CN100401558C - Method of preparing Li ion cell material-LiNixMn2-X04 - Google Patents

Abstract

The invention discloses a method for preparing lithium ion battery material LiNi _x Mn _2-x O ₄ . The method for preparing lithium ion battery material LiNi _x Mn _2-x O ₄ provided by the present invention comprises the following steps: 1) adding NH ₄ HCO ₃ or (NH ₄ ) ₂ CO ₃ to the Mn ²⁺ and Ni ²⁺ solution adjusting the pH to 6-9, and reacting to obtain Mn and Ni basic carbonate solids; 2) decomposing the obtained Mn and Ni basic carbonate solids at 600-650° C. to obtain Mn and Ni oxides; 3) Mix the obtained oxides of Mn and Ni with LiOH·H ₂ O or Li ₂ CO ₃ and react at 750-850° C. to obtain LiNi _x Mn _2-x O ₄ as a lithium ion battery material. The LiNi _x Mn _2-x O ₄ material prepared by the method of the present invention is a pure-phase spinel product. Under the charge and discharge rate of 0.4C, the first discharge specific capacity of the product can reach 140mAh/g, which is close to the theoretical capacity. After 50 discharges, the maximum capacity retention rate can be maintained above 90%, and the charge-discharge cycle performance is very good, which has broad application prospects.

Description

A kind of method for preparing lithium ion battery material LiNixMn2-xO4

technical field

The invention relates to a preparation method of lithium ion battery material LiNi _x Mn _2-x O ₄ .

Background technique

Lithium-ion batteries are the latest generation of secondary batteries after nickel-cadmium and nickel-metal hydride batteries. Compared with traditional secondary batteries, lithium-ion batteries have outstanding advantages: high working voltage (3.6V), three times the working voltage of nickel-cadmium and nickel-hydrogen batteries; high specific energy (140Wh/kg), which is higher than nickel-cadmium 3 times that of batteries, 1.5 times that of Ni-MH batteries; long cycle life, the current cycle life of lithium-ion batteries has reached more than 1,000 times, and can reach tens of thousands of times at low discharge depths; small self-discharge (monthly self-discharge rate is only 6 -8%), much lower than nickel-cadmium batteries (25-30%) and nickel-metal hydride batteries (30-40%); no memory effect, can be charged at any time according to requirements, without reducing battery performance; in lithium-ion batteries There are no harmful substances, so there is no pollution to the environment, and it is a veritable "green battery". Lithium-ion batteries have been widely used in portable electronic devices such as mobile phones, notebook computers, and small cameras, and are expected to be widely used in ground and space military fields such as electric vehicles, satellites, and aerospace.

However, a major problem with current lithium-ion batteries is that they are still relatively small in power. There are mainly three kinds of cathode materials used in lithium-ion batteries, namely LiCoO ₂ , LiMn ₂ O ₄ and LiNiO ₂ , and their operating voltages are all below 4.0V. In order to further improve the performance of lithium-ion batteries, it is necessary to increase the discharge voltage of the positive electrode material. A certain amount of Ni element can be added to the material LiMn ₂ O ₄ to obtain LiNi _x Mn _2-x O ₄ (X is 0.2-0.6) material. After doping the Ni element, the Fermi energy level _EF of the material is improved, thereby increasing the working voltage of the battery material. Although structurally, doped Ni atoms occupy part of the positions occupied by Mn atoms in the original LiMn ₂ O ₄ material, but because the material LiNi _x Mn _2-x O ₄ still belongs to the spinel structure, the material still retains Stability of spinel materials. The experimental results show that the discharge voltage of the doped material LiNi _x Mn _2-x O ₄ can reach 4.6V, and it has a high discharge capacity and good charge-discharge cycle performance. An increase in the discharge voltage of the positive electrode material will increase the output power of the battery, and the application field of the battery will be broadened. For example, if it is used in an electric vehicle, the number of series and parallel batteries required is less than that of ordinary batteries. It will bring great convenience to the maintenance and use, and will improve the safety performance.

At present, the method of synthetic material LiNi _x Mn _2-x O ₄ mainly includes sol-gel method (Y.-K.Sun, Y.-S.Lee, M.Yoshio, K.Amine, Electrochem.Solid-State Lett .5(2002) A99), co-precipitation method (T.Ohzuku, S.Takeda, M.Iwanaga, J.Power Sources 81(1999)90), latex drying method (S.-T.Myung, S.Komaba, N.Kumagai, H.Yashiro, H.-T.Chung, T.-H.Cho, Electrochem.Acta 47 (2002) 2543), molten salt synthesis (J.-H.Kim, S.-T.Myung , Y.-K.Sun, Electrochimica Acta 49(2004)219-227) and carbonate precipitation method (YSLee, YKSun, S.Ota, T.Miyashita, M.Yoshio, Electrochemistry Communications 4(2002)989-994) etc., but the initial discharge capacity of materials synthesized by these methods is low (between 125-140mAh/g), and its charge-discharge stability is also relatively poor. There is also an ordinary solid-phase synthesis method, using MnO ₂ , Li ₂ CO ₃ and Ni(OH) ₂ as raw materials to synthesize the material LiNi _x Mn _2-x O ₄ under certain conditions. The diffraction angle of the obtained product on XRD is The positions of 37.5°, 43.5° and 63.4° often contain impurities such as NiO and Li _x Ni _1-x O, which lead to a decrease in the electrochemical performance of the material.

Contents of the invention

The object of the present invention is to provide a method for preparing lithium ion battery material LiNi _x Mn _2-x O ₄ with high capacity and stable charge and discharge performance.

The method for preparing lithium ion battery material LiNi _x Mn _2-x O ₄ provided by the present invention comprises the following steps: 1) adding NH ₄ HCO ₃ or (NH ₄ ) ₂ CO ₃ to the Mn ²⁺ and Ni ²⁺ solution adjusting the pH to 6-9, and reacting to obtain Mn and Ni basic carbonate solids; 2) decomposing the obtained Mn and Ni basic carbonate solids at 600-650° C. to obtain Mn and Ni oxides; 3) Mix the obtained oxides of Mn and Ni with LiOH·H ₂ O or Li ₂ CO ₃ and react at 750-850°C to obtain lithium ion battery material LiNi _x Mn _2-x O ₄ ; among them, lithium ion X=0.2-2/3 in the battery material LiNi _x Mn _2-x O ₄ .

When the reaction substances Mn ²⁺ and Ni ²⁺ react with CO ₃ ^2- , the molar ratios of Mn ²⁺ and Ni ²⁺ are different, and products with different Ni contents will be obtained. Because the solubility product Ksp(MnCO ₃ ) of MnCO ₃ is smaller than the solubility product Ksp(NiCO ₃ ) of NiCO ₃ , Mn ²⁺ is easier than Ni ²⁺ to react with NH ₄ HCO ₃ to generate carbonate precipitation, and step 1) In the Mn ²⁺ and Ni ²⁺ solution, the molar ratio of Mn ²⁺ : Ni ²⁺ is controlled within 2-4: 1, and finally the obtained lithium ion battery material LiNi _x Mn _2-x O ₄ has better Electrochemical performance, wherein, the molar ratio of Mn ²⁺ : Ni ²⁺ is preferably 2.6:1, and the lithium ion battery material obtained at this time is LiNi _0.5 Mn _1.5 O ₄ , which has the best electrochemical performance.

Step 1) The temperature of the reaction is 25-50° C., and the reaction stirring speed is 300-600 r/min.

The time of the decomposition reaction in step 2) can generally be controlled at about 5-10 hours.

Step 3) The molar ratio of the oxides of Mn and Ni to LiOH·H ₂ O is 0.22-0.25:1; the reaction temperature is preferably 780-810°C; the reaction time is 5-20 hours, preferably 8-15 hours .

The reaction process when synthesizing LiNi _0.5 Mn _1.5 O ₄ is as follows:

The inventive method has the following advantages and effects: due to the synthesis of materials, the reaction substance is first dissolved in the solution to obtain uniform mixing on the molecular level, and the basic carbonate containing Mn and Ni obtained in step 1) is chemically stable It has good properties, and Mn and Ni are already miscible in it. Therefore, in the next reaction, not only the reaction temperature is relatively low, but the reaction process can be completed in the air atmosphere, and the product LiNi _x Mn ₂ without impurities can also be obtained. _-x O ₄ . The LiNi _x Mn _2-x O ₄ material prepared by the method of the present invention is a pure-phase spinel product. Under the charge and discharge rate of 0.4C, the first discharge specific capacity of the product can reach 140mAh/g, which is close to the theoretical capacity. After 50 discharges, the maximum capacity retention rate can be kept above 90%, and the charge-discharge cycle performance is very good, which has broad application prospects.

Description of drawings

Figure 1 is the charge and discharge curve of LiNi _0.5 Mn _1.5 O ₄ ;

Figure 2 is the charge-discharge cycle performance curve of LiNi _0.5 Mn _1.5 O ₄ ;

Figure 3 is the charge and discharge curve of LiNi _0.46 Mn _1.54 O ₄ ;

Figure 4 is the charge-discharge curve of LiMn ₂ O ₄ .

Detailed ways

Embodiment 1, the preparation of LiNi _0.5 Mn _1.5 O ₄ and its performance test

Weigh Mn(NO ₃ ) ₂ and Ni(NO ₃ ) ₂ ·6H ₂ O with a molar ratio of 2.6:1, dissolve them in an aqueous solution, and use the Liquid NH ₄ HCO ₃ adjusts the pH of the solution to 7.2 to obtain a solid basic carbonate of manganese and nickel. Decompose at a high temperature of 650°C for 6 hours to decompose the basic carbonate into oxides of manganese and nickel. The obtained oxides of manganese and nickel were mixed with LiOH·H ₂ O at a molar ratio of 0.25:1, and reacted at 800° C. for 15 hours to obtain LiNi _0.5 Mn _1.5 O ₄ with a spinel structure. The particle morphology of the product is spherical, with a diameter of 2-5 μm.

The electrochemical performance of the material was tested as follows: the prepared LiNi _0.5 Mn _1.5 O ₄ material was uniformly mixed with conductive carbon black (5wt%) and PVDF (polyvinyl difluoride, 5wt%) and coated on aluminum foil as a battery positive electrode; metal lithium sheet is used as the negative electrode, and the diaphragm is made of microporous polypropylene material; the electrolyte is prepared by dissolving LiPF ₆ in ethylene carbonate (EC) and propylene carbonate (DMC), and the concentration of LiPF ₆ is 1.0 mol/L, the volume ratio of EC and DMC is 1:1. The cathode, separator, electrolyte and anode were assembled into a Li/LiPF ₆ -EC+DMC/LiNi _0.5 Mn _1.5 O ₄ simulated battery in an argon-filled glove box, and the constant current charge and discharge were performed with a Japanese Bts-2004 detector Performance test and differential chronopotential analysis, the test voltage range is 3.5-5.0V, and the current density is 0.5mA/cm ² and 2.0mA/cm ² .

The charge-discharge curve of the material when the current density is 0.5mA/ ^cm2 is shown in Figure 1 (with the increase of capacity, the potential rises as the charge curve; with the increase of capacity, the potential decreases as the discharge curve), the material at the current density The charge-discharge cycle performance curve at 0.5mA/cm ² is shown in Figure 2. The results show that the material forms a discharge platform at 4.65V, and the initial discharge capacity is 140mAh/g. After 50 cycles, the capacity is 134mAh/g, and the capacity remains The rate is 96%.

The material is similar to the above when the current density is 2.0mA/cm ² , forming a discharge platform at 4.65V, the first discharge capacity is 127mAh/g, after 50 cycles, the capacity is 119mAh/g, and the capacity retention rate is 94%.

From the charge and discharge process of the material, it can be seen that the material LiNi _0.5 Mn _1.5 O ₄ undergoes oxidation and reduction reactions between Ni ²⁺ /Ni ⁴⁺ in the high voltage range (4.65V), thus forming a high voltage charge and discharge platform; And there is no charge-discharge plateau at 4.0V, indicating that there is no oxidation and reduction process between Mn ³⁺ /Mn ⁴⁺ .

Embodiment 2, the preparation of LiNi _0.46 Mn _1.54 O ₄ and its performance test

Weigh Mn(NO ₃ ) ₂ and Ni(NO ₃ ) ₂ ·6H ₂ O with a molar ratio of 2.2:1, dissolve them in aqueous solution, and use Liquid NH ₄ HCO ₃ adjusts the pH of the solution to 7.4 to obtain the basic carbonate solid of manganese and nickel. Decompose at a high temperature of 650°C for 8 hours to decompose the basic carbonate into oxides of manganese and nickel, and then mix the obtained oxides of manganese and nickel with LiOH·H ₂ O in a molar ratio of 0.24:1, at 830 The reaction was carried out at ℃ for 12 hours to obtain LiNi _0.46 Mn _1.54 O ₄ with a spinel structure.

Measure the electrochemical properties of the material LiNi _0.46 Mn _1.54 O ₄ according to the method of Example 1. The charge-discharge curve at a current density of 2.0mA/cm ² is shown in Figure 3. The results show that the material LiNi _0.46 Mn _1.54 O ₄ is at 4.60 A discharge platform is formed at V, and the initial discharge capacity is 114mAh/g. After 50 charge-discharge cycles, the capacity is 91mAh/g, and the capacity retention rate is 80%.

From the discharge capacity of LiNi _0.5 Mn _1.5 O ₄ and LiNi _0.46 Mn _1.54 O ₄ obtained in embodiment 1 and embodiment 2, all surpassed the result of bibliographical report, promptly discharge capacity is 95mAh/g (Xianglan Wu, Seung Bin Kim , Journal of Power Sources 109(2002) 53).

Embodiment 3, the preparation of LiMn ₂ O ₄ and its performance test (comparative example)

Mn(NO ₃ ) ₂ was dissolved in water, and the pH of the solution was adjusted to 8.0 with liquid NH ₄ HCO ₃ at a temperature of 30°C and a stirring speed of 500 r/min to obtain manganese carbonate solid. Then decompose the carbonate at a high temperature of 600°C, and then react the obtained manganese oxide with LiOH·H ₂ O (the molar ratio of the two is 2:1) at 790°C for 10 hours , to obtain the pure-phase spinel product LiMn ₂ O ₄ .

Using the same method as in Example 1 to measure the electrochemical performance of the material, the charge-discharge curve of the material LiMn ₂ O ₄ when the current density is 0.5mA/cm ² is shown in Figure 4, the results show that the material LiMn ₂ O ₄ at 4.0V There are two discharge platforms at 4.1V and 4.1V, and the first discharge capacity is 120mAh/g.

Compared with the above three examples, after doping the metal element Ni into the spinel LiMn ₂ O ₄ , the obtained doped material LiNi _x Mn _2-x O ₄ has a high charge and discharge voltage, which improves the electrochemical performance of the material.

Example 4, preparation of LiNi _0.38 Mn _1.62 O ₄

Weigh MnSO ₄ and NiSO ₄ ·6H ₂ O with a molar ratio of 4:1, dissolve them in aqueous solution, and use liquid (NH ₄ ) ₂ CO ₃ Adjust the pH of the solution to 8.4 to obtain a basic carbonate solid of manganese and nickel. Decompose at a high temperature of 600°C for 10 hours to decompose the basic carbonate into oxides of manganese and nickel, and then mix the obtained oxides of manganese and nickel with Li ₂ CO ₃ in a molar ratio of 0.22:1 and heat at 750°C The reaction was carried out for 18 hours to obtain LiNi _0.38 Mn _1.62 O ₄ with a spinel structure.

The discharge platform of the obtained material is 4.63V, and its initial charge and discharge capacity is 112mAh/g.

Claims (9)

1. one kind prepares lithium ion battery material LiNi _xMn _2-xO ₄Method, comprise the steps: 1) to Mn ²⁺And Ni ²⁺Add NH in the solution ₄HCO ₃Or (NH ₄) ₂CO ₃Regulate pH to 6-9, reaction obtains the subcarbonate solid of Mn and Ni; 2) the subcarbonate solid with gained Mn and Ni decomposes down at 600-650 ℃, obtains the oxide of Mn and Ni; 3) with oxide and the LiOHH of gained Mn and Ni ₂O or Li ₂CO ₃Mix, under 750-850 ℃ of condition, react, obtain lithium ion battery material LiNi _xMn _2-xO ₄Wherein, lithium ion battery material LiNi _xMn _2-xO ₄In X=0.2-2/3.

2. method according to claim 1 is characterized in that: the described Mn of step 1) ²⁺And Ni ²⁺Mn in the solution ²⁺: Ni ²⁺Mol ratio be 2-4: 1.

3. method according to claim 2 is characterized in that: the described Mn of step 1) ²⁺And Ni ²⁺Mn in the solution ²⁺: Ni ²⁺Mol ratio be 2.6: 1.

4. method according to claim 1 is characterized in that: the temperature of the described reaction of step 1) is 25-50 ℃, and the reaction mixing speed is 300-600r/min.

5. method according to claim 1 is characterized in that: step 2) time of described decomposition reaction is 5-10 hour.

6. according to the arbitrary described method of claim 1-5, it is characterized in that: oxide and the LiOHH of described Mn of step 3) and Ni ₂O or Li ₂CO ₃Mol ratio be 0.22-0.25: 1.

7. according to the arbitrary described method of claim 1-5, it is characterized in that: the described reaction temperature of step 3) is 780-810 ℃.

8. method according to claim 7 is characterized in that: the described reaction time of step 3) is 5-20 hour.

9. method according to claim 8 is characterized in that: the described reaction time of step 3) is 8-15 hour.

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