KR20010029695A - A method for manufacturing the cathode material of the secondary lithium electric cell - Google Patents

Abstract

PURPOSE: A process for preparing positive electrode material used in lithium rechargeable battery capable of controlling composition and particle size of powdered positive electrode material and enhancing cycling feature of the battery is accomplished by means of two-staged heat treatments at desired temperature. CONSTITUTION: A preparation process of positive electrode material useful in lithium rechargeable battery is performed by dissolving citric acid and ethylene glycol in water to form a solution, admixing this solution with a water solution containing metal salt and additives and heating the mixture at a certain temperature to produce powdered product as a first heat treatment step. Subsequently, the powdered product is dried in a pre-heated dryer as a second heat treatment step. The final dried powder is delivered into and under calcining process in a furnace.

Description

A method for manufacturing the cathode material of the secondary lithium electric cell}

The present invention relates to a method of manufacturing a positive electrode material of a lithium secondary battery, and more particularly, to manufacture a positive electrode material of a lithium secondary battery that can easily control the composition and size of the positive electrode material powder and improve the cycle characteristics of the battery. It is about a method.

In general, the lithium secondary battery is a battery that can be reused many times while being continuously charged. Recently, the lithium secondary battery has been widely used in a mobile phone or a notebook computer. The lithium secondary battery is largely composed of an electrode, a separator, and an electrolyte. The electrode includes a cathode, which is an electrode that receives electrons from an external conductor, and a cathode active material is reduced, and an anode, which is an electrode that emits electrons to the conductor as the anode active material is oxidized. The separator is a separator for preventing physical contact between the two electrodes, and the electrolyte is a medium that enables the movement of a predetermined material so that the reduction reaction at the positive electrode and the oxidation reaction at the negative electrode are chemically coordinated. The material that moves in the electrolyte is Li ions, and the charge and discharge of the battery is performed by the movement between the positive and negative electrodes of the Li ions.

On the other hand, the performance of such a lithium secondary battery greatly varies depending on the manufacturing method of each element forming the battery. In particular, a material of the positive electrode of the two electrodes is a lot of LiMn ₂ O ₄ or LiCoO ₂ is used, the LiMn ₂ O ₄ or LiCoO ₂ is mainly produced by the Pechini method (dry method or solid phase reaction method). Hereinafter, the dry method and the Pechini method will be briefly described.

The dry method is a method of preparing a powder by mechanically mixing the raw material powder in a solid state. The powder used at this time is mainly an oxide system. However, according to this dry method, since the raw material powders in the solid state are mechanically mixed, there is a limitation in uniform mixing, and there is a problem in that the uniformity of the composition and size of the resulting powder is low.

Therefore, calcination for a long time at a high temperature of 800 ℃ in order to make a powder of a uniform composition. In this case, however, the powder becomes hard and aggregates are formed. Therefore, a crushing step must be performed to crush the aggregates. This crushing step is a process in which the powder is pulverized by friction between the ball and the powder by using a ball of high strength, such as an alumina ball or a zirconia ball, mainly in a cutting barrel. However, in the process of pulverizing the powder using alumina balls or zirconia balls, the alumina balls are also worn out by friction and there is a possibility of contamination.

On the other hand, the pechini method dissolves the raw material powder in citric acid and ethylene glycol to produce LiMn ₂ O ₄ powder or LiCoO ₂ powder, so that the composition of the powder and the uniformity of powder crystals are higher than those of the dry method. In addition, since the polymer material can be evenly mixed on an atomic scale, it can be calcined at a relatively low temperature in a short time. Since it is calcined at a low temperature in a short time, the powder is fine and does not require a grinding process, and can prevent contamination due to the use of balls. However, the conventional Pechini method has the following problems.

First, the conventional Pechini method has a disadvantage in that it is not easy to control the powder size and composition of the positive electrode material by the complicated chemical reaction of the mixed solution depending on the reaction conditions. In addition, when volatilization of ethylene glycol (Ethylene glycol) added in the manufacturing process of the cathode material LiMn ₂ O ₄ or LiCoO ₂ according to the manufacturing method has a disadvantage that it is difficult to control the composition of the powder.

Second, the conventional pechini method is to mix the citric acid and ethylene glycol in the raw material powder at the same time, it is difficult to obtain a mixed powder of uniform composition because the chain formation between citric acid and ethylene glycol is suppressed. Therefore, the existing Pechini method has a disadvantage in that reproducibility and yield are poor.

Third, it is generally known that the cycle characteristics of a battery depend on the valence of Mn in LiMn ₂ O ₄ or the valence of Co in LiCoO ₂ , but the valence of manganese or cobalt cannot be controlled by the manufacturing method. There is a problem that the cycle characteristics are greatly reduced during discharge.

Fourth, in the mass production of the powder of the positive electrode material, not only can the furnace be contaminated by a polymer composed of citric acid and ethylene glycol as a mixed solution, but there is also a risk of explosion due to the heat of reaction when the decomposition reaction of the solvent polymer occurs in an enclosed space. .

An object of the present invention to solve the above problems is to provide a positive electrode material manufacturing method of a lithium secondary battery that can easily control the composition and size of the positive electrode material powder.

A second object of the present invention is to provide a method for producing a positive electrode material of a lithium secondary battery that improves the reproducibility and yield of the manufacturing method.

A third object of the present invention is to provide a method of manufacturing a positive electrode material for a lithium secondary battery that can significantly improve cycle characteristics during charging and discharging of a battery by controlling the valence of manganese or cobalt.

A fourth object of the present invention is to provide a method of manufacturing a cathode material of a lithium secondary battery, which can reduce the contamination and explosion potential of a furnace during mass production of LiMn ₂ O ₄ or LiCoO ₂ .

1 is a process diagram schematically showing a positive electrode material manufacturing process of a preferred embodiment according to the present invention.

Figure 2 is a process chart showing the manufacturing process of the positive electrode material LiMn ₂ O _{2 according} to the present invention.

Figure 3 is a graph showing a change in the oxygen pore concentration according to the calcination temperature in the positive electrode material LiMn ₂ O ₂ according to the present invention.

4 is a graph showing the change in valence of Mn according to the calcination temperature in the cathode material LiMn ₂ O ₂ according to the present invention.

5 is a graph showing a change in lattice constant according to calcination temperature in the positive electrode material LiMn ₂ O ₂ according to the present invention.

6 is a graph showing a change in cycle characteristics according to calcination temperature in a battery using the positive electrode material LiMn ₂ O _{2 according} to the present invention.

7 is a process chart showing the manufacturing process of the positive electrode material LiCoO _{2 according} to the present invention.

8 is a view showing the microstructure of the positive electrode material LiCoO _{2 according} to the present invention.

9 is a graph showing the crystallinity of the positive electrode material LiCoO _{2 according} to the present invention.

10 is a graph showing a cycle characteristic change of a battery using a positive electrode material LiCoO _{2 according} to the present invention.

In the method for producing a cathode material of a lithium secondary battery of the present invention for achieving the above object, after dissolving citric acid and ethylene glycol in a predetermined amount of water to form a melt, the melt is mixed with a metal salt solution in which metal salt is dissolved Mixture manufacturing step of preparing a; A first heat treatment step of heating the mixture to produce a powder; And a calcining step of calcining the dried powder.

According to the above constitution, since the citric acid and ethylene glycol are gradually dissolved to prepare the metal salt solution, the chemical stability of the melt is improved. Therefore, there is an advantage that not only the composition and size of the powder of the positive electrode material can be easily controlled, but also the reproducibility and yield can be improved.

According to a specific embodiment of the present invention, the positive electrode material manufacturing method of the lithium ion battery according to the present invention, before the calcination step after the first heat treatment step in advance to have a predetermined dry atmosphere just before the powder is exothermic reaction by ignition It is characterized in that it further comprises a secondary heat treatment step of drying in a heated dryer.

According to the above configuration, the powder can be sufficiently removed just before the powder is exothermic by ignition, that is, by breaking the chain between citric acid and ethylene glycol, thereby reducing the risk of contamination and explosion that may occur during mass production. There is an advantage.

According to another specific embodiment of the present invention, in the calcination step, the temperature is adjusted to 500-700 ° C. to increase the valence of Mn, characterized in that to improve the cycle characteristics of the battery.

According to the above configuration, by lowering the calcining temperature, there is an advantage that the cycle characteristics of the battery can be improved by increasing the valence of Mn and the concentration of oxygen vacancies.

According to another embodiment of the present invention, the ratio of Mn / Li is 0.9 to 1.05 when the metal salt solution is prepared.

As described above, when the ratio of Mn / Li is 0.9 to 1.05, there is an advantage that the cycle characteristics of the battery can be significantly increased by maintaining the valence of Mn at 3.5 or more by controlling the calcination temperature.

BEST MODE Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings. The method for producing a lithium secondary battery positive electrode material according to the present invention is a modification of the above Pechin method.

As shown in FIG. 1, the method of manufacturing a cathode material of a lithium secondary battery according to the present invention includes a melt 212 formed by dissolving citric acid and ethylene glycol in a predetermined amount of water, and a predetermined additive. And mixing (216) a metal salt solution (214) containing a metal salt dissolved therein to prepare a mixture, and heating the mixture prepared in the mixture manufacturing step (210) to a predetermined temperature to obtain a powder. A first heat treatment step 222 to be produced, a second heat treatment step 224 of drying the powder by putting it in a pre-heated dryer and a calcining step 226 of calcining the dried powder in a furnace It is composed.

The mixture manufacturing step 210 consists of a process (216) of preparing the melt and the metal salt solution separately (212, 214) and then mixing the metal salt solution into the prepared melt. Looking at this in detail, the melt is prepared by slowly dissolving the citric acid and ethylene glycol as the main raw materials in a predetermined amount of water for 150 to 200 minutes at 100 ~ 110 ℃ (212). Next, a metal salt is mixed with a predetermined amount of water to prepare the metal salt solution (214). The melt and the metal salt solution thus prepared are mixed (216). An additive may be added to the metal salt solution.

When the melt is slowly dissolved at a suitable temperature as described above, the melt is chemically stabilized to form a plurality of chains between citric acid and ethylene glycol and polymerize. When the metal salt solution is mixed in a stable state in this way, it is possible to solve the problem by the conventional Pechini method of mixing the melt and the metal powder at the same time. That is, the problem that lithium evaporates together when volatilization of ethylene glycol does not occur, and the metal powder can be mixed uniformly, thereby improving the uniformity of the composition of the powder, the reproducibility of the manufacturing method, and the yield.

The first heat treatment is a step of heating and powdering until an exothermic reaction occurs (222), and before the calcination step after the first heat treatment step, the powder is heated in advance so as to have a predetermined dry atmosphere immediately before the powder is exothermicly ignited. The secondary heat treatment to dry in a dry dryer is performed (224). The drying atmosphere of the dryer in the second heat treatment step 224 refers to an air atmosphere or a vacuum atmosphere. However, there is an advantage that the reaction is accelerated when the atmosphere of the dryer is vacuumed.

By performing the second heat treatment, it is possible to sufficiently remove carbon and the like by breaking the chain between citric acid and ethylene glycol immediately after the powder is exothermic and ignited, thereby reducing the risk of contamination and explosion that may occur during mass production. There is an advantage to that.

As described above, in the positive electrode material manufacturing method according to the present invention, since the melt is chemically stabilized, mixed, and subjected to two heat treatments, the positive electrode material having a uniform composition can be safely and efficiently mass-produced. In addition, the calcination temperature can be lowered relatively, and the cycle characteristics of the battery using the positive electrode material according to the present invention can be improved.

2 is a process chart showing a manufacturing process of the cathode material LiMn ₂ O _{2 according} to the present invention.

As shown in the process of Figure 1 by putting the citric acid and ethylene glycol in a predetermined amount of water to maintain a temperature of 100 ~ 110 ℃ for 150 to 200 minutes to prepare a melt (212a), the Li salt and Mn salt in water To prepare a metal salt solution by mixing with (214a).

In this case, the Li salt powder may be selected from one or more than one of oxide (oxide), nitrate (nitrate), acetate (acetate), the Co powder may be selected from one or more of oxide, nitrate, acetate. In addition, the Li salt powder and Mn salt powder may be one having a purity of 90% or more, and an additive consisting of Ga, Sr, Co, Ni, Cu, Ru, Fe, or Sn may be added to the metal salt solution.

On the other hand, when mixing the Li salt powder and Mn salt powder, when Mn / Li is 0.9-1.5, by controlling the calcination temperature to maintain the valence of Mn above 3.5 to significantly increase the cycle characteristics of the battery There is an advantage. In general, LiMn ₂ O ₄ , a cathode material for lithium secondary batteries, is known to increase the cycle characteristics of the battery when the Mn atom is 3.5 or more, and the capacity is close to the theoretical value when the Mn / Li ratio is close to two. Accordingly, the present invention improves the cycle characteristics of the battery using the above principle.

Next, a first heat treatment step 222a is performed to heat the mixture prepared through the mixture manufacturing step 210a. In the first heat treatment step (222a) is heated to just before the mixture is ignited at a temperature of 100 ~ 150 ℃ to produce a powder.

Then, the second heat treatment step 224a, the powder produced in the first heat treatment step (222a) causes an exothermic reaction and the powder is 150 ~ 250 ℃ in advance to have a predetermined dry atmosphere at the time of rapid ignition occurs It is put in a dryer heated with and maintained for 12 hours to dry. In the secondary heat treatment step 224a, the drying atmosphere of the dryer is performed in an air atmosphere or a vacuum atmosphere. However, there is an advantage that the reaction is accelerated when the atmosphere of the dryer is vacuumed.

As described above, if the secondary heat treatment 224a is performed before calcination at a high temperature, the polymer chain of the melted substance remaining in the powder can be completely removed, and thus the mass production of LiMn ₂ O ₄ powder, which is a positive electrode material, It can reduce the possibility of contamination and explosion.

In the calcining step 226a of calcining the powder, the final step is calcined to a heat treatment condition having a temperature rise / cold rate of 1 ° C./min or less through the second heat treatment step 224 a. From this, the powder of the positive electrode material LiMn ₂ O _{4 in} the final state is produced. On the other hand, the crystallinity of the powder can be changed to suit the purpose by adjusting the temperature rise / cold temperature.

Preferably the calcination step (226a) is performed at 500 ~ 750 ℃. 3 is a graph showing the change in oxygen pore concentration according to the calcination temperature, wherein the calcination time was 4 hours. 4 is a graph showing the change in valence of Mn according to the calcination temperature, Figure 5 is a graph showing the change of lattice constant according to the calcination temperature. As shown in Figures 3 to 5, the lower the calcination temperature, the higher the concentration of oxygen, the oxidation number of Mn and the lower the lattice constant.

Therefore, as described above, the higher the oxidation number of Mn, the better the cycle characteristics of the battery. The lower the calcination temperature, the higher the cycle characteristics of the battery. This is well illustrated in FIG. 6, which is a graph showing a change in cycle characteristics of a battery according to calcination temperature. The electrochemical properties of the powder were measured by changing the voltage while applying a constant current in an argon atmosphere after adding a conductive agent and a binder to the powder.

On the other hand, it is preferable to set calcining time as 2 to 48 hours. Longer calcination time results in the same result as raising the calcination temperature, so that the calcination time can be shortened to improve the cycle characteristics of the battery.

Hereinafter, an embodiment of manufacturing the LiCoO ₂ positive electrode material shown in FIG. 7 will be described. That is, the Example in which Co salt powder was used instead of Mn salt powder when manufacturing a metal salt is demonstrated in detail.

Compared with the embodiment for preparing the LiMn ₂ O ₂ positive electrode material, the overall order and principle of operation are the same, but there is a difference in the addition ratio and the specific heat treatment temperature.

That is, the prepared melt 212b is mixed with the metal salt solution 214b in which Li salt powder, Co salt powder, and water are mixed (216b). The Li salt powder and the Co salt powder are mixed so that the Co / Li ratio is 0.8 to 1.2. At this time, the cycle characteristics of the battery are most improved. Mn, Ni, Sr, Ga, Cu, Ru, Fe, Sn and the like may be added to the metal salt solution.

The Li powder may be selected from one or more of oxide, carbonate, nitrate, and acetate, and the Co powder may be selected from one of oxide, carbonate, nitrate, and acetate. You can select more than one.

On the other hand, the second heat treatment step after the first heat treatment (222b) for 3 to 24 hours at 80 ~ 200 ℃ is carried out for 1 to 24 hours while maintaining 150 to 400 ℃ (224b).

And, the calcination step is carried out for 1 to 48 hours at 500 ~ 850 ℃ (226b).

8 is a view showing a microstructure of the positive electrode material LiCoO ₂ according to the invention, Figure 9 is the graph showing the crystallinity of the positive electrode material LiCoO ₂ according to the present invention, LiCoO ₂ positive electrode according to the invention As can be seen from this, According to the material production method, the crystallinity of the positive electrode material LiCoO ₂ is increased.

Since the crystallinity of the positive electrode material LiCoO ₂ according to the present invention is improved as described above, a cycle of a battery using the positive electrode material LiCoO _{2 according} to the present invention as shown in FIG. 10 (when calcined at 800 ° C. for 24 hours). The properties are also improved.

In the above, the embodiment of performing the heat treatment twice has been described, but various embodiments are possible without departing from the technical spirit described in the claims of the present invention, including the case where the heat treatment is performed only once.

As described above, the method for manufacturing a lithium secondary battery positive electrode material according to the present invention changes the order of mixing a melt and a metal powder, that is, positively because the metal salt solution is mixed after stably mixing citric acid and ethylene glycol. The composition and size of the material powder can be easily controlled, and the effect of improving reproducibility and yield can be achieved.

According to the present invention, since two heat treatment steps before calcination, the effect of lowering the contamination and explosion of the furnace during mass production of LiMn ₂ O ₄ or LiCoO ₂ can be achieved.

In addition, another effect of the present invention is that because the calcination at a relatively low temperature within a short time, the valence of manganese can be maximized to increase the initial capacity or cycle efficiency of the lithium secondary battery.

Claims (21)

In the method of manufacturing a lithium secondary battery positive electrode material, Preparing a mixture by dissolving citric acid and ethylene glycol in a predetermined amount of water and then mixing the melt with a metal salt solution in which the metal salt is dissolved; A first heat treatment step of heating the mixture to produce a powder; And Method for producing a positive electrode material of a lithium secondary battery comprising a calcination step of calcining the dried powder. The method of claim 1, wherein during the preparation of the melt in the mixture manufacturing step, the cathode material manufacturing method of a lithium secondary battery, characterized in that performed for 150-200 minutes at 100 ~ 110 ℃. The method according to claim 1 or 2, further comprising a second heat treatment step of drying in a preheated dryer to have a predetermined drying atmosphere after the first heat treatment step and before the calcining step, before the calcination step is exothermic. Method for producing a positive electrode material of a lithium secondary battery, characterized in that. The method of claim 3, wherein the drying atmosphere of the drying step is a vacuum atmosphere. The method of claim 1 or 2, wherein the calcination step is performed at a ramp / cold rate of 1 ° C / min or less. The method of claim 1 or 3, wherein the metal salt of the mixture preparation step comprises a Li salt powder and a Mn salt powder. The method of claim 6, wherein the Li salt powder, one or more of the oxide (carbonate), carbonate (nitrate), acetate (acetate) to manufacture a positive electrode material of a lithium secondary battery Way The method of claim 6, wherein the Mn salt powder comprises one or more of oxide, nitrate, and acetate. The method of claim 6, wherein the first heat treatment step is performed at 100 ~ 150 ℃ positive electrode material manufacturing method of a lithium secondary battery. The method of claim 6, wherein the secondary heat treatment step is performed at 150 ~ 250 ℃ positive electrode material manufacturing method of a lithium secondary battery. 7. The method of claim 6, wherein in the calcining step, the temperature is adjusted to 500-700 ° C. to increase the valence of Mn. 12. The method of claim 11, wherein in the calcination step, the calcination time is 2-48 hours to increase the valence of Mn. The method of manufacturing a positive electrode material of a lithium secondary battery according to claim 6, wherein the ratio of Mn / Li is 0.9 to 1.05 when the metal salt solution is prepared. The method of claim 6, wherein the metal salt contains Ga, Sr, Co, Ni, Cu, Ru, Fe, or Sn as an additive. 4. The method of claim 1 or 3, wherein the metal salt in the mixture preparation step comprises a Li salt powder and a Co salt powder. The method of claim 15, wherein the Li powder comprises one or more of oxide, carbonate, nitrate, and acetate. . 16. The method of claim 15, wherein the Co powder comprises one or more of oxides, carbonates, nitrates, and acetates. The method of claim 15, wherein the first heat treatment step is performed at 80 ~ 200 ℃. The method of claim 15, wherein the secondary heat treatment step is performed at 150 ~ 400 ℃. The method of manufacturing a positive electrode material of a lithium secondary battery according to claim 15, wherein the calcination step is performed at 500 to 850 ° C. The method of claim 20, wherein the calcination step is performed for 1 to 48 hours.