JPH08264184A - Electrode substance preparation for lithium secondary battery - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manufacturing process of both electrode materials of a lithium secondary battery which can improve a characteristic of charge and discharge. SOLUTION: After 1/2 Li2 CO3 , yCo(NO3 )2 .6H2 O, (1-y) Ni (NO3 )2 .6H2 O, C6 H8 O7 are dissolved in distilled water and brought into solution, NH4 OH is added to this solution, adjusted to pH = 3 to 4, and a citricsol is made, then a citratesol is heat-treated. Thus, things about manufacturing method of electrode materials for a lithium secondary battery and electrode materials of LiCo O2 and LiCoyNi1-y O2 (0<y<1) are formed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrode material for a lithium (Li) secondary battery, and more particularly to a method for producing an electrode material for a lithium secondary battery having a high charge / discharge electrode.

[0002]

2. Description of the Related Art It is a material for both electrodes of a lithium secondary battery.
LiCoO ₂ , LiNiO ₂ and LiCo _y Ni _1-y O ₂ compounds are
ck-salt superlattice) one α-NaFeO ₂ structure.

The ideal structures of these compounds are Li ions and Co at the octahedral sites of oxygen which are cubic, dense and packed (cubic close packing).
(Or Ni ion is located, and it has a layered structure in which these M _O 2 layers (M-Co (or Ni) and Li layers are repeated.

LiCo as a battery electrode material by the high temperature solid-state method
Method for producing O2 and _{LiC o} yN i1- y _O 2 is as follows.

First, 1) L _i 2C _O 3 is L _i 2C _O 3 and _Co 3 _O 4 or CoC _O 3
Is quantitatively mixed, a temperature of 900 ° C. is added in an oxygen atmosphere, and heat treatment is performed for 20 hours to manufacture.

2) LiC _o yN _i1- y _O 2 is L _i 2C _O 3, Ni
It is manufactured by mixing O and _Co 3 _O 4 in a molar ratio and heat-treating in an oxygen atmosphere.

At this time, the heat treatment is performed at 500 ° C. for 10 hours and 600 ° C.
After heat treatment for 10 hours at 800 ° C and 48 hours at 800 ° C
The temperature is reduced at a rate of ℃ / min, and if the amount of cobalt (Co) in the resulting product is large, heat treatment is performed again at 900 ℃.

LiNi _O 2 is (L _i1- zN ⁱ² ₊ z) depending on the synthesis conditions.
(N ⁱ³ + N ⁱ² ₊ z) _O 2 (0 <z ≦ 0.2) Nonstoichiometric compound (non
This is L because it forms a stoichiometric compound).
^{Since i} + ions are included in the compound, Li is sandwiched (in
The space for tercalation) becomes smaller, and Li diffusion is difficult.

Therefore, the disorder (di
(sorder) has an undesired effect on electrode characteristics such as operating voltage and charge / discharge capacity.

Then, if the amount of addition of Li is reduced to 0.5 or less, rearrangement of the structure is performed to induce an irreversible electrochemical reaction.

[0011] In contrast LiCo _O 2 is Li ions and Co ions are perfect ordering because of the a (ordering) sequence, is substituted Co ions between Co _O 2 layer as in LiNi _O 2 dimensional it is no fear that forming a structure, reversibility in comparison with LiNi _O 2 (reversibil
ity) is also good. However, the battery voltage from LiNiC _O 2 (cell vol
From a practical point of view, there is a problem that most electrolytes exceed the electrochemical window, and the cost is higher than Co as compared with Ni.

The liquid method includes a coprecipitation method and a sol-gel method as a conventional method for producing a metal oxide.

In the case of the coprecipitation method, it is possible only if there is a pH range in which the compound to be synthesized is coprecipitated. However, the sol-gel method is a solvent in which all the starting materials are dissolved and is gelled. Additives that can give (eg citric acid
It is possible to obtain a fine powder, and it is often used for the synthesis of ultrafine powder materials.

[0014] Such a sol - using the gel method of bipolar active material for lithium secondary battery LiCo _O 2 and _LiC o y
N _{i1 y} O ₂ compounds well developed secondary limit structure is by one synthesized by the existing high temperature solid phase method By synthesizing, the characteristics of the electrodes it is possible to synthesize the magnitude is small compound particles It will be improved.

The method for producing the compound by the known sol-gel method is as follows.

Co (N _O 3 ₎ 2, LiOH and citric acid (succin
ics acid), oxalic acid (oxalic acid), malic acid (malic acid), mixed with tartaric acid (tartaric acid)) the same molar ratio (mol rate), adjusted with 4-8 pH with N _H 4OH to a solution To make.

This solution is dried in vacuum at a temperature of about 60 to 150 ° C. to form a powder, and organic substances are removed at 400 ° C.

Then, the powder was sampled at a pressure of 400 kg / ^cm 2 and heat-treated at about 650 ° C. for about 6 hours, then 9
00 ° C. 20 h sintered to from producing LiCo _O 2. It was known that the compound prepared by using succinic acid was the best among the compounds thus prepared, and had the electrode property.

[0019]

However, the bipolar material for a lithium secondary battery manufactured by the above-mentioned conventional technique has a limit in maintaining the capacity of the battery for a long time and is unstable at a high current density. The battery has poor charge / discharge characteristics.

An object of the present invention, in order to solve the above-mentioned problems of the prior art, is to provide a method for producing a bipolar material for a lithium secondary battery, which can improve charge / discharge characteristics.

[0021]

The present invention SUMMARY OF THE INVENTION To achieve the above object _{1 / 2L i 2C O yyCO (} N O 3) 2 · 6 H 2O, (1-y) Ni (N O 3) 2 · 6
_After dissolving _H 2 _O and _C 6 _H 8 _O 7 in distilled water to make a solution,
Add _NH 4 OH to this solution and adjust to pH = 3-4 to adjust citric s
It is characterized by including a step of producing ol and a step of heat-treating the citrate sol.

[0022]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will now be described in detail with reference to the drawings.

In the present invention, succinic acid (succ) having the best electrode characteristics among the conventional methods using an organic acid is used.
proposed a method of manufacturing the LiCo _O 2 and _{LiC o} yN i1- y _O 2 compounds by using citric acid umbrella is larger than succinic acid as both an electrode material of a lithium secondary battery instead of INIC acid) method using To do.

FIG. 1 is a flow chart showing a method for producing a bipolar material using citric acid, and an embodiment of the present invention will be described with reference to the flow chart as follows.

[0025] _{First, 1 / 2L i 2C O 3} , yCo (N O 3) 2 · 6 H 2O, (1-y)
_{Ni (N O 3) 2 ·} 6 H 2O, after forming a solution by pouring distilled water _C 6 _H 8 _O 7, the solution pH = 3 to 4 and two adjusted by using the appropriate N _H 4OH A citric acid sol (s1) and a heat treatment step using the citric acid sol under vacuum conditions (10 to 20 mmH
The first heat treatment step of forming a solid organometallic deposit through gelation by evaporating the solvent contained in the citric acid sol by heating at 80-95 ° C. for 18-20 hours in (g). s
And 2), the organometallic clothes was heated for 3-4 hours at 300 to 350 ° C. by decomposing organic substance LiCo _O 2 and _{LiC o yN i1- y O 2 (} 0 <
y <1) The second heat treatment step (s3) to obtain the precursor of the compound, and the precursor (precursor) of 600
A third heat treatment step (s4) of calcitation at ~ 650 ° C for 6 hours and annealing of the compound at 800 ~ 850 ° C for 20 hours to be used as an electrode material for a lithium secondary battery. It is manufactured fourth through heat treatment stage (s5) to obtain LiCo _O 2 and _{LiC o} yN i1- y _O 2 compounds.

Manufactured by the above manufacturing process
LiCo _O 2 is _{L i 2C O 3, Co (} N O 3) 2 · 6 H 2O, C 6 H 8 O 7 , respectively 1:
1: has a 2 molar _ratio, LiC _o yN i1- y _O 2 is _{L i 2C O 3, Co (} N O 3
₎ 2.6 _H 2 _O , Ni (N _O 3 ₎ 2.6 _H 2 _O , _C 6 _H 8 _O 7 1: y: (1-y):
It has a molar ratio of 3.

[0027] At that time, during the production of LiCo _O 2 compound in Preparation process, _{first, 1 / 2L i 2C o 3} , yCo (N O 3) 2 · 6 H 2O, (1-y) Ni (N
_{O 3) 2 · 6 H 2O} , y to determine the reclamation ratio of each compound in the starting material of _C 6 _H 8 _O 7 is to have a range of (0 <y <1).

[0028] Figures 2 and 3, sol _{LiC o yN i1- y O 2 (} y = 0 3.) The compounds of X- ray diffraction analysis pattern and the present invention produced by the hot solid phase method - gel process LiC were prepared using citric acid _{o yN i1- y O 2 (y} = 0. 3) showed X- ray diffraction analysis patterns of the compound.

LiC _o Y _N1- y _O 2 synthesized using citric acid
Table 1 shows the X-ray diffraction analysis results of the _{(y =} 0.3) compound.

[0030]

[Table 1]

According to FIGS. 2 and 3, all hexagonal systems
As shown in FIG. 3, the compound for an electrode material having a crystal structure of gonal symmetry and produced using citric acid has a (006) peak and a (012) peak separated from each other. As shown in FIG. 2, it can be seen that the compound produced by the high temperature solid phase method does not separate these two peaks, and the separation of the (018) and (110) 2 peaks is not clear.

[0032] Thus, LiC _o produced using citric acid
_{yN i1- y O 2 (y =} 0. 3) compound, LiC _o y produced in a high temperature solid phase method
It can be seen that the crystallinity is better than that of the N _i1- y _O 2 _{(y = 0.3} ) compound.

[0033] LiC _o yN Table 1, which was prepared using citric acid
_i1- y _O 2 _{(y = 0.3} ) L produced by high temperature solid phase method
2 shows the X-ray diffraction analysis results for the iC _o yN _i1- y _O 2 _{(y = 0.3} ) compound.

Generally, in LiM _O 2 (M: V, Cr, Co, Fe, Ni), lithium ions and M ions located in each layer are oxygen anions which are cubic, dense, and dense. It is placed in a cudic close packing octahedral position.

If M ions are located at the octahedral position of the Li layer, the relative intensity of the peak of the X-ray line analysis pattern (003) decreases. That is, the strong (003) peak is LiM _O 2
Means that the two-dimensional structure of has been developed.

That is, as shown in Table 1, the relative intensity of the (003) peak of the compound synthesized by using citric acid is more than the relative intensity of the (003) peak of the compound synthesized by the high temperature solid phase method. Although the size can be known, this means that the compound synthesized by using citric acid has a more developed two-dimensional structure than the compound synthesized by the high temperature solid phase method.

Therefore, in producing LiCo _O 2 and LiC _o yN _i1- y _O 2, it should be _noted that the method using citric acid can obtain a compound having better crystallinity than the conventional high temperature solid phase method. Can be done. LiCo _O 2 and _{LiC o0. 3N i0. 7 O} 2 respectively 60mg and acetylene black (acetylene black) (10%)
To form an anode, the cathode is Li metal, and the electrolyte is propylene carbonate and 1 mol of LiCl _O 4.
4 and 5 show the primary charge / discharge curves measured at a current density of 200 μA / ^cm 3 when a battery was constructed using a solution that dissolves the above.

As can be seen from FIGS. 4 and 5, these compounds maintain a high voltage of 3.5 V or more, and the difference in intercalation rate is −.
0.05 ^e- If manufactured by other methods such as the following-0.0
9 ^e- smaller than L _e y CoO2 and Li xC
_o0. 3N _i0. discharge capacity of 7 _O 2 discharge capacity (Discharge capacity) also each ~130mAh / g and ~160mAh / g These compounds prepared by conventional methods such as ～120MAh /
g and ~ 140 mAh / g.

Alternatively, the polarization of the voltage during the process of charging ((a) in FIGS. 4 and 5) and discharging ((b) in FIGS. 4 and 5).
tion) is also decreasing. This is evidence that the particle size of these compounds is so small and the polarization is so small that Li tends to diffuse.

That is, as described above, the particle size of the compound synthesized using citric acid is smaller than that of the compound synthesized by the high temperature solid phase method, and the Li ion diffusion occurs during the intercalation reaction. Occurs, which is more advantageous in terms of reaction rate.

Therefore, when the above substances and the like are produced by using citric acid, the particles obtained are smaller than those obtained by the conventional different methods, and the electric capacity can be maintained for a longer time, and the high current can be maintained. Since the density is stable, the charging / discharging characteristics are improved when it is actually applied to a battery.

When citric acid is used to produce the above compound, the volume of citric acid is larger than that of succinic acid, so that the reactivity at the time of high temperature heat treatment is improved and the crystallinity is improved. Therefore, the electrode characteristics are improved as compared with conventional compounds synthesized by different methods.

[Brief description of drawings]

FIG. 1 is a flow chart showing a method for producing a bipolar substance using citric acid according to an embodiment of the present invention.

FIG. 2 LiCoy _N1- y _O 2 produced by a conventional high temperature solid phase method
It is a graph which shows the X-ray-diffraction analysis result of _(y-0. 3).

[3] using citric acid in the form of embodiment of the present invention the sol - is a graph showing the X-ray diffraction analysis of LiCoy prepared gel method _{N1- y O 2 (y = 0} 3.).

4 is a graph showing the 1 TsugiTakashi discharge curve of L _i xCo _O 2 compound prepared utilizing citric acid in the form of embodiment of the present invention.

5 is a graph showing the 1 TsugiTakashi discharge curve of _{L i xC o0. 3N i0.} 2 O 2 compound prepared utilizing citric acid in the form of embodiment of the present invention.

Front Page Continuation (72) Inventor Chang Ki-ho Republic of Korea Daejeon Yousung Ou-dong Dong Han-bit Apartment 105-703

Claims (7)

[Claims] 1. 1 / 2Li ₂ CO ₃ ,, yCo (NO ₃ ) ₂ .6H ₂ O, (1-y) Ni (NO
_{3) 2} · 6H ₂ O, after making the solution state by dissolving C ₆ H ₈ O ₇ in distilled water, citric acid sol was adjusted NH ₄ OH was added to this solution to pH = 3 to 4 ( citric sol) and a step of heat treating the citric acid sol. 2. LiCoO ₂ or Li according to the heat treatment step
The method for producing an electrode material for a lithium secondary battery according to claim 1, wherein a Co _y Ni _1-y O ₂ compound is formed. 3. LiCoO ₂ is formed when y becomes 1 and LiCoO ₂ is formed.
_The method for producing an electrode material for a lithium secondary battery according to claim 1 or _{2, wherein y} Ni _1-y O ₂ is formed when y is in the range of (0 <y <1). 4. The LiCoO ₂ is Li ₂ CO ₃ , Co (NO ₃ ) ₂ .6H ₂ O, C ₆
The method for producing an electrode material for a lithium secondary battery according to claim 2, further comprising a compound in which H ₈ O ₇ is mixed at a molar ratio of 1: 1: 2. Wherein said LiCo _y Ni _1-y O ₂ is _{Li 2 CO 3, Co (NO} 3) 2 · 6
_{H 2 O, Ni (NO 3} ) 2 · 6H 2 O, a _{C 6 H 8 O 7 1:} y: (1-y): 3
The method for producing an electrode material for a lithium secondary battery according to claim 1, which comprises a compound mixed in a mol ratio. 6. The method for producing an electrode material for a lithium secondary battery according to claim _{1, wherein y of} said LiCo _y Ni _1-y O ₂ is 0.3. 7. The heat treatment step is performed under vacuum condition (10 to 20 mmH).
g) first heat treatment step of heating 18-20 hours to a temperature of 80 to 95 ° C. under, 300 to 350 and heated for 3-4 hours to decompose the organic matter ° C. with LiCoO ₂ and LiCo _y Ni _1-y O ₂ A second heat treatment step to produce a (0 <y <1) compound, and the compound at 600-650 ° C for 6
The third heat treatment stage of time calcination, 800 ~
LiCoO ₂ and LiCo _y Ni _1-y O after annealing at 850 ℃ for 20 hours
_The method for producing an electrode material for a lithium secondary battery according to claim 1, further comprising a fourth heat treatment step of producing an electrode material with a ₂ (0 <y <1) compound.