CN103117385B

CN103117385B - A kind of defect sturcture LiFePO4The rich lithium layer-layer positive electrode of surface modification and preparation method

Info

Publication number: CN103117385B
Application number: CN201310022221.4A
Authority: CN
Inventors: 水淼; 杨天赐; 舒杰; 程亮亮; 冯琳; 任元龙; 郑卫东; 高珊
Original assignee: Ningbo University
Current assignee: Ningbo University
Priority date: 2013-01-05
Filing date: 2013-01-05
Publication date: 2016-05-18
Anticipated expiration: 2033-01-05
Also published as: CN103117385A

Abstract

Layer-layer composite lithium-rich anode material of defect sturcture LiFePO4 surface modification, the stoichiometric equation of its surface reforming layer is LiFe_1-2yP_1-yO_4-δ, δ=4-[(1-2y) and * 2+1+ (1-y) * 5]/2, y=0.01-0.06; The stoichiometric equation of layer-layer composite lithium-rich anode material is xLi₂MnO₃.(1-x)LiMn0.5Ni_0.5O₂(0≤x≤0.5); The amount of substance of surface reforming layer is the 1%-10% of positive electrode amount. The positive electrode of this surface modification has high circulation volume hold facility and outstanding multiplying power property.

Description

A kind of defect sturcture LiFePO4The rich lithium layer-layer positive electrode of surface modification and preparation method

Technical field

The present invention relates to a kind of anode material for lithium-ion batteries and manufacture field.

Background technology

Lithium ion battery have volume, weight energy than high, voltage is high, self-discharge rate is low, memory-less effect, have extended cycle life, the high absolute advantage of power density, have the occupation rate of market that exceedes 30,000,000,000 dollars of/year shares and far exceed other batteries in global portable power source market, the electrochmical power source [Wu Yuping most with future develop, Wan Chunrong, Jiang Changyin, lithium rechargeable battery, Beijing: Chemical Industry Press, 2002.]. But since lithium ion battery commercialization in 1991, the actual specific capacity of positive electrode is hovered all the time between 100-180mAh/g, the low bottleneck that promotes lithium ion battery specific energy that become of positive electrode specific capacity. If want effectively to improve the energy density of lithium ion battery, must be from the viewpoint of improving the voltage difference between positive and negative pole material and developing two of height ratio capacity electrode materials.

The current commercial lithium ion battery the most widely positive electrode of practicality is LiCoO₂, the theoretical specific capacity of cobalt acid lithium is 274mAh/g, and actual specific capacity is between 130-140mAh/g, and cobalt is strategic materials, expensive and have larger toxicity. Therefore in recent years, the researcher of countries in the world is devoted to the research and development of Olivine-type Cathode Material in Li-ion Batteries always, up till now, the lithium ion cell positive filtering out reaches tens of kinds, but really has potential commercial applications prospect or appeared at positive electrode on market very few really. As lithium manganate having spinel structure LiMn₂O₄Its cost is lower, than being easier to preparation, security performance is also relatively good, but capacity is lower, and theoretical capacity is 148mAh/g, actual capacity is at 100-120mAh/g, and this material capacity circulation hold facility is not good, under high temperature, capacity attenuation is very fast, and researcher is being perplexed in the John-Teller effect of Mn3+ and the dissolving in electrolyte for a long time. The LiNiO of layer structure₂And LiMnO₂Although there is larger theoretical specific capacity, be respectively 275mAh/g and 285mAh/g, their preparations are very difficult, poor heat stability, cyclicity is very poor, and capacity attenuation is very fast. And business-like LiFePO4 LiFePO progressively at present₄Cost is low, Heat stability is good, environmental friendliness, but its theoretical capacity approximately only has 170mAh/g, and actual capacity is in 140mAh/g left and right.

In recent years, researcher gradually by high lithium than on positive electrode, particularly the high lithium of manganese base manganese-nickel binary and manganese base manganese-nickel-cobalt ternary solid solution system compares positive electrode, these materials have very high Capacity Ratio, high stability and relative cheap cost and are subject to people's concern [Young-SikHong, YongJoonPark, etal., SolidStateIonics, 2005,176:1035～1042]. Rich lithium material can be regarded Li as₂MnO₃And LiM ' O₂(M′＝Mn，Co，Ni，Mn_0.5Ni_0.5Deng) continuous solid solution xLi₂MnO₃. (1-x) LiM ' O2. As M '=Mn_0.5Ni_0.5Time, be xLi₂MnO₃.(1-x)LiMn_0.5Ni_0.5O₂The rich lithium composite positive pole of layer-layer. Li₂MnO₃Have halite structure, symmetry is C2/m. Can be write as Li[Li_1/3Mn_2/3]O₂Form is the layer structure of Li layer and manganese layer formation, Li⁺And Mn⁴⁺Common formation manganese layer, each octahedra Li⁺By six octahedra Mn⁴⁺The formation Li (Mn) that surrounds₆Structure, and lithium ion in Li layer is tetrahedral structure. Li₂MnO₃Electro-chemical activity lower, electronic conductivity and ionic conductivity are also very little. As itself and the LiMn that is all layer structure_0.5Ni_0.5O₂After compound, form the rich lithium layered cathode material xLi of layered-layered structure₂MnO₃.(1-x)LiMn_0.5Ni_0.5O₂, make the positive electrode of this structure have the discharge capacity that exceedes 200mAh/g. This material is in the time that charging voltage is less than 4.6V, and Mn keeps+4 valencys constant, Li₂MnO₃Structure keeps inertia, and the stability of positive electrode structure is provided, and prevents that material structure caves in charge and discharge process, and Ni, from+become+4 valencys of divalent state, is the active component of generation capacity. In the time that charging voltage exceedes 4.6V, will there will be a platform, Li in 4.6V position₂O is from Li₂MnO₃In lattice, deviate from completely and become MnO₂, more than at this moment cell voltage will reach 4.8V; In the time that battery starts to discharge, the Li previously having deviate from₂O does not return in lattice, along with the Ni that carries out of electric discharge⁴⁺Be reduced to gradually Ni²⁺, the Mn in material subsequently⁴⁺Also be reduced participation electrochemical process, therefore Li₂MnO₃Activation while exceeding 4.6V is that this material has the reason [Johnson, C.S., N.Li, etal., Electrochemistrycommunications, 2007,9 (4): 787-795.] that exceedes 200mAh/g.

But, in fact xLi₂MnO₃.(1-x)LiM′O₂The microstructure of the rich lithium layered cathode material of layered-layered structure is very complicated, as ThackerayM.M.[ThackerayMM, KangS-H, JohnsonCS, etal.JournalofMaterialsChemistry, 2007,17:3112-3125.] etc. people point out like that, the result of study of XRD and x ray absorption near edge structure test all shows xLi₂MnO₃.(1-x)LiMn_0.5Ni_0.5O₂O₂The rich lithium layered cathode material of layered-layered structure is not pure solid solution, and excessive lithium ion is distributed in transition metal layer by arest neighbors Mn⁴⁺Surround, form the LiMn of local cluster₆Structure, and LiMn₆Li just₂MnO₃Feature structure. Therefore xLi₂MnO₃.(1-x)LiMn_0.5Ni_0.5O₂Material structure is regarded stratiform Li as₂MnO₃With stratiform LiMn_0.5Ni_0.5O₂Compound on nanoscale, its lithium ion and the arranging shortrange order of transition metal ions and long-range is unordered more suitable. Like this, due to insulation phase Li₂MnO₃Existence, Li₂MnO₃The electronic conductivity of feature structure and ionic conductivity are all very low, on the other hand, and xLi₂MnO₃.(1-x)LiMn_0.5Ni_0.5O₂Laminate Li₂MnO₃Interlamellar spacing and LiMn_0.5Ni_0.5O₂It is larger that interlamellar spacing differs, and both coupling causes the embedding of lithium ion and deviate from more difficultly, causes the overall lithium ion conductivity of composite low, and lithium ion diffusion coefficient is 10^-12-10^-13S/cm²Between. So xLi₂MnO₃.(1-x)LiMn_0.5Ni_0.5O₂Cyclical stability not good, repeatedly circulation after capacity attenuation very fast, in the time that charging and discharging currents increases, capacity attenuation is very fast.

Finishing is a kind of very effective method of improving rich lithium stratiform anode material for compound lithium ion battery cyclical stability and multiplying power property, such as sour pretreatment can be xLi₂MnO₃.(1-x)LiMn_0.5Ni_0.5O₂In structure, LiO composition filters out in advance, thereby makes the efficiency for charge-discharge of circulation in first week bring up to more than 90% [KangSH, ThackerayMM., ElectrochemicalSociety, 2008,155:A269-A275.]. Some oxides are as Al₂O₃，ZrO₂，ZnO，CeO₂[MyungST, IzumiK, KomabaS, etal.J.Phys.Chem.C, 2007,111 (10): 4061-4067] the coated Surface Oxygen activity that can be reduced in rich lithium stratiform anode material for compound lithium ion battery under high voltage in surface, isolated electrode material and electrolyte to a certain extent, slow down the destruction that discharges effects on surface lattice structure due to HF, thereby improve its cyclic discharge capacity hold facility. But current finishing component only plays the effect of guard electrode surface of active material structure conventionally, more limited to improving its multiplying power property effect; Thereby and finishing material does not often have the discharge capacity of electro-chemical activity reduction material monolithic. Therefore further explore the finishing of this positive electrode to developing the high performance xLi of composite lithium-rich anode material layer by layer₂MnO₃.(1-x)LiMn_0.5Ni_0.5O₂There is very important meaning. Defect sturcture LiFePO4 is as LiFe_0.9P_0.95O_3.775Here Fe: P stoichiometric proportion departs from former 1: 1 stoichiometric proportion slightly, owing to there being micro-Fe in material structure: P mismatch and ionic conductivity is increased sharply. Adopt this material to carry out finishing and can overcome the too low and material electrochemical performance defect that causes of composite lithium-rich anode material ionic conductivity layer by layer.

Summary of the invention

Technical problem to be solved by this invention is layer-layer composite lithium-rich anode material xLi of a kind of defect sturcture LiFePO4 surface modification of providing for existing background technology₂MnO₃.(1-x)LiMn_0.5Ni_0.5O₂(0≤x≤0.5). In LiFePO4 system, introduce non-stoichiometric Fe: P defect sturcture LiFe_1-2yP_1-yO_4-δ, δ is for balancing charge δ=4-[(1-2y) and * 2+1+ (1-y) * 5]/2, wherein y=0.01-0.06; Ionic conductivity increases substantially, when it is coated to layer-layer composite lithium-rich anode material xLi₂MnO₃.(1-x)LiMn_0.5Ni_0.5O₂When (0≤x≤0.5) is upper, be reduced on the one hand the Surface Oxygen activity of rich lithium stratiform anode material for compound lithium ion battery under high voltage, reduced positive electrode has reduced HF release effects on surface lattice structure destruction with contacting of electrolyte; LiFe in addition_1-2yP_1-yO_4-δItself be exactly a kind of positive electrode active materials of higher capacity, be conducive to keep the high power capacity of material monolithic; Fe simultaneously³⁺/Fe²⁺Lower and the good reversibility of oxidation-reduction potential, receives and in charging, deviates from and embedding is returned in rich lithium material again lithium ion reduces irreversible capacity loss; Particularly advantageously its high-lithium ion electrical conductivity has greatly been improved the low shortcoming of positive electrode lithium ion conductivity; These factors make layer-layer composite lithium-rich anode material xLi₂MnO3_.(1-x)LiMn_0.5Ni_0.5O₂(0≤x≤0.5) has better circulation volume hold facility and multiplying power property.

The present invention reaches by the following technical solutions, and this technical scheme provides layer-layer composite lithium-rich anode material xLi of defect sturcture LiFePO4 surface modification₂MnO₃.(1-x)LiMn_0.5Ni_0.5O₂(0≤x≤0.5); The stoichiometric equation of its surface reforming layer is LiFe_1-2yP_1-yO_4-δ, δ=4-[(1-2y) and * 2+1+ (1-y) * 5]/2, y=0.01-0.06; The amount of substance of surface reforming layer is the 1%-10% of positive electrode amount.

In this technical scheme, will be according to stoichiometric equation xLi₂MnO₃.(1-x)LiMn_0.5Ni_0.5O₂The soluble lithium compounds of (0≤x≤0.5), soluble manganese salt, soluble nickel salt are dissolved in deionized water, and adding amount of substance is that all metal ions total amount 1.2-2.0 tartaric acid doubly stirs to dissolving completely; By the temperature rise of system, to 70-85 DEG C of lasting stirring until the water of 70-85% evaporates, at this moment solution becomes gradually thickness and forms gelatin. Gelatin material is ground to 10-30 minute after dry 20-48 hour in the baking oven of 130-200 DEG C in mortar. The powder obtaining is warmed up to 500-600 DEG C and at this temperature lower calcination 3-5 hour with the speed of 2-10 DEG C/min in tube furnace, cooling rear taking-up powder, in mortar, continue to grind 10-30 minute, powder is pressed into sheet with the pressure of 100-300MPa, in tube furnace, be warmed up to 850-950 DEG C of calcining 5-15 hour with the speed of 2-10 DEG C/min, obtain lithium-rich anode material after cooling with stove. Will be according to stoichiometric equation LiFe_1-2yP_1-yO_4-δ, wherein: y=0.01-0.06; Soluble lithium compounds, soluble ferrite, ammonium dihydrogen phosphate (ADP) be dissolved in deionized water at normal temperature and continue and stir, adding amount of substance is that all metal ions total amount 2.5-4.0 tartaric acid doubly stirs to dissolving completely; Add the lithium-rich anode material that 10-100 doubly measures to form suspension; continuing under the condition stirring; the temperature of rising suspension is to 75-85 DEG C; slow evaporation moisture; until system becomes the muddy of thickness; this material is put into after 100-160 DEG C of oven drying 10-20 hour and taken out under nitrogen atmosphere protection and be warmed up to 600-850 DEG C of calcining 10-15 hour with the speed of 2-10 DEG C/min, with the cooling layer-layer composite lithium-rich anode material that obtains defect sturcture LiFePO4 surface modification of stove. Wherein: solubility lithium salts is LiNO₃、CH₃One in COOLi; Soluble manganese salt is Mn (CH₃COO)₂·4H₂O、MnSO₄·H₂One in O; Soluble nickel salt is Ni (CH₃COO)₂·4H₂O、NiSO₄·6H₂One in O; Soluble ferric iron salt is Fe (CH₃COO)₂、Fe(Cl)₂·4HxO、Fe(NO₃)₂·6H₂One in O.

Compared with prior art, the invention has the advantages that: as this defect sturcture LiFe_1-2yP_1-yO_4-δBe compound to layer-layer composite lithium-rich anode material xLi₂MnO₃.(1-x)LiMn_0.5Ni_0.5O₂When (0≤x≤0.5) is upper, be reduced on the one hand the Surface Oxygen activity of rich lithium stratiform anode material for compound lithium ion battery under high voltage, reduced positive electrode has reduced HF release effects on surface lattice structure destruction with contacting of electrolyte; LiFe in addition_1-2yP_1-yO_4-δItself be exactly a kind of positive electrode active materials of higher capacity, be conducive to keep the high power capacity of material monolithic; Fe simultaneously³⁺/Fe²⁺Lower and the good reversibility of oxidation-reduction potential, receives and in charging, deviates from and embedding is returned in rich lithium material again lithium ion reduces irreversible capacity loss; Particularly advantageously its high-lithium ion electrical conductivity has greatly been improved the low shortcoming of positive electrode lithium ion conductivity; These factors make layer-layer composite lithium-rich anode material xLi₂MnO₃.(1-x)LiMn_0.5Ni_0.5O₂(0≤x≤0.5) has better circulation volume hold facility and multiplying power property.

Detailed description of the invention

Below in conjunction with embodiment, the present invention is described in further detail.

Embodiment 1: by LiNO₃∶Mn(CH₃COO)₂·4H₂O∶Ni(CH₃COO)₂·4H₂O=1.1: the ratio of 0.55: 0.45 (mol ratio) is evenly mixed, is dissolved in deionized water, and adding amount of substance is that the tartaric acid of 1.2 times of all metal ions total amounts stirs to dissolving completely; The temperature rise to 70 of system DEG C is continued to stir until 71% water evaporates, and at this moment solution becomes gradually thickness and forms gelatin. Gelatin material is ground 10 minutes after dry 22 hours in the baking oven of 130 DEG C in mortar. The powder obtaining is warmed up to 500 DEG C and this temperature lower calcination 3 hours with the speed of 2 DEG C/min in tube furnace, cooling rear taking-up powder, in mortar, continue to grind 10 minutes, powder is pressed into sheet with the pressure of 100MPa, then in tube furnace, be warmed up to 850 DEG C of calcinings 5 hours with the speed of 2 DEG C/min, obtain this lithium-rich anode material after cooling with stove. By LiNO₃、Fe(CH₃COO)₂, ammonium dihydrogen phosphate (ADP)=1.0: be dissolved at 0.98: 0.99 in deionized water at normal temperature, its total amount of substance is lithium-rich anode material 2%, adding amount of substance is that the tartaric acid of 2.5 times of all metal ions total amounts stirs to dissolving completely, continue to stir rising system temperature to 70 DEG C, above-mentioned lithium-rich anode material powder is joined in clear liquid and forms suspension, slow evaporation moisture, until system becomes the muddy of thickness, by this material put into 120 DEG C of oven dryings after 10 hours, take out with the speed of 2 DEG C/min be warmed up to 600 DEG C calcining 10 hours, with the cooling layer-layer composite lithium-rich anode material that obtains defect sturcture LiFePO4 surface modification of stove.

Embodiment 2: by LiNO₃∶Mn(CH₃COO)₂·4H₂O∶Ni(CH₃COO)₂·4H₂O=1.5: the ratio of 0.75: 0.25 (mol ratio) is evenly mixed, is dissolved in deionized water, and adding amount of substance is that the tartaric acid of 1.6 times of all metal ions total amounts stirs to dissolving completely; The temperature rise to 80 of system DEG C is continued to stir until 75% water evaporates, and at this moment solution becomes gradually thickness and forms gelatin. Gelatin material is ground 20 minutes after dry 40 hours in the baking oven of 150 DEG C in mortar. The powder obtaining is warmed up to 550 DEG C and this temperature lower calcination 4 hours with the speed of 5 DEG C/min in tube furnace, cooling rear taking-up powder, in mortar, continue to grind 20 minutes, powder is pressed into sheet with the pressure of 200MPa, then in tube furnace, be warmed up to 900 DEG C of calcinings 5 hours with the speed of 5 DEG C/min, obtain this lithium-rich anode material after cooling with stove. By CHxCOOLi, Fe (Cl)₂·4H₂O, ammonium dihydrogen phosphate (ADP)=1.0: be dissolved at 0.88: 0.94 in deionized water at normal temperature, its total amount of substance is lithium-rich anode material 5%, adding amount of substance is that the tartaric acid of 4.0 times of all metal ions total amounts stirs to dissolving completely, continue to stir rising system temperature to 85 DEG C, slow evaporation moisture, until system becomes the muddy of thickness, by this material put into 140 DEG C of oven dryings after 15 hours, take out with the speed of 6 DEG C/min be warmed up to 850 DEG C calcining 15 hours, with the cooling layer-layer composite lithium-rich anode material that obtains defect sturcture LiFePO4 surface modification of stove.

Embodiment 3: by LiNO₃∶Mn(CH₃COO)₂·4H₂O∶Ni(CH₃COO)₂·4H₂O=1.2: the ratio of 0.6: 0.4 (mol ratio) is evenly mixed, is dissolved in deionized water, and adding amount of substance is that the tartaric acid of 2.0 times of all metal ions total amounts stirs to dissolving completely; The temperature rise to 85 of system DEG C is continued to stir until 83% water evaporates, and at this moment solution becomes gradually thickness and forms gelatin. Gelatin material is ground 30 minutes after dry 48 hours in the baking oven of 200 DEG C in mortar. The powder obtaining is warmed up to 600 DEG C and this temperature lower calcination 5 hours with the speed of 10 DEG C/min in tube furnace, cooling rear taking-up powder, in mortar, continue to grind 30 minutes, powder is pressed into sheet with the pressure of 300MPa, then in tube furnace, be warmed up to 950 DEG C of calcining l5 hour with the speed of 9 DEG C/min, obtain this lithium-rich anode material after cooling with stove. By LiNO₃、Fe(Cl)₂·4H₂O, ammonium dihydrogen phosphate (ADP)=1.0: be dissolved at 0.94: 0.97 in deionized water at normal temperature, its total amount of substance is lithium-rich anode material 9%, adding amount of substance is that the tartaric acid of 3.0 times of all metal ions total amounts stirs to dissolving completely, continue to stir rising system temperature to 80 DEG C, above-mentioned lithium-rich anode material powder is joined in clear liquid and forms suspension, at slow evaporation moisture, until system becomes the muddy of thickness, by this material put into 160 DEG C of oven dryings after 20 hours, take out with the speed of 9 DEG C/min be warmed up to 750 DEG C calcining 12 hours, with the cooling layer-layer composite lithium-rich anode material that obtains defect sturcture LiFePO4 surface modification of stove.

Embodiment 4: by CH₃COOLi∶MnSO₄·H₂O∶Ni(CH₃COO)₂·4H₂O=1.5: the ratio of 0.75: 0.25 (mol ratio) is evenly mixed, is dissolved in deionized water, and adding amount of substance is that the tartaric acid of 1.8 times of all metal ions total amounts stirs to dissolving completely; The temperature rise to 75 of system DEG C is continued to stir until 75% water evaporates, and at this moment solution becomes gradually thickness and forms gelatin. Gelatin material is ground 15 minutes after dry 20 hours in the baking oven of 160 DEG C in mortar. The powder obtaining is warmed up to 520 DEG C and this temperature lower calcination 4 hours with the speed of 4 DEG C/min in tube furnace, cooling rear taking-up powder, in mortar, continue to grind 10 minutes, powder is pressed into sheet with the pressure of 150MPa, then in tube furnace, be warmed up to 920 DEG C of calcinings 10 hours with the speed of 8 DEG C/min, obtain this lithium-rich anode material after cooling with stove. By LiNO₃、Fe(NO₃)₂6HxO, ammonium dihydrogen phosphate (ADP)=1.0: be dissolved at 0.96: 0.98 in deionized water at normal temperature, its total amount of substance is lithium-rich anode material 6%, adding amount of substance is that the tartaric acid of 3.5 times of all metal ions total amounts stirs to dissolving completely, continue to stir rising system temperature to 78 DEG C, above-mentioned lithium-rich anode material powder is joined in clear liquid and forms suspension, slow evaporation moisture, until system becomes the muddy of thickness, by this material put into 160 DEG C of oven dryings after 20 hours, take out with the speed of 9 DEG C/min be warmed up to 800 DEG C calcining 12 hours, with the cooling layer-layer composite lithium-rich anode material that obtains defect sturcture LiFePO4 surface modification of stove.

Embodiment 5: by LiNO₃∶Mn(CH₃COO)₂·4H₂O∶NiSO₄·6H₂O=1.3: the ratio of 0.65: 0.35 (mol ratio) is evenly mixed, is dissolved in deionized water, and adding amount of substance is that the tartaric acid of 1.4 times of all metal ions total amounts stirs to dissolving completely; The temperature rise to 78 of system DEG C is continued to stir until 80% water evaporates, and at this moment solution becomes gradually thickness and forms gelatin. Gelatin material is ground 15 minutes after dry 40 hours in the baking oven of 180 DEG C in mortar. The powder obtaining is warmed up to 600 DEG C and this temperature lower calcination 5 hours with the speed of 8 DEG C/min in tube furnace, cooling rear taking-up powder, in mortar, continue to grind 30 minutes, powder is pressed into sheet with the pressure of 250MPa, then in tube furnace, be warmed up to 950 DEG C of calcinings 15 hours with the speed of 9 DEG C/min, obtain this lithium-rich anode material after cooling with stove. By CH₃COOLi、Fe(Cl)₂·4H₂O, ammonium dihydrogen phosphate (ADP)=1.0: be dissolved at 0.94: 0.97 in deionized water at normal temperature, its total amount of substance is lithium-rich anode material 6%, adding amount of substance is all metal ions total amount, the tartaric acid of 2.8 times stirs to dissolving completely, continue to stir rising system temperature to 82 DEG C, above-mentioned lithium-rich anode material powder is joined in clear liquid and forms suspension, slow evaporation moisture, until system becomes the muddy of thickness, by this material put into 160 DEG C of oven dryings after 20 hours, take out with the speed of 9 DEG C/min be warmed up to 780 DEG C calcining 13 hours, with the cooling layer-layer composite lithium-rich anode material that obtains defect sturcture LiFePO4 surface modification of stove.

Claims

1. layer-layer composite lithium-rich anode material xLi of a defect sturcture LiFePO4 surface modification₂MnO₃·(1-x)LiMn_0.5Ni_0.5O₂，0≤x≤0.5, the stoichiometric equation of its surface reforming layer is LiFe_1-2yP_1-yO_4-δ，δ＝4-[(1-2y)*2+1+(1-y)*5]/2，Y=0.01-0.06; The amount of substance of surface reforming layer is the 1%-10% of positive electrode amount; Its preparation process is carried out in two steps; First,Will be according to stoichiometric equation xLi₂MnO₃·(1-x)LiMn_0.5Ni_0.5O₂, 0≤x≤0.5, soluble lithium compounds, soluble manganese salt,Soluble nickel salt is dissolved in deionized water, and adding amount of substance is that all metal ions total amount 1.2-2.0 tartaric acid doubly fully stirsMix evenly to dissolving completely; The temperature of rising system is to 70-85 DEG C of lasting stirring until the water of 70-85% evaporates, and it is sticky that solution becomesThick and form gelatinly, gelatin material is ground to 10-30 after dry 20-48 hour in the baking oven of 130-200 DEG C in mortarMinute, the powder obtaining is warmed up to 500-600 DEG C with the speed of 2-10 DEG C/min in tube furnace, and at this temperature lower calcination3-5 hour, cooling rear taking-up powder continues to grind 10-30 minute in mortar, powder is pressed with the pressure of 100-300MPaIn flakes, in tube furnace, be warmed up to 850-950 DEG C of calcining 5-15 hour with the speed of 2-10 DEG C/min, obtain rich lithium with stove is coolingPositive electrode; Secondly, will be according to stoichiometric equation LiFe_1-2yP_1-yO_4-δ, wherein: y=0.01-0.06; Soluble lithium compounds,Soluble ferrite, ammonium dihydrogen phosphate (ADP) are dissolved in deionized water at normal temperature and continue and stir, to add amount of substance be all metals fromSub-total amount 2.5-4.0 tartaric acid doubly stirs to dissolving completely; Add the lithium-rich anode material that 10-100 doubly measures to formSuspension, is continuing under the condition stirring, and the temperature of rising suspension is to 75-85 DEG C, and slow evaporation moisture, until system becomesThe muddy of thickness, by this material put into take out after 100-160 DEG C of oven drying 10-20 hour under nitrogen atmosphere protection withThe speed of 2-10 DEG C/min is warmed up to 600-850 DEG C of calcining 10-15 hour, with the cooling defect sturcture LiFePO4 surface that obtains of stoveLayer-layer composite lithium-rich anode material of modification; Above-mentioned soluble lithium compounds is LiNO₃、CH₃One in COOLi; CanDissolubility manganese salt is Mn (CH₃COO)₂·4H₂O、MnSO₄·H₂One in O; Soluble nickel salt is Ni (CH₃COO)₂·4H₂O、NiSO₄·6H₂One in O; Soluble ferrite is Fe (CH₃COO)₂、Fe(Cl)₂·4H₂O、Fe(NO₃)₂·6H₂In OA kind of.