CN105047898B - A kind of twin spherical lithium ion secondary battery lithium-rich anode material and preparation method thereof - Google Patents

Abstract

The invention belongs to the technical field of lithium-ion batteries, and in particular relates to a lithium-rich cathode material for a twin-spherical lithium-ion secondary battery and a preparation method thereof. The anode material Li _1.13 Ni _0.3 Mn _0.57 O ₂ for a lithium ion secondary battery described in the present invention is a uniform twin-spherical lithium-rich material with a size of about 2 μm formed by symbiotic connection of two spheres with a diameter of about 1 μm. The invention adopts a simple method of chemical precipitation and mixed sintering to prepare a lithium-rich cathode material with a twin-spherical shape, which is simple in synthesis and low in cost. The electrochemical characterization of the material shows that the cycle performance of the material has been significantly improved, the structure of the material is stable during the constant current charge-discharge cycle, and the median voltage attenuation is extremely small.

Description

A lithium-rich cathode material for a twin-spherical lithium-ion secondary battery and a preparation method thereof

technical field

The invention belongs to the technical field of lithium-ion batteries, and in particular relates to a lithium-rich cathode material for a twin-spherical lithium-ion secondary battery and a preparation method thereof.

Background technique

Due to its high energy density, low self-discharge rate, long cycle life, and no memory effect, lithium-ion batteries have become mainstream power sources in portable electronic devices. The performance of a lithium-ion battery is often determined by the performance of its cathode material.

Lithium cobalt oxide (LiCoO ₂ ), a layered material, is widely used in portable devices due to its high operating voltage, stable charging and discharging, and high electrical conductivity. However, due to its high price, poor anti-overcharge performance, and certain toxicity, it is difficult to be used in the production of power batteries. The anode material of commercial power batteries is mainly lithium iron phosphate (LiFePO ₄ ), which is rich in raw materials and low in cost, but the capacity of lithium iron phosphate batteries is not high and the conductivity is poor. In order to reduce the cost and increase the specific capacity, lithium-rich cathode materials have received extensive attention in recent years. It has a high discharge specific capacity, rich sources of raw materials, and low prices. At present, there are still some problems with lithium-rich cathode materials, such as low initial Coulombic efficiency, fast capacity decay during cycling, and low rate performance, etc., all of which need to be further improved. During cycling, the sharp decay of the median voltage will lead to The reduction of energy density also limits its commercial application to a large extent.

Contents of the invention

The object of the present invention is to provide a preparation method of lithium ion secondary battery cathode material Li _1.13 Ni _0.3 Mn _0.57 O ₂ with cheap raw materials, simple preparation process, synthetic twin-spherical morphology, and greatly improved material cycle stability , the steps are as follows:

1) After weighing MnSO ₄ ·H ₂ O and Na ₂ CO ₃ in a molar ratio of 1:1, dissolve them in deionized water and stir for 10-20 minutes to form a clear solution _; Pour 10-15% of its volume into absolute ethanol, then pour into Na ₂ CO ₃ solution, keep stirring for 1-6 hours, deionized water and absolute ethanol are centrifuged several times, and then vacuum-dried at 50-80°C for 6 ~12h, get MnCO ₃ powder;

2) Treat the obtained MnCO ₃ powder in the air at 400-500°C (heating rate 1-5°C/min) for 3-6 hours, and naturally cool down to room temperature to obtain black MnO ₂ solid powder;

3) According to Li _1.13 Ni _0.3 Mn _0.57 O ₂ chemical formula Li, Ni, Mn stoichiometric ratio weighed LiOH · H ₂ O (in order to compensate for the volatilization of lithium at high temperature, a slight excess of 2 ~ 5%), Ni (NO ₃ ) ₂ 6H ₂ O and dissolved in deionized water together, add MnO ₂ powder, stir at 40-80°C until the deionized water is evaporated to dryness;

4) The product of step 3) was treated at 800-950° C. for 6-18 hours to obtain Li _1.13 Ni _0.3 Mn _0.57 O ₂ anode material for lithium-ion secondary battery of the present invention.

A lithium-ion secondary battery positive electrode material according to the present invention is characterized in that it is prepared by the above method, and a uniform twin spherical precursor material with a size of about 2 μm formed by symbiotic connection of two spheres with a diameter of about 1 μm is obtained. , and keep the shape and size well in the subsequent reaction, and prepare a lithium-rich material with a uniform twin-spherical shape.

The beneficial effects of the present invention are:

(1) The prepared lithium-rich material Li _1.13 Ni _0.3 Mn _0.57 O ₂ has a twin-spherical morphology with high purity and good repeatability.

(2) The equipment used for the preparation is simple, without the use of expensive equipment, and the raw materials are cheap and easy to obtain, and the cost is low.

(3) The process is very simple and has good repeatability, which can be used for both experimental operation and large-scale industrial production.

(4) The positive electrode material for lithium ion batteries prepared by the present invention has particularly stable cycle rate performance, stable median voltage, and no rapid decay of median voltage that is usually exhibited by lithium-rich materials.

The invention adopts a simple method of chemical precipitation and mixed sintering to prepare a lithium-rich cathode material with a twin-spherical shape, which is simple in synthesis and low in cost. The electrochemical characterization of the material shows that the cycle performance of the material has been significantly improved, the structure of the material is stable during the constant current charge-discharge cycle, and the median voltage attenuation is extremely small.

Description of drawings

In order to more clearly illustrate the technical solution in the present invention and the properties of the prepared materials, relevant diagrams are given below.

Fig. 1 is a scanning electron microscope image (SEM) of the MnCO ₃ material prepared in Example 1 and the final lithium-rich material Li _1.13 Ni _0.3 Mn _0.57 O ₂ . Figure (a) is the scanning electron microscope image (SEM) of MnCO ₃ at 2 μm scale. Figure (b) is the scanning electron microscope image (SEM) of Li _1.13 Ni _0.3 Mn _0.57 O ₂ at a scale of 2 μm. From the scanning electron microscope pictures, it can be seen that the final prepared Li _1.13 Ni _0.3 Mn _0.57 O ₂ twin spheres have good morphology, uniform size and no agglomeration.

FIG. 2 is an x-ray diffraction (XRD) spectrum of the Li _1.13 Ni _0.3 Mn _0.57 O ₂ material prepared in Example 1. From the x-ray diffraction (XRD) spectrum, it can be concluded that there are no impurity peaks in the x-ray diffraction (XRD) spectrum of the prepared material, which proves that the prepared material is a pure-phase lithium-rich material Li _1.13 Ni _0.3 Mn _0.57 O ₂ .

Fig. 3 is a cycle performance diagram of a half-cell prepared by using Li _1.13 Ni _0.3 Mn _0.57 O ₂ prepared in Example 1 as the positive electrode material of a lithium-ion battery, and a lithium sheet as a counter electrode. It can be seen from the figure that at a current density of 40m A/g, the initial discharge specific capacity of the material is 212.4mAh/g. After 50 cycles, the discharge specific capacity can still reach 208.6mAh/g, and the discharge specific capacity remains The ratio is 98.2%, which shows that the material has very good cycle stability.

Fig. 4 shows that Li _1.13 Ni _0.3 Mn _0.57 O ₂ prepared in Example 1 is used as the positive electrode material, and the lithium sheet is used as the counter electrode. Constant current test rate performance diagrams at different current densities of g, 2A/g, and 100mA/g. It can be seen from the figure that the material cycled stably under various current density tests, and at high currents of 1A/g and 2A/g, the specific capacity of the material can still reach 127mAh/g and 87mAh/g respectively, which proves that the material It has excellent rate performance.

Fig. 5 is a graph showing the variation of the median voltage of the Li _1.13 Ni _0.3 Mn _0.57 O ₂ positive electrode material prepared in Example 1 at a current density of 40mA/g and 50 constant current cycles. It can be seen from the figure that the median voltage of the material changes very little during the cycle, and only decays by 0.058V after 50 cycles. Compared with the battery assembled with lithium-rich materials prepared by the usual method, the battery is very stable. excellent.

Fig. 6 is the Li _1.13 Ni _0.3 Mn _0.57 O ₂ cathode material prepared in embodiment 1 under the current density of 40mA/g, the differential curve (dQ /dV curve). Differentiate the specific capacity versus voltage for the 1st, 2nd, 10th, 20th, 30th, 40th, and 50th discharge processes respectively. It can be seen from the graph that the peak shape of the curve is particularly stable, with little change, which indicates that the positive electrode material structure framework of the battery is very stable during the entire cycle, which is consistent with the measured stable cycle performance of the battery.

detailed description

Example 1:

Weigh MnSO ₄ ·H ₂ O (0.507g) and Na ₂ CO ₃ (0.3179g) at a molar ratio of 1:1 and dissolve them in 70mL of deionized water, stir for 20min to fully dissolve the drug and form a clear solution, and then add to MnSO ₄ Pour 7 mL of absolute ethanol and Na ₂ CO ₃ solution into the solution in turn, stir for 3 h, deionized water and absolute ethanol were centrifuged and washed 3 times, and dried in vacuum at 60°C for 8 h to obtain MnCO ₃ powder; transfer the MnCO ₃ powder Go to a muffle furnace (heating rate 2°C/min) and treat at 400°C for 5h under air conditions to obtain about 0.25g of MnO ₂ solid powder.

To synthesize the final Li-rich material, we weighed 0.16g MnO ₂ powder, and weighed LiOH·H ₂ O (5% excess, 0.1607g) and Ni(NO ₃ ) ₂ ·6H ₂ O (0.2817 g) Mix the obtained powder with deionized water, stir and evaporate the deionized water to dryness, then transfer to a muffle furnace and treat at 850°C for 12 hours to obtain Li _1.13 Ni _0.3 Mn _0.57 O ₂ electrode material, about 0.28g.

Weigh 0.075g lithium-rich material Li _1.13 Ni _0.3 Mn _0.57 O ₂ , conduction aid (super P is conductive carbon black), binder (PVDF is polyvinylidene fluoride) and mix according to the mass ratio of 7.5:1.5:1, the obtained The slurry was coated on the aluminum foil, dried in vacuum at 120°C, and then cut into square positive electrode pieces with a side length of 8 mm. The lithium sheet is selected as the negative electrode, and the electrolyte is selected as the commonly used lithium-ion battery electrolyte, that is, 1mol/L lithium hexafluorophosphate (LiPF ₆ )/ethylene carbonate (EC): dimethyl carbonate (DMC): ethyl methyl carbonate (EMC ) mixture=1:1:8 (volume ratio), assembled into a 2032-type button battery, and performed corresponding electrochemical tests. The cycle performance curve of the prepared battery is shown in Figure 3, and the current density is 40mA/g. It can be seen that the cycle performance of the battery is very good. The rate performance graph is shown in Figure 4. The current densities are 40mA/g, 100mA/g, 200mA/g, 500mA/g, 1A/g, 2A/g, and 100mA/g, indicating that the battery has better rate performance. The median voltage situation is shown in Figure 5. The median voltage of the battery discharge is stable and the attenuation is small. The differential curve of the specific capacity and voltage of the battery is shown in Figure 6, the peak shape changes little, and the battery is stable.

Claims (4)

1. A kind of preparation method of lithium-rich positive electrode material Li _1.13 Ni _0.3 Mn _0.57 O ₂ of twin-shaped spherical lithium ion secondary battery, its steps are as follows: 1) After weighing MnSO ₄ ·H ₂ O and Na ₂ CO ₃ in a molar ratio of 1:1, dissolve them in deionized water and stir for 10-20 minutes to form a clear solution _; Pour 10-15% of its volume into absolute ethanol, then pour into Na ₂ CO ₃ solution, keep stirring for 1-6 hours, deionized water and absolute ethanol are centrifuged several times, and then vacuum-dried at 50-80°C for 6 ~12h, get MnCO ₃ powder; 2) Treat the obtained MnCO ₃ powder in the air at 400-500°C for 3-6 hours, and naturally cool down to room temperature to obtain a black MnO ₂ solid powder; 3) Weigh LiOH·H ₂ O, Ni(NO ₃ ) ₂ ·6H ₂ O and dissolve them in deionized water together, add the MnO ₂ powder prepared in step 2), LiOH·H ₂ O, Ni(NO ₃ ) _2. The amount of 6H ₂ O and MnO ₂ is consistent with the stoichiometric ratio of Li, Ni, and Mn in the chemical formula of Li _1.13 Ni _0.3 Mn _0.57 O _2. Stir at 40-80°C until the deionized water is evaporated to dryness; 4) The product of step 3) was treated at 800-950° C. for 6-18 hours to obtain Li _1.13 Ni _0.3 Mn _0.57 O ₂ , a lithium-rich cathode material for a twin-spherical lithium-ion secondary battery. 2. The preparation method of Li _1.13 Ni _0.3 Mn _0.57 O ₂ , a lithium-rich cathode material for a twin-spherical lithium-ion secondary battery as claimed in claim 1, characterized in that the heating rate of step 2) is 1-5°C/min . 3. A method for preparing lithium-rich positive electrode material Li _1.13 Ni _0.3 Mn _0.57 O ₂ for a twin-shaped spherical lithium-ion secondary battery as claimed in claim 1, characterized in that: in step 3), the excess of LiOH·H ₂ O is 2 ~5%. 4. A Li _1.13 Ni _0.3 Mn _0.57 O ₂ lithium-rich cathode material for a twin-shaped lithium-ion secondary battery, characterized in that it is prepared by any one of the methods in claims 1-3.