CN101859889B - Lithium-manganese composite oxide for active material of anode of secondary lithium battery and preparation method thereof - Google Patents

Abstract

The present invention provides a lithium-manganese composite oxide for positive electrode active materials of secondary lithium batteries, characterized in that the lithium-manganese composite oxide is composed of the general formula Mn-O/M-Mn-OLi ₄ Mn ₅ O ₁₂ ( I) represents, in formula (I), M is metal, in the lithium manganese composite oxide shown in general formula (I), Mn-O/M-Mn-O is as the nucleus of described lithium manganese composite oxide, Li ₄ Mn ₅ O ₁₂ is coated on the outside of the Mn-O/M-Mn-O to form a shell. Experimental results show that the lithium-manganese composite oxide has good charge-discharge performance when used as a cathode material for a lithium battery.

Description

Lithium-manganese composite oxide for positive electrode active material of secondary lithium battery and preparation method thereof

technical field

The invention relates to the field of inorganic non-metallic materials, in particular to a lithium-manganese composite oxide used as an anode active material of a lithium battery and a preparation method thereof.

Background technique

Lithium batteries were first successfully developed and commercialized by Sony in the 1990s. They have been widely used in portable electronic devices, and are currently being studied for their application in electric vehicles, hybrid vehicles and other fields. As a new type of green energy battery, lithium batteries are expected to replace nickel-metal hydride batteries and nickel-cadmium batteries. Research on lithium batteries has become one of the hot spots in a series of international scientific and technological development plans.

One of the key factors affecting the performance of lithium batteries is the activity of lithium battery cathode materials. Currently, the commonly used cathode active materials for lithium batteries include three-element lithium-oxygen materials such as LiCoO ₂ , LiNiO ₂ , and Ni-Co-Mn. The above-mentioned cathode materials have Higher capacity, such as LiCoO ₂ unit weight capacity can reach 140-150mAh/g. However, the above-mentioned materials also have inevitable defects, such as poor thermal stability, so there are serious safety hazards; moreover, the above-mentioned positive electrode materials also need to use expensive and toxic elements such as Co and Ni, so their use is limited. At present, finding high-energy, stable cycle performance, high safety, pollution-free, and low-cost lithium battery cathode materials is an important research direction for lithium battery cathode materials.

Studies have shown that lithium manganese oxides (LMOs) have the advantages of good thermal stability and high safety performance when used as positive electrode active materials for lithium batteries; moreover, since lithium manganese oxides use abundant resources, low cost, and non-toxic manganese to Instead of elements such as Ni and Co, it is expected to become the most promising cathode material for lithium batteries. In the prior art, various lithium manganese oxides for lithium battery positive electrode materials have been disclosed. In the known lithium manganese oxide cathode materials, either the battery capacity is low, or the cycle stability is poor, and it is difficult to meet the requirements of high capacity and good cycle performance at the same time.

In view of the above shortcomings in the prior art, it is necessary to provide a lithium-manganese composite oxide for positive electrode active materials of lithium batteries, which has good cycle performance and high capacity

Contents of the invention

The problem to be solved by the present invention is to provide a lithium-manganese composite oxide used as a positive electrode active material of a lithium battery. The lithium-manganese composite oxide has good cycle performance and high capacity.

In order to solve the above technical problems, the present invention provides a lithium-manganese composite oxide for positive electrode active materials of secondary lithium batteries, characterized in that the lithium-manganese composite oxide is composed of the general formula Mn-O/M-Mn-OLi ₄ Mn ₅ O ₁₂ (I) represents that in formula (I), M is a metal;

In the lithium-manganese composite oxide shown in general formula (I), Mn-O/M-Mn-O is used as the core of the lithium-manganese composite oxide, and Li ₄ Mn ₅ O ₁₂ is coated on the Mn-O/ The outside of M-Mn-O forms a shell.

Preferably, the molar ratio of Mn-O/M-Mn-O to Li ₄ Mn ₅ O ₁₂ in the lithium manganese composite oxide is 10:1˜1:10.

Preferably, the molar ratio of Mn-O/M-Mn-O to Li ₄ Mn ₅ O ₁₂ in the lithium manganese composite oxide is 5:1˜1:5.

The present invention is also a preparation method of lithium-manganese composite oxide, which is characterized in that, comprising:

Mix the manganese-oxygen composite particles represented by the general formula Mn-O/M-Mn-O(II) with lithium salt to obtain a mixture. In the formula (II), M is a metal;

Heating the mixture to 350°C to 450°C causes the Li ⁺ intercalation reaction between the surface of the Mn-O/M-Mn-O particles and the Li ⁺ in the lithium salt to form a lithium-manganese composite oxide, and the lithium-manganese composite oxide The oxide is represented by the general formula Mn-O/M-Mn-OLi ₄ Mn ₅ O ₁₂ (I);

In the lithium-manganese composite oxide shown in general formula (I), Mn-O/M-Mn-O is used as the core of the lithium-manganese composite oxide, and Li ₄ Mn ₅ O ₁₂ is coated on the Mn-O/ The outside of M-Mn-O forms a shell.

Preferably, the reaction temperature of the Li ⁺ insertion reaction is 380°C-420°C.

Preferably, the reaction temperature of the Li ⁺ insertion reaction is 390°C-410°C.

Preferably, the reaction time of the Li ⁺ insertion reaction is 1 hour to 20 hours.

Preferably, the lithium salt is one or more of lithium nitrate, lithium chloride, lithium acetate, lithium sulfate or lithium carbonate.

The present invention also provides a lithium battery positive electrode, comprising:

The lithium manganese composite oxide, conductive agent and binder described in the above technical solution.

The present invention also provides a lithium battery, comprising:

The positive pole of the lithium battery described in the technical solution; the negative pole; and an organic electrolyte solution.

The present invention provides lithium-manganese composite oxides for positive electrode active materials of lithium batteries, characterized in that the lithium-manganese composite oxides are represented by the general formula Mn-O/M-Mn-OLi ₄ Mn ₅ O ₁₂ (I), In the lithium-manganese composite oxide shown in general formula (I), Mn-O/M-Mn-O is used as the core of the lithium-manganese composite oxide, and Li ₄ Mn ₅ O ₁₂ is coated on the Mn-O/ The outside of M-Mn-O forms a shell. Experimental results show that the lithium-manganese composite oxide has good thermal stability and good charge-discharge performance when used as a cathode material for a lithium battery.

Description of drawings

Fig. 1 is the SEM figure of 2000 times of the lithium manganese composite oxide prepared in embodiment 1;

Fig. 2 is the SEM figure of 10,000 times of lithium manganese composite oxide shown in Fig. 1;

Fig. 3 is the SEM figure of 100,000 times of lithium manganese composite oxide shown in Fig. 1;

Fig. 4 is the lithium manganese composite oxide prepared in embodiment 1 and α- _MnO The X-ray diffraction pattern;

Fig. 5 is the first 50 charge and discharge curves of the lithium battery prepared in Example 1;

FIG. 6 is the result of the charge-discharge cycle performance of the lithium battery prepared in Example 1.

Detailed ways

In order to further understand the present invention, the preferred embodiments of the present invention are described below in conjunction with the examples, but it should be understood that these descriptions are only to further illustrate the features and advantages of the present invention, rather than limiting the claims of the present invention.

The invention provides a lithium-manganese composite oxide, which is represented by the general formula Mn-O/M-Mn-OLi ₄ Mn ₅ O ₁₂ (I), and the lithium-manganese composite oxide represented by the general formula (I) In the composite oxide, Mn-O/M-Mn-O is used as the core of the lithium-manganese composite oxide, and Li ₄ Mn ₅ O ₁₂ is coated on the outside of the Mn-O/M-Mn-O to form a shell, In the general formula (I), M is a metal;

According to the present invention, the specific example of the general formula can be one of MnO ₂ , Mn ₂ O ₃ , manganate, preferably MnO ₂ , Mn ₂ O ₃ or alkali (earth) metal manganate, more preferably MnO ₂ .

According to the present invention, the lithium-manganese composite oxide has a core-shell structure, wherein Li ₄ Mn ₅ O ₁₂ as the outer shell is coated on the outside of the Mn-O/M-Mn-O as the core, for the lithium manganese The ratio of Mn-O/M-Mn-O and Li ₄ Mn ₅ O ₁₂ in the oxide is not particularly limited in the present invention. Preferably, Mn-O/M-Mn-O and Li in the lithium manganese oxide The molar ratio of ₄ Mn ₅ O ₁₂ is 10:1˜1:10, more preferably 5:1˜1:5. The present invention has no particular limitation on the particle size of the lithium manganese oxide, and lithium manganese oxides with different particle sizes can be produced as required.

According to the present invention, when preparing the lithium manganese oxide with the core-shell structure, it is preferable to use Mn-O/M-Mn-O particles as raw materials, and then make the surface of the Mn-O/M-Mn-O particles contact with Li ⁺ A reaction occurs to form a Li ₄ Mn ₅ O ₁₂ shell, thereby obtaining a core-shell structure of Mn-O/M-Mn-O-Li ₄ Mn ₅ O ₁₂ . According to the present invention, the reaction process in which Mn-O/M-Mn-O reacts with Li ⁺ to generate Li ₄ Mn ₅ O ₁₂ is named Li ⁺ insertion reaction. The preparation method of Mn-O/M-Mn-OLi ₄ Mn ₅ O ₁₂ with core-shell structure provided by the present invention specifically includes:

Get Mn-O/M-Mn-O particle and lithium salt and mix evenly, described lithium salt is preferably the inorganic salt of lithium, specific example can be one in lithium nitrate, lithium chloride, lithium acetate, lithium sulfate or lithium carbonate one or more, but not limited to. A preferred lithium salt is lithium nitrate. For the mixing method of Mn-O/M-Mn-O particles and lithium salt, the present invention is not particularly limited, such as using mechanical or manual stirring methods, as long as the Mn-O/M-Mn-O particles can be mixed with lithium Salt is mixed well.

After uniformly mixing the Mn-O/M-Mn-O particles and the lithium salt, the mixture is placed in a high-temperature container. The preferred high-temperature container can be a ceramic crucible that does not participate in the reaction, and a specific example can be a corundum crucible. Then a layer of lithium salt is covered on the surface of the mixture, the purpose of which is to protect the reaction between Li ⁺ and Mn-O/M-Mn-O, and avoid the direct contact of the reactants with the air. The temperature of the Li ⁺ insertion reaction is preferably 350°C-430°C. If the temperature is too low, the reaction process will be slow, and if the temperature is too high, the rock salt phase Li ₂ MnO ₃ will be easily formed. The temperature of the Li ⁺ insertion reaction is more preferably 350°C to 450°C, more preferably 380°C to 420°C, and more preferably 390°C to 410°C. For the reaction time of the Li ⁺ insertion reaction, it is preferably 1 hour to 20 hours. The longest reaction time is based on the fact that other lithium manganese oxides other than Li ₄ Mn ₅ O ₁₂ are not formed on the surface, and the shortest reaction time is when the surface begins to form Based on Li ₄ Mn ₅ O ₁₂ , the more preferred reaction time is 8 hours to 15 hours, and the thickness of the shell Li ₄ Mn ₅ O ₁₂ can be controlled by controlling the Li ⁺ insertion reaction time.

The present invention has no particular limitation on the source of the Mn-O/M-Mn-O used. When Mn-O/M-Mn-O is MnO ₂ , it is preferably α-MnO ₂ (Hollandite), the preparation method of α-MnO ₂ can be the method well-known to those skilled in the art, for example adopt normal temperature synthesis, raw material can For MnSO ₄ , and (NH ₄ ) ₂ S ₂ O ₄ , mix the two raw materials, add concentrated sulfuric acid under stirring, then add AgNO ₃ as a catalyst to react, and then put the obtained reactant in a dark place to stand , precipitation, filtration, and washing to obtain α-MnO ₂ , and α-MnO ₂ can also be purchased from the market, which is not particularly limited in the present invention.

The present invention also provides a lithium battery positive electrode, including the lithium-manganese composite oxide described in the above technical solution, a conductive agent and a binder. The conductive agent can be carbon black well known to those skilled in the art, but is not limited thereto. Specific examples of the binder may be vinylidene fluoride/hexafluoropropylene copolymer, polyvinylidene fluoride, polyacrylonitrile, polymethyl methacrylate, polytetrafluoroethylene or their mixtures, but not limited thereto. When making the positive electrode, the above-mentioned lithium manganese composite oxide, conductive agent, and binder can be uniformly stirred in a solvent, and then dried. The solvent can be a solvent well known to those skilled in the art such as nitrogen methyl pyrrolidone, acetone, etc., but not limited to this.

The present invention also provides a lithium battery, including the above lithium battery positive electrode, negative electrode and organic electrolyte solution, the specific examples of the negative electrode can be metal lithium, lithium alloy, carbonaceous material and graphite, but not limited thereto. The organic electrolyte solution can be an electrolyte solvent in which lithium salt is dissolved, and specific examples of lithium salt can be LiClO ₄ , LiCF ₃ SO ₃ , LiPF ₆ , LiN(CF ₃ SO ₂ ), LiBF ₄ , LiC(CF ₃ SO ₂ ) ₃ or LiN(C ₂ F ₅ SO ₂ ) ₂ , the electrolyte solvent can be one of ethylene carbonate, diethyl carbonate, dimethyl carbonate or their mixture well known to those skilled in the art, in the organic electrolyte solution The concentration of the lithium salt may be 0.5M-2M. According to the present invention, diaphragm can also be set between positive pole and negative pole, and the specific example of diaphragm can be glass fiber, polyester, polyethylene, polypropylene, polytetrafluoroethylene or their mixture, and the present invention is not particularly limited to this .

Example 1

Preparation of α- _MnO2 particles:

In 200ml of water, add 8mmol of MnSO ₄ and (NH ₄ ) ₂ SO ₄ respectively, add 8ml of concentrated sulfuric acid and an appropriate amount of AgNO ₃ as a catalyst under stirring, stop stirring after 10 minutes of reaction, and put the reactant in a dark place Set aside for 2 days to precipitate, filter the precipitate, wash with water and absolute ethanol in turn, and then dry the precipitate at 70°C to obtain α-MnO ₂ particles.

Get 0.2g of the α-MnO ₂ and 2.0g LiNO ₃ in an agate mortar and mix them into a corundum crucible, then take an appropriate amount of LiNO ₃ and cover the MnO ₂ and _2.0g LiNO in the crucible The surface of the mixture; Heat the crucible to 400°C to react for 12 hours. The obtained product is washed with water and absolute ethanol, filtered, and then dried at 70°C to obtain lithium manganese composite oxide MnO ₂ -Li ₄ Mn ₅ O ₁₂ . SEM observation, X-ray diffraction experiment, and charge-discharge performance experiment were carried out sequentially for the lithium-manganese composite oxide.

(1), SEM observation results

The obtained lithium-manganese composite oxide was observed by SEM, and the results are shown in Figure 1, Figure 2, and Figure 3, Figure 1 is a 200-fold SEM image, Figure 2 is a 10,000-fold SEM image, and Figure 3 is a 100,000-fold SEM image, It can be clearly seen from the figure that the obtained lithium manganese oxide MnO ₂ -Li ₄ Mn ₅ O ₁₂ is a microsphere with a particle size of 4-6 μm, and the diameter of the outer shell of the ball is about 20-30 nm, with a core-shell structure.

(2) X-ray diffraction results

Take α-MnO ₂ and the prepared lithium manganese composite oxide MnO ₂ -Li ₄ Mn ₅ O ₁₂ respectively for X-ray diffraction, the results are shown in curve a and curve b in Figure 4, where curve a is α-MnO ₂ Diffraction pattern, curve b is the X-ray diffraction pattern of MnO ₂ -Li ₄ Mn ₅ O ₁₂ .

表示的α-MnO₂衍射峰，其它峰则与标准JCPDS卡46-0810即尖晶石相Li₄Mn₅O₁₂相对应，说明表面生成了尖晶石相Li₄Mn₅O₁₂。In curve b, the diffraction peaks of α-MnO ₂ and Li ₄ Mn ₅ O ₁₃ are clearly marked, that is, the inverted triangle

The α-MnO ₂ diffraction peak indicated by , and the other peaks correspond to the standard JCPDS card 46-0810, that is, the spinel phase Li ₄ Mn ₅ O ₁₂ , indicating that the spinel phase Li ₄ Mn ₅ O ₁₂ is formed on the surface.

(3) Charge and discharge experiment

Take 70 parts by weight of lithium-manganese composite oxide prepared in this example as the positive electrode active material and 20 parts by weight of acetylene black (KS-6) as the conductive agent and mix evenly, then add polyvinylidene fluoride binder solution and mix evenly Dry on an aluminum foil with a thickness of 15 μm to obtain a positive electrode film. Lithium sheet is used as the negative electrode, UBE film produced by Ube Corporation of Japan is used as the diaphragm, and ethylene carbonate (EC): diethyl carbonate (DEC): dimethyl carbonate (DMCA) with a concentration of 1.0M LiPF ₆ is used. The mixed solvent of 1:1:1 is used as the electrolytic solution, the operating voltage range is 2.0-4.0V, and the current density is 10mA/g. The electrical performance test results are shown in Figure 5 and Figure 6. Among them, Figure 5 is the charge-discharge curve of the first 50 times, and Figure 6 is the cycle performance. As shown in Figure 5, there is a charging and discharging platform at about 3.0v and 2.8v respectively, showing the charging and discharging characteristics of Li ₄ Mn ₅ O ₁₂ ; from Figure 6 it can be seen that the charging and discharging capacity of the battery increases with the cycle The increase of the number of times shows an increasing trend, and the cycle performance is good.

The core-shell structure Mn-O/M-Mn-OLi ₄ Mn ₅ O ₁₂ provided by the present invention and its preparation method are described above in detail. In this paper, specific examples are used to illustrate the principle and implementation of the present invention, and the descriptions of the above embodiments are only used to help understand the method and core idea of the present invention. It should be pointed out that for those skilled in the art, without departing from the principle of the present invention, some improvements and modifications can be made to the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims (4)

1. a complex Li-Mn-oxide that is used for active material of anode of secondary lithium battery is characterized in that described complex Li-Mn-oxide is by formula M nO ₂@Li ₄Mn ₅O ₁₂(I) expression;

In the complex Li-Mn-oxide shown in the general formula (I), MnO ₂As the nuclear of described complex Li-Mn-oxide, Li ₄Mn ₅O ₁₂Be coated on described MnO ₂The outside form shell;

The preparation method of described complex Li-Mn-oxide is for being specially:

In 200ml water, add the MnSO of 8mmol respectively ₄(NH ₄) ₂SO ₄, under stirring, add the 8ml concentrated sulfuric acid successively and add an amount of AgNO ₃As catalyst, stop to stir behind the reaction 10min, reactant is put in the dark place left standstill 2 days, precipitation is filtered sediment, and water and absolute ethanol washing obtain α-MnO at 70 ℃ with drying precipitate then successively ₂Particle;

Get the described α-MnO of 0.2g ₂With 2.0g LiNO ₃In agate mortar, pack into behind the mixing in the corundum crucible, get an amount of LiNO again ₃Cover the MnO in the described crucible ₂With 2.0g LiNO ₃The mixture surface; Heating crucible to 400 ℃ reacts, and the reaction time is 12h, and the product water that obtains and absolute ethanol washing, filtration obtain complex Li-Mn-oxide in 70 ℃ of dryings then.

2. the preparation method of a complex Li-Mn-oxide is characterized in that, comprising:

In 200ml water, add the MnSO of 8mmol respectively ₄(NH ₄) ₂SO ₄, under stirring, add the 8ml concentrated sulfuric acid successively and add an amount of AgNO ₃As catalyst, stop to stir behind the reaction 10min, reactant is put in the dark place left standstill 2 days, precipitation is filtered sediment, and water and absolute ethanol washing obtain α-MnO at 70 ℃ with drying precipitate then successively ₂Particle;

Get the described α-MnO of 0.2g ₂With 2.0g LiNO ₃In agate mortar, pack into behind the mixing in the corundum crucible, get an amount of LiNO again ₃Cover the MnO in the described crucible ₂With 2.0g LiNO ₃The mixture surface; Heating crucible to 400 ℃ reacts, and the reaction time is 12h, and the product water that obtains and absolute ethanol washing, filtration obtain complex Li-Mn-oxide in 70 ℃ of dryings then; Described complex Li-Mn-oxide is by formula M nO ₂@Li ₄Mn ₅O ₁₂(I) expression;

In the complex Li-Mn-oxide shown in the general formula (I), MnO ₂As the nuclear of described complex Li-Mn-oxide, Li ₄Mn ₅O ₁₂Be coated on described MnO ₂The outside form shell.

3. lithium battery anode comprises:

The described complex Li-Mn-oxide of claim 1, conductive agent and adhesive.

4. lithium battery comprises:

The described lithium battery anode of claim 3;

Negative pole; And organic electrolyte solution.

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