CN103311543A - Anode material hydroxyl iron phosphate for lithium ion batteries and preparation method thereof - Google Patents

Abstract

The invention discloses a lithium ion battery cathode material hydroxy iron phosphate and a preparation method thereof. The anode material iron hydroxyphosphate used in the lithium-ion battery has a molecular formula of Fe _1.5 (PO ₄ )(OH), which is prepared by a hydrothermal synthesis method, that is, by adjusting different hydrothermal temperatures and pHs to obtain different shapes and different Fe _1.5 (PO ₄ )(OH) cathode material with electrochemical performance. Especially when the hydrothermal temperature is 150°C and the pH value is 2.5, the Fe _1.5 (PO ₄ )(OH) positive electrode material synthesized at the charge and discharge rate of 0.1C and 0.3C has a specific capacity of 176mAh/g for the first time. , 154mAh/g; after 60 cycles, the specific capacity remained at 165mAh/g and 150mAh/g respectively. The preparation method has the characteristics of simple process, convenient operation, suitable for large-scale production and the like.

Description

Lithium-ion battery cathode material iron hydroxyphosphate and preparation method thereof

technical field

The present invention relates to a lithium-ion battery cathode material, ferric hydroxyphosphate, and a preparation method thereof.

Background technique

Since Goodenough [1] reported the reversible intercalation and delithiation characteristics of LiFePO ₄ in 1997, iron-based lithium-ion battery cathode materials have wider sources of raw materials, lower prices, no environmental pollution, environmental friendliness, and good thermal stability. The advantages have attracted great attention of researchers, and it is one of the most competitive anode materials for next-generation lithium-ion batteries.

There are actually two types of cathode materials for iron-based lithium-ion batteries, one is lithium-ion-containing cathode materials represented by LiFePO ₄ , and the other is lithium-ion-free cathode materials. Taking _FePO4 as an example, during the _LiFePO4 charging process, lithium ions and corresponding electrons are extracted from the material, thereby forming a new _FePO4 phase in the material and forming a phase interface. During discharge, lithium ions and corresponding electrons intercalate into the material, thereby forming a new LiFePO ₄ phase outside the FePO ₄ phase. Therefore, FePO ₄ can also be used as a cathode material for lithium-ion batteries [2,3].

Ferric hydroxyphosphate is a mineral that widely exists in nature and has been extensively studied by many mineralogists. Gheithi named the tetragonal compound Fe _2-y (PO4)(OH) _3y-2 as "lipscombite" [4]. Whittinghan et al. [5] reported the synthesis, crystal structure, electrochemical properties and magnetic properties of Fe _2-y □ _y (PO4) (OH) _3y-2 (H ₂ O) _3y-2 (□ represents Fe vacancy).

Hydroxy iron phosphate material has many advantages as the cathode material of lithium-ion batteries: (1) The synthesis process is simpler, because there is no Fe(II) component in the synthesis, no atmosphere protection is required, and corresponding equipment and cost investment are saved; ( 2) The synthesis of iron hydroxyphosphate materials is a binary synthesis system, which is more convenient to control and optimize the synthesis conditions; (3) Since Fe(III) compounds are used as raw materials, the sources of synthetic raw materials are wider. All these advantages can make the iron hydroxyphosphate material have the advantages of low cost and large-scale production, and it is expected to become a rising star of LiFePO ₄ lithium ion battery cathode material.

However, there is no report on iron hydroxyphosphate materials with the molecular formula Fe _1.5 (PO ₄ )(OH) at present.

references

[1], A. Padhi, K. Nanjundaswamy, J.B. Goodenough, Journal of the Electrochemical Society, 144 (1997) 1188-1194.

[2], J. Allen, T. Jow, J. Wolfenstine, Journal of Solid State Electrochemistry, 12 (2008) 1031-1033.

[3], P. Reale, B. Scrosati, C. Delacourt, C. Wurm, M. Morcrette, C. Masquelier, Chemistry of materials, 15 (2003) 5051-5058.

[4], M. Lindberg, C. Christ, Acta Crystallographica, 12 (1959) 695-697.

[5], Y. Song, P.Y. Zavalij, N.A. Chernova, M.S. Whittingham, Chemistry of materials, 17 (2005) 1139-1147.

Contents of the invention

One of the objectives of the present invention is to provide a positive electrode material for a lithium-ion battery with a molecular formula of Fe _1.5 (PO ₄ )(OH).

The second object of the present invention is to provide a method for preparing the above-mentioned anode material for hydroxyiron phosphate lithium ion battery whose molecular formula is Fe _1.5 (PO ₄ )(OH).

Technical scheme of the present invention

A lithium-ion battery cathode material, ferric hydroxyphosphate, is prepared by hydrothermal synthesis, and its molecular formula is Fe _1.5 (PO ₄ )(OH);

The described ferric hydroxyphosphate with the molecular formula Fe _1.5 (PO ₄ )(OH) is a layered chain formed by sharing coplanar surfaces of FeO ₆ octahedrons along the [1 0 0] and [0 1 0] crystal directions respectively and through The FeO ₄ tetrahedron shares a vertex with two adjacent FeO ₆ octahedrons respectively and connects the two adjacent layered chains in a layered rod-like crystal structure.

The above-mentioned anode material for a lithium ion battery, i.e. a method for synthesizing iron hydroxyphosphate with a molecular formula of Fe _1.5 (PO ₄ ) (OH), specifically comprises the following steps:

(1) Add the surfactant sodium dodecylbenzenesulfonate 0.0002mol/L to the 0.02mol/L Fe(NO ₃ ) ₃ ·9H ₂ O aqueous solution, and then add 0.02mol/L NH ₄ H ₂ Pour the PO ₄ aqueous solution into it to obtain a mixed solution, stir it uniformly with electromagnetic stirring, adjust the pH to 1.5-4.5 with 15% ammonia water, then transfer it to a hydrothermal reaction kettle, and control the temperature at 150-200°C for hydrothermal reaction for 24 hours get the reaction solution;

The amount of 0.02mol/L Fe(NO ₃ ) ₃ ·9H ₂ O aqueous solution, 0.02mol/L NH ₄ H ₂ PO ₄ aqueous solution and surfactant sodium dodecylbenzenesulfonate in the mixed solution is as follows: Calculate the molar ratio of Fe ³⁺ , PO ₄ ^3- and surfactant sodium dodecylbenzene sulfonate, that is, Fe ³⁺ : PO ₄ ^3- : surfactant sodium dodecylbenzene sulfonate is 1:1 : 0.01;

(2) Centrifuge the reaction solution obtained in step (1), add absolute ethanol to the obtained filter cake, and heat-treat the final obtained filter cake to obtain a lithium-ion battery with the molecular formula Fe _1.5 (PO ₄ )(OH) Positive electrode material iron hydroxyphosphate;

The heat treatment is to place the filter cake in a quartz tube, sinter in a tube furnace at 120°C for 1 hour, 160°C for 1 hour, and 400°C for 3 hours, and control the heating rate to 3°C/min during each heating process;

The heat treatment process is carried out under the environment of blowing air.

Beneficial effects of the present invention

The present invention proposes a positive electrode material for a lithium iron phosphate lithium ion battery with a molecular formula of Fe _1.5 (PO ₄ )(OH). Through experimental detection, it is found that it has higher specific capacity and specific power than FePO ₄ , the positive electrode material of iron-based lithium-ion batteries, especially Fe _1.5 (PO ₄ )(OH) synthesized when the hydrothermal temperature is 150°C and the pH value is 2.5. When the charge and discharge rate of the positive electrode material is 0.1C and 0.3C, the first discharge specific capacity is 176mAh/g and 154mAh/g respectively; after 60 cycles, the specific capacity remains at 165mAh/g and 150mAh/g respectively. Therefore, a lithium iron phosphate lithium ion battery cathode material with a molecular formula of Fe _1.5 (PO ₄ )(OH) in the present invention can further improve the performance of the lithium ion battery, making it possible for the lithium ion battery to be used in large-scale energy storage batteries.

Further, the preparation of the anode material of the hydroxyiron phosphate lithium ion battery whose molecular formula is Fe _1.5 (PO ₄ ) (OH) of the present invention adopts the hydrothermal synthesis method, so the preparation process is simple, the operation is convenient, and it is suitable for large-scale production, etc. features.

Description of drawings

Figure 1, Examples 1, 2, 3 and 4, that is, Fe _1.5 (PO ₄ )(OH) and standard Fe obtained under the pH value of 2.5 and hydrothermal temperature of 150°C, 170°C, 180°C and 200°C respectively XRD pattern of _1.5 (PO ₄ )(OH), where A is standard Fe _1.5 (PO ₄ )(OH), B is Fe _1.5 (PO ₄ )(OH) obtained at 150°C, and C is obtained at 170°C Fe _1.5 (PO ₄ )(OH), D is Fe _1.5 (PO ₄ )(OH) obtained at 180°C, E is Fe _1.5 (PO ₄ )(OH) obtained at 200°C;

Fig. 2, Examples 5, 3, 6, and 7, that is, the hydrothermal temperature is 180°C, and the pH value is respectively 1.5, 2.5, 3.5, and 4.5 The XRD patterns of Fe _1.5 (PO ₄ ) (OH) synthesized under the conditions, wherein A is the standard Fe _1.5 (PO ₄ ) (OH), B is the Fe _1.5 (PO ₄ ) (OH) obtained at a pH of 1.5, and C is the Fe _1.5 (PO ₄ ) (OH) obtained at a pH of 2.5 ), D is the Fe _1.5 (PO ₄ ) (OH) obtained at a pH value of 3.5, and E is the Fe _1.5 (PO ₄ ) (OH) obtained at a pH value of 4.5;

Figure 3. XRD patterns of Fe _1.5 (PO ₄ )(OH) synthesized under hydrothermal conditions at 200°C, where A is standard Fe _1.5 (PO ₄ )(OH), and B is Fe _1.5 (PO ₄ ) obtained at 200°C )(OH);

Figure 4A, the crystal structure diagram of Fe _1.5 (PO ₄ )(OH) sample along the [1 0 0] crystal direction;

Figure 4B, the crystal structure diagram of Fe _1.5 (PO ₄ )(OH) sample along the [0 1 0] crystal direction;

Figure 5A1 and Figure 5A2, the SEM images of Fe _1.5 (PO ₄ )(OH) obtained under different magnifications in Example 1, that is, the pH value is 2.5, and the hydrothermal temperature is 150°C;

Figure 5B1 and Figure 5B2, the SEM images of Fe _1.5 (PO ₄ )(OH) obtained under different magnifications in Example 2, namely, the pH value is 2.5, and the hydrothermal temperature is 170°C.

Figure 5C1, Figure 5C2 and Figure 5C3, the SEM images of Fe _1.5 (PO ₄ )(OH) obtained under different magnifications in Example 3, that is, the pH value is 2.5, and the hydrothermal temperature is 180°C.

Figure 5D1 and Figure 5D2, the SEM images of Fe _1.5 (PO ₄ )(OH) obtained under different magnifications in Example 4, that is, the pH value is 2.5, and the hydrothermal temperature is 200°C.

Figure 6A1 and Figure 6A2, Example 5, namely, the SEM spectra of Fe _1.5 (PO ₄ )(OH) synthesized at different magnifications under the condition of hydrothermal temperature of 180°C and pH value of 1.5;

Fig. 6B1, Fig. 6B2 and Fig. 6B3, Example 3, that is, the SEM spectra of Fe _1.5 (PO ₄ )(OH) synthesized at different magnifications under the condition of hydrothermal temperature of 180°C and pH value of 2.5;

Figure 6C1, Figure 6C2 and Figure 6C3, and Example 6 are the SEM spectra of Fe _1.5 (PO ₄ )(OH) synthesized at different magnifications under the condition of hydrothermal temperature of 180°C and pH value of 3.5;

Figure 6D1 and Figure 6D2, Example 7, namely, the SEM spectra of Fe _1.5 (PO ₄ )(OH) synthesized under the conditions of hydrothermal temperature of 180°C and pH value of 4.5 at different magnifications;

Fig. 7, Examples 1, 2, 3 and 4, that is, the pH value is 2.5, and the hydrothermal temperature is 150°C, 170°C, 180°C and 200°C respectively, Fe _1.5 (PO ₄ )(OH) at 0.1C The first charge and discharge curve;

Figure 8, Examples 5, 3, 6, and 7, that is, the hydrothermal temperature is 180 ° C, and the pH value is 1.5, 2.5, 3.5, and 4.5, respectively. Synthesized Fe _1.5 (PO ₄ ) (OH) at 0.1 ° C The first charge and discharge curve;

Figure 9, Examples 1, 2, 3 and 4, that is, the pH value is 2.5, and the hydrothermal temperature is 150 ° C, 170 ° C, 180 ° C and 200 ° C respectively Fe _1.5 (PO ₄ ) (OH) at 0.1 C and Cycle performance curve at 0.3C;

Figure 10, Examples 5, 3, 6, and 7, that is, Fe _1.5 (PO ₄ ) (OH) synthesized under the conditions of hydrothermal temperature of 180°C and pH values of 1.5, 2.5, 3.5, and 4.5 at 0.1C and 0.3 The cycle performance curve at C.

Detailed ways

The present invention will be further described below through specific embodiments in conjunction with the accompanying drawings, but the present invention is not limited.

Preparation of cathode materials and assembly of batteries

Preparation of cathode material

The present invention adopts CR2016 button battery to test the electrochemical performance of the material.

Calculated according to the mass ratio, that is, the positive electrode material of the lithium iron phosphate lithium ion battery with the molecular formula Fe _1.5 (PO ₄ )(OH): the conductive agent is mixed at a ratio of 75:17, then ball milled with a planetary ball mill, and an appropriate amount of alcohol is added at a speed of 500 rad/ min ball milling for 2 hours, and then dried in an oven at 120°C for 12 hours;

The conductive agent is carbon black:graphite configured in a mass ratio of 6:4.

Accurately weigh 0.0150g of the ball-milled lithium iron phosphate lithium ion battery positive electrode material with the molecular formula Fe _1.5 (PO ₄ )(OH) and the conductive agent mixture, put it in an agate mortar, absorb the binder with a microliter syringe, and then polymerize. Tetrafluoroethylene emulsion is added thereinto, diluted with absolute ethanol and then ground to dryness, so that the positive electrode material of lithium iron phosphate lithium ion battery with the molecular formula Fe _1.5 (PO ₄ )(OH) and the binder are fully and uniformly mixed to obtain a slurry;

Among them, the mixed material of ferric hydroxyphosphate and conductive agent: polytetrafluoroethylene emulsion is added at a mass ratio of 92:8, and the amount of absolute ethanol is calculated at a mass ratio, that is, the ratio of binder: absolute ethanol is 1:100.

Apply the above-mentioned slurry obtained after grinding evenly on a stainless steel mesh, put it in a 120°C oven to dry for 4 hours, then compact it under a pressure of 2Mpa for 3 minutes, then put it in a 120°C oven and dry it for 4 hours to obtain hydroxyphosphoric acid Iron positive sheet, ready to assemble the battery.

battery assembly

Lithium metal is used as the negative electrode, the iron hydroxyphosphate positive electrode sheet obtained above is used as the positive electrode, the porous polypropylene diaphragm Celgard2400 is used as the diaphragm, and the electrolyte is: DMC:EMC:EC(1:1:1)(W/W)LiPF ₆ The concentration is 1.0M (Zhangjiagang Guotai Huarong Chemical New Material Co., Ltd.), the positive and negative battery shells are LIR2016 and assembled into button batteries. The assembly process is carried out _in a glove box filled with protective atmosphere (Ar gas) (M. <0.1ppm, H ₂ O<0.1ppm) in a glove box.

After the battery is assembled, put it in a desiccator and let it rest for more than 3 hours before performing the electrochemical test.

Physical Characterization of Materials

A German (Bruker, D8 Advance) XRD powder diffractometer was used to analyze the phase of the anode material of lithium iron phosphate lithium ion battery with the molecular formula Fe _1.5 (PO ₄ )(OH) obtained in the present invention. The test conditions: Cu _kɑ =1.54056?, The voltage is 40KV, the current is 200mA, the step size is 0.02°, the scanning speed is 5°/min, and the scanning range is 10°～90°.

The morphology and size of the lithium iron phosphate lithium ion battery cathode material with the molecular formula Fe _1.5 (PO ₄ )(OH) obtained in the present invention were observed by using a Japanese SU70 field emission scanning electron microscope FE-SEM.

Constant current charge and discharge test

The obtained molecular formula of the present invention is Fe _1.5 (PO ₄ ) (OH) The constant current charge and discharge performance test of the lithium iron phosphate lithium ion battery positive electrode material is carried out in the electrochemical test equipment with program control, and what the present invention uses is a LAND battery Test system CT2001A.

The charge and discharge test conditions of the battery are carried out at room temperature (25°C), the charge and discharge rates are 0.1C and 0.3C, and the test voltage range is 2.0-4.0V.

Example 1

A method for synthesizing the anode material of a lithium iron phosphate lithium ion battery with a molecular formula of Fe _1.5 (PO ₄ ) (OH), specifically comprising the following steps:

(1) Add 0.348g of surfactant sodium dodecylbenzenesulfonate to 50 ml of 0.02 mol/L Fe(NO ₃ ) ₃ ·9H ₂ O aqueous solution, and then add 50 ml of 0.02 mol/L NH Pour _{the 4} H ₂ PO ₄ aqueous solution into it to obtain a mixed solution, stir it evenly, adjust the pH to 2.5 with 15% ammonia water, then transfer it to a hydrothermal reaction kettle, and control the temperature at 150°C for hydrothermal synthesis reaction 24h to get the reaction solution;

(2) Transfer the reaction solution obtained in step (1) to a centrifuge tube, centrifuge at a controlled speed of 5000 rpm for 10 minutes, then pour off the upper clear layer, add absolute ethanol to wash, filter, repeat the above-mentioned absolute ethanol washing, Filtration process 3 times, the obtained filter cake is placed in a quartz tube, and under the condition of ventilation, it is sintered at 120°C for 1h, 160°C for 1h, and 400°C for 3h in a tube furnace, and the heating process is controlled each time. The heating rate is 3°C/min. Under air conditions, heat treatment can remove ammonium nitrate impurities and crystal water, and obtain the positive electrode material of lithium iron phosphate lithium ion battery with the molecular formula of Fe _1.5 (PO ₄ )(OH).

Example 2

A method for synthesizing the anode material of a lithium iron phosphate lithium ion battery with a molecular formula of Fe _1.5 (PO ₄ ) (OH), specifically comprising the following steps:

(1) Add 0.348g of surfactant sodium dodecylbenzenesulfonate to 50ml of 0.02mol/L Fe(NO ₃ ) ₃ ·9H ₂ O aqueous solution, then add 50ml of 0.02mol/L NH ₄ Pour the H ₂ PO ₄ aqueous solution into it to obtain a mixed solution, stir it uniformly with electromagnetic, adjust the pH to 2.5 with 15% ammonia water, then transfer it to a hydrothermal reaction kettle, and control the temperature at 170°C for hydrothermal synthesis reaction for 24 hours to obtain The reaction solution;

(2) Transfer the reaction solution obtained in step (1) to a centrifuge tube, centrifuge at a controlled speed of 5000rpm for 10 minutes, then pour off the upper clear layer, add absolute ethanol to wash and filter, and repeat the above-mentioned absolute ethanol wash and filter Process 3 times, the obtained filter cake is placed in a quartz tube, and under the condition of ventilation, it is sintered in a tube furnace at 120°C for 1h, 160°C for 1h, and 400°C for 3h, and the temperature rise is controlled during each heating process The speed is 3°C/min, and under air conditions, heat treatment can remove ammonium nitrate impurities and crystal water, and obtain the positive electrode material of lithium iron phosphate lithium ion battery with the molecular formula of Fe _1.5 (PO ₄ )(OH).

Example 3

A method for synthesizing the anode material of a lithium iron phosphate lithium ion battery with a molecular formula of Fe _1.5 (PO ₄ ) (OH), specifically comprising the following steps:

(1) Add 0.348g of surfactant sodium dodecylbenzenesulfonate to 50ml of 0.02mol/L Fe(NO ₃ ) ₃ ·9H ₂ O aqueous solution, then add 50ml of 0.02mol/L NH ₄ Pour the H ₂ PO ₄ aqueous solution into it to obtain a mixed solution, stir it uniformly with electromagnetic, adjust the pH to 2.5 with 15% ammonia water, then transfer it to a hydrothermal reaction kettle, and control the temperature at 180°C for hydrothermal synthesis reaction for 24 hours to obtain The reaction solution;

(2) Transfer the reaction solution obtained in step (1) to a centrifuge tube, centrifuge at a controlled speed of 5000rpm for 10 minutes, then pour off the upper clear layer, add absolute ethanol to wash and filter, and repeat the above-mentioned absolute ethanol wash and filter Process 3 times, the obtained filter cake is placed in a quartz tube, and under the condition of ventilation, it is sintered in a tube furnace at 120°C for 1h, 160°C for 1h, and 400°C for 3h, and the temperature rise is controlled during each heating process The speed is 3°C/min, and under air conditions, heat treatment can remove ammonium nitrate impurities and crystal water, and obtain the positive electrode material of lithium iron phosphate lithium ion battery with the molecular formula of Fe _1.5 (PO ₄ )(OH).

Example 4

A method for synthesizing the anode material of a lithium iron phosphate lithium ion battery with a molecular formula of Fe _1.5 (PO ₄ ) (OH), specifically comprising the following steps:

(1) Add 0.348g of surfactant sodium dodecylbenzenesulfonate to 50ml of 0.02mol/L Fe(NO ₃ ) ₃ ·9H ₂ O aqueous solution, then add 50ml of 0.02mol/L NH ₄ Pour the H ₂ PO ₄ aqueous solution into it to obtain a mixed solution, stir it uniformly with electromagnetic, adjust the pH to 2.5 with 15% ammonia water, then transfer it to a hydrothermal reaction kettle, and control the temperature at 200°C for hydrothermal synthesis reaction for 24 hours to obtain The reaction solution;

(2) Transfer the reaction solution obtained in step (1) to a centrifuge tube, centrifuge at a controlled speed of 5000rpm for 10 minutes, then pour off the upper clear layer, add absolute ethanol to wash and filter, and repeat the above-mentioned absolute ethanol wash and filter Process 3 times, the obtained filter cake is placed in a quartz tube, and under the condition of ventilation, it is sintered in a tube furnace at 120°C for 1h, 160°C for 1h, and 400°C for 3h, and the temperature rise is controlled during each heating process The speed is 3°C/min, and under air conditions, heat treatment can remove ammonium nitrate impurities and crystal water, and obtain the positive electrode material of lithium iron phosphate lithium ion battery with the molecular formula of Fe _1.5 (PO ₄ )(OH).

Example 5

A method for synthesizing the anode material of a lithium iron phosphate lithium ion battery with a molecular formula of Fe _1.5 (PO ₄ ) (OH), specifically comprising the following steps:

(1) Add 0.348g of surfactant sodium dodecylbenzenesulfonate to 50ml of 0.02mol/L Fe(NO ₃ ) ₃ ·9H ₂ O aqueous solution, then add 50ml of 0.02mol/L NH ₄ Pour the H ₂ PO ₄ aqueous solution into it to obtain a mixed solution, stir it uniformly with electromagnetic, adjust the pH to 1.5 with 15% ammonia water, then transfer the reactant to a hydrothermal reaction kettle, and control the temperature at 180°C for hydrothermal synthesis React 24h to get the reaction solution;

(2) Transfer the reaction solution obtained in step (1) to a centrifuge tube, centrifuge at a controlled speed of 5000rpm for 10 minutes, then pour off the upper clear layer, add absolute ethanol to wash and filter, and repeat the above-mentioned absolute ethanol wash and filter Process 3 times, the obtained filter cake is placed in a quartz tube, and under the condition of ventilation, it is sintered in a tube furnace at 120°C for 1h, 160°C for 1h, and 400°C for 3h, and the temperature rise is controlled during each heating process The speed is 3°C/min, and under air conditions, heat treatment can remove ammonium nitrate impurities and crystal water, and obtain the positive electrode material of lithium iron phosphate lithium ion battery with the molecular formula of Fe _1.5 (PO ₄ )(OH).

Example 6

A method for synthesizing the anode material of a lithium iron phosphate lithium ion battery with a molecular formula of Fe _1.5 (PO ₄ ) (OH), specifically comprising the following steps:

(1) Add 0.348g of surfactant sodium dodecylbenzenesulfonate to 50ml of 0.02mol/L Fe(NO ₃ ) ₃ ·9H ₂ O aqueous solution, then add 50ml of 0.02mol/L NH ₄ Pour the H ₂ PO ₄ aqueous solution into it to obtain a mixed solution, stir it uniformly with electromagnetic, adjust the pH to 3.5 with 15% ammonia water, then transfer it to a hydrothermal reaction kettle, and control the temperature at 180°C for hydrothermal synthesis reaction for 24 hours to obtain The reaction solution;

(2) Transfer the reaction solution obtained in step (1) to a centrifuge tube, centrifuge at a controlled speed of 5000rpm for 10 minutes, then pour off the upper clear layer, add absolute ethanol to wash and filter, and repeat the above-mentioned absolute ethanol wash and filter Process 3 times, the obtained filter cake is placed in a quartz tube, and under the condition of ventilation, it is sintered in a tube furnace at 120°C for 1h, 160°C for 1h, and 400°C for 3h, and the temperature rise is controlled during each heating process The speed is 3°C/min, and under air conditions, heat treatment can remove ammonium nitrate impurities and crystal water, and obtain the positive electrode material of lithium iron phosphate lithium ion battery with the molecular formula of Fe _1.5 (PO ₄ )(OH).

Example 7

A method for synthesizing the anode material of a lithium iron phosphate lithium ion battery with a molecular formula of Fe _1.5 (PO ₄ ) (OH), specifically comprising the following steps:

(1) Add 0.348g of surfactant sodium dodecylbenzenesulfonate to 50ml of 0.02mol/L Fe(NO ₃ ) ₃ ·9H ₂ O aqueous solution, then add 50ml of 0.02mol/L NH ₄ Pour the H ₂ PO ₄ aqueous solution into it to obtain a mixed solution, stir it uniformly with electromagnetic, adjust the pH to 4.5 with 15% ammonia water, then transfer it to a hydrothermal reaction kettle, and control the temperature at 180°C for hydrothermal synthesis reaction for 24 hours to obtain The reaction solution;

(2) Transfer the reaction solution obtained in step (1) to a centrifuge tube, centrifuge at a controlled speed of 5000rpm for 10 minutes, then pour off the upper clear layer, add absolute ethanol to wash and filter, and repeat the above-mentioned absolute ethanol wash and filter Process 3 times, the obtained filter cake is placed in a quartz tube, and under the condition of ventilation, it is sintered in a tube furnace at 120°C for 1h, 160°C for 1h, and 400°C for 3h, and the temperature rise is controlled during each heating process The speed is 3°C/min, and under air conditions, heat treatment can remove ammonium nitrate impurities and crystal water, and obtain the positive electrode material of lithium iron phosphate lithium ion battery with the molecular formula of Fe _1.5 (PO ₄ )(OH).

To the Fe obtained by the present invention _1.5 (PO ₄ )(OH) XRD for characterization

The phase analysis of the lithium iron phosphate lithium ion battery cathode materials with the molecular formula Fe _1.5 (PO ₄ )(OH) obtained in the above-mentioned Examples 1 to 7 was carried out by using an XRD powder diffractometer in Germany (Bruker, D8 Advance). The test conditions used: Cu _kɑ =1.54056?, voltage 40KV, current 200mA, step size 0.02°, scanning speed 5°/min, scanning range 10°～90°.

Figure 1 is the XRD of Fe _1.5 (PO ₄ )(OH) obtained in Examples 1, 2, 3 and 4 respectively, that is, the pH value is 2.5, and the hydrothermal temperature is 150°C, 170°C, 180°C and 200°C respectively Spectrum, Figure 2 is the XRD of Fe _1.5 (PO ₄ )(OH) synthesized under the conditions of Examples 5, 3, 6, and 7 respectively, that is, the hydrothermal temperature is 180°C and the pH value is 1.5, 2.5, 3.5, and 4.5. Atlas. According to the JCPDS card, the main diffraction peaks of Fe _1.5 (PO ₄ ) (OH) synthesized under various conditions correspond to the standard spectrum peaks of Fe _1.5 (PO ₄ ) (OH), indicating that it has high purity and crystallinity. properties, the unit cell parameters are a=5.28?, c=12.83?.

It can be seen from Figure 1 that the peak intensity of the (1 0 3) crystal plane increases with the increase of hydrothermal temperature, indicating that its crystallinity also increases with the increase of hydrothermal temperature. However, the peak intensity of the (4 0 0) crystal plane initially increases with the increase of hydrothermal temperature, and its peak decreases again when the hydrothermal temperature reaches 200 °C. This may be due to the fact that the growth of crystals along the (4 0 0) crystal plane initially increases with the increase of hydrothermal temperature, and when the temperature further increases, the growth of the (4 0 0) crystal plane is inhibited.

It can be seen from Figure 2 that the peak intensity of the (1 0 3) crystal plane increases with the increase of pH value, indicating that its crystallinity also increases with the increase of pH value. However, the peak intensity of the (4 0 0) crystal plane initially increased with the increase of pH value, and its peak value decreased when the pH value reached 4.5. This may be due to the fact that the growth of crystals along the (4 0 0) crystal plane starts to increase with the increase of pH value, and when the pH value further increases, the growth of (4 0 0) crystal plane is inhibited.

Fig. 3 is the XRD spectrum of Fe _1.5 (PO ₄ )(OH) synthesized in Example 4 under the condition of hydrothermal temperature of 200°C. It can be seen from Figure 3 that its main component is still Fe _1.5 (PO ₄ )(OH). However, the XRD pattern shows that there are other impurity phases. This is because the hydrothermal temperature is too high, so that Fe _1.5 (PO ₄ ) (OH) undergoes crystal form and structure transformation.

The multi-angle crystal structure diagram of Fe _1.5 (PO ₄ )(OH) sample obtained by materials studio5.0 is shown in Fig. 4A and Fig. 4B.

Figure 4A and Figure 4B are the crystal structure diagrams of Fe _1.5 (PO ₄ )(OH) along the [1 0 0] and [0 1 0] crystal directions, respectively. It can be seen from Fig. 4A and Fig. 4B that the anode material of lithium iron phosphate lithium ion battery with the molecular formula Fe _1.5 (PO ₄ ) (OH) obtained in the present invention is composed of FeO ₆ octahedra along [1 0 0] and [0 1 0] Layered chains formed by sharing coplanar crystal directions and two adjacent layered chains connected by FeO ₄ tetrahedron sharing a vertex with adjacent two FeO ₆ octahedrons respectively. .

To the Fe obtained by the present invention _1.5 (PO ₄ )(OH) SEM for characterization

The morphology and size of the Fe _1.5 (PO ₄ ) (OH) samples obtained in Examples 1 to 7 were observed using a Japanese SU70 field emission scanning electron microscope FE-SEM

Fig. 5A1 and Fig. 5A2 are SEM images of Fe _1.5 (PO ₄ ) (OH) obtained under different magnifications in Example 1, that is, the pH value is 2.5 and the hydrothermal temperature is 150°C. It can be seen from Fig. 5A1 that when hydrothermal The temperature is 150°C, the shape of the particles is spherical, and the particle size distribution is uniform. It can be seen from Figure 5A2 that the surface of the particles is relatively rough, and it can be seen that it is formed by the secondary aggregation of numerous nanoparticles. The diameter is about 1 μm.

Figure 5B1 and Figure 5B2 are the SEM images of Fe _1.5 (PO ₄ )(OH) obtained under different magnifications in Example 2, that is, the pH value is 2.5 and the hydrothermal temperature is 170°C. It can be seen from Figure 5B1 that the The morphology is cube-like, and the particle size distribution is uniform. It can be seen from Figure 5B2 that the particle surface is smooth, the shape is regular, and the particle size is about 4 μm.

Figure 5C1, Figure 5C2, and Figure 5C3 are SEM images of Fe _1.5 (PO ₄ )(OH) obtained under different magnifications in Example 3, that is, the pH value is 2.5 and the hydrothermal temperature is 180°C. It can be seen from Figure 5C1 It can be seen from Figure 5C2 and Figure 5C3 that the particles have two similar shapes, one is a dendritic structure connected by six arms with four edges, and the other is a A dendritic structure composed of more than six arms with four edges, the surface of the particles is smooth and compact, regular in shape, and the particle size is about 10 μm.

Figure 5D1 and Figure 5D2 are SEM images of Fe _1.5 (PO ₄ )(OH) obtained in Example 4 at a pH value of 2.5 and a hydrothermal temperature of 200°C at different magnifications, and its particles can be seen from Figure 5D1 The shape is cross-shaped, and the particle size distribution is uniform. From Figure 5D2, it can be seen that it is a cross composed of four arms with a length of about 5 μm and a diameter of about 2 μm. The middle is hollow, and the surface is dense and smooth. About 12 μm.

Figure 6A1 and Figure 6A2 are the SEM spectra of Fe _1.5 (PO ₄ )(OH) synthesized under different magnifications in Example 5, that is, the hydrothermal temperature is 180°C and the pH value is 1.5. It can be seen from Figure 6A1 that the pH value When the particle size is 1.5, the particle shape is spherical, and the particle size distribution is uniform. It can be seen from Figure 6A2 that the particle surface is relatively rough, which is formed by secondary agglomeration of countless nanoparticles, with regular shape and particle size of About 4μm.

Figure 6B1, Figure 6B2, and Figure 6B3 are the SEM spectra of Fe _1.5 (PO ₄ )(OH) synthesized under different magnifications in Example 3, that is, the hydrothermal temperature is 180°C and the pH value is 2.5, and it can be seen from Figure 6B1 It can be seen that the particle size distribution is uniform. It can be seen from Figure 6B2 that the particles mainly have two similar shapes, one is a dendritic structure connected by six arms with four edges, and Figure 6B3 is composed of more than It is a dendritic structure composed of six four-sided arms. The surface of the particles is smooth and dense, regular in shape, and the particle size is about 10 μm.

Figure 6C1, Figure 6C2, and Figure 6C3 are the SEM spectra of Fe _1.5 (PO ₄ )(OH) synthesized in Example 6 under the condition of hydrothermal temperature of 180°C and pH value of 3.5 at different magnifications, as can be seen from Figure 6C1 , the particle size distribution is uniform, as can be seen from Figure 6C2, the number of arms increases, and the particles are larger, about 15 μm. It can be seen from Figure 6C3 that the surface is denser.

Figure 6D1 and Figure 6D2 are the SEM spectra of Fe _1.5 (PO ₄ )(OH) synthesized in Example 7 under the conditions of hydrothermal temperature of 180°C and pH value of 4.5 at different magnifications. It can be drawn from Figure 6D1 , its particle morphology is a leafy structure composed of four serrated arms with a length of about 15 μm and a diameter of about 4 μm. It can be seen from Figure 6D2 that the surface is dense and irregular, and a large number of branches grow on the side of the arms , forming jagged arms, the particle size is about 30 μm, and the number of leaf-like arms is relative to pH 2.5, which decreases at 3.5, which may be due to the fact that when the pH continues to rise to 4.5, the crystals are inhibited on the (4 0 0) crystal plane Due to the growth, the conclusion can be confirmed by Figure 2.

In summary, different pH values have a significant impact on the particle morphology and size of Fe _1.5 (PO ₄ ) (OH) cathode materials.

Fig. 7 is the Fe _1.5 (PO ₄ ) (OH) obtained under the conditions of Examples 1, 2, 3 and 4, that is, the pH value is 2.5, and the hydrothermal temperature is 150°C, 170°C, 180°C and 200°C respectively at 0.1C The first charge and discharge curve. It can be seen from FIG. 7 that the Fe _1.5 (PO ₄ )(OH)Fe _1.5 (PO ₄ )(OH) cathode materials obtained in Examples 1, 2, 3 and 4 all have a stable charge-discharge platform. Example 1, that is, the hydrothermal temperature is 150°C, the particle shape is spherical, and the positive electrode material with a particle size of 1 μm has excellent electrochemical performance, and its first discharge specific capacity reaches 176mAh/g, and under the same rate, the implementation In Example 2, the hydrothermal temperature is 170°C (cubic, 4 μm), in Example 3, the hydrothermal temperature is 180°C (dendritic, 10 μm), in Example 4, the hydrothermal temperature is 200°C (cross-shaped, 12 μm) ) of the first discharge specific capacity were 156mAh/g, 142mAh/g and 135mAh/g. In addition, the discharge specific capacity is small at 200°C, which may be due to the existence of other inactive impurity phases in addition to the particle shape and size. The conclusion can be confirmed by Figure 3.

Figure 8 is the temperature of Fe _1.5 (PO ₄ )(OH) synthesized under the conditions of Examples 5, 3, 6, and 7, that is, the hydrothermal temperature is 180°C, and the pH value is 1.5, 2.5, 3.5, and 4.5 at 0.1°C. The first charge and discharge curve. As can be seen from Figure 8, in Example 5, that is, when the pH value is 1.5, the particle morphology is spherical, and the positive electrode material with a particle size of 4 μm has excellent electrochemical performance, and its initial discharge specific capacity reaches 154mAh/g, while Under the same magnification, Example 3 is pH 2.5 (dendritic, 10 μm), Example 6 is pH 3.5 (dendritic, 15 μm), and Example 7 is pH 4.5 (dendritic, 30 μm). The specific discharge capacities are 135mAh/g, 120mAh/g, and 100mAh/g respectively.

The results show that embodiment 1, that is, the hydrothermal temperature is 150 ° C, and the pH value is 2.5. The spherical shape and the molecular formula of the small-sized particles obtained under the conditions are respectively Fe _1.5 (PO ₄ ) (OH) Lithium-ion battery cathode material has superior Excellent charge and discharge performance, this is due to the larger specific surface area of spherical particles and small-sized particle materials, which provide a larger reaction interface for electrochemical reactions. In addition, the spherical particles and small size can shorten the diffusion path of lithium ions, which is beneficial to improve the diffusion kinetics of lithium ions in cathode materials.

To the Fe obtained by the present invention _1.5 (PO ₄ )(OH) Cycle Performance Test of Lithium-ion Battery Cathode Materials

Use the LAND battery test system CT2001A to conduct charge and discharge tests on the batteries assembled from the Fe _1.5 (PO ₄ )(OH) lithium ion battery cathode materials obtained in Examples 1 to 7. The charge and discharge tests of the batteries are at room temperature (25°C) The charge and discharge rates are 0.1C and 0.3C, and the test voltage range is 2.0-4.0V. The results are shown in Figure 9 and Figure 10.

Fig. 9 is the Fe _1.5 (PO ₄ ) (OH) obtained at 0.1C and The cycle performance curve at 0.3C, as can be seen from Figure 9, the Fe _1.5 (PO ₄ )(OH) sample synthesized at the discharge rate of 0.1C When the discharge rate is 0.3C, the first discharge specific capacity is 176mAh/g, and after 60 cycles, the discharge specific capacity is still maintained at 165mAh/g; when the discharge rate is 0.3C, the first discharge specific capacity is 159mAh/g, and it still remains after 40 cycles. At 150mAh/g. At other hydrothermal temperatures, its cycle performance and rate performance are also better.

Figure 10 shows the Fe _1.5 (PO ₄ )(OH) synthesized under the conditions of Examples 5, 3, 6, and 7, that is, the hydrothermal temperature is 180°C and the pH value is 1.5, 2.5, 3.5, and 4.5 at 0.1°C and 0.3°C respectively. The cycle performance curve at C, as can be seen from Figure 10, the Fe _1.5 (PO ₄ ) (OH) sample synthesized when the pH value of Example 5 is 1.5, when the discharge rate is 0.1C, the first discharge specific capacity is 154mAh /g, after 60 cycles, its discharge specific capacity still remains at 150mAh/g; when the discharge rate is 0.3C, the first discharge specific capacity is 142mAh/g, and after 20 cycles it still remains at 135mAh/g. Under other pH conditions, its cycle performance and rate performance are also good. This shows that the anode material of lithium iron phosphate lithium ion battery with the molecular formula Fe _1.5 (PO ₄ )(OH) of the present invention has good cycle performance and rate performance.

In summary, the present invention obtains the anode material of hydroxyiron phosphate lithium ion battery with molecular formula Fe _1.5 (PO ₄ )(OH) by hydrothermal synthesis method, and various special shapes can be obtained by adjusting the hydrothermal synthesis temperature and pH value cathode material for lithium-ion batteries. In particular, Fe _1.5 (PO ₄ ) (OH) lithium-ion battery anode materials with spherical morphology and small-sized particles have superior charge and discharge performance, which is due to the large specific surface area of spherical particles and small particle materials, which is an electrochemical The reaction provides a larger reaction interface. In addition, the spherical particles and small size can shorten the diffusion pathway of lithium ions, which is beneficial to improve the diffusion kinetics of lithium ions in cathode materials.

The cycle performance test confirmed that the lithium iron phosphate lithium ion battery cathode material with the molecular formula Fe _1.5 (PO ₄ )(OH) has good cycle performance and rate performance. Therefore, the hydroxyiron phosphate lithium ion battery anode material with the molecular formula Fe _1.5 (PO ₄ )(OH) of the present invention is a novel lithium ion battery anode material with superior electrochemical performance and has considerable application prospects.

The above content is only a basic description of the concept of the present invention, and any equivalent transformation made according to the technical solution of the present invention shall belong to the protection scope of the present invention.

Claims (4)

1. An anode material for a lithium ion battery, iron hydroxyphosphate, is characterized in that the anode material for a lithium ion battery is iron hydroxyphosphate with a molecular formula of Fe _1.5 (PO ₄ ) (OH), prepared by a hydrothermal synthesis method. 2. the synthetic method of a kind of lithium-ion battery cathode material iron hydroxyphosphate as claimed in claim 1, is characterized in that specifically comprising the steps: (1) Add surfactant sodium dodecylbenzenesulfonate to 0.02mol/L Fe(NO ₃ ) ₃ ·9H ₂ O aqueous solution, then pour 0.02mol/L NH ₄ H ₂ PO ₄ aqueous solution Put it into it to get a mixed solution, stir evenly, adjust the pH to 1.5-4.5 with 15% ammonia water, then transfer it to a hydrothermal reaction kettle, control the temperature at 150-200°C for hydrothermal synthesis reaction for 24 hours to obtain a reaction solution ; The amount of 0.02mol/L Fe(NO ₃ ) ₃ ·9H ₂ O aqueous solution, 0.02mol/L NH ₄ H ₂ PO ₄ aqueous solution and surfactant sodium dodecylbenzenesulfonate in the mixed solution is as follows: Calculate the molar ratio of Fe ³⁺ , PO ₄ ^3- and surfactant sodium dodecylbenzene sulfonate, that is, Fe ³⁺ : PO ₄ ^3- : surfactant sodium dodecylbenzene sulfonate is 1:1 : 0.01; (2) The reaction liquid obtained in step (1) is separated by centrifugation and washed by adding absolute ethanol, and finally the obtained filter cake is heat-treated in the presence of air to obtain ferric hydroxyphosphate, a positive electrode material for lithium-ion batteries. 3 . The method for synthesizing ferric hydroxyphosphate, a cathode material for lithium-ion batteries, according to claim 2 , wherein the hydrothermal synthesis temperature in step (1) is 150° C., and the pH value is 2.5. 4. A method for synthesizing iron hydroxyphosphate, a positive electrode material for lithium-ion batteries, as claimed in claim 3, characterized in that the heat treatment described in step (2) is to place the filter cake in a quartz tube and heat it in a tube furnace , in the presence of air, sequentially sintering at 120°C for 1h, 160°C for 1h, and 400°C for 3h, and control the heating rate at 3°C/min during each heating process.

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