Summary of the invention
The object of the present invention is to provide a kind of low temperature battery lithium iron phosphate/carbon composite cathode material and preparation method thereof, composite positive pole obtained by this method has higher specific capacity and good low temperature charge-discharge performance.
The preparation method of low temperature battery LiFePO 4 of anode material/carbon composite of the present invention, is characterized in that: comprise the following steps:
A. ferro-compound, lithium compound, phosphorus compound and carbon source is disperseed respectively to be formed in deionized water solution or suspension-turbid liquid that concentration is 0.5-1.5mol/L; Described ferro-compound in molar ratio: lithium compound: phosphorus compound=0.98 ~ 1:1:1 ~ 1.02; Described carbon source is 1% ~ 10% of the quality by basic material gained lithium iron phosphate positive material;
B. join in the liquid-phase reduction agent of certain volume by gained solution or suspension-turbid liquid in step a, after forming mixed solution, under uniform temperature, atmospheric pressure reflux reacts 4-16h, and then Separation of Solid and Liquid obtains ferric lithium phosphate precursor powder;
C. ferric lithium phosphate precursor powder is placed in inert atmosphere sintering furnace and is warming up to 550-750 DEG C of calcining 1-5h, after cooling, namely obtain low form lithium iron phosphate/carbon composite cathode material.
Further, described ferro-compound is one or more mixtures in ferrous acetate, ferrous carbonate, ferrous phosphate, ferrous sulfate, ferrous oxalate, frerrous chloride; Described lithium compound is one or more mixtures in lithium hydroxide, lithium carbonate, lithium acetate, lithium oxalate, lithium nitrate; One or more mixtures in described phosphorus compound organic phosphorus sources; Described carbon source is one or more mixtures in organic acid, organic carbohydrate, inorganic conductive agent;
Further, described phosphorus compound is one or more mixtures in ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, phytic acid; Described carbon source is one or more mixtures in citric acid, ascorbic acid, glucose, sucrose, fructose, acetylene black, carbon nano-tube, electrically conductive graphite;
Further, in step b, join in the liquid-phase reduction agent of certain volume according to following order, form mixed solution: first add ferro-compound solution or suspension-turbid liquid, then add phosphorus compound solution, then add carbon source solution or suspension-turbid liquid, finally add lithium compound solution or suspension-turbid liquid;
Further, described liquid-phase reduction agent is the mixture of one or more arbitrary proportions in ethylene glycol, diethylene glycol (DEG), triethylene glycol, tetraethylene glycol, methyl-sulfoxide, glycerol, oleyl amine; The volume ratio of liquid-phase reduction agent and deionized water is: liquid-phase reduction agent: deionized water=1:0.2 ~ 5;
Further, in step b, reaction temperature is 150 DEG C of boiling temperatures to liquid-phase reduction agent;
Further, described Separation of Solid and Liquid comprises centrifugation step, decompression distillation step, filtration step;
Further, in step c, the heating rate in calcination process is 2 ~ 5 DEG C/min;
Further, described ferro-compound in molar ratio: lithium compound: phosphorus compound=1.0:1.0:1.0 disperses the ferrous phosphate turbid liquid concentration formed afterwards in deionized water to be 1.5mol/L respectively, and the concentration of lithium hydroxide, phosphoric acid, citric acid solution is respectively 1.0mol/L, 0.5mol/L, 0.5mol/L;
The present invention also discloses a kind of low form lithium iron phosphate/carbon composite cathode material, and described composite positive pole is obtained by the preparation method of above-mentioned low temperature battery LiFePO 4 of anode material/carbon composite.
Beneficial effect of the present invention: the preparation method of low temperature battery LiFePO 4 of anode material/carbon composite of the present invention, synthesis technique is simple, and without the need to high energy milling equipment and high pressure reactor, process conditions are gentle, raw material sources are extensive, greatly reduce energy consumption and production cost; The strongly reducing atmosphere utilizing liquid-phase reduction agent to provide, prevents ferrous oxidation; Presoma crystallization is more complete, shortens the high-temperature calcination time, stops the reduction of growing up, promoting energy consumption of particle further; Realize in-situ carbon coated, LiFePO4 particle diameter is little, under normal temperature 0.1C first discharge capacity be greater than 150, at-20 DEG C, capability retention is 70%.
Embodiment
The preparation method of the low temperature battery LiFePO 4 of anode material/carbon composite of the present embodiment, is characterized in that: comprise the following steps:
A. ferro-compound, lithium compound, phosphorus compound and carbon source is disperseed respectively to be formed in deionized water solution or suspension-turbid liquid that concentration is 0.5-1.5mol/L; Described ferro-compound in molar ratio: lithium compound: phosphorus compound=0.98 ~ 1:1:1 ~ 1.02; Described carbon source is 1% ~ 10% of the quality by basic material gained lithium iron phosphate positive material;
B. join in the liquid-phase reduction agent of certain volume by gained solution or suspension-turbid liquid in step a, after forming mixed solution, under uniform temperature, atmospheric pressure reflux reacts 4-16h, and then Separation of Solid and Liquid obtains ferric lithium phosphate precursor powder;
C. ferric lithium phosphate precursor powder is placed in inert atmosphere sintering furnace and is warming up to 550-750 DEG C of calcining 1-5h, after cooling, namely obtain low form lithium iron phosphate/carbon composite cathode material.
In the present embodiment, described ferro-compound is one or more mixtures in ferrous acetate, ferrous carbonate, ferrous phosphate, ferrous sulfate, ferrous oxalate, frerrous chloride; Described lithium compound is one or more mixtures in lithium hydroxide, lithium carbonate, lithium acetate, lithium oxalate, lithium nitrate; One or more mixtures in described phosphorus compound organic phosphorus sources; Described carbon source is one or more mixtures in organic acid, organic carbohydrate, inorganic conductive agent;
In the present embodiment, described phosphorus compound is one or more mixtures in ammonium dihydrogen phosphate, diammonium hydrogen phosphate, phosphoric acid, phytic acid; Described carbon source is one or more mixtures in citric acid, ascorbic acid, glucose, sucrose, fructose, acetylene black, carbon nano-tube, electrically conductive graphite;
In the present embodiment, in step b, join in the liquid-phase reduction agent of certain volume according to following order, form mixed solution: first add ferro-compound solution or suspension-turbid liquid, then add phosphorus compound solution, then add carbon source solution or suspension-turbid liquid, finally add lithium compound solution or suspension-turbid liquid;
In the present embodiment, described liquid-phase reduction agent is the mixture of one or more arbitrary proportions in ethylene glycol, diethylene glycol (DEG), triethylene glycol, tetraethylene glycol, methyl-sulfoxide, glycerol, oleyl amine; The volume ratio of liquid-phase reduction agent and deionized water is: liquid-phase reduction agent: deionized water=1:1 ~ 5;
In the present embodiment, in step b, reaction temperature is 150 DEG C of boiling temperatures to liquid-phase reduction agent;
In the present embodiment, described Separation of Solid and Liquid comprises centrifugation step, decompression distillation step, filtration step;
In the present embodiment, in step c, the heating rate in calcination process is 2 ~ 5 DEG C/min;
In the present embodiment, described ferro-compound in molar ratio: lithium compound: phosphorus compound=1.0:1.0:1.0 disperses the ferrous phosphate turbid liquid concentration formed afterwards in deionized water to be 1.5mol/L respectively, and the concentration of lithium hydroxide, phosphoric acid, citric acid solution is respectively 1.0mol/L, 0.5mol/L, 0.5mol/L;
The low form lithium iron phosphate/carbon composite cathode material of this enforcement, described composite positive pole is obtained by the preparation method of above-mentioned low temperature battery LiFePO 4 of anode material/carbon composite.
Below by specific embodiment, the present invention is further elaborated.
Embodiment 1
Take basic material ferrous phosphate according to the ratio of elemental mole ratios Fe:Li:P=1.0:1.0:1.0, lithium hydroxide and phosphoric acid, the amount taking carbon source citric acid by acquisition lithium iron phosphate positive material 10%, above-mentioned raw materials is disperseed in deionized water separately, ferrous phosphate turbid liquid concentration is 1.5mol/L, the concentration of lithium hydroxide, phosphoric acid and citric acid solution is respectively 1.0mol/L, 0.5mol/L and 0.5mol/L, the volume summation of suspension-turbid liquid and solution and the volume ratio of liquid-phase reduction agent triethylene glycol are 1.0, join in liquid-phase reduction agent according to following order, stir while adding: ferrous phosphate suspension-turbid liquid-phosphoric acid solution-citric acid solution-lithium hydroxide solution, after mixing at 250 DEG C back flow reaction 8h, carry out centrifugally operated after cooling and realize Separation of Solid and Liquid, namely course of reaction obtains the more complete ferric lithium phosphate precursor material of crystallization of Surface coating one deck conductive agent without the need to inert gas shielding, after the vacuumize of gained presoma in inert atmosphere sintering furnace with the speed that heating rate is 5 DEG C/min, 650 DEG C of insulation 2h, namely lithium iron phosphate/carbon combination electrode is obtained with after stove cooling.
SEM Fig. 1 and XRD Fig. 2 of the lithium iron phosphate/carbon combination electrode material that this embodiment obtains can find out, the average grain diameter of corynebacterium lithium iron phosphate/carbon composite material is 100-200nm, and be olivine-type orthohormbic structure, perfect crystalline is without dephasign.First charge-discharge curve under the experiment half-cell room temperature made by embodiment 1 gained positive electrode is shown in Fig. 3, and its 0.1C first discharge specific capacity is 160mAh/g as seen, and at-20 DEG C, the discharge capacity first of 0.1C is 110mAh/g.
Embodiment 2
Take basic material ferrous carbonate according to the ratio of elemental mole ratios Fe:Li:P=0.98:1.0:1.0, lithium acetate and ammonium dihydrogen phosphate, the amount taking carbon source glucose by acquisition lithium iron phosphate positive material 10%, above-mentioned raw materials is disperseed in deionized water separately, ferrous carbonate turbid liquid concentration is 1.2mol/L, the concentration of lithium acetate, ammonium dihydrogen phosphate and glucose solution is respectively 0.5mol/L, 1.0mol/L and 1.0mol/L, the volume summation of suspension-turbid liquid and solution and the volume ratio of liquid-phase reduction agent diethylene glycol (DEG) are 0.5, join in liquid-phase reduction agent according to following order, stir while adding: ferrous carbonate suspension-turbid liquid-ammonium dihydrogen phosphate-glucose solution-lithium acetate solution, after mixing at 240 DEG C back flow reaction 12h, carry out centrifugally operated after cooling and realize Separation of Solid and Liquid, namely course of reaction obtains the more complete ferric lithium phosphate precursor material of crystallization of Surface coating one deck conductive agent without the need to inert gas shielding, after the vacuumize of gained presoma in inert atmosphere sintering furnace with the speed that heating rate is 4 DEG C/min, 700 DEG C of insulation 2h, namely lithium iron phosphate/carbon combination electrode is obtained with after stove cooling.
The surface sweeping electromicroscopic photograph of the lithium iron phosphate/carbon combination electrode material that this embodiment obtains as shown in Figure 1, therefrom the XRD figure of lithium iron phosphate/carbon composite material, first charge-discharge curve chart under room temperature and low temperature and Fig. 2 to Fig. 4 without essential distinction, repeat no more herein.Room temperature 0.1C first charge-discharge capacity is 158mAh/g, at-20 DEG C 0.1C first discharge capacity be 109mAh/g.
Embodiment 3
Take basic material ferrous oxalate according to the ratio of elemental mole ratios Fe:Li:P=1.0:1.02:1.0, careless lithium and phosphoric acid, the amount taking carbon source sucrose by acquisition lithium iron phosphate positive material 8%, above-mentioned raw materials is disperseed in deionized water separately, ferrous oxalate turbid liquid concentration is 1.0mol/L, the concentration of lithium oxalate, phosphoric acid and sucrose solution is respectively 1.5mol/L, 1.0mol/L and 1.0mol/L, and the volume summation of suspension-turbid liquid and solution and the volume ratio of liquid-phase reduction agent ethylene glycol are 0.5, join in liquid-phase reduction agent according to following order, stir while adding: ferrous oxalate suspension-turbid liquid-phosphoric acid solution-sucrose solution-lithium oxalate solution, after mixing at 180 DEG C back flow reaction 14h, carry out centrifugally operated after cooling and realize Separation of Solid and Liquid, namely course of reaction obtains the more complete ferric lithium phosphate precursor material of crystallization of Surface coating one deck conductive agent without the need to inert gas shielding, after the vacuumize of gained presoma in inert atmosphere sintering furnace with the speed that heating rate is 3 DEG C/min, 750 DEG C of insulation 2h, namely lithium iron phosphate/carbon combination electrode is obtained with after stove cooling.
The surface sweeping electromicroscopic photograph of the lithium iron phosphate/carbon combination electrode material that this embodiment obtains as shown in Figure 1, therefrom the XRD figure of lithium iron phosphate/carbon composite material, first charge-discharge curve chart under room temperature and low temperature and Fig. 2 to Fig. 4 without essential distinction, repeat no more herein.Room temperature 0.1C first charge-discharge capacity is 155mAh/g, at-20 DEG C 0.1C first discharge capacity be 109mAh/g.
Embodiment 4
Take basic material ferrous sulfate according to the ratio of elemental mole ratios Fe:Li:P=0.98:1.2:1.0, lithium carbonate and phytic acid, the amount taking conductive agent acetylene black by acquisition lithium iron phosphate positive material 3%, above-mentioned raw materials is disperseed in deionized water separately, copperas solution concentration is 2.0mol/L, the concentration of lithium carbonate suspension-turbid liquid, phytic acid and acetylene black suspension-turbid liquid is respectively 0.5mol/L, 1.0mol/L and 1.0mol/L, the volume summation of suspension-turbid liquid and solution and the volume ratio of liquid-phase reduction agent triethylene glycol are 2.0, join in liquid-phase reduction agent according to following order, stir while adding: copperas solution-plant acid solution-acetylene black suspension-turbid liquid-lithium carbonate suspension-turbid liquid, after mixing at 280 DEG C back flow reaction 16h, carry out centrifugally operated after cooling and realize Separation of Solid and Liquid, namely course of reaction obtains the more complete ferric lithium phosphate precursor material of crystallization of Surface coating one deck conductive agent without the need to inert gas shielding, after the vacuumize of gained presoma in inert atmosphere sintering furnace with the speed that heating rate is 2 DEG C/min, 650 DEG C of insulation 2h, namely lithium iron phosphate/carbon combination electrode is obtained with after stove cooling.
The surface sweeping electromicroscopic photograph of the lithium iron phosphate/carbon combination electrode material that this embodiment obtains as shown in Figure 1, therefrom the XRD figure of lithium iron phosphate/carbon composite material, first charge-discharge curve chart under room temperature and low temperature and Fig. 2 to Fig. 4 without essential distinction, repeat no more herein.Room temperature 0.1C first charge-discharge capacity is 155mAh/g, at-20 DEG C 0.1C first discharge capacity be 108mAh/g.
What finally illustrate is, above embodiment is only in order to illustrate technical scheme of the present invention and unrestricted, although with reference to preferred embodiment to invention has been detailed description, those of ordinary skill in the art is to be understood that, can modify to technical scheme of the present invention or equivalent replacement, and not departing from aim and the scope of technical solution of the present invention, it all should be encompassed in the middle of right of the present invention.