CN113611863A - Cation-doped lithium iron phosphate positive electrode material and preparation method and application thereof - Google Patents
Cation-doped lithium iron phosphate positive electrode material and preparation method and application thereof Download PDFInfo
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Abstract
The invention discloses a cation-doped lithium iron phosphate positive electrode material, a preparation method and application thereof, wherein the molecular formula of the positive electrode material is Li1‑ yMxFePO4Wherein: x is less than or equal to 0.03, and M is one or more of Na, Mg, Al, Cr, Ti, Zr, Nb and W; the preparation method comprises the following steps: and uniformly mixing the iron phosphate, the lithium source, the doping agent containing the element M and the carbonaceous reducing agent in proportion, and then, preserving the heat for 6-15h at the temperature of 800 ℃ in a protective atmosphere to obtain the material. The invention can improve the carrier concentration in the material by doping Ti in the form of cation distributed in the olivine-structured lithium iron phosphate anode material, thereby improving the electronic conductivity,the grain size can be reduced, and the diffusion distance of lithium ions can be shortened, so that the ion conductivity is improved, and the multiplying power performance of the prepared cation-doped lithium iron phosphate anode material in the circulation process is improved in a synergistic manner.
Description
Technical Field
The invention belongs to the technical field of lithium ion battery materials, relates to a lithium ion battery anode material and a preparation method thereof, and more particularly relates to a cation-doped lithium iron phosphate anode material and a preparation method and application thereof.
Background
With the rapid growth of population and the gradual increase of social productivity level, the problems of environmental pollution and energy shortage are becoming more serious. The development of environment-friendly and renewable new energy sources is imperative. However, new energy sources such as solar energy and wind energy have high dependence on the environment, and the generated electric energy has strong fluctuation and needs a matched energy storage and conversion device. As a novel secondary power supply, the lithium ion secondary battery has the advantages of high energy density, high working voltage, small self-discharge, no memory effect, long cycle life, environmental friendliness and the like, is widely applied to the fields of portable electronic products, electric vehicles, large-scale power supplies, energy storage and the like, and becomes one of the most reliable energy storage devices. Cathode materials are a central factor that has limited the development of high performance power batteries because they represent a significant portion of the cost, weight, and volume of the battery.
At present, the olivine-type lithium iron phosphate positive electrode material has the advantages of rich raw material sources, environmental friendliness, good thermal stability, long cycle life, flat charge/discharge platform and the like, and is a research hotspot in academia and industry. However, the current lithium iron phosphate has the defect of poor electronic and ionic conductivity, and the practical application of the lithium iron phosphate in power batteries is limited. Therefore, a suitable dopant-doped modified lithium iron phosphate cathode material is sought, and the large-scale preparation of the olivine-type lithium iron phosphate with high rate performance becomes one of the key problems in the related technology of the lithium ion battery.
In view of this, the invention is particularly proposed.
Disclosure of Invention
Aiming at the defects of the lithium iron phosphate anode material in the prior art, the invention aims to provide a cation-doped lithium iron phosphate anode material and a preparation method and application thereof.
In order to achieve the purpose, the technical scheme of the invention is as follows:
a positive ion-doped lithium iron phosphate positive electrode material has a molecular formula as follows: li1-yMxFePO4The lithium iron phosphate positive electrode material has an olivine structure.
Wherein: m is one or more of Na, Mg, Al, Cr, Ti, Zr, Nb and W.
In the above technical solution, when M is Na, y is x; when M is Mg, y is 2 x; when M is Al or Cr, y is 3 x; when M is Ti or Zr, y is 4 x; when M is Nb, y is 5 x; when M is W, y is 6 x;
preferably, in the above technical scheme, M is Ti, x is not more than 0.01, and the doping element Ti is uniformly distributed in the lithium iron phosphate positive electrode material.
In detail, in the technical scheme, the capacity of the lithium iron phosphate positive electrode material is more than 130mAh/g when the discharge rate is 10C, and the capacity retention rate is more than 90% after 1000 cycles.
The invention also provides a preparation method of the cation-doped lithium iron phosphate cathode material, which comprises the following steps:
and uniformly mixing the iron phosphate, the lithium source, the doping agent containing the element M and the carbonaceous reducing agent in proportion, and then, preserving the heat for 6-15h at the temperature of 800 ℃ in a protective atmosphere to obtain the material.
Preferably, in the above technical solution, in the sintering process, when the temperature is higher than 500 ℃, the temperature rise rate is controlled to be 2-5 ℃/min.
Further, in the above technical solution, the lithium source is one or more of lithium carbonate, lithium hydroxide monohydrate, lithium hydroxide, lithium acetate, and lithium nitrate.
Further, in the above technical solution, the dopant containing the element M is one or more of an oxide, a carbonate, an acetate, and a hydroxide of M.
Further, in the above technical solution, the carbonaceous reducing agent is one or more of glucose, sucrose and citric acid.
Further, in the above technical solution, the protective atmosphere is argon.
Still further, in the above technical solution, the sintering is two-stage high temperature sintering, which specifically includes: keeping the temperature at 400 ℃ for 1-6h at 250 ℃ and then keeping the temperature at 800 ℃ for 6-12h at 600 ℃.
In a preferred embodiment of the present invention, the preparation method of the cation-doped lithium iron phosphate positive electrode material specifically includes the following steps:
s1, weighing iron phosphate, a lithium source, a doping agent containing an element M and a carbonaceous reducing agent according to a proportion, adding the weighed materials into a ball milling tank, adding ethanol according to the proportion of 0.5-1.8g/mL of material-liquid ratio, ball milling for 6-12h at 400-800rpm, and then drying for 6-12h in vacuum at 60-100 ℃ to obtain a powdery mixture raw material;
s2, placing the powdery mixture raw material in S1 in an argon atmosphere, heating to 250-400 ℃ at the speed of 2-10 ℃/min, carrying out heat preservation sintering for 1-6h, heating to 600-800 ℃ at the speed of 2-4 ℃/min, carrying out heat preservation sintering for 6-12h, cooling to 450 ℃ at the speed of 3.5-6 ℃/min, and cooling with a furnace to obtain the high-temperature-resistant aluminum alloy.
The invention also provides a positive pole piece which comprises the positive ion-doped lithium iron phosphate positive pole material.
The invention further provides a lithium ion battery, which comprises the positive pole piece.
Compared with the prior art, the invention has the following advantages:
(1) according to the cation-doped lithium iron phosphate positive electrode material provided by the invention, doped Ti is distributed in the lithium iron phosphate positive electrode material with an olivine structure in a cation form, and titanium cation doping can improve the carrier concentration in the material, so that the electronic conductivity of the material is improved, the grain size can be reduced, the lithium ion diffusion distance is shortened, the ionic conductivity is improved, and the multiplying power performance of the lithium iron phosphate positive electrode material in the circulation process is finally improved in a synergistic manner;
(2) the cation-doped lithium iron phosphate cathode material provided by the invention can synchronously obtain multiple modification advantages, and the titanium-modified lithium iron phosphate cathode material is used for testing the electrochemical performance of a lithium ion battery, and the result shows that the capacity can reach 135mAh/g under the current density of 2.5-4.2V and 10C, and after 1000 cycles (1C is 170mA/g), the capacity retention rate is up to 91.3 percent, which indicates that the material has excellent rate capability and long cycle stability as the lithium ion battery cathode material;
(3) the preparation process of the cation-doped lithium iron phosphate anode material provided by the invention is simple, environment-friendly, capable of realizing large-scale production and easy to popularize, and is a method for effectively improving the multiplying power performance of the lithium iron phosphate anode material.
Drawings
FIG. 1 is SEM pictures of LFP/C samples prepared in example 1 of the present invention at different magnifications (wherein: a is SEM picture magnified by 5000 times and b is SEM picture magnified by 30000 times);
FIG. 2 is SEM pictures of Ti-LFP/C samples prepared in example 2 of the present invention at different magnifications (wherein: a is SEM picture magnified by 5000 times, and b is SEM picture magnified by 30000 times);
FIG. 3 is a TEM photograph of the Ti-LFP/C sample prepared in example 2 of the present invention (wherein a is a bright field image of the sample morphology, b is a high angle annular dark field image, and C, d, e and f are the mappings of Fe, O, P and Ti elements in the same region, respectively);
FIG. 4 shows X-ray diffraction patterns of the LFP/C sample prepared in example 1 and the Ti-LFP/C sample prepared in example 2;
FIG. 5 is a graph of the cycling specific capacity of the LFP/C sample prepared in example 1 and the Ti-LFP/C sample prepared in example 2 cycled 100 times at a current density of 1C (the first three cycles are all activated at a current density of 0.1C);
FIG. 6 is a graph of the specific capacity for 1000 cycles at 10C current density for the LFP/C sample made in example 1 and the Ti-LFP/C sample made in example 2 of the present invention (the first three cycles are all activated at O.1C current density);
FIG. 7 is a graph showing the rate capability of the LFP/C sample prepared in example 1 and the Ti-LFP/C sample prepared in example 2;
FIG. 8 is a plot of cyclic voltammograms at a sweep rate of 1mV/s for the LFP/C sample prepared in example 1 and the Ti-LFP/C sample prepared in example 2.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.
In the examples, the means used are conventional in the art unless otherwise specified.
The terms "comprises," "comprising," or any other variation thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, process, method, article, or apparatus that comprises a list of elements is not necessarily limited to only those elements but may include other elements not expressly listed or inherent to such composition, process, method, article, or apparatus.
In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.
In the examples of the present invention, the experimental raw materials used were all conventional commercial products.
In the embodiments of the present invention, the equipment and instruments used are commercially available or prepared by the prior art.
Example 1
The embodiment of the invention provides a preparation method of a lithium iron phosphate anode material, which comprises the following steps:
s1, weighing 4.525g of iron phosphate, 1.259g of lithium hydroxide monohydrate, 0.901g of glucose and 10ml of ethanol, adding into a ball milling tank, adding zirconia balls, carrying out ball milling at 600rpm for 12 hours to obtain mixture slurry, and then carrying out vacuum drying at 60 ℃ for 12 hours to obtain a powdery mixture raw material;
s2, transferring the powdery mixture raw material in the S1 into a corundum ark, placing the corundum ark in a tube furnace filled with argon atmosphere, heating to 300 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 2h, heating to 600 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 10h, and cooling along with the furnace to obtain the lithium iron phosphate cathode material LFP/C.
Example 2
The embodiment of the invention provides a preparation method of a titanium-doped lithium iron phosphate positive electrode material, which specifically comprises the following steps:
s1, weighing 4.525g of iron phosphate, 1.234g of lithium hydroxide monohydrate, 0.901g of glucose, 11.99mg of titanium dioxide and 10ml of ethanol, adding into a ball milling tank, adding zirconia balls, carrying out ball milling at 600rpm for 12 hours to obtain mixture slurry, and then carrying out vacuum drying at 60 ℃ for 12 hours to obtain a powdery mixture raw material;
s2, transferring the powdery mixture raw material in the S1 into a corundum ark, placing the corundum ark in a tube furnace filled with argon atmosphere, heating to 300 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 2h, heating to 650 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 10h, and cooling along with the furnace to obtain the lithium iron phosphate anode material Ti-LFP/C.
Example 3
The embodiment of the invention provides a preparation method of a titanium-doped lithium iron phosphate positive electrode material, which specifically comprises the following steps:
s1, weighing 4.525g of iron phosphate, 1.234g of lithium hydroxide monohydrate, 0.901g of glucose, 11.99mg of titanium dioxide and 10ml of ethanol, adding into a ball milling tank, adding zirconia balls, carrying out ball milling at 600rpm for 12 hours to obtain mixture slurry, and then carrying out vacuum drying at 60 ℃ for 12 hours to obtain a powdery mixture raw material;
s2, transferring the powdery mixture raw material in the S1 into a corundum ark, placing the corundum ark in a tube furnace filled with argon atmosphere, heating to 300 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 2h, heating to 600 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 10h, and cooling along with the furnace to obtain the lithium iron phosphate anode material Ti-LFP/C.
Example 4
The embodiment of the invention provides a preparation method of a titanium-doped lithium iron phosphate positive electrode material, which specifically comprises the following steps:
s1, weighing 4.525g of iron phosphate, 1.234g of lithium hydroxide monohydrate, 0.901g of glucose, 11.99mg of titanium dioxide and 10ml of ethanol, adding into a ball milling tank, adding zirconia balls, carrying out ball milling at 600rpm for 12 hours to obtain mixture slurry, and then carrying out vacuum drying at 60 ℃ for 12 hours to obtain a powdery mixture raw material;
s2, transferring the powdery mixture raw material in the S1 into a corundum ark, placing the corundum ark in a tube furnace filled with argon atmosphere, heating to 300 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 2h, heating to 700 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 10h, and cooling along with the furnace to obtain the lithium iron phosphate anode material Ti-LFP/C.
Example 5
The embodiment of the invention provides a preparation method of a titanium-doped lithium iron phosphate positive electrode material, which specifically comprises the following steps:
s1, weighing 4.525g of iron phosphate, 1.234g of lithium hydroxide monohydrate, 0.901g of glucose, 11.99mg of titanium dioxide and 10ml of ethanol, adding into a ball milling tank, adding zirconia balls, carrying out ball milling at 600rpm for 12 hours to obtain mixture slurry, and then carrying out vacuum drying at 60 ℃ for 12 hours to obtain a powdery mixture raw material;
s2, transferring the powdery mixture raw material in the S1 into a corundum ark, placing the corundum ark in a tube furnace filled with argon atmosphere, heating to 300 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 2h, heating to 650 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 8h, and cooling along with the furnace to obtain the lithium iron phosphate anode material Ti-LFP/C.
Example 6
The embodiment of the invention provides a preparation method of a titanium-doped lithium iron phosphate positive electrode material, which specifically comprises the following steps:
s1, weighing 4.525g of iron phosphate, 1.234g of lithium hydroxide monohydrate, 0.901g of glucose, 11.99mg of titanium dioxide and 10ml of ethanol, adding into a ball milling tank, adding zirconia balls, carrying out ball milling at 600rpm for 12 hours to obtain mixture slurry, and then carrying out vacuum drying at 60 ℃ for 12 hours to obtain a powdery mixture raw material;
s2, transferring the powdery mixture raw material in the S1 into a corundum ark, placing the corundum ark in a tube furnace filled with argon atmosphere, heating to 300 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 2h, heating to 650 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 12h, and cooling along with the furnace to obtain the lithium iron phosphate anode material Ti-LFP/C.
Example 7
The embodiment of the invention provides a preparation method of a titanium-doped lithium iron phosphate positive electrode material, which specifically comprises the following steps:
s1, weighing 4.525g of iron phosphate, 1.246g of lithium hydroxide monohydrate, 0.901g of glucose, 5.995mg of titanium dioxide and 10ml of ethanol, adding into a ball milling tank, adding zirconia balls, carrying out ball milling at 600rpm for 12 hours to obtain mixture slurry, and then carrying out vacuum drying at 60 ℃ for 12 hours to obtain a powdery mixture raw material;
s2, transferring the powdery mixture raw material in the S1 into a corundum ark, placing the corundum ark in a tube furnace filled with argon atmosphere, heating to 300 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 2h, heating to 650 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 10h, and cooling along with the furnace to obtain the lithium iron phosphate anode material Ti-LFP/C.
Example 8
The embodiment of the invention provides a preparation method of a titanium-doped lithium iron phosphate positive electrode material, which specifically comprises the following steps:
s1, weighing 4.525g of iron phosphate, 1.221g of lithium hydroxide monohydrate, 0.901g of glucose, 17.98mg of titanium dioxide and 10ml of ethanol, adding into a ball milling tank, adding zirconia balls, carrying out ball milling at 600rpm for 12 hours to obtain mixture slurry, and then carrying out vacuum drying at 60 ℃ for 12 hours to obtain a powdery mixture raw material;
s2, transferring the powdery mixture raw material in the S1 into a corundum ark, placing the corundum ark in a tube furnace filled with argon atmosphere, heating to 300 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 2h, heating to 650 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 10h, and cooling along with the furnace to obtain the lithium iron phosphate anode material Ti-LFP/C.
Example 9
The embodiment of the invention provides a preparation method of a titanium-doped lithium iron phosphate positive electrode material, which specifically comprises the following steps:
s1, weighing 4.525g of iron phosphate, 1.209g of lithium hydroxide monohydrate, 0.901g of glucose, 23.97mg of titanium dioxide and 10ml of ethanol, adding into a ball milling tank, adding zirconia balls, carrying out ball milling at 600rpm for 12 hours to obtain mixture slurry, and then carrying out vacuum drying at 60 ℃ for 12 hours to obtain a powdery mixture raw material;
s2, transferring the powdery mixture raw material in the S1 into a corundum ark, placing the corundum ark in a tube furnace filled with argon atmosphere, heating to 300 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 2h, heating to 650 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 10h, and cooling along with the furnace to obtain the lithium iron phosphate anode material Ti-LFP/C.
Example 10
The embodiment of the invention provides a preparation method of a titanium-doped lithium iron phosphate positive electrode material, which specifically comprises the following steps:
s1, weighing 4.525g of iron phosphate, 1.234g of lithium hydroxide monohydrate, 0.901g of glucose, 11.99mg of titanium dioxide and 10ml of ethanol, adding into a ball milling tank, adding zirconia balls, carrying out ball milling at 600rpm for 12 hours to obtain mixture slurry, and then carrying out vacuum drying at 60 ℃ for 12 hours to obtain a powdery mixture raw material;
s2, transferring the powdery mixture raw material in the S1 into a corundum ark, placing the corundum ark in a tube furnace filled with argon atmosphere, heating to 250 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 2h, heating to 650 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 10h, and cooling along with the furnace to obtain the lithium iron phosphate anode material Ti-LFP/C.
Example 11
The embodiment of the invention provides a preparation method of a titanium-doped lithium iron phosphate positive electrode material, which specifically comprises the following steps:
s1, weighing 4.525g of iron phosphate, 1.234g of lithium hydroxide monohydrate, 0.901g of glucose, 11.99mg of titanium dioxide and 10ml of ethanol, adding into a ball milling tank, adding zirconia balls, carrying out ball milling at 600rpm for 12 hours to obtain mixture slurry, and then carrying out vacuum drying at 60 ℃ for 12 hours to obtain a powdery mixture raw material;
s2, transferring the powdery mixture raw material in the S1 into a corundum ark, placing the corundum ark in a tube furnace filled with argon atmosphere, heating to 350 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 2h, heating to 650 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 10h, and cooling along with the furnace to obtain the lithium iron phosphate anode material Ti-LFP/C.
Example 12
The embodiment of the invention provides a preparation method of a titanium-doped lithium iron phosphate positive electrode material, which specifically comprises the following steps:
s1, weighing 4.525g of iron phosphate, 1.234g of lithium hydroxide monohydrate, 0.901g of glucose, 11.99mg of titanium dioxide and 10ml of ethanol, adding into a ball milling tank, adding zirconia balls, carrying out ball milling at 600rpm for 12 hours to obtain mixture slurry, and then carrying out vacuum drying at 60 ℃ for 12 hours to obtain a powdery mixture raw material;
s2, transferring the powdery mixture raw material in the S1 into a corundum ark, placing the corundum ark in a tube furnace filled with argon atmosphere, heating to 300 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 2h, heating to 650 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 10h, cooling to 450 ℃ at the speed of 5 ℃/min, and carrying out furnace cooling to obtain the lithium iron phosphate anode material Ti-LFP/C.
Example 13
The embodiment of the invention provides a preparation method of a Nb-doped lithium iron phosphate cathode material, which specifically comprises the following steps:
s1, weighing 4.525g of iron phosphate, 1.234g of lithium hydroxide monohydrate, 0.901g of glucose, 39.87mg of niobium pentoxide and 10ml of ethanol, adding into a ball milling tank, adding zirconia balls, carrying out ball milling for 12 hours at 600rpm to obtain mixture slurry, and then carrying out vacuum drying for 12 hours at 60 ℃ to obtain a powdery mixture raw material;
s2, transferring the powdery mixture raw material in the S1 into a corundum ark, placing the corundum ark in a tube furnace filled with argon atmosphere, heating to 300 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 2h, heating to 650 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 10h, and cooling along with the furnace to obtain the lithium iron phosphate cathode material Nb-LFP/C.
Example 14
The embodiment of the invention provides a preparation method of an Mg-doped lithium iron phosphate positive electrode material, which specifically comprises the following steps:
s1, weighing 4.525g of iron phosphate, 1.234g of lithium hydroxide monohydrate, 0.901g of glucose, 6.05mg of magnesium oxide and 10ml of ethanol, adding into a ball milling tank, adding zirconia balls, carrying out ball milling at 600rpm for 12 hours to obtain mixture slurry, and then carrying out vacuum drying at 60 ℃ for 12 hours to obtain a powdery mixture raw material;
s2, transferring the powdery mixture raw material in the S1 into a corundum ark, placing the corundum ark in a tube furnace filled with argon atmosphere, heating to 300 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 2h, heating to 650 ℃ at the speed of 2 ℃/min, carrying out heat preservation sintering for 10h, and cooling along with the furnace to obtain the lithium iron phosphate anode material Mg-LFP/C.
The LFP/C samples prepared in example 1 and the Ti-LFP/C samples prepared in example 2 were characterized.
Fig. 1-a and 1-b are SEM photographs of the LFP/C sample prepared in example 1 of the present invention at 5000 times and 30000 times, respectively, and it can be seen from the SEM photographs that the prepared lithium iron phosphate positive electrode material exists in the form of a single particle, and the particle size is about 200-500 nm; fig. 2-a and 2-b are SEM photographs of Ti-LFP/C samples prepared in example 2 of the present invention at 5000 times and 30000 times magnification, respectively, and it can be seen from the SEM photographs that the prepared titanium-doped lithium iron phosphate positive electrode material exists in the form of a single particle, and the particle size is about 50-200 nm; as can be seen from a comparison of the results in fig. 1 and fig. 2, the particles of the titanium-doped lithium iron phosphate positive electrode material are significantly reduced compared to the undoped lithium iron phosphate positive electrode material.
FIG. 3 is a TEM image of a Ti-LFP/C sample prepared in example 2 of the present invention, wherein: a is a bright field image of the appearance of the sample, b is a high-angle annular dark field image, and c, d, e and f are respectively the mapping of Fe, O, P and Ti elements in the same region; as can be seen from the figure, the elements Fe, O, P and Ti are uniformly distributed in the material, and the segregation phenomenon of the element Ti does not occur.
FIG. 4 shows X-ray diffraction patterns of the LFP/C sample prepared in example 1 and the Ti-LFP/C sample prepared in example 2; as can be seen from the figure, the prepared LFP/C sample and the Ti-LFP/C sample both have olivine structures, and the corresponding space group is pnma.
Table 1 shows the results of measuring the conductivity and the particle size of the samples prepared in the examples of the present invention.
TABLE 1 results of measurement of conductivity and particle size of each sample obtained in examples 1 to 13
The samples prepared in the examples 1 to 14 are respectively used as the anode materials of the lithium ion batteries to prepare the anode pole piece, and the specific process is as follows:
(1) uniformly mixing the prepared powdery positive electrode material with acetylene black (a conductive agent) and polyvinylidene fluoride (PVDF, a binder) according to the mass ratio of 8: 1, dropwise adding a proper amount of N-methyl pyrrolidone (NMP) serving as a dispersing agent, and grinding into slurry; then, uniformly coating the slurry on an aluminum foil, carrying out vacuum drying at 120 ℃ for 12h, and transferring the aluminum foil into an argon atmosphere glove box for later use;
(2) assembling a half cell in an argon atmosphere glove box, taking metal lithium as a counter electrode and LiPF6Ethylene carbonate (EC: DMC: DEC: 1 in volume ratio) was used as an electrolyte, and a CR2016 type coin cell was assembled and charged in a constant current charge-discharge mode.
FIG. 5 is a graph of the cyclic specific capacity of the LFP/C sample prepared in example 1 and the Ti-LFP/C sample prepared in example 2 according to the present invention (the first three cycles of the cycle are activated at a current density of 0.1C) for 100 cycles at a current density of 1C (1C: 170 mA/g); as can be seen from fig. 5, the first-loop discharge capacities of the button cell prepared by the LFP/C sample prepared in example 1 and the Ti-LFP/C sample prepared in example 2 are 137.7mAh/g and 155.6mAh/g, respectively, that is, the first-time discharge capacity of the titanium-doped lithium iron phosphate positive electrode material is significantly improved.
FIG. 6 is a graph of the cyclic specific capacity of the LFP/C sample prepared in example 1 and the Ti-LFP/C sample prepared in example 2 of the present invention (the first three cycles of the cycle are activated at O.1C current density) for 1000 cycles at 10C (1C 170 mA/g); as can be seen from FIG. 6, the first-loop discharge capacities of the button cells obtained by the LFP/C sample obtained in example 1 and the Ti-LFP/C sample obtained in example 2 are 113.4mAh/g and 135.0mAh/g, respectively; in addition, the retention rate of the capacity of the button cell prepared from the Ti-LFP/C sample prepared in example 2 after 1000 cycles is as high as 91.7%, while the retention rate of the capacity of the button cell prepared from the LFP/C sample prepared in example 1 after 1000 cycles is only 67.3%, i.e. the titanium-doped lithium iron phosphate positive electrode material has excellent high-rate cycling stability.
FIG. 7 is a graph showing the rate capability of the LFP/C sample prepared in example 1 and the Ti-LFP/C sample prepared in example 2; as can be seen from fig. 7, the capacities of the button cells prepared from the Ti-LFP/C samples prepared in example 2 at current densities of 0.1C, 1C, 2C, 5C, 10C and 20C are 159.6, 156.7, 151.8, 143.1, 135.5 and 125.9mAh/g, respectively, while the capacities of the button cells prepared from the LFP/C samples prepared in example 1 at current densities of 0.1C, 1C, 2C, 5C, 10C and 20C are 157.0, 140.2, 128.4, 113.0, 103.2 and 94.1mAh/g, respectively, i.e., the titanium-doped lithium iron phosphate positive electrode material has excellent rate capability.
Table 2 shows the discharge capacity retention rate and rate capability test results of button cell batteries prepared from samples prepared in the embodiments of the present invention after 1000 cycles.
Table 2 long cycle stability and rate capability test results for samples prepared in each example
FIG. 8 is a cyclic voltammogram at a sweep rate of 1mV/s for a button cell prepared from the LFP/C sample prepared in example 1 and the Ti-LFP/C sample prepared in example 2; as can be seen from fig. 8, the button cells prepared from the LFP/C sample prepared in example 1 and the Ti-LFP/C sample prepared in example 2 both exhibit a pair of reversible redox peaks, but the comparison shows that the potential difference between the redox peaks of the button cell prepared from the Ti-LFP/C sample prepared in example 2 is much smaller than that of the button cell prepared from the LFP/C sample prepared in example 1, i.e. the titanium-doped lithium iron phosphate positive electrode material has smaller polarization.
The above-mentioned embodiments only express several embodiments of the present invention, and the description thereof is more specific and detailed, but not construed as limiting the scope of the invention.
It should be noted that, for a person skilled in the art, several variations and modifications can be made without departing from the inventive concept, which falls within the scope of the present invention. Therefore, the protection scope of the present patent shall be subject to the appended claims.
Claims (10)
1. A positive ion doped lithium iron phosphate anode material is characterized in that,
the molecular formula is as follows: li1-yMxFePO4The lithium iron phosphate positive electrode material has an olivine structure;
wherein:
x≤0.03；
m is one or more of Na, Mg, Al, Cr, Ti, Zr, Nb and W.
2. The cation-doped lithium iron phosphate positive electrode material according to claim 1,
when M is Na, y is x; when M is Mg, y is 2 x; when M is Al or Cr, y is 3 x; when M is Ti or Zr, y is 4 x; when M is Nb, y is 5 x; when M is W, y is 6 x;
preferably, M is Ti, x is less than or equal to 0.01, and the doping element Ti is uniformly distributed in the lithium iron phosphate anode material.
3. The cation-doped lithium iron phosphate positive electrode material according to claim 1 or 2,
the capacity of the lithium iron phosphate anode material is more than 130mAh/g when the discharge rate is 10C, and the capacity retention rate is more than 90% after 1000 cycles.
4. The method for producing a cation-doped lithium iron phosphate positive electrode material according to any one of claims 1 to 3,
the method comprises the following steps:
uniformly mixing iron phosphate, a lithium source, a doping agent containing an element M and a carbon-containing reducing agent in proportion, and then, carrying out heat preservation for 6-15h at the temperature of 600-800 ℃ in a protective atmosphere to obtain the material;
preferably, in the sintering process, after the temperature is higher than 500 ℃, the temperature rise rate is controlled to be 2-5 ℃/min.
5. The method for preparing a cation-doped lithium iron phosphate positive electrode material according to claim 4,
the lithium source is one or more of lithium carbonate, lithium hydroxide monohydrate, lithium hydroxide, lithium acetate and lithium nitrate;
and/or the doping agent containing the element M is one or more of oxide, carbonate, acetate and hydroxide of M;
and/or the carbonaceous reducing agent is one or more of glucose, sucrose and citric acid.
6. The method for preparing a cation-doped lithium iron phosphate positive electrode material according to claim 4,
the protective atmosphere is argon.
7. The method for producing a cation-doped lithium iron phosphate positive electrode material according to any one of claims 4 to 6,
the sintering is two-section high-temperature sintering, and specifically comprises the following steps: keeping the temperature at 400 ℃ for 1-6h at 250 ℃ and then keeping the temperature at 800 ℃ for 6-12h at 600 ℃.
8. The method for producing a cation-doped lithium iron phosphate positive electrode material according to any one of claims 4 to 7,
the method specifically comprises the following steps:
s1, weighing iron phosphate, a lithium source, a doping agent containing an element M and a carbonaceous reducing agent according to a proportion, adding the weighed materials into a ball milling tank, adding ethanol according to the proportion of 0.5-1.8g/mL of material-liquid ratio, ball milling for 6-12h at 400-800rpm, and then drying for 6-12h in vacuum at 60-100 ℃ to obtain a powdery mixture raw material;
s2, placing the powdery mixture raw material in S1 in an argon atmosphere, heating to 250-400 ℃ at the speed of 2-10 ℃/min, carrying out heat preservation sintering for 1-6h, heating to 600-800 ℃ at the speed of 2-4 ℃/min, carrying out heat preservation sintering for 6-12h, cooling to 450 ℃ at the speed of 3.5-6 ℃/min, and cooling with a furnace to obtain the high-temperature-resistant aluminum alloy.
9. A positive electrode plate is characterized in that,
the positive electrode piece comprises the cation-doped lithium iron phosphate positive electrode material as claimed in any one of claims 1 to 3.
10. A lithium ion battery is characterized in that,
the lithium ion battery comprises the positive electrode sheet of claim 9.
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| CN102509801A (en) * | 2011-11-15 | 2012-06-20 | 河北师范大学 | Method for preparing metal-doped lithium iron phosphate as cathode material of lithium ion battery |
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| CN101651204A (en) * | 2009-09-24 | 2010-02-17 | 安徽工业大学 | Method for preparing multi-element doping lithium iron phosphate by taking ferrous metallurgy sludge as main raw material |
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