source material is an organic carbon source, preferably selected from the group consisting of glucose, sucrose, citric acid, oxalic acid, acetic acid, or a combination thereof.
  • T1 is 130-180 ° C, preferably 140-170 ° C, more preferably 145-160 ° C;
  • T1 is 1-150h, preferably 10-100h, more preferably 20-85h;
  • T2 is 400-800 ° C, preferably 500-700 ° C;
  • T2 is from 0.1 to 5 h, preferably from 0.5 to 3 h.
  • the mixing ratio of the product obtained in step 4) and the carbon source material in step 5) is from 1 to 5:1, preferably from 2 to 3.5:1.
  • a positive electrode active material of the positive electrode comprising the silicate positive electrode material of the first aspect of the invention or the silicate positive electrode material of the first aspect of the invention is provided. .
  • the positive electrode further contains a conductive agent and a binder.
  • a lithium ion battery comprising the positive electrode of the third aspect of the invention.
  • Example 1 is an XRD pattern of Li 1.9 CoSi 0.9 P 0.1 O 4 and Li 1.9 CoSi 0.9 P 0.1 O 4 /C obtained in Example 1.
  • Example 2 is a SEM picture of Li 1.9 CoSi 0.9 P 0.1 O 4 obtained in Example 1.
  • Example 3 is a charge and discharge test result of a lithium ion battery in which Li 1.9 CoSi 0.9 P 0.1 O 4 and Li 1.9 CoSi 0.9 P 0.1 O 4 /C obtained in Example 1 were used as positive electrode active materials, respectively.
  • Example 4 is an XRD pattern of Li 1.9 CoSi 0.9 V 0.1 O 4 and Li 1.9 CoSi 0.9 V 0.1 O 4 /C obtained in Example 2.
  • Fig. 5 is a SEM picture of Li 1.9 CoSi 0.9 V 0.1 O 4 obtained in Example 2.
  • Fig. 6 is a charge and discharge test result of a lithium ion battery in which Li 1.9 CoSi 0.9 V 0.1 O 4 and Li 1.9 CoSi 0.9 V 0.1 O 4 /C obtained in Example 2 were used as positive electrode active materials, respectively.
  • Example 7 is an XRD pattern of Li 2 Co 0.9 Mn 0.1 SiO 4 and Li 2 Co 0.9 Mn 0.1 SiO 4 /C obtained in Example 3.
  • Example 9 is a charge and discharge test result of a lithium ion battery in which Li 2 Co 0.9 Mn 0.1 SiO 4 and Li 2 Co 0.9 Mn 0.1 SiO 4 /C obtained in Example 3 were used as positive electrode active materials, respectively.
  • Fig. 10 is an XRD pattern of Li 2 CoSiO 4 and Li 2 CoSiO 4 /C obtained in Comparative Example 1.
  • Figure 11 is a SEM picture of Li 2 CoSiO 4 obtained in Comparative Example 1.
  • Fig. 12 is a charge and discharge test result of a lithium ion battery in which Li 2 CoSiO 4 and Li 2 CoSiO 4 /C obtained in Comparative Example 1 are positive electrode active materials, respectively.
  • the inventors unexpectedly prepared a lithium ion battery silicate positive electrode material with stable structure, good chemical property, simple and controllable preparation process, good safety and low cost. On this basis, the inventors completed the present invention.
  • the present invention provides a silicate positive electrode material comprising a core Li a Co x T 1-x Si y M 1-y O 4 and coated on an outer surface of the inner core a carbon coating, and the silicate positive electrode material has the composition shown in Formula I:
  • T is a metal ion selected from the group consisting of metal elements: Mn, Fe, Ni, Ca, Mg, Al, La, Y, Sc, Zn, Cu, V, Mo, Tc, Ru, Rh, Pd, Cr Or a combination thereof; and the valence of T is the same as the valence of Co in formula I;
  • M is an ion selected from the group consisting of P, V, Ti, Ge, Ga, N, F, S, or a combination thereof;
  • the value of a is such that the valence of the core Li a Co x T 1-x Si y M 1-y O 4 is 0 as a whole.
  • a is selected from the group consisting of: 2, 1.9.
  • the silicate positive electrode material is a solid solution material.
  • the silicate positive electrode material is a solid solution material, which means that when the valence of T is the same as the valence of Co in formula I, the T moiety replaces Co in the Co oxygen tetrahedron to form a T oxygen tetrahedral anion. group.
  • T and Co are both solid solution components in the silicate positive electrode material.
  • the valence of Co and T in Formula I is selected from the group consisting of +2, +3, or a combination thereof.
  • M is a doping element in the silicate positive electrode material.
  • M is a doping element in the silicate positive electrode material
  • M is a doping element in the Si oxytetrahedral anion group
  • the silicate positive electrode material is a polymorphic material.
  • the silicate positive electrode material is a polymorphic material means that the silicate positive electrode material comprises a Pmn 2 1 phase and a phase optionally selected from the group consisting of Pbn 2 1 phase, P 2 1 / n phase, or a combination thereof.
  • the silicate positive electrode material has a bimodal group characteristic, and preferably, the bimodal group characteristic is stably present during a charge and discharge cycle.
  • the silicate positive electrode material simultaneously comprises two types of tetrahedral oxygen ion groups: a T-substituted or unsubstituted Co oxygen tetrahedral oxygen ion group, M-doped or undoped Si. Oxygen tetrahedral oxygen ion group.
  • the silicate positive electrode material has a particle diameter of 5 to 500 nm.
  • the silicate positive electrode material has a particle diameter of 10 to 300 nm, preferably 15 to 200 nm, more preferably 20 to 100 nm.
  • the core Li 2 Co x T 1-x Si y M 1-y O 4 has a diameter of 15 to 100 nm, preferably 20 to 100 nm.
  • the carbon coating layer has a thickness of 10 to 100 nm, preferably 20 to 50 nm.
  • the silicate positive electrode material is in the form of particles.
  • the silicate positive electrode material has one or more characteristics selected from the group consisting of:
  • the discharge voltage platform of the lithium ion battery prepared by using the silicate cathode material as the cathode active material is higher than 4V;
  • a lithium ion battery prepared by using the silicate positive electrode material as a positive electrode active material does not exhibit a structural voltage drop in the cycle.
  • the present invention provides a polymorphic silicate solid solution material having the composition of Formula I, wherein 0 ⁇ x ⁇ 1, 0 ⁇ y ⁇ 1, T is a solid solution component, and M is a doping group.
  • the material particles are in the range of 5-200 nm, and the Xrd has a bimodal group characteristic; the lithium ion battery prepared by using the solid solution material as the positive electrode active material does not undergo a structural voltage change in the charge and discharge cycle, and V has a stable discharge.
  • a discharge reversible specific capacity higher than 130 Ah/kg can be obtained.
  • the present invention discloses a polymorphic silicate solid solution material composed of a tetrahedral oxygen ion group, the solid solution material having the chemical formula of Formula I:
  • T is a metal element selected from the group consisting of Mn, Fe, Ni, Ca, Mg, Al, La, Y, Sc, Li, Zn, Cu, V, Mo, Tc, Ru, Rh, Pd, Cr or a combination thereof;
  • M is an element selected from the group consisting of P, V, Ti, Ge, Ga, Al, N, F, S or a combination thereof;
  • Co and T are metal ions having a nominal valence of +2, and a tetrahedral anion group is formed with oxygen ions, which is a solid solution component in a polymorphic crystal lattice; M is a metal or non-metallic structure in a skeleton structure composed of Si oxygen tetrahedral units. Metal doping components with different nominal valences;
  • the lithium ion battery prepared by using the solid solution material as a positive electrode active material has a reversible discharge specific capacity higher than 130 Ah/kg when discharged at a current density of 5 mA/g at room temperature, and the voltage platform does not undergo a structural phase in the charge and discharge cycle. The movement caused by the change.
  • the Xrd structure polymorph of the solid solution material composed of the tetrahedral oxygen ion group includes a bimodal group characteristic of one or more of Pmn2 1 , Pbn 2 1 and P 2 1 /n phases, and the bimodal group features charging and discharging. The process also does not change; preferably Pmn2 1 .
  • the "bimodal group feature” means that the Pmn2 1 , Pbn2 1 and P2 1 /n phase XRD patterns of the polymorphic material have distinct bimodal structures at 21.8° and 23.1°, including Peak groups such as bimodal-bimodal, unimodal-three-peak; the characteristics of the bimodal group are determined by the preparation conditions, but do not change with the charge-discharge cycle process.
  • the solid solution material is in the form of particles, and the polymorphic solid solution material has a particle diameter of 5 to 200 nm, preferably 5 to 30 nm, 30 to 60 nm, or 60 to 90 nm.
  • Pmn2 1 phase material after doping the silicon position of the scaffold and M-modified carbon-coated particles, multi-phase morphology of the material does not occur becomes mixed phase, but remains Pmn2 1 phase, and not with the charge
  • the discharge cycle process changes.
  • the lithium ion battery prepared by using the polymorphic solid solution material as a positive electrode active material is charged at 5 mA/g in a voltage range of 2.5-4.6 V.
  • Discharge, discharge specific capacity is not less than 130mAh / g, while the charging platform is maintained at about 4.3V, the discharge platform is maintained at about 4.1V, there will be no structural voltage drop in the cycle.
  • a significant voltage drop occurs during the first to second laps, and is not present in the Li2CoSiO4 material from the first to the second.
  • the T element selects +2, or a +3 valent metal element or a combination thereof.
  • the M element selects a high valence metal or a non-metal element or a combination thereof.
  • the charging platform of the positive electrode material is about 4.3 V, and the discharge platform is about 4.1 V.
  • the Pmn2 1 structure is preferred.
  • the carbon coating layer on the outer surface of the positive electrode material of the present invention can effectively improve the electrochemical activity of the obtained positive electrode material.
  • the invention also provides a preparation method of the silicate positive electrode material, the method comprising the following steps:
  • the first solution comprises a first solvent, a lithium source material, and a silicon source material;
  • the second solution comprises a second solvent, a cobalt source material, a T source material, and/or an M source material;
  • step 5) mixing the product obtained in step 4) and the carbon source material, and calcining the resulting mixture at a second temperature T2 for t2 to obtain the silicate positive electrode material.
  • the first solvent is selected from the group consisting of water, ethanol, ethylene glycol, aqueous ammonia, or a combination thereof, preferably deionized water.
  • the second solvent is selected from the group consisting of ethylene glycol, water, ethanol, or a combination thereof.
  • the lithium source material is selected from the group consisting of lithium hydroxide, lithium oxide, or a combination thereof;
  • the silicon source material is selected from the group consisting of silicon oxide, tetraethyl orthosilicate, methyl orthosilicate, silicate, silicone, or a combination thereof;
  • the cobalt source material is a cobalt salt selected from the group consisting of acetate, hydrochloride, sulfate, nitrate, carbonate, hydrogencarbonate, citrate, halogenated salt, or a combination thereof;
  • the T source material is a T salt selected from the group consisting of acetate, hydrochloride, sulfate, nitrate, carbonate, hydrogencarbonate, citrate, halogenated salt, or a combination thereof;
  • the M source material is a substance selected from the group consisting of an M element: an acid, an ammonium salt, an oxide, a lipid substance;
  • the carbon source material is an organic carbon source, preferably selected from the group consisting of glucose, sucrose, citric acid, oxalic acid, acetic acid, or a combination thereof.
  • T1 is 130-180 ° C, preferably 140-170 ° C, more preferably 145-160 ° C;
  • T1 is 1-150h, preferably 10-100h, more preferably 20-85h;
  • T2 is 400-800 ° C, preferably 500-700 ° C;
  • T2 is from 0.1 to 5 h, preferably from 0.5 to 3 h.
  • the mixing ratio of the product obtained in step 4) and the carbon source material in step 5) is from 1 to 5:1, preferably from 2 to 3.5:1.
  • the present invention also provides a positive electrode of a lithium ion battery, the positive active material of the positive electrode comprising or consisting of the silicate positive electrode material.
  • the positive electrode further contains a conductive agent and a binder.
  • the present invention also provides a lithium ion battery comprising the positive electrode.
  • the present invention has the following main advantages:
  • the silicate positive electrode material has the advantages of high energy density, good safety, low cost, and stable structure
  • the lithium ion battery with the silicate positive electrode material as the positive electrode active material can have a charging capacity of up to 304 mAh/g at 5 mA/g, and the discharge capacity can be as high as 155 mAh/g; the discharge voltage of the lithium ion battery can be as high as 4.1V.
  • XRD equipment adopts Shimadzu XRD-6100 model, and the radiation source is adopted.
  • the SEM uses FEI and QUANTA 250 FEG models.
  • the silicate positive electrode material obtained by the invention is uniformly mixed with the conductive agent acetylene black and the binder polyvinylidene fluoride (PVDF) in a solvent of nitrogen methylpyrrolidone (NMP), the silicate positive electrode material, acetylene black and the bonding.
  • the mass ratio of the agent was 80:10:10, and then the obtained slurry was coated on an aluminum foil, dried, sliced, and tableted to obtain a positive electrode tab of a lithium ion battery.
  • the positive electrode tab, the separator, the electrolyte, and the negative electrode were assembled into a CR2032 button battery in a glove box protected by a high purity argon atmosphere.
  • the negative electrode is made of lithium, the separator is Celgard 2550, and the electrolyte is dissolved in 1M LiPF 6 in a volume ratio of 1:1 EC/DMC.
  • the battery is charged and discharged using Blue Power 2001A, room temperature 25 ° C, voltage 2.5-4.6V.
  • the 1.5 dried product and the 1.7 obtained silicate positive electrode material 1 were respectively subjected to ICP (Inorganic Element Analysis), XRD and SEM tests, and lithium was respectively obtained as a positive electrode active material with 1.5 dried product and 1.7 obtained silicate positive electrode material 1, respectively. Ion batteries are tested for charge and discharge and cycle performance.
  • composition of the product after drying by 1.5 was Li 1.9 CoSi 0.9 P 0.1 O 4
  • composition of the obtained silicate positive electrode material 1 was Li 1.9 CoSi 0.9 P 0.1 O 4 /C.
  • Example 1 is an XRD pattern of Li 1.9 CoSi 0.9 P 0.1 O 4 and Li 1.9 CoSi 0.9 P 0.1 O 4 /C obtained in Example 1.
  • the uncoated Li 1.9 CoSi 0.9 P 0.1 O 4 material is pure Pmn2 1 phase, and the XRD pattern has a distinct bimodal structure at 21.8° and 23.1°; the coated material Li 1.9 CoSi 0.9 P 0.1 O 4 / C structure still has significant peaks at 21.8 ° and 23.1 °, 16.3 ° and 24.3 ° in the new peak does not appear, Pmn2 1 phase is maintained, but the emergence of a Co single peak was at 44 °.
  • the above results show that the structure of Li 1.9 CoSi 0.9 P 0.1 O 4 before and after carbon coating is not changed, and only a small amount of Co ions are reduced to elemental Co.
  • Example 2 is a SEM picture of Li 1.9 CoSi 0.9 P 0.1 O 4 obtained in Example 1.
  • the Li 1.9 CoSi 0.9 P 0.1 O 4 particles are uniform and have a size of about 50 nm.
  • Example 3 is a charge and discharge test result of a lithium ion battery in which Li 1.9 CoSi 0.9 P 0.1 O 4 and Li 1.9 CoSi 0.9 P 0.1 O 4 /C obtained in Example 1 were used as positive electrode active materials, respectively.
  • the lithium ion battery with Li 1.9 CoSi 0.9 P 0.1 O 4 as the positive electrode active material has a first charge capacity of 134 mAh/g, a first discharge capacity of 34 mAh/g, and Li 1.9 when charged and discharged at 5 mA/g.
  • the first charge capacity of the lithium ion battery with CoSi 0.9 P 0.1 O 4 /C as the positive electrode active material is 270 mAh/g, and the initial discharge capacity is 143 mAh/g; and, whether it is Li 1.9 CoSi 0.9 P 0.1 O 4 as the positive electrode active material
  • the lithium ion battery is also a lithium ion battery with Li 1.9 CoSi 0.9 P 0.1 O 4 /C as the positive electrode active material, and its charging platform is basically at 4.3V and has a significant discharge platform at 4.1V.
  • Li, Si according to a molar ratio of 4:1, lithium hydroxide (such as 1.2mol) and silica nanopowder (such as 0.27mol) were added to the deionized water and stirred thoroughly, configured as a suspension, and then placed in an ultrasonicator. 3h;
  • composition of the product after drying by 2.5 was Li 1.9 CoSi 0.9 V 0.1 O 4
  • composition of the obtained silicate positive electrode material 2 was Li 1.9 CoSi 0.9 V 0.1 O 4 /C.
  • Example 4 is an XRD pattern of Li 1.9 CoSi 0.9 V 0.1 O 4 and Li 1.9 CoSi 0.9 V 0.1 O 4 /C obtained in Example 2.
  • the uncoated Li 1.9 CoSi 0.9 V 0.1 O 4 material is pure Pmn2 1 phase, and the XRD pattern has a distinct bimodal structure at 21.8° and 23.1°; the coated Li 1.9 CoSi 0.9 V 0.1 O 4 / C material still has significant peaks at 21.8 ° and structure of 23.1 °, a new peak does not appear at 16.3 ° and 24.3 °, maintained Pmn2 1 phase, but the emergence of a Co single peak was at 44 °.
  • the above results show that the structure of Li 1.9 CoSi 0.9 V 0.1 O 4 before and after carbon coating is not changed, and only a small amount of Co ions are reduced to elemental Co.
  • Fig. 5 is a SEM picture of Li 1.9 CoSi 0.9 V 0.1 O 4 obtained in Example 2.
  • the Li 1.9 CoSi 0.9 V 0.1 O 4 particles are uniform and have a size of about 50 nm.
  • Fig. 6 is a charge and discharge test result of a lithium ion battery in which Li 1.9 CoSi 0.9 V 0.1 O 4 and Li 1.9 CoSi 0.9 V 0.1 O 4 /C obtained in Example 2 were used as positive electrode active materials, respectively.
  • the lithium ion battery with Li 1.9 CoSi 0.9 V 0.1 O 4 as the positive electrode active material has a first charge capacity of 146.5 mAh/g and a first discharge capacity of 52.9 mAh/g when charged and discharged at 5 mA/g;
  • Li 1.9 CoSi 0.9 V 0.1 O 4 /C is a positive electrode active material for a lithium ion battery with a first charge capacity of 304.3 mAh/g and an initial discharge capacity of 139.1 mAh/g; and, regardless of Li 1.9 CoSi 0.9 V 0.1 O 4
  • a lithium ion battery that is a positive active material or a lithium ion battery with Li 1.9 CoSi 0.9 V 0.1 O 4 /C as a positive active material has a charging platform of substantially 4.3 V and a significant discharge platform at 4.1 V.
  • Li, Si according to a molar ratio of 4:1, lithium hydroxide (such as 1.2 mol) and silica nano-powder (such as 0.3 mol) were added to the deionized water and stirred thoroughly, and then placed in a suspension, and then placed in an ultrasonicator. 3h;
  • composition of the product after 3.5 drying was Li 2 Co 0.9 Mn 0.1 SiO 4 by ICP, and the composition of the obtained silicate positive electrode material 3 was Li 2 Co 0.9 Mn 0.1 SiO 4 /C.
  • Example 7 is an XRD pattern of Li 2 Co 0.9 Mn 0.1 SiO 4 and Li 2 Co 0.9 Mn 0.1 SiO 4 /C obtained in Example 3.
  • the uncoated Li 2 Co 0.9 Mn 0.1 SiO 4 material is pure Pmn2 1 phase, and the XRD pattern has a distinct bimodal structure at 21.8° and 23.1°; the coated Li 2 Co 0.9 Mn
  • the 0.1 SiO 4 /C material still has a distinct bimodal structure at 21.8° and 23.1°, but peaks also appear at 16.3 and 24.3°, showing a mixed phase of Pmn2 1 and Pbn2 1 while a Co appears at 44°. Elemental peak.
  • the above results show that the structure of Li 2 Co 0.9 Mn 0.1 SiO 4 is not changed before and after carbon coating, and only a small amount of Co ions are reduced to elemental Co.
  • the Li 1.9 Co 0.9 Mn 0.1 SiO 4 particles are uniform and have a size of about 50 nm.
  • Example 9 is a charge and discharge test result of a lithium ion battery in which Li 2 Co 0.9 Mn 0.1 SiO 4 and Li 2 Co 0.9 Mn 0.1 SiO 4 /C obtained in Example 3 were used as positive electrode active materials, respectively.
  • the lithium ion battery with Li 2 Co 0.9 Mn 0.1 SiO 4 as the positive electrode active material has a first charge capacity of 165.4 mAh/g and a first discharge capacity of 43.5 mAh/g when charged and discharged at 5 mA/g;
  • Li 2 Co 0.9 Mn 0.1 SiO 4 /C is a positive electrode active material for a lithium ion battery with a first charge capacity of 281 mAh/g and a first discharge capacity of 155 mAh/g; and, regardless of Li 2 Co 0.9 Mn 0.1 SiO 4 as a positive electrode
  • the lithium ion battery of the active material is also a lithium ion battery with Li 2 Co 0.9 Mn 0.1 SiO 4 /C as the positive electrode active material, and the charging platform is basically 4.3V and has a remarkable discharge platform at 4.1V.
  • C1.2 weigh the appropriate amount of cobalt chloride (such as 0.3mol), fully dissolved in ethylene glycol;
  • the C1.5 dried product (such as 1.5g) is mixed with sucrose (such as 0.42g), ball milled for 12h, then placed in a tube furnace, heated in an inert atmosphere at 5 ° C / min to 600 ° C calcined for 1h;
  • composition of the product after drying by C1.5 was Li 2 CoSiO 4
  • composition of the silicate positive electrode material C1 obtained by C1.7 was Li 2 CoSiO 4 /C.
  • Fig. 10 is an XRD pattern of Li 2 CoSiO 4 and Li 2 CoSiO 4 /C obtained in Comparative Example 1.
  • the uncoated Li 2 CoSiO 4 material is a pure Pmn 2 1 phase, and the XRD pattern has a distinct bimodal structure at 21.8° and 23.1°; the coated Li 2 CoSiO 4 /C material is at 21.8. ° and 23.1° still have a distinct bimodal structure, but peaks also appear at 16.3° and 24.3°, showing a mixed phase of Pmn2 1 and Pbn2 1 while a Co elemental peak appears at 44°.
  • the above results show that the structure of Li 2 CoSiO 4 does not change before and after carbon coating, and only a small amount of Co ions are reduced to elemental Co.
  • Figure 11 is a SEM picture of Li 2 CoSiO 4 obtained in Comparative Example 1.
  • the Li 1.9 CoSiO 4 particles are uniform and have a size of about 50 nm.
  • Fig. 12 is a charge and discharge test result of a lithium ion battery in which Li 2 CoSiO 4 and Li 2 CoSiO 4 /C obtained in Comparative Example 1 are positive electrode active materials, respectively.
  • the lithium ion battery using Li 2 CoSiO 4 as a positive electrode active material has a first charge capacity of 120 mAh/g, and the first discharge capacity is 40 mAh/g; with Li 2 CoSiO 4 /C
  • the lithium ion battery which is a positive electrode active material has a first charge capacity of 226 mAh/g and an initial discharge capacity of 112 mAh/g; and, whether it is a lithium ion battery using Li 2 CoSiO 4 as a positive electrode active material, or Li 2 CoSiO 4 / C is a lithium ion battery with a positive active material, and its charging platform is basically at 4.3V and has a significant discharge platform at 4.1V.

Abstract

本发明涉及一种锂离子电池硅酸盐正极材料及其制备和应用。具体地，本发明公开了一种硅酸盐正极材料，所述硅酸盐正极材料包含内核LiaCoxT1-xSiyM1-yO4和包覆于所述内核外表面的碳包覆层。本发明还公开了所述正极材料的制备和应用。以所述正极材料为正极活性材料制备的锂离子电池在5mA/g的放电密度下的放电容量大于130mAh/g，且其放电电压平台大于4V。

Description

一种锂离子电池硅酸盐正极材料及其制备和应用 技术领域
本发明涉及材料领域，具体地涉及一种锂离子电池硅酸盐正极材料及其制备和应用。
背景技术
作为一种碱金属离子二次电池，锂离子电池由于具有高容量被认为是最有潜力的能量存储系统并广泛应用于各种便携式设备。与传统的镍氢电池、镍镉电池、铅酸电池相比，锂离子电池不仅仅能够比他们提供高2-3倍的能量密度和5-6倍的功率密度，而且还具有循环寿命长、平均输出电压高、输出功率大、无记忆效应、自放电小等优点。然而，随着锂离子电池从小型便携设备的应用逐渐向大功率储能设备特别是动力电源的发展，对其能量密度的要求也越来越高，然而正极材料的限制阻碍了锂离子电池的进一步发展。
目前常用的正极材料主要有钴酸锂(LiCoO 2)、锰酸锂(LiMn 2O 4)、磷酸铁锂(LiFePO 4)、镍钴锰酸锂三元材料(LiNi 1/3Co 1/3Mn 1/3O 2)等。这些正极材料都以金属或非金属氧离子六面体集团为结构单元，只能提供一个锂离子的嵌入和脱出，限定了正极材料可逆容量的理论范围。且其较低的嵌入势(CV峰<4V)限制了其放电能量密度的提高空间，这极大地制约了它们在新型5V电池技术中的发展潜力和在大型储能设备、动力电源中的产业应用，因此，电化学储能领域迫切需要开发一种能量密度更高、性价比更优良的正极材料，以满足新型能源产业对高能量密度电池的技术需求。
正硅酸盐(Li 2TSiO 4，T＝Fe、Mn、Co、Ni)是除磷酸铁锂外另一类新的聚阴离子型锂离子电池正极材料。由于Si和P在元素周期表中位于同一周期的相邻位置，所以硅酸盐和磷酸盐具有相近的化学性质。并且，Si-O键同P-O键相比具有更强的化学键合成，使得Li 2TSiO 4晶体结构的稳定性更强。与磷酸盐材料相比，正硅酸盐以金属或非金属氧离子四面体集团为结构单元，理论上允许嵌入和脱出两个锂离子(T 2+/T 3+,T 3+/T 4+氧化还原对)，因而可具有两倍于六面体氧离子集团正极材料的理论容量。这使得硅酸盐材料成为非常有吸引力的新型结构的高容量锂离子电池正极材料。硅酸盐锂离子电池正极材料Li 2TSiO 4(T＝Fe、Mn、Co)由于其低成本、高能量密度和安全性能好等优点越来越受到学术界和产业界的关注。
2005年，瑞典乌普萨拉大学的Nyten博士首次报道了一种新型的硅酸盐锂离 子电池正极材料Li 2FeSiO 4，其中，利用固相烧结法合成的Li 2FeSiO 4/C正极材料具有良好的电化学特性；通过对合成样品的Xrd分析，发现所有的阳离子都以四面体配位形式存在，晶体结构属于正交晶系，空间群为Pmn2 1，晶格参数为：a＝6.2661(5)，b＝5.3295(5)，c＝5.0148(4)；在60℃、C/16(20mA/g)倍率下充放电时，前两次的充电容量可达165mAh/g，非常接近脱嵌一个锂时的理论容量，放电容量为120mAh/g。经过纳米化技术和碳包覆合成的不断提高，Dinesh Rangappa等在2012年实验合成的Li 2FeSiO 4和Li 2MnSiO 4已经取得近2个锂离子的可逆脱嵌，表明稳定容量已超过300mAh/g，不仅是首次报道容量140-165mAh/g的两倍，也是橄榄石结构LiFePO 4容量(160-170mAh/g)的两倍，证实了硅酸盐正极材料可以使锂离子电池能量密度提高近两倍。但是，以上实验显示Li 2FeSiO 4和Li 2MnSiO 4的放电电压小于3V，并且在电化学循环过程中，第一和随后循环之间的充电电压发生结构性电压降现象；且Li 2MnSiO 4材料的微纳结构在电化学循环过程中向无定形结构转化。实验上制备的Li 2CoSiO 4的充放电电压平台大于4V，并且对称性为Pmn2 1、Pbn2 1和P2 1/n的三种多形态材料在充放电过程都没有显示结构性电压降迹象。然而，由于钴系材料在制备上的困难，迄今，Li 2CoSiO 4多形态材料的放电比容量在2.0-4.6V的放电窗口中都低于100Ah/kg，电化学性能的进展要远落后于铁、锰系硅酸盐。因此，发展合适的材料改性技术，提高钴系硅酸盐材料的比容量是过去十多年硅酸盐材料研究和开发的主要困难和挑战。
发明内容
本发明的目的在于提供一种锂离子电池钴系硅酸盐正极材料及其制备和应用。
本发明的第一方面，提供了一种硅酸盐正极材料，所述硅酸盐正极材料包含内核Li aCo xT 1-xSi yM 1-yO 4和包覆于所述内核外表面的碳包覆层，并且所述硅酸盐正极材料具有式I所示组成：
Li aCo xT 1-xSi yM 1-yO 4/C I
其中，T为选自下组的金属元素的金属离子：Mn、Fe、Ni、Ca、Mg、Al、La、Y、Sc、Zn、Cu、V、Mo、Tc、Ru、Rh、Pd、Cr、或其组合；且T的化合价与式I中Co的化合价相同；
M为选自下组元素的离子：P、V、Ti、Ge、Ga、N、F、S、或其组合；
0＜x≤1，0＜y≤1，且x和y不同时为1；
a的取值使得内核Li aCo xT 1-xSi yM 1-yO 4的化合价整体为0。
在另一优选例中，a选自下组：2、1.9。
在另一优选例中，当T为V且M为V时，V的化合价为3+为T，V的化合价为5+为M。
在另一优选例中，0.01＜x≤1，较佳地0.1＜x≤1，更佳地0.3＜x≤1，最佳地0.5＜x≤1。
在另一优选例中，0.01＜y≤1，较佳地0.1＜y≤1，更佳地0.3＜y≤1，最佳地0.5＜y≤1。
在另一优选例中，所述硅酸盐正极材料为固溶体材料。
在另一优选例中，所述硅酸盐正极材料为固溶体材料是指：在T的化合价与式I中Co的化合价相同时，T部分取代Co氧四面体中的Co形成T氧四面体阴离子集团。
在另一优选例中，T和Co均为所述硅酸盐正极材料中的固溶体组分。
在另一优选例中，式I中Co和T的化合价选自下组：+2、+3、或其组合。
在另一优选例中，M为所述硅酸盐正极材料中的掺杂元素。
在另一优选例中，“M为所述硅酸盐正极材料中的掺杂元素”是指：M为Si氧四面体阴离子集团中的掺杂元素。
在另一优选例中，所述硅酸盐正极材料为多形态材料。
在另一优选例中，所述硅酸盐正极材料为多形态材料是指：所述硅酸盐正极材料包含Pmn2 1相和任选地选自下组的相：Pbn2 1相、P2 1/n相、或其组合。
在另一优选例中，所述硅酸盐正极材料具有双峰群特征，优选地，所述双峰群特征在充放电循环过程中稳定存在。
在另一优选例中，所述硅酸盐正极材料同时包含如下两类四面体氧离子基团：T取代或未取代的Co氧四面体氧离子基团、M掺杂或未掺杂的Si氧四面体氧离子基团。
在另一优选例中，所述硅酸盐正极材料的粒径为5-500nm。
在另一优选例中，所述硅酸盐正极材料的粒径为10-300nm，较佳地15-200nm，更佳地20-100nm。
在另一优选例中，所述内核Li 2Co xT 1-xSi yM 1-yO 4的直径为15－100nm，较佳地20－100nm。
在另一优选例中，所述碳包覆层的厚度为10－100nm，较佳地20－50nm。
在另一优选例中，所述硅酸盐正极材料为颗粒状。
在另一优选例中，所述硅酸盐正极材料具有选自下组的一个或多个特征：
1)以所述硅酸盐正极材料为正极活性材料制备的锂离子电池在5mA/g电流密度下放电时，可逆放电比容量高于130Ah/kg；
2)以所述硅酸盐正极材料为正极活性材料制备的锂离子电池的放电电压平台高于4V；
3)以所述硅酸盐正极材料为正极活性材料制备的锂离子电池在循环中不会出现结构性电压降。
本发明的第二方面，提供了一种本发明第一方面所述的硅酸盐正极材料的制备方法，所述方法包括如下步骤：
1)提供第一溶液、第二溶液和碳源材料，其中，
所述第一溶液包含第一溶剂、锂源材料和硅源材料；
所述第二溶液包含第二溶剂、钴源材料、T源材料和/或M源材料；
2)在搅拌条件下，混合所述第一溶液和所述第二溶液，得到前驱体溶液；
3)将所述前驱体溶液转移至反应釜中，在第一温度T1下反应t1时间；
4)抽滤并任选地洗涤干燥步骤3)所得产物，得到本发明第一方面所述的硅酸盐正极材料的内核；
5)混合步骤4)所得产物和所述碳源材料，将所得混合物在第二温度T2下煅烧处理t2时间，得到本发明第一方面所述的硅酸盐正极材料。
在另一优选例中，所述第一溶剂选自下组：水、乙醇、乙二醇、氨水、或其组合，优选为去离子水。
在另一优选例中，所述第二溶剂选自下组：乙二醇、水、乙醇、或其组合。
在另一优选例中，所述锂源材料选自下组：氢氧化锂、氧化锂、或其组合；
所述硅源材料选自下组：氧化硅、正硅酸乙酯、正硅酸甲酯、硅酸盐、有机硅、或其组合；
所述钴源材料为选自下组的钴盐：乙酸盐、盐酸盐、硫酸盐、硝酸盐、碳酸盐、碳酸氢盐、柠檬酸盐、卤化盐、或其组合；
所述T源材料为选自下组的T盐：乙酸盐、盐酸盐、硫酸盐、硝酸盐、碳酸盐、 碳酸氢盐、柠檬酸盐、卤化盐、或其组合；
所述M源材料为包含M元素的选自下组的物质：酸、铵盐、氧化物、脂类物质；
所述碳源材料为有机碳源，优选地选自下组：葡萄糖、蔗糖、柠檬酸、草酸、乙酸、或其组合。
在另一优选例中，T1为130-180℃，较佳地140-170℃，更佳地145-160℃；
t1为1-150h，较佳地10-100h，更佳地20-85h；
T2为400-800℃，较佳地500-700℃；
t2为0.1-5h，较佳地0.5-3h。
在另一优选例中，步骤5)中步骤4)所得产物和所述碳源材料的混料比为1－5：1，较佳地2－3.5：1。
本发明的第三方面，提供了一种锂离子电池正极，所述正极的正极活性材料包含本发明第一方面所述硅酸盐正极材料或由本发明第一方面所述硅酸盐正极材料组成。
在另一优选例中，所述正极还包含导电剂、粘结剂。
本发明的第四方面，提供了一种锂离子电池，所述锂离子电池包含本发明第三方面所述的正极。
应理解，在本发明范围内中，本发明的上述各技术特征和在下文(如实施例)中具体描述的各技术特征之间都可以互相组合，从而构成新的或优选的技术方案。限于篇幅，在此不再一一累述。
附图说明
图1为实施例1所得Li 1.9CoSi 0.9P 0.1O 4和Li 1.9CoSi 0.9P 0.1O 4/C的XRD图谱。
图2为实施例1所得Li 1.9CoSi 0.9P 0.1O 4的SEM图片。
图3为分别以实施例1所得Li 1.9CoSi 0.9P 0.1O 4和Li 1.9CoSi 0.9P 0.1O 4/C为正极活性材料的锂离子电池的充放电测试结果。
图4为实施例2所得Li 1.9CoSi 0.9V 0.1O 4和Li 1.9CoSi 0.9V 0.1O 4/C的XRD图谱。
图5为实施例2所得Li 1.9CoSi 0.9V 0.1O 4的SEM图片。
图6为分别以实施例2所得Li 1.9CoSi 0.9V 0.1O 4和Li 1.9CoSi 0.9V 0.1O 4/C为正极活性材 料的锂离子电池的充放电测试结果。
图7为实施例3所得Li 2Co 0.9Mn 0.1SiO 4和Li 2Co 0.9Mn 0.1SiO 4/C的XRD图谱。
图8为实施例3所得Li 2Co 0.9Mn 0.1SiO 4的SEM图片。
图9为分别以实施例3所得Li 2Co 0.9Mn 0.1SiO 4和Li 2Co 0.9Mn 0.1SiO 4/C为正极活性材料的锂离子电池的充放电测试结果。
图10为对比例1所得Li 2CoSiO 4和Li 2CoSiO 4/C的XRD图谱。
图11为对比例1所得Li 2CoSiO 4的SEM图片。
图12为分别以对比例1所得Li 2CoSiO 4和Li 2CoSiO 4/C为正极活性材料的锂离子电池的充放电测试结果。
具体实施方式
本发明人经过长期而深入的研究，意外地制备得到一种结构稳定、化学性能较好、制备工艺简单可控、安全性好、成本低的锂离子电池硅酸盐正极材料。在此基础上，发明人完成了本发明。
硅酸盐正极材料
具体地，本发明提供了一种硅酸盐正极材料，所述硅酸盐正极材料包含内核Li aCo xT 1-xSi yM 1-yO 4和包覆于所述内核外表面的碳包覆层，并且所述硅酸盐正极材料具有式I所示组成：
Li aCo xT 1-xSi yM 1-yO 4/C  I
其中，T为选自下组的金属元素的金属离子：Mn、Fe、Ni、Ca、Mg、Al、La、Y、Sc、Zn、Cu、V、Mo、Tc、Ru、Rh、Pd、Cr、或其组合；且T的化合价与式I中Co的化合价相同；
M为选自下组元素的离子：P、V、Ti、Ge、Ga、N、F、S、或其组合；
0＜x≤1，0＜y≤1，且x和y不同时为1；
a的取值使得内核Li aCo xT 1-xSi yM 1-yO 4的化合价整体为0。
在另一优选例中，a选自下组：2、1.9。
在另一优选例中，当T为V且M为V时，V的化合价为3+为T，V的化合价为5+为M。
在另一优选例中，0.01＜x≤1，较佳地0.1＜x≤1，更佳地0.3＜x≤1，最佳地 0.5＜x≤1。
在另一优选例中，0.01＜y≤1，较佳地0.1＜y≤1，更佳地0.3＜y≤1，最佳地0.5＜y≤1。
在本发明中，所述硅酸盐正极材料为固溶体材料。
在另一优选例中，所述硅酸盐正极材料为固溶体材料是指：在T的化合价与式I中Co的化合价相同时，T部分取代Co氧四面体中的Co形成T氧四面体阴离子集团。
在另一优选例中，T和Co均为所述硅酸盐正极材料中的固溶体组分。
在另一优选例中，式I中Co和T的化合价选自下组：+2、+3、或其组合。
在本发明中，M为所述硅酸盐正极材料中的掺杂元素。
在另一优选例中，“M为所述硅酸盐正极材料中的掺杂元素”是指：M为Si氧四面体阴离子集团中的掺杂元素。
在另一优选例中，所述硅酸盐正极材料为多形态材料。
在另一优选例中，所述硅酸盐正极材料为多形态材料是指：所述硅酸盐正极材料包含Pmn2 1相和任选地选自下组的相：Pbn2 1相、P2 1/n相、或其组合。
在另一优选例中，所述硅酸盐正极材料具有双峰群特征，优选地，所述双峰群特征在充放电循环过程中稳定存在。
在另一优选例中，所述硅酸盐正极材料同时包含如下两类四面体氧离子基团：T取代或未取代的Co氧四面体氧离子基团、M掺杂或未掺杂的Si氧四面体氧离子基团。
在本发明中，所述硅酸盐正极材料的粒径为5-500nm。
在另一优选例中，所述硅酸盐正极材料的粒径为10-300nm，较佳地15-200nm，更佳地20-100nm。
在另一优选例中，所述内核Li 2Co xT 1-xSi yM 1-yO 4的直径为15－100nm，较佳地20－100nm。
在另一优选例中，所述碳包覆层的厚度为10－100nm，较佳地20－50nm。
在另一优选例中，所述硅酸盐正极材料为颗粒状。
在本发明中，所述硅酸盐正极材料具有选自下组的一个或多个特征：
1)以所述硅酸盐正极材料为正极活性材料制备的锂离子电池在5mA/g电流密度下放电时，可逆放电比容量高于130Ah/kg；
2)以所述硅酸盐正极材料为正极活性材料制备的锂离子电池的放电电压平台高于 4V；
3)以所述硅酸盐正极材料为正极活性材料制备的锂离子电池在循环中不会出现结构性电压降。
更具体地，本发明提供了一种具有式I所示组成的多形态硅酸盐固溶体材料，其中0＜x≤1，0＜y≤1，T为固溶组分，M为掺杂组分；所述材料颗粒在5-200nm左右，Xrd具有双峰群特征；以所述固溶体材料为正极活性材料制备的锂离子电池在充放电循环中不发生结构性电压变化，V具有稳定的放电平台，可获得高于130Ah/kg以上的放电可逆比容量。
更具体地，本发明公开了一种四面体氧离子集团构成的多形态硅酸盐固溶体材料，所述固溶体材料具有式I所示化学式：
Li aCo xT 1-xSi yM 1-yO 4  I
式中，0＜x≤1，0＜y≤1，且T为选自下组的金属元素：Mn,Fe,Ni,Ca，Mg,Al,La,Y，Sc，Li，Zn，Cu，V，Mo，Tc，Ru，Rh，Pd，Cr或其组合；M为选自下组的元素：P,V,Ti，Ge，Ga，Al，N，F，S或其组合；
并且，Co与T是具有+2名义化合价的金属离子，与氧离子构成四面体阴离子集团，是多形态晶体点阵中固溶体组分；M是Si氧四面体单元构成的骨架结构中金属或非金属掺杂组分，具有不同名义化合价；
并且，以所述固溶体材料为正极活性材料制备的锂离子电池，在室温以5mA/g电流密度放电时，可逆放电比容量高于130Ah/kg，该电压平台在充放电循环中不发生结构相变所致的移动。
并且，所述四面体氧离子集团构成的固溶体材料Xrd结构多形态包括Pmn2 1，Pbn2 1和P2 1/n相中一种或多种的的双峰群特征，且双峰群特征在充放电过程也不会发生变化；优选地为Pmn2 1。
在另一优选例中，所述“双峰群特征”是指所述多形态材料的Pmn2 1,Pbn2 1和P2 1/n相XRD图谱在21.8°和23.1°具有明显的双峰结构，包括双峰-双峰、单峰-三峰等峰群组；双峰群特征由制备条件决定，但不随充放电循环过程改变。
在另一优选例中，所述固溶体材料为颗粒状，且所述多形态固溶体材料的颗粒粒径为5-200nm，优选地5-30nm，30-60nm，或60-90nm。
在另一优选例中，Pmn2 1相材料经过硅位骨架M掺杂和颗粒碳包覆改性之后，多形态材料不会发生相变成为混合相，而是保持为Pmn2 1相，且不随充放电循环过程改变。
在另一优选例中，经过固溶、掺杂和碳包覆改性之后，以所述多形态固溶体材料为正极活性材料制备的锂离子电池在2.5-4.6V电压范围内以5mA/g充放电，放电比容量不低于130mAh/g，同时充电平台保持在4.3V左右，放电平台保持在4.1V左右，循环中不会出现结构性电压降。具体地，在Li2FeSiO4和Li2MnSiO4材料中，第一圈到第二圈的时候就会发生明显的电压降现象，在Li2CoSiO4材料中第一圈到第二圈的时候就没有。
优选地，T元素选择+2,或+3价金属元素或其组合。
优选地，M元素选择高价金属或非金属元素或其组合。
优选地，正极材料的充电平台在4.3V左右，放电平台在4.1V左右。
优选地，四面体氧离子集团构成的固溶体材料的多形态特征中，Pmn2 1结构较佳。
应理解，本发明所述正极材料外表面的碳包覆层可有效提高所得正极材料的电化学活性。
应理解，在现有的典型的硅酸盐正极材料Li 2CoSiO 4中，同时存在Co氧四面体和Si氧四面体阴离子基团。
制备方法
本发明还提供了一种所述的硅酸盐正极材料的制备方法，所述方法包括如下步骤：
1)提供第一溶液、第二溶液和碳源材料，其中，
所述第一溶液包含第一溶剂、锂源材料和硅源材料；
所述第二溶液包含第二溶剂、钴源材料、T源材料和/或M源材料；
2)在搅拌条件下，混合所述第一溶液和所述第二溶液，得到前驱体溶液；
3)将所述前驱体溶液转移至反应釜中，在第一温度T1下反应t1时间；
4)抽滤并任选地洗涤干燥步骤3)所得产物，得到所述的硅酸盐正极材料的内核；
5)混合步骤4)所得产物和所述碳源材料，将所得混合物在第二温度T2下煅烧处理t2时间，得到所述的硅酸盐正极材料。
在另一优选例中，所述第一溶剂选自下组：水、乙醇、乙二醇、氨水、或其组合，优选为去离子水。
在另一优选例中，所述第二溶剂选自下组：乙二醇、水、乙醇、或其组合。
在本发明中，所述锂源材料选自下组：氢氧化锂、氧化锂、或其组合；
所述硅源材料选自下组：氧化硅、正硅酸乙酯、正硅酸甲酯、硅酸盐、有机硅、或其组合；
所述钴源材料为选自下组的钴盐：乙酸盐、盐酸盐、硫酸盐、硝酸盐、碳酸盐、碳酸氢盐、柠檬酸盐、卤化盐、或其组合；
所述T源材料为选自下组的T盐：乙酸盐、盐酸盐、硫酸盐、硝酸盐、碳酸盐、碳酸氢盐、柠檬酸盐、卤化盐、或其组合；
所述M源材料为包含M元素的选自下组的物质：酸、铵盐、氧化物、脂类物质；
所述碳源材料为有机碳源，优选地选自下组：葡萄糖、蔗糖、柠檬酸、草酸、乙酸、或其组合。
在本发明中，T1为130-180℃，较佳地140-170℃，更佳地145-160℃；
t1为1-150h，较佳地10-100h，更佳地20-85h；
T2为400-800℃，较佳地500-700℃；
t2为0.1-5h，较佳地0.5-3h。
在另一优选例中，步骤5)中步骤4)所得产物和所述碳源材料的混料比为1－5：1，较佳地2－3.5：1。
应用
本发明还提供了一种锂离子电池正极，所述正极的正极活性材料包含所述硅酸盐正极材料或由所述硅酸盐正极材料组成。
在另一优选例中，所述正极还包含导电剂、粘结剂。
本发明还提供了一种锂离子电池，所述锂离子电池包含所述的正极。
与现有技术相比，本发明具有以下主要优点：
(1)所述硅酸盐正极材料具有高能量密度、安全性好、成本低、结构稳定的优点；
(2)所述硅酸盐正极材料的制备方法简单可控、安全性好、成本低；
(3)以所述硅酸盐正极材料为正极活性材料的锂离子电池在5mA/g的充电容量可高达304mAh/g，放电容量可高达155mAh/g；所述锂离子电池的放电电压可高达4.1V。
下面结合具体实施例，进一步阐述本发明。应理解，这些实施例仅用于说明本发明而不用于限制本发明的范围。下列实施例中未注明具体条件的实验方法，通常按照常规条件或按照制造厂商所建议的条件。除非另外说明，否则百分比和份数按重量计算。
除非另行定义，文中所使用的所有专业与科学用语与本领域熟练人员所熟悉的意义相同。此外，任何与所记载内容相似或均等的方法及材料皆可应用于本发明方法中。文中所述的较佳实施方法与材料仅作示范之用。
通用测试方法
XRD
XRD设备采用Shimadzu公司XRD-6100型号，射线源采用
Figure PCTCN2018083524-appb-000001
SEM
SEM采用FEI公司、QUANTA 250 FEG型号的设备。
充放电性能
锂离子电池的制备
将本发明所得硅酸盐正极材料分别与导电剂乙炔黑、粘结剂聚偏氟乙烯(PVDF)在氮甲基吡咯烷酮(NMP)溶剂中均匀混合，硅酸盐正极材料、乙炔黑和粘结剂的质量比为80:10:10，然后将所得浆料涂覆在铝箔上，烘干，切片，压片，制得锂离子电池正极极片。在高纯氩气氛保护的手套箱中，将正极极片，隔膜，电解液以及负极组装为CR2032扣式电池。其中负极采用锂片，隔膜采用Celgard 2550，电解液采用1M LiPF 6溶于体积比1:1的EC/DMC中。
充放电性能的测试
电池充放电采用蓝电2001A，室温25℃，电压2.5-4.6V。
实施例1 硅酸盐正极材料1(Li 1.9CoSi 0.9P 0.1O 4/C)
1.1将Li、Si按照摩尔比例4:1称取氢氧化锂(如1.2mol)和氧化硅纳米粉末(如0.27mol)加入去离子水充分搅拌，配置成悬浮液，然后置于超声器里超声3h；
1.2称取适量氯化钴(如0.3mol)和H 3PO 4(如0.03mol)，加入乙二醇中充分溶解；
1.3在1.1所得溶液中缓慢均匀加入1.2所得溶液，同时搅拌，转速1500转/分；
1.4将1.3得到的混合溶液转移至反应釜中，150℃反应72h；
1.5将1.4反应产物抽滤，多次洗涤后干燥；
1.6将1.5干燥后产物(如1.5g)与蔗糖(如0.42g)混合，球磨12h，然后置于管式炉中，在惰性气氛以5℃/min升温到600℃煅烧1h；
1.7自然冷却后取出产物，所得产物即为制得的硅酸盐正极材料1。
结果
对1.5干燥后产物和1.7所得硅酸盐正极材料1分别进行ICP(无机元素分析)、XRD和SEM测试，对分别以1.5干燥后产物和1.7所得硅酸盐正极材料1为正极活性材料的锂离子电池进行充放电测试和循环性能测试。
经ICP检测，1.5干燥后产物的组成为Li 1.9CoSi 0.9P 0.1O 4，1.7所得硅酸盐正极材料1的组成为Li 1.9CoSi 0.9P 0.1O 4/C。
图1为实施例1所得Li 1.9CoSi 0.9P 0.1O 4和Li 1.9CoSi 0.9P 0.1O 4/C的XRD图谱。
从图1可以看出：未包覆的Li 1.9CoSi 0.9P 0.1O 4材料为纯Pmn2 1相，XRD图谱在21.8°和23.1°具有明显的双峰结构；包覆后的材料Li 1.9CoSi 0.9P 0.1O 4/C在21.8°和23.1°仍具有明显的双峰结构，在16.3°和24.3°未出现新峰，维持Pmn2 1相，但在44°出现一个Co单质峰。上述结果表明：碳包覆前后Li 1.9CoSi 0.9P 0.1O 4的结构并未改变，同时只有少量的Co离子被还原成单质Co。
图2为实施例1所得Li 1.9CoSi 0.9P 0.1O 4的SEM图片。
从图2可知：Li 1.9CoSi 0.9P 0.1O 4颗粒均匀，大小约为50nm。
图3为分别以实施例1所得Li 1.9CoSi 0.9P 0.1O 4和Li 1.9CoSi 0.9P 0.1O 4/C为正极活性材料的锂离子电池的充放电测试结果。
从图3可知：以5mA/g充放电时，以Li 1.9CoSi 0.9P 0.1O 4为正极活性材料的锂离子电池的首次充电容量为134mAh/g，首次放电容量为34mAh/g；以Li 1.9CoSi 0.9P 0.1O 4/C为正极活性材料的锂离子电池的首次充电容量为270mAh/g，首次放电容量为143mAh/g；并且，无论是以Li 1.9CoSi 0.9P 0.1O 4为正极活性材料的锂离子电池，还是以 Li 1.9CoSi 0.9P 0.1O 4/C为正极活性材料的锂离子电池，其充电平台基本在4.3V且在4.1V具有明显的放电平台。
实施例2 硅酸盐正极材料2(Li 1.9CoSi 0.9V 0.1O 4/C)
2.1将Li、Si按照摩尔比例4:1称取氢氧化锂(如1.2mol)和氧化硅纳米粉末(如0.27mol)加入去离子水充分搅拌，配置成悬浮液，然后置于超声器里超声3h；
2.2称取适量氯化钴(如0.3mol)和NH 4VO 3(如0.03mol)，加入乙二醇中充分溶解；
2.3在2.1所得溶液中缓慢均匀加入2.2所得溶液，同时搅拌，转速1500转/分；
2.4将2.3得到的混合溶液转移至反应釜中，150℃反应72h；
2.5将2.4反应产物抽滤，多次洗涤后干燥；
2.6将2.5干燥后产物(如1.5g)与蔗糖(如0.42g)混合，球磨12h，然后置于管式炉中，在惰性气氛以5℃/min升温到600℃煅烧1h；
2.7自然冷却后取出产物，所得产物即为制得的硅酸盐正极材料2。
结果
经ICP检测，2.5干燥后产物的组成为Li 1.9CoSi 0.9V 0.1O 4,2.7所得硅酸盐正极材料2的组成为Li 1.9CoSi 0.9V 0.1O 4/C。
图4为实施例2所得Li 1.9CoSi 0.9V 0.1O 4和Li 1.9CoSi 0.9V 0.1O 4/C的XRD图谱。
从图4可以看出：未包覆的Li 1.9CoSi 0.9V 0.1O 4材料为纯Pmn2 1相，XRD图谱在21.8°和23.1°具有明显的双峰结构；包覆后的Li 1.9CoSi 0.9V 0.1O 4/C材料在21.8°和23.1°仍具有明显的双峰结构，在16.3°和24.3°未出现新峰，维持Pmn2 1相，但在44°出现一个Co单质峰。上述结果表明：碳包覆前后Li 1.9CoSi 0.9V 0.1O 4的结构并未改变，同时只有少量的Co离子被还原成单质Co。
图5为实施例2所得Li 1.9CoSi 0.9V 0.1O 4的SEM图片。
从图5可知：Li 1.9CoSi 0.9V 0.1O 4颗粒均匀，大小约为50nm。
图6为分别以实施例2所得Li 1.9CoSi 0.9V 0.1O 4和Li 1.9CoSi 0.9V 0.1O 4/C为正极活性材料的锂离子电池的充放电测试结果。
从图6可知：以5mA/g充放电时，以Li 1.9CoSi 0.9V 0.1O 4为正极活性材料的锂离子 电池的首次充电容量为146.5mAh/g，首次放电容量为52.9mAh/g；以Li 1.9CoSi 0.9V 0.1O 4/C为正极活性材料的锂离子电池的首次充电容量为304.3mAh/g，首次放电容量为139.1mAh/g；并且，无论是以Li 1.9CoSi 0.9V 0.1O 4为正极活性材料的锂离子电池，还是以Li 1.9CoSi 0.9V 0.1O 4/C为正极活性材料的锂离子电池，其充电平台基本在4.3V且在4.1V具有明显的放电平台。
实施例3 硅酸盐正极材料3(Li 2Co 0.9Mn 0.1SiO 4/C)
3.1将Li、Si按照摩尔比例4:1称取氢氧化锂(如1.2mol)和氧化硅纳米粉末(如0.3mol)加入去离子水充分搅拌，配置成悬浮液，然后置于超声器里超声3h；
3.2称取适量氯化钴(如0.27mol)和氯化锰(如0.03mol)，加入乙二醇中充分溶解；
3.3在3.1所得溶液中缓慢均匀加入3.2所得溶液，同时搅拌，转速1500转/分；
3.4将3.3得到的混合溶液转移至反应釜中，150℃反应72h；
3.5将3.4反应产物抽滤，多次洗涤后干燥；
3.6将3.5干燥后产物(如1.5g)与蔗糖(如0.42g)混合，球磨12h，然后置于管式炉中，在惰性气氛以5℃/min升温到600℃煅烧1h；
3.7自然冷却后取出产物，所得产物即为制得的硅酸盐正极材料3。
结果
经ICP检测，3.5干燥后产物的组成为Li 2Co 0.9Mn 0.1SiO 4，3.7所得硅酸盐正极材料3的组成为Li 2Co 0.9Mn 0.1SiO 4/C。
图7为实施例3所得Li 2Co 0.9Mn 0.1SiO 4和Li 2Co 0.9Mn 0.1SiO 4/C的XRD图谱。
从图7可以看出：未包覆的Li 2Co 0.9Mn 0.1SiO 4材料为纯Pmn2 1相，XRD图谱在21.8°和23.1°具有明显的双峰结构；包覆后的Li 2Co 0.9Mn 0.1SiO 4/C材料在21.8°和23.1°仍具有明显的双峰结构，但是在16.3和24.3°也出现了峰，显示为Pmn2 1和Pbn2 1的混合相，同时在在44°出现一个Co单质峰。上述结果表明：碳包覆前后Li 2Co 0.9Mn 0.1SiO 4的结构并未改变，同时只有少量的Co离子被还原成单质Co。
图8为实施例3所得Li 2Co 0.9Mn 0.1SiO 4的SEM图片。
从图8可知：Li 1.9Co 0.9Mn 0.1SiO 4颗粒均匀，大小约为50nm。
图9为分别以实施例3所得Li 2Co 0.9Mn 0.1SiO 4和Li 2Co 0.9Mn 0.1SiO 4/C为正极活性材料的锂离子电池的充放电测试结果。
从图9可知：以5mA/g充放电时，以Li 2Co 0.9Mn 0.1SiO 4为正极活性材料的锂离子电池的首次充电容量为165.4mAh/g，首次放电容量为43.5mAh/g；以Li 2Co 0.9Mn 0.1SiO 4/C为正极活性材料的锂离子电池的首次充电容量为281mAh/g，首次放电容量为155mAh/g；并且，无论是以Li 2Co 0.9Mn 0.1SiO 4为正极活性材料的锂离子电池，还是以Li 2Co 0.9Mn 0.1SiO 4/C为正极活性材料的锂离子电池，其充电平台基本在4.3V且在4.1V具有明显的放电平台。
对比例1 硅酸盐正极材料C1(Li 2CoSiO 4/C)
C1.1将Li、Si按照摩尔比例4:1称取氢氧化锂(如1.2mol)和氧化硅纳米粉末(如0.3mol)加入去离子水充分搅拌，配置成悬浮液，然后置于超声器里超声3h；
C1.2称取适量氯化钴(如0.3mol)，加入乙二醇中充分溶解；
C1.3在C1.1所得溶液中缓慢均匀加入C1.2所得溶液，同时搅拌，转速1500转/分；
C1.4将C1.3得到的混合溶液转移至反应釜中，150℃反应72h；
C1.5将C1.4反应产物抽滤，多次洗涤后干燥；
C1.6将C1.5干燥后产物(如1.5g)与蔗糖(如0.42g)混合，球磨12h，然后置于管式炉中，在惰性气氛以5℃/min升温到600℃煅烧1h；
C1.7自然冷却后取出产物，所得产物即为制得的硅酸盐正极材料C1。
结果
经ICP检测，C1.5干燥后产物的组成为Li 2CoSiO 4，C1.7所得硅酸盐正极材料C1的组成为Li 2CoSiO 4/C。
图10为对比例1所得Li 2CoSiO 4和Li 2CoSiO 4/C的XRD图谱。
从图10可以看出：未包覆的Li 2CoSiO 4材料为纯Pmn2 1相，XRD图谱在21.8°和23.1°具有明显的双峰结构；包覆后的Li 2CoSiO 4/C材料在21.8°和23.1°仍具有明显的双峰结构，但是在16.3°和24.3°也出现了峰，显示为Pmn2 1和Pbn2 1的混合相，同时在在44°出现一个Co单质峰。上述结果表明：碳包覆前后Li 2CoSiO 4的结构并未改变，同时只有少量的Co离子被还原成单质Co。
图11为对比例1所得Li 2CoSiO 4的SEM图片。
从图11可知：Li 1.9CoSiO 4颗粒均匀，大小约为50nm。
图12为分别以对比例1所得Li 2CoSiO 4和Li 2CoSiO 4/C为正极活性材料的锂离子电池的充放电测试结果。
从图12可知：以5mA/g充放电时，以Li 2CoSiO 4为正极活性材料的锂离子电池的首次充电容量为120mAh/g，首次放电容量为40mAh/g；以Li 2CoSiO 4/C为正极活性材料的锂离子电池的首次充电容量为226mAh/g，首次放电容量为112mAh/g；并且，无论是以Li 2CoSiO 4为正极活性材料的锂离子电池，还是以Li 2CoSiO 4/C为正极活性材料的锂离子电池，其充电平台基本在4.3V且在4.1V具有明显的放电平台。
在本发明提及的所有文献都在本申请中引用作为参考，就如同每一篇文献被单独引用作为参考那样。此外应理解，在阅读了本发明的上述讲授内容之后，本领域技术人员可以对本发明作各种改动或修改，这些等价形式同样落于本申请所附权利要求书所限定的范围。

Claims (10)

  1. 一种硅酸盐正极材料，其特征在于，所述硅酸盐正极材料包含内核Li aCo xT 1-xSi yM 1-yO 4和包覆于所述内核外表面的碳包覆层，并且所述硅酸盐正极材料具有式I所示组成：
    Li aCo xT 1-xSi yM 1-yO 4/C  I
    其中，T为选自下组的金属元素的金属离子：Mn、Fe、Ni、Ca、Mg、Al、La、Y、Sc、Zn、Cu、V、Mo、Tc、Ru、Rh、Pd、Cr、或其组合；且T的化合价与式I中Co的化合价相同；
    M为选自下组元素的离子：P、V、Ti、Ge、Ga、N、F、S、或其组合；
    0＜x≤1，0＜y≤1，且x和y不同时为1；
    a的取值使得内核Li aCo xT 1-xSi yM 1-yO 4的化合价整体为0。
  2. 如权利要求1所述的硅酸盐正极材料，其特征在于，所述硅酸盐正极材料为固溶体材料。
  3. 如权利要求1所述的硅酸盐正极材料，其特征在于，M为所述硅酸盐正极材料中的掺杂元素。
  4. 如权利要求1所述的硅酸盐正极材料，其特征在于，所述硅酸盐正极材料的粒径为5-500nm。
  5. 如权利要求1所述的硅酸盐正极材料，其特征在于，所述硅酸盐正极材料具有选自下组的一个或多个特征：
    1)以所述硅酸盐正极材料为正极活性材料制备的锂离子电池在5mA/g电流密度下放电时，可逆放电比容量高于130Ah/kg；
    2)以所述硅酸盐正极材料为正极活性材料制备的锂离子电池的放电电压平台高于4V；
    3)以所述硅酸盐正极材料为正极活性材料制备的锂离子电池在循环中不会出现结构性电压降。
  6. 一种权利要求1所述的硅酸盐正极材料的制备方法，其特征在于，所述方法包括如下步骤：
    1)提供第一溶液、第二溶液和碳源材料，其中，
    所述第一溶液包含第一溶剂、锂源材料和硅源材料；
    所述第二溶液包含第二溶剂、钴源材料、T源材料和/或M源材料；
    2)在搅拌条件下，混合所述第一溶液和所述第二溶液，得到前驱体溶液；
    3)将所述前驱体溶液转移至反应釜中，在第一温度T1下反应t1时间；
    4)抽滤并任选地洗涤干燥步骤3)所得产物，得到权利要求1所述的硅酸盐正极材料的内核；
    5)混合步骤4)所得产物和所述碳源材料，将所得混合物在第二温度T2下煅烧处理t2时间，得到权利要求1所述的硅酸盐正极材料。
  7. 如权利要求6所述的方法，其特征在于，所述锂源材料选自下组：氢氧化锂、氧化锂、或其组合；
    所述硅源材料选自下组：氧化硅、正硅酸乙酯、正硅酸甲酯、硅酸盐、有机硅、或其组合；
    所述钴源材料为选自下组的钴盐：乙酸盐、盐酸盐、硫酸盐、硝酸盐、碳酸盐、碳酸氢盐、柠檬酸盐、卤化盐、或其组合；
    所述T源材料为选自下组的T盐：乙酸盐、盐酸盐、硫酸盐、硝酸盐、碳酸盐、碳酸氢盐、柠檬酸盐、卤化盐、或其组合；
    所述M源材料为包含M元素的选自下组的物质：酸、铵盐、氧化物、脂类物质；
    所述碳源材料为有机碳源，优选地选自下组：葡萄糖、蔗糖、柠檬酸、草酸、乙酸、或其组合。
  8. 如权利要求6所述的方法，其特征在于，T1为130-180℃；
    t1为1-150h；
    T2为400-800℃；
    t2为0.1-5h。
  9. 一种锂离子电池正极，其特征在于，所述正极的正极活性材料包含权利要求1所述硅酸盐正极材料或由权利要求1所述硅酸盐正极材料组成。
  10. 一种锂离子电池，其特征在于，所述锂离子电池包含权利要求9所述的正极。
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