CN105810943B - A kind of method that zinc doping LiFePO4 is prepared using phosphatization slag - Google Patents

Abstract

The invention belongs to the technical field of new energy material preparation, and specifically relates to a method for preparing zinc-doped lithium iron phosphate by using phosphating slag. The method of the present invention specifically comprises the following steps: first, the ferric phosphate containing trace zinc is purified from the phosphating slag by pickling method, then the lithium source, the carbon source and the ferric phosphate containing trace zinc are mixed in a certain proportion, ball milled and dried , roasted in a protective atmosphere, and cooled to obtain zinc-doped lithium iron phosphate. The method proposed by the invention realizes resource utilization of the main component of iron phosphate contained in phosphating slag, and the obtained zinc-doped lithium iron phosphate cathode material with high specific capacity and good cycle performance has important practical application value.

Description

A method for preparing zinc-doped lithium iron phosphate by using phosphating slag

technical field

The invention relates to the technical field of preparation of new energy materials, in particular to a method for preparing zinc-doped lithium iron phosphate by using phosphating slag.

Background technique

Phosphating is one of the important pretreatment methods before metal coating, and it is widely used in chemical industry, metallurgy, automobile, aerospace, household appliances and other fields. Phosphating slag is a solid waste produced during phosphating. Its main components are iron phosphate and zinc phosphate, and it also contains a small amount of nickel, cadmium, and manganese. If it is not disposed of properly, it will inevitably cause serious pollution to the environment. Therefore, it is of great significance to study the technology of turning phosphating slag into treasure to improve resource utilization and reduce environmental pollution.

Lithium iron phosphate with olivine structure has the advantages of high theoretical capacity (170mAh/g), good cycle stability, reliable safety and low price, and has become the preferred cathode material for power lithium-ion batteries. Iron phosphate is one of the main raw materials for preparing lithium iron phosphate. At present, the industrially produced lithium iron phosphate uses high-cost iron phosphate chemical reagents as raw materials. Using inductively coupled plasma (ICP) testing and analysis, it is found that the content of iron phosphate in phosphating slag is 75%~80%. If iron phosphate can be extracted from phosphating slag as a raw material for preparing lithium iron phosphate, it can not only reduce the It will not only pollute the environment, but also can significantly reduce the production cost of lithium iron phosphate, and realize the reuse of resources.

Chinese patent CN103832990A discloses a method for extracting iron phosphate from phosphating waste residue. Dissolve the phosphating slag with concentrated hydrochloric acid first, and then add sodium hydroxide to remove impurity ions in the solution by precipitation reaction. This method has problems such as high production cost and a large amount of acid-base wastewater. Chinese patent CN102593450A adopts the method of oxidation and pickling to purify phosphating slag, and then prepares multi-element doped lithium iron phosphate by using the purified phosphating slag as raw material. However, the above method has the disadvantages of complex technical process and low purity of the purified ferric phosphate.

Contents of the invention

In order to solve the deficiencies of the prior art, the object of the present invention is to provide a method for preparing zinc-doped lithium iron phosphate by using phosphating slag. Its operation is simple, economical, and secondary pollution is small.

The technical solution of the present invention is specifically introduced as follows.

The invention provides a method for preparing zinc-doped lithium iron phosphate by using phosphating slag, the specific steps are as follows:

(1) Mix the phosphating slag and distilled water evenly, let it stand still, remove the floating matter on the surface of the suspension, then add the first inorganic acid to it, react at 30~150℃ under normal pressure for 1~24h, and pump out after cooling Filter to obtain filter cake;

(2) Mix the filter cake in step (1) with distilled water, add the second inorganic acid, react in a reaction kettle at a temperature of 80~250°C, under a pressure of 1~4MPa, for 1~24h under high pressure, and filter with suction. The cake is dried and ground to obtain iron phosphate powder containing zinc;

(3) Add lithium source and carbon source to iron phosphate powder containing zinc, use absolute ethanol as medium, mix by ball milling, and dry;

(4) The sample obtained in step (3) is treated in a tube furnace at a temperature of 50-1000°C for 1-24 hours under a protective atmosphere, then cooled, and the sintered material is pulverized to obtain a zinc-doped lithium iron phosphate cathode material .

In the present invention, the first inorganic acid and the second inorganic acid are independently selected from any one or more of concentrated phosphoric acid, sulfuric acid, nitric acid or hydrochloric acid.

In the above step (1), the mass ratio of the first inorganic acid to the phosphating slag is 0.5:40~6:40, preferably 0.8:40~5:40, more preferably 0.9:40~4.5:40 .

In the above step (1), the reaction temperature is preferably 50-120°C, more preferably 60-100°C; the reaction time is preferably 5-18h, more preferably 6-12h.

In the above step (2), the mass ratio of the second inorganic acid to the phosphating slag is 0.2:40-4:40, preferably 0.3:40-3.5:40, more preferably 0.5:40-3:40.

In the above step (2), the reaction temperature is preferably 90-200°C, more preferably 100-180°C; the reaction time is preferably 4-19h, more preferably 5-16h.

In the above step (3), the molar ratio of iron phosphate containing zinc to lithium source and carbon source is 1: (0.90~1.1): (0.02~2.5), preferably 1: (0.93~1.08): (0.04~2.2 ), more preferably 1: (0.95~1.04): (0.05~2.1).

In the above step (3), the lithium source is one or more of lithium nitrate, lithium carbonate, lithium hydroxide or lithium acetate; the carbon source is one or more of glucose, citric acid, sucrose or ascorbic acid.

In the above step (4), the protective atmosphere is one of argon, nitrogen or helium, preferably under a nitrogen atmosphere.

In the above step (4), the reaction temperature is preferably 550-900°C, more preferably 600-850°C; the reaction time is preferably 5-20h, more preferably 7-16h.

The zinc-doped lithium iron phosphate prepared by the above-mentioned preparation method of the present invention can be used as a positive electrode material of a lithium battery.

In the present invention, by controlling the amount of the first inorganic acid, it can be ensured that when the iron phosphate in the suspension is not dissolved, most of the zinc phosphate, nickel phosphate, cadmium phosphate, etc. State, and then through suction filtration, remove most of the impurity ions such as zinc, nickel, cadmium and so on in the phosphating slag. By controlling the amount of the second inorganic acid, it can be ensured that the ferric phosphate in the suspension is not dissolved, and a small amount of residual zinc phosphate, nickel phosphate, cadmium phosphate and other substances are dissolved in an ion state, and then by pumping Filtration to remove a small amount of residual zinc, nickel, cadmium and other impurity ions in the phosphating slag to obtain ferric phosphate with high purity.

The crystal structure of the material in the present invention is tested by a German Bruker D8 ADVANCE X-ray diffractometer, using a Cu-Kα radiation source, with a tube voltage of 40KV, a tube current of 40mA, and a scanning range of 10º~80º.

The electrical performance of the lithium iron phosphate positive electrode material in the present invention is tested by using the Wuhan LAND CT-2001 battery test system, and the voltage range of the button battery test is 2.5~4.2V.

The specific capacity of the first charge of the battery of the present invention = (the first charge capacity at 0.1C current/mass of active material) × 1000.

The specific capacity of the first discharge of the battery of the present invention = (first discharge capacity at 0.1C current/mass of active material) × 1000.

The first coulombic efficiency of the battery in the present invention=(first discharge capacity/first charge capacity)×100.

The invention has the following beneficial effects: the iron phosphate particles purified by the method have good crystallinity and high purity, and the ICP test result shows that the iron phosphate content is above 98%; the effective components in the phosphating slag can be fully utilized and a large amount of phosphorus can be saved , iron resources; provide a feasible treatment method for phosphating slag, which can recycle millions of tons of discarded phosphating slag every year and reduce damage to the environment and ecosystem; the zinc-doped phosphoric acid prepared by this method Lithium iron is suitable for the lithium battery industry, has a huge market capacity, and can bring huge economic benefits.

Description of drawings

Fig. 1 is the X-ray diffraction (XRD) pattern of the ferric phosphate sample that embodiment 1 is purified and obtained.

2 is an X-ray diffraction (XRD) spectrum of the zinc-doped lithium iron phosphate prepared in Example 1.

3 is a scanning electron microscope (SEM) image of the zinc-doped lithium iron phosphate prepared in Example 1.

Fig. 4 is the first charge and discharge curve of the zinc-doped lithium iron phosphate positive electrode material prepared in Example 1.

FIG. 5 is a graph showing the cycle performance of the zinc-doped lithium iron phosphate positive electrode material prepared in Example 1. FIG.

Detailed ways

The embodiments of the present invention will be described in further detail below in conjunction with the accompanying drawings, but the scope of protection of the present invention is not limited to the following embodiments.

Example 1

Dissolve 80g of phosphating slag in 60g of distilled water, stir to remove floating matter on the surface of the suspension, then add 8.5g of concentrated phosphoric acid (concentration: 85wt%), mix well, react at 70°C under normal pressure for 10h, and filter with suction to obtain The filter cake was mixed with distilled water again, 4.2g of concentrated phosphoric acid (concentration: 85wt%) was added to it, reacted under high pressure in a reactor at 160°C for 12h, filtered with suction, washed to neutral, dried at 90°C, and ground After passing through a 200-mesh sieve, iron phosphate powder containing trace zinc can be obtained. The ICP test results show that the iron phosphate content in the lithium iron phosphate sample obtained in this embodiment is 99.1%.

Take 30g of iron phosphate powder, add 7.2g of lithium carbonate and 5.6g of glucose at the same time, use absolute ethanol as the medium, ball mill and mix at a speed of 500r/min for 5h, then dry at 70°C, put the obtained sample into a crucible, and Under a nitrogen atmosphere, the temperature was kept in a tube furnace at 750°C for 10 hours. After cooling, the zinc-doped lithium iron phosphate cathode material was obtained, and its electrochemical performance was tested after being made into a button battery.

The X-ray diffraction (XRD) collection of patterns of the iron phosphate sample gained in the present embodiment is as shown in Figure 1. The spectrum and diffraction data of the sample are very similar to the standard spectrum and diffraction data of iron phosphate (card number: 29-0715), indicating that the obtained iron phosphate has a high purity.

The X-ray diffraction (XRD) spectrum of the lithium iron phosphate sample obtained in this embodiment is shown in Figure 2. Comparing the sample spectrum and diffraction data with the standard spectrum and diffraction data of lithium iron phosphate (card number: 81-1173), there is almost no obvious impurity phase, indicating that a small amount of zinc has entered the lattice of lithium iron phosphate to form zinc-doped iron phosphate lithium.

The scanning electron microscope (SEM) image of the lithium iron phosphate sample obtained in this embodiment is shown in FIG. 3 . It can be seen from the figure that the prepared zinc-doped lithium iron phosphate sample has uniform particle size and good dispersion.

The initial charge-discharge curve of the lithium iron phosphate cathode material obtained in this embodiment is shown in FIG. 4 . Under the current of 0.1c, the first charge specific capacity is 154.75mAh·g ^-1 , the first discharge specific capacity is 144.74mAh·g ^-1 , and the first Coulombic efficiency is 93.53%.

The cycle performance curve of the lithium iron phosphate cathode material obtained in this embodiment is shown in FIG. 5 . Under 1c current, after 20 charge-discharge cycles, the charge specific capacity is 129.87mAh·g ^-1 , and the capacity retention rate is 94.55%.

Example 2

Dissolve 80g of phosphating slag in 60g of distilled water, stir to remove floating matter on the surface of the suspension, then add 8.9g of concentrated sulfuric acid (concentration: 98wt%), mix well, react at 30°C under normal pressure for 20h, and filter with suction to obtain The filter cake was mixed with distilled water again, 5.5g of dilute hydrochloric acid (concentration: 8wt%) was added thereto, reacted under high pressure in a reactor at 220°C for 5h, filtered with suction, the filter cake was washed to neutral, dried at 90°C, and ground After passing through a 200-mesh sieve, iron phosphate powder containing trace zinc can be obtained. The ICP test result shows that the iron phosphate content in the lithium iron phosphate sample obtained in this embodiment is 98.5%.

Take 30g of iron phosphate powder, add 7.2g of lithium carbonate and 5.6g of sucrose at the same time, use absolute ethanol as the medium, ball mill and mix at a speed of 500r/min for 5h, then dry at 70°C, put the obtained sample into a crucible, and Under a nitrogen atmosphere, the temperature was maintained in a tube furnace at 1000°C for 4 hours. After cooling, the zinc-doped lithium iron phosphate cathode material was obtained, and its electrochemical performance was tested after being made into a button battery. At 0.1c current, the first charge specific capacity is 157.79mAh·g ^-1 , the first discharge specific capacity is 149.59mAh·g ^-1 , and the first Coulombic efficiency is 94.8%. After 20 charge-discharge cycles at 1c current, the charge specific capacity is 149.77mAh·g ^-1 , and the capacity retention rate is 94.92%.

Example 3

Dissolve 80g of phosphating slag in 60g of distilled water, stir to remove floating matter on the surface of the suspension, then add 7.1g of concentrated nitric acid (concentration: 68wt%), mix well, react at 150°C under normal pressure for 2h, and suction filter to obtain Mix the filter cake with distilled water again, add 3.5g of concentrated phosphoric acid (concentration: 85wt%) to it, react in a reactor at 90°C for 22h under high pressure, filter with suction, wash the filter cake to neutrality, dry it at 90°C, grind After passing through a 200-mesh sieve, iron phosphate powder containing trace zinc can be obtained. The ICP test result shows that the iron phosphate content in the lithium iron phosphate sample obtained in this embodiment is 98.3%.

Take 30g of iron phosphate powder, add 4.6g of lithium hydroxide and 5.6g of ascorbic acid at the same time, use absolute ethanol as the medium, ball mill and mix at a speed of 500r/min for 5h, then dry at 70°C, and put the obtained sample into a crucible. In a nitrogen atmosphere, the temperature was maintained in a tube furnace at 600°C for 18 hours. After cooling, the zinc-doped lithium iron phosphate cathode material was obtained, and its electrochemical performance was tested after being made into a button battery. At 0.1c current, the first charge specific capacity is 146.84mAh·g ^-1 , the first discharge specific capacity is 136.05mAh·g ^-1 , and the first Coulombic efficiency is 92.65%. After 20 charge-discharge cycles at 1c current, the charge specific capacity is 119.65mAh·g ^-1 , and the capacity retention rate is 92.43%.

Example 4

Dissolve 80g of phosphating slag in 60g of distilled water, stir to remove floating matter on the surface of the suspension, then add 10g of concentrated phosphoric acid (concentration: 85wt%), mix well, and react at 90°C for 8 hours under normal pressure, and filter with suction. Mix the cake with distilled water again, add 6.5g of dilute nitric acid (concentration: 15wt%) to it, react under high pressure in a reactor at 140°C for 15h, filter with suction, wash the filter cake to neutrality, and then dry it at 90°C. After grinding, Pass through a 200-mesh sieve to obtain iron phosphate powder containing trace zinc. The ICP test result shows that the iron phosphate content in the iron phosphate sample obtained in this embodiment is more than 99.2%.

Take 30g of iron phosphate powder, add 7.2g of lithium carbonate and 5.6g of glucose at the same time, use absolute ethanol as the medium, ball mill and mix at a speed of 500r/min for 5h, then dry at 70°C, put the obtained sample into a crucible, and Under a nitrogen atmosphere, the temperature was maintained in a tube furnace at 900°C for 7 hours. After cooling, the zinc-doped lithium iron phosphate cathode material was obtained, and its electrochemical performance was tested after being made into a button battery. At 0.1c current, the first charge specific capacity is 150.32mAh·g ^-1 , the first discharge specific capacity is 139.53mAh·g ^-1 , and the first Coulombic efficiency is 92.82%. After 20 charge-discharge cycles at 1c current, the charge specific capacity is 139.83mAh·g ^-1 , and the capacity retention rate is 93.02%.

Example 5

Dissolve 80g of phosphating slag in 60g of distilled water, stir to remove floating matter on the surface of the suspension, then add 7.8g of concentrated sulfuric acid (concentration: 98wt%), mix well, react at 120°C under normal pressure for 6h, and filter with suction to obtain The filter cake was mixed with distilled water again, 4.5g of concentrated nitric acid (concentration: 85wt%) was added thereto, reacted under high pressure in a reactor at 180°C for 10h, filtered with suction, washed to neutral, then dried at 90°C, and ground After passing through a 200-mesh sieve, iron phosphate powder containing trace zinc can be obtained. The ICP test result shows that the iron phosphate content in the iron phosphate sample obtained in this embodiment is 98.7%.

Take 30g of iron phosphate powder, add 4.6g of lithium hydroxide and 5.6g of sucrose at the same time, use absolute ethanol as the medium, ball mill and mix at a speed of 500r/min for 5h, then dry at 70°C, put the obtained sample into a crucible, In a nitrogen atmosphere, the temperature was kept in a tube furnace at 850°C for 9 hours, and after cooling, the zinc-doped lithium iron phosphate cathode material was obtained, and its electrochemical performance was tested after being made into a button battery. At 0.1c current, the first charge specific capacity is 154.69mAh·g ^-1 , the first discharge specific capacity is 138.09mAh·g ^-1 , and the first Coulombic efficiency is 89.27%. After 20 charge-discharge cycles at 1c current, the charge specific capacity is 125.11mAh·g ^-1 , and the capacity retention rate is 91.12%.

comparative example

Take 30g of iron phosphate powder (AR, Sinopharm Chemical Reagent Co., Ltd.), add 7.2g of lithium carbonate and 5.6g of glucose at the same time, use absolute ethanol as the medium, ball mill and mix at a speed of 500r/min for 5h, and then bake at 70°C After drying, the obtained sample was put into a crucible, and kept in a tube furnace at 750°C for 10 hours under a nitrogen atmosphere. After cooling, the lithium iron phosphate cathode material was obtained, and its electrochemical performance was tested after being made into a button battery. At 0.1c current, the first charge specific capacity is 149.82mAh·g ^-1 , the first discharge specific capacity is 134.63mAh·g ^-1 , and the first Coulombic efficiency is 89.86%. After 20 charge-discharge cycles at 1c current, the charge specific capacity is 121.32mAh·g ^-1 , and the capacity retention rate is 91.61%.

Table 1 is the data related to the charge and discharge performance of the examples and comparative samples.

Table 1 embodiment and comparative sample charge and discharge test data

As can be seen from the above test results, the zinc-doped lithium iron phosphate cathode material prepared by the present invention has uniform particles and good dispersibility; it has higher first-time Coulombic efficiency and better cycle performance; in addition, the cyclic voltammetry test results show that , the zinc-doped lithium iron phosphate cathode material prepared by the invention has good reversibility.

Claims (5)

1. a method utilizing phosphating slag to prepare zinc-doped lithium iron phosphate, is characterized in that, concrete steps are as follows: (1) Mix the phosphating slag and distilled water evenly, let it stand still, remove the floating matter on the surface of the suspension, then add the first inorganic acid to it, react at 30~150℃ under normal pressure for 1~24h, and pump out after cooling Filter to obtain filter cake; (2) Mix the filter cake in step (1) with distilled water, add the second inorganic acid, react in a reaction kettle at a temperature of 80~250°C, under a pressure of 1~4MPa, for 1~24h under high pressure, and filter with suction. The cake is dried and ground to obtain iron phosphate powder containing zinc; (3) Add lithium source and carbon source to iron phosphate powder containing zinc, use absolute ethanol as medium, mix by ball milling, and dry; (4) The sample obtained in step (3) is treated at a constant temperature in a tube furnace under a protective atmosphere, cooled, and the sintered material is pulverized to obtain a zinc-doped lithium iron phosphate material; wherein: the reaction temperature is 550~900°C ; The reaction time is 5 ~ 20h; wherein: The first inorganic acid and the second inorganic acid are independently selected from any one or more of concentrated phosphoric acid, concentrated sulfuric acid, concentrated nitric acid or concentrated hydrochloric acid; In step (1), the mass ratio of the first inorganic acid to phosphating slag is 0.5:40~6:40, the reaction temperature is 50~120°C; the reaction time is 5~18h; In step (2), the mass ratio of the second inorganic acid to the phosphating slag is 0.2:40-4:40; the reaction temperature is 90-200° C., and the reaction time is 4-19 hours. 2 . The method according to claim 1 , wherein in step (3), the molar ratio of zinc-containing iron phosphate to lithium source and carbon source is 1: (0.90-1.1): (0.02-2.5). 3. The method according to claim 1, characterized in that: in step (3), the lithium source is selected from one or more of lithium nitrate, lithium carbonate, lithium hydroxide or lithium acetate; the carbon source is selected from glucose , citric acid, sucrose or ascorbic acid in one or more. 4. The method according to claim 1, characterized in that: in step (4), the protective atmosphere is one of argon, nitrogen or helium. 5. The method according to any one of claims 1-4, wherein the prepared zinc-doped lithium iron phosphate is used as a lithium battery cathode material.