CN102709554A

CN102709554A - LiMnPO4/C composite cathode material preparation method for lithium ion battery

Info

Publication number: CN102709554A
Application number: CN2012101743680A
Authority: CN
Inventors: 陈晨; 袁安保; 赵宏斌; 徐甲强
Original assignee: University of Shanghai for Science and Technology
Current assignee: University of Shanghai for Science and Technology
Priority date: 2012-02-22
Filing date: 2012-05-31
Publication date: 2012-10-03
Anticipated expiration: 2032-05-31
Also published as: CN102709554B

Abstract

The invention relates to a LiMnPO4/C composite cathode material preparation method for a lithium ion battery, and belongs to the technical field of lithium ion batteries. Lithium acetate, manganese acetate and ammonium dihydrogen phosphate are taken as raw materials, an oxalic acid is taken as a precipitating agent, and sucrose is taken as a carbon source. The method comprises the following steps of: preparing a precipitation precursor, and performing calcinations to prepare a micro-nano LiMnPO4/C composite cathode material with high electrical conductivity. The method is easy, feasible, energy-saving and time-saving; LiMnPO4 in the prepared material is high in purity and crystallinity; surface coating carbon can be obtained by a one-step method; and the proportion of the LiMnPO4 and the conductive carbon in the composite material is easily controlled, so that the performance optimization of the material is facilitated.

Description

Lithium ion cell positive is with the preparation method of manganese phosphate lithium/carbon composite material

Technical field

The present invention relates to adopt the precipitation transformation method preparation to be used for lithium manganese phosphate/carbon (LiMnPO of lithium ion cell positive ₄/ C) composite material belongs to technical field of lithium ion.

Background technology

Along with the progress of society and the fast development of electronic information technology, the miniaturization gradually of electronic instrument and communication equipment, therefore the demand to portable power source increases apace, simultaneously its performance is also had higher requirement.In addition, the research and development of electric motor car in recent years and electrical source of power thereof and application also receive much concern.Lithium ion battery is the secondary cell of one type of high-energy-density.At present, the capacity of anode material for lithium-ion batteries is lower than negative material, and therefore exploitation cheapness, environmental protection and high performance positive electrode are the research and development emphasis of lithium ion battery always.In anode material for lithium-ion batteries, the LiCoO of layer structure ₂Obtained commercial application.Yet the rare and fancy price of cobalt resource has limited its large-scale application.

The olivine-type LiMPO that can reversiblely discharge and recharge in recent years, ₄(M=Fe, Mn, Ni, Co) anode material for lithium-ion batteries has caused people's attention.In this type material, that research and develop morely at present is LiFePO ₄Material is regarded as the safer power lithium-ion battery positive electrode of electric vehicle.With LiFePO ₄Electrode is compared, LiMnPO ₄The theoretical capacity of electrode and LiFePO ₄Quite, but its work potential (4.1 V vs. Li ⁺/ Li) but apparently higher than LiFePO ₄Electrode (3.4 V vs. Li ⁺/ Li).Therefore, with LiMnPO ₄Lithium ion battery as positive pole has potential higher energy density and power density.In addition, LiMnPO ₄Also having the low and good advantage of Environmental compatibility of cost, is a kind of positive electrode with development prospect.But LiMnPO ₄Material has electron conduction difference and the slow shortcoming of lithium ion diffusion velocity.In order to improve LiMnPO ₄Conductivity, can adopt the material and the LiMnPO of good conductivity ₄Compound or at LiMnPO ₄The surface of material coats one deck conductive carbon, to improve its chemical property.

Compare with the non-aqueous solution lithium ion battery, aqueous solution lithium ion battery has the advantage that fail safe is good, cost is low and electrolytic conductivity is high.2006, seminar's reported first of Australian Univ Murdoch LiMnPO ₄The chemical property of electrode in the saturated LiOH aqueous solution.The initial discharge capacity of this electrode is about 75 mAh/g, and through after 10 charge and discharge cycles, capacity is reduced to 38 mAh/g.The present invention adopts precipitation transformation method to prepare LiMnPO ₄/ C composite material, this composite material is at 2 mol/L Li ₂SO ₄Charge and discharge cycles stability in the neutral aqueous solution electrolyte obviously is superior to above-mentioned material.

Summary of the invention

The objective of the invention is to adopt a kind of new method, i.e. the synthetic a kind of new type lithium ion battery anode composite material LiMnPO of precipitation transformation method ₄/ C, preparation technology is easy for this method, and is with low cost.

A kind of lithium ion cell positive of the present invention is used LiMnPO ₄The preparation method of/C composite material is characterized in that having following preparation process and step:

A. oxalic acid and the lithium acetate mol ratio by 2:1 is dissolved in the deionized water, adds an amount of sucrose, magnetic agitation mixes it; The silly addition of sugarcane is 80～86wt% of lithium acetate quality;

B. will be dissolved in respectively in a certain amount of deionized water with the manganese acetate and the phosphoric acid dihydro amine of mol ratios such as lithium acetate; Under magnetic agitation; The speed of manganese acetate solution with 1 droplet/second is added drop-wise in the mixed solution of oxalic acid, lithium salts and sucrose, obtains the pink deposition, drip the biphosphate amine aqueous solution again; Lithium acetate, manganese acetate and phosphoric acid dihydro amine three's mol ratio is 1:1:1;

C. with above-mentioned system transpiring moisture in 70 ℃ of water-baths, then in vacuum drying chamber in 120 ℃ of dryings, grind into powder obtains precursor.Precursor programming rate with 2 ℃/min under blanket of nitrogen slowly is warmed up to 650 ℃, and calcines 12 h down, obtain black lithium manganese phosphate/carbon (LiMnPO of coated with carbon at 650 ℃ ₄/ C) composite material.

The present invention has the following advantages:

1, prepares LiMnPO with precipitation transformation method ₄The technical process of/C composite material is simple, and is pollution-free, and LiMnPO in the composite material ₄Be easy to control with the ratio of C.Wherein use oxalic acid as precipitation reagent, oxalic acid generates reducibility gas after high-temperature calcination, can stop the oxidation of divalent manganesetion, and oxalic acid all is converted into gas after calcining, does not influence the stoichiometry of phosphorus content.

2, in the preparation process of material, the compound of carbon obtains through one-step method, need not preparation LiMnPO earlier ₄Material carries out charing again to be handled, and therefore saves time and energy.And before deposition formed, carbon source was just evenly mixed with reactant, so after deposition formed, carbon source material was evenly distributed in sedimentary surface, after heat treatment, obtains the LiMnPO of good conductivity ₄/ C composite material.

3, carbon is compound can effectively improve LiMnPO ₄The conductivity of material, thus its chemical property improved, like electro-chemical activity and cyclical stability.

4, the LiMnPO for preparing ₄/ C composite material is the nano-micro structure material, is suitable as the positive electrode of lithium ion battery.The too small meeting of active material particle causes material capacity attenuation in cyclic process fast, and the excessive diffusion that is unfavorable for lithium ion of particle influences chemical property.

Description of drawings

Fig. 1 is the LiMnPO by embodiment 1 preparation ₄The XRD figure of/C composite material.

Fig. 2 is the LiMnPO by embodiment 1 preparation ₄The TEM figure of/C composite material.

Fig. 3 is the LiMnPO by embodiment 1 preparation ₄The cycle performance of/C composite electrode.

Embodiment

Embodiment 1

The present embodiment lithium ion cell positive may further comprise the steps with the preparation method of manganese phosphate lithium/carbon composite material:

(1) take by weighing 0.04mol oxalic acid, 0.02mol lithium acetate crystal places the clean beaker of a 500mL, measures the 60ml deionized water it is dissolved, and magnetic agitation mixes, and adds 1.7444g sucrose again, and magnetic agitation 30min is referred to as mixed solution A.

(2) take by weighing the clean beaker that 0.02mol manganese acetate crystal places a 50mL, measure the 30mL deionized water it is dissolved, magnetic agitation is even, is made into the manganese acetate solution of 0.67mol/L.With plastic dropper the speed of the manganese acetate solution for preparing with 1 droplet/second is added drop-wise in the mixed solution A, and carries out powerful magnetic agitation during the course, form the mixture of pink deposition and solution, be referred to as mixture B.Get 0.02mol phosphoric acid dihydro amine crystal and place former 50ml beaker, measure the 30mL deionized water it is dissolved, magnetic agitation is even, is made into 0.67mol/L's

The biphosphate ammonia solution is added drop-wise to this solution among the mixture B with speed slowly, and magnetic agitation is even, still the mixture of pink deposition and solution, be referred to as mixture C.After getting 20mL deionization moisture several times cleaning 50mL beaker again, pour in the mixture, stir.

(3) with said mixture system transpiring moisture in 70 ℃ of water-baths, continuous magnetic agitation is up to obtaining dry pink spawn.This substance transfer to the surface plate of dried and clean, is evenly spread out, place vacuum drying chamber (vacuum degree for-0.07MPa) behind 120 ℃ of dry 12h, close drying box and keep vacuum state to lower the temperature naturally, fully grinding promptly gets presoma behind the cool to room temperature.Presoma is placed tube furnace, in the nitrogen protection atmosphere, slowly be warmed up to 650 ℃ with the programming rate of 2 ℃/min; And at 650 ℃ of following calcining 12 h; Still in the nitrogen protection atmosphere, reduce to room temperature, obtain target product, be i.e. black lithium manganese phosphate/carbon (LiMnPO of coated with carbon ₄/ C) composite material.

LiMnPO ₄ The cycle performance test of/C composite electrode material

Charge-discharge test adopts three-electrode system:

Work electrode preparation: lithium manganese phosphate-carbon composite: acetylene black: PTFE=75%/20%/5% (mass ratio); After the mixing and stirring; Blade coating is in the titanium mesh grid of cleaning, and dry 12h under 105 ℃ is flattened into experience thickness through roll squeezer in vacuum drying chamber.

The auxiliary electrode preparation: active carbon: acetylene black: PTFE=80%/10%/10% (mass ratio), after the mixing and stirring, blade coating is on the nickel screen of cleaning, and dry 12h under 105 ℃ is flattened into experience thickness through roll squeezer in vacuum drying chamber.

Reference electrode is saturated calomel electrode (SCE), and electrolyte is with deionized water and Li ₂SO ₄H ₂The 2M Li that the configuration of O white crystalline powder forms ₂SO ₄Solution, the voltage range that discharges and recharges are 0 ~ 1.1V Vs. SCE.LAND battery performance test appearance is used in the measurement that discharges and recharges the life-span, and charge-discharge magnification is 0.1C.

Each item instrument detecting result of present embodiment products therefrom is shown in following each accompanying drawing.

Fig. 1 is LiMnPO ₄The X-ray diffraction of/C material (XRD) spectrogram.Visible by figure, the equal and LiMnPO of all diffraction maximums ₄Standard spectrogram (PDF no. 33-0804) match, show the LiMnPO in this material ₄LiMnPO for mutually pure olivine-type structure ₄(rhombic system, space group are Pmnb), and have good degree of crystallinity.

Fig. 2 is LiMnPO ₄The transmission electron microscope of/C material (TEM) photo.Visible by figure, this material is made up of the particle that is of a size of the hundreds of nanometer, belongs to the nano-micro structure material.

Fig. 3 is LiMnPO ₄/ C electrode is at 2 mol/L Li ₂SO ₄Charge-discharge performance in the neutral aqueous solution electrolyte.Visible by figure, except that the discharge capacity of the 2nd circulation descends to some extent, overall relatively steadily.Cyclical stability is superior to the situation of bibliographical information ^[1]Because LiMnPO ₄/ C is unstable in the aqueous solution, and the existence of analysing the oxygen side reaction is arranged, and has limited the performance of its capacity, and the research of domestic this respect also is in blank at present.Bibliographical information LiMnPO before ₄/ C is very unstable in the saturated LiOH aqueous solution, and preceding ten times discharge capacity decays to 50%.Consider on the one hand in alkaline solution, to be easy to analyse the oxygen side reaction, this patent adopts 2 mol/L Li first ₂SO ₄Neutral electrolyte has suppressed the generation of side reaction to a certain extent, and the efficient that main reaction takes place is guaranteed; The particle of preparation is that carbon coats intact nano-micro structure on the other hand, reduce with aqueous solution contact area in, brought into play its maximum chemical property.These 2 cause specific discharge capacity and the cycle performance shown in this figure all to be superior to previous bibliographical information.

List of references:

M.?Minakshi,?P.?Singh,?S.?Thurgate,?K.?Prince,?Electrochem.?Solid-State?Lett.?9?(2006)?A471。

Claims

1. a lithium ion cell positive is characterized in that having following preparation process and step with the preparation method of manganese phosphate lithium/carbon composite material:

A. oxalic acid and the lithium acetate mol ratio by 2:1 is dissolved in the deionized water, adds an amount of sucrose, magnetic agitation mixes it; The addition of sucrose is 80～86wt% of lithium acetate quality;

C. with above-mentioned system transpiring moisture in 70 ℃ of water-baths, then in vacuum drying chamber in 120 ℃ of dryings, grind into powder obtains precursor; Precursor programming rate with 2 ℃/min under blanket of nitrogen slowly is warmed up to 650 ℃, and calcines 12 h down, obtain black lithium manganese phosphate/carbon (LiMnPO of coated with carbon at 650 ℃ ₄/ C) composite material.