JP3087240B2 - Lithium secondary battery - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a lithium secondary battery, and more particularly to a lithium secondary battery capable of preventing formation of lithium dendrites.

[0002]

2. Description of the Related Art A primary lithium battery is a card-type calculator,
In recent years, it has been used in large quantities as a power source for portable electronic products such as cameras and watches, but commercialization of lithium secondary batteries has been delayed at present. The reason is that when pure lithium is used as the negative electrode material of a lithium secondary battery, lithium dendrites that penetrate the separator during the charging and discharging process are generated, resulting in short-circuiting and ensuring safety. Because they cannot do it.

[0003] Therefore, a safer lithium secondary battery is provided.
Use pure lithium as the anode material
Research using various alternative substances instead of
Specifically, for example, a lithium alloy such as LiAl,
Insertion of lithium ions such as carbon powder and layered compounds (in
Suitable for tercalation and deintercalation
Attempts have been made to use such substances. For example, Weiss et al.
Ti (HPO_Four )_Two ・ H_Two Chemical formula of O
The use of α-titanium phosphate (α-TiP)
[M. A. Weiss and E. Michael. Z. Naturfo
rsch, B22, 1100 (1967)], and S. Allulli et al.
Is Ti (PO_Four )_Two (H_Two PO_Four ) ・ 2H _Two Chemical formula of O
Use of γ-titanium phosphate (γ-TiP)
[S. Allulli, C. Ferragina, A. LaGinestra,
 M. A. Massucci and N. J. Tomassini, Inorg. Nuc
l. Chem. 39, 1043 (1977)].

However, none of the lithium secondary batteries can completely prevent the formation of lithium dendritic crystals, and has not yet achieved sufficient safety. In this respect, the characteristics of the battery cannot be sufficiently exhibited.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and it is an object of the present invention to prevent the formation of dendritic crystals of lithium, resulting in a safe,
It is another object of the present invention to provide a lithium secondary battery having excellent characteristics required for a battery, such as a large operating voltage and a large discharge capacity and a constant discharge voltage.

[0006]

The lithium secondary battery of the present invention, which can solve the above-mentioned problems, uses a layered titanium phosphate: TiO (OH) (H ₂ PO ₄ ) as a negative electrode material. It has a gist. The layered titanium phosphate is preferably a mixture of (a) a mixture of tetramethylammonium hydroxide, titanium dioxide and phosphoric acid.
It is obtained by heating at a temperature of 0 ° C. or higher, (b) and then subjecting it to hydrogen cation exchange, and (c) performing a vacuum heat treatment.

It is preferable to use LiCoO ₂ or LiNiO ₂ as the material for the positive electrode used in the lithium secondary battery of the present invention. The electrolyte used in the lithium secondary battery of the present invention is one equivalent to an equivalent solution of ethylene carbonate and dimethyl carbonate (v / v) or one equivalent solution of propylene carbonate and diethyl carbonate (v / v). Mole of Li
Those containing ClO ₄ are preferred.

[0008]

The feature of the lithium secondary battery of the present invention is that, as a material for a negative electrode, layered titanium phosphate having an interlayer structure and having a variable interlayer distance when lithium ions are inserted and desorbed [chemical formula: TiO ( OH) (H ₂ PO ₄ ), and the above-mentioned layered titanium phosphate is abbreviated as LTP]. Since the LTP is not pure lithium but a lithium compound having an interlayer structure, the lithium metal does not crystallize on the negative electrode during the charging or discharging process, and thus can prevent the formation of dendritic crystals of lithium. Since it contains reducible titanium ions that can be reduced, the redox reaction in which the ions are electrochemically inserted easily proceeds. For example, the above LTP
When is used as a material for a negative electrode, the following reaction takes place in n-butyllithium. Thus, under the above reaction, the Li _x LTP compound is 2
Since lithium ions can be contained, insertion of lithium ions can be performed smoothly.

In preparing LTP used in the present invention,
The so-called hydrothermal reaction using hot water as a solvent
Preferably, the reaction conditions are as follows:
It is appropriately selected depending on the substance, the reaction container, and the like. LTP key
An example of the manufacturing method will be described with reference to FIG. Figure 1 shows the LTP
Stainless steel pressure reaction used in the manufacturing process
1 is a schematic view of a vessel 21.
book composed of a and a Teflon lining layer 21b
It consists of a body and a stainless steel lid 21c screwed into the body.
The stainless steel lid 21c and the main body are made of stainless steel.
It can be sealed by a spring 21d. First Tet
Lamethylammonium / titanium phosphate (NMe_Four With TP
Abbreviated) is prepared by a hydrothermal reaction. NMe_Four TP
The method for preparing the compound is not particularly limited.
Thilammonium [N (CH_Three ) _Four OH] solution: 0.0
5 mol of phosphoric acid: 0.15 mol and anatase type diacid
Titanium chloride (TiO_Two ): Obtained by mixing 0.05 mol
Pressed mixture made of stainless steel with Teflon lining
After sealing in a reactor, temperature above 150 ° C (preferably
Or 180 ° C) for 3 days
You. Then, after cooling it, open the pressurized reactor and
Is filtered, washed with distilled water and dried in air.
NMe_Four Get TP.

Next, the NMe ₄ TP thus obtained is obtained.
In a concentrated hydrochloric acid solution and subjected to hydrogen cation exchange at room temperature for 5 days to obtain pure layered titanium phosphate [TiO 2].
₂ (H ₂ PO ₄ ) (H ₃ O)]. Then 1
By performing a vacuum heat treatment at 10 ° C., the LTP used in the present invention can be prepared.

The LTP thus obtained is usually about 1
Note that it contains moles of water of crystallization and the interlayer distance between the crystal planes is 10 Å. FIG. 2 shows the X-ray diffraction (XRD) pattern of the LTP. Since lithium metal has high reactivity with water, the layered structure of LTP may be broken by a strong base generated by the reaction between lithium and water, and therefore, water of crystallization is removed prior to insertion of lithium ions. It is necessary. After removing the water of crystallization, the interlayer distance becomes 8.9 angstroms.

The lithium secondary battery of the present invention is characterized in that it defines the material for the negative electrode as described above, and the other constituent elements (the material for the positive electrode, the electrolyte, etc.) constituting the battery are particularly limited. It does not do. In a preferred embodiment, the positive electrode material used in the present invention is LiCoO ₂ or LiNiO ₂ , and the electrolyte used in the present invention is an equivalent solution of ethylene carbonate and dimethyl carbonate (v / v) or propylene carbonate. Equivalent solution of diethyl carbonate (v / v)
, Each containing 1 mol of LiClO ₄ . Alternatively, as the electrolyte, ethylene carbonate,
For a mixed solution of two or more of dimethyl carbonate, propylene carbonate, and diethyl carbonate, a solution containing LiClO ₄ can also be used.

In the present invention, LTP is used as the material for the negative electrode.
And LiCoO ₂ , LiNiO as a positive electrode material
Lithium secondary battery using ₂ or Li-LTP
Since the cell voltage is 4 V, the practical operating voltage is 3 V, the charging voltage and the discharging voltage are steady, it can be suitably used for portable electronic products (3 volts).

Hereinafter, the present invention will be described in more detail with reference to Examples. However, the following Examples do not limit the present invention, and all modifications that can be made without departing from the spirit of the present invention will be described. Within the technical scope of

[0015]

EXAMPLES In the following examples, test batteries shown in FIG. 3 were used. In the figure, reference numeral 10 denotes a glass tube. Specifically, circular caps 8, 8 'made of Teflon are screwed to ends 11, 11' with female threads, respectively. It has a structure with a smaller diameter. 1 and 7
Are stainless steel rods used as power supply lines for the negative current and the positive current, respectively. The diameter of these stainless steel rods 1 and 7 is substantially the same as the inner diameter of the glass tube 10 and has a threaded end 11,
As a result of being inserted into the glass tube 10 from 11 ′ through the circular caps 8 and 8 ′, a closed space 12 is formed. 2 is a copper collector, 3 is a negative electrode,
4 is a separator made of a permeable substance, 5 is a positive electrode, and 6 is an aluminum collector. The outer ends of the stainless steel rods 1 and 7 are respectively connected to electric wires (not shown) for inputting current from a power supply, and the sealed space 12 is filled with an electrolyte.

In Examples 2 and 3 below, the negative electrode 3
Means negative electrode powder [LTP powder: 85% by weight, acetylene black: 5% by weight, polyvinylidene fluoride (PVDF):
10% by weight] and an equivalent (w / w) of a solvent is prepared by applying the paste to an aluminum foil. The positive electrode 5 is prepared by applying a paste obtained by mixing LiCoO ₂ powder or LiNiO ₂ powder: 85% by weight, acetylene black: 5% by weight, and PVDF: 10% by weight to an aluminum foil. .

The electrolyte is prepared from an equivalent solution (v / v) of ethylene carbonate (EC) and dimethyl carbonate (DMC) or an equivalent solution (v / v) of propylene carbonate (PC) and diethyl carbonate (DEC). Used are each containing 1 mol of LiClO ₄ .

Example 1 In this example, experiments were conducted on the characteristics of lithium ion insertion and desorption from the LTP used in the present invention. In the test battery shown in FIG. 3, an equimolar solution (v / v) of EC and DMC containing lithium as the material for the negative electrode, LTP as the material for the positive electrode, and 1 mol of LiCLO ₄ as the electrolyte was used. The test battery has a cut-off voltage of 0.
The battery was charged at a current density of 0.4 mA / cm ² until the voltage reached 1 V, and then discharged at a current density of 0.2 mA / cm ² until the cut-off voltage reached 2.4 V. FIG. 4 is a graph showing the obtained charging curve and discharging curve.

As shown in FIG. 4, in the charging process, that is, in the process of inserting lithium ions, the operating voltage is quite steady and about 0.14.
In the discharging process, that is, in the process of desorbing lithium ions, the operating voltage was about 0.5 V, which was also steady. This indicates that the LTP used in the present invention has excellent lithium ion insertion and desorption characteristics.

Example 2 In the test battery shown in FIG. 3, LT
P, LiCoO ₂ or LiNiO as positive electrode material
_2. Equivalent solution (v / v) of EC and DMC to which 1 mol of LiClO ₄ was added as an electrolyte was used. The test cell was subjected to a current density of 0.8 mA / cm ² until the cutoff voltage reached 4 V.
And discharged at a current density of 0.4 mA / cm ² until the cutoff voltage reached 2.5 V.

FIG. 5 is a graph showing the obtained charging curve and discharging curve. As shown in FIG. 5, when LiCoO ₂ or LiNiO ₂ was used as the material for the positive electrode, in the discharge curves, after the operating voltage decreased from 4 V to 3 V, the operating voltage remained steady at 3 V.

FIG. 6 is a graph showing the relationship between the discharge capacity and the cycle in this embodiment. As shown in FIG. 6, when LTP was used as the negative electrode material and LiCoO ₂ was used as the positive electrode material, the average discharge capacity in the first 10 cycles was 200 mA.
h / g, and when LTP was used as the negative electrode material and LiNiO ₂ was used as the positive electrode material, the average discharge capacity in the first 10 cycles was 175 mAh / g. As is clear from the results, when LTP is used as the negative electrode material and LiNiO ₂ or LiCoO ₂ is used as the positive electrode material,
A discharge capacity in the range of 175 mAh / g to 225 mAh / g was obtained, and this value was almost the same as that obtained when carbon powder from coke was used as the negative electrode material, and was very good. .

Example 3 In the test battery shown in FIG. 3, LT
An equivalent solution (v / v) of PC and DEC to which P, LiCoO ₂ as a positive electrode material and 1 mol of LiClO ₄ as an electrolyte were added was used. The test battery was charged at a current density of 0.8 mA / cm ² until the cutoff voltage reached 4 V, and then the current density until the cutoff voltage reached 2.5 V:
Discharge was performed at 0.4 mA / cm ² .

FIG. 7 is a graph showing the relationship among the obtained discharge capacity, efficiency and cycle. As shown in FIG. 7, in the first 10 cycles, the average discharge capacity: about 195 mAh /
g, efficiency: very good results of about 60% were obtained, so that LTP was used as the negative electrode material and Li was used as the positive electrode material.
It can be seen that even when CoO ₂ is used and a mixed solution of PC and DEC is used as the electrolyte, the characteristics as a battery are extremely excellent.

[0025]

Since the lithium secondary battery of the present invention is constructed as described above, no dendritic crystals of lithium are formed during the charging and discharging processes, the operating voltage is high, the discharging capacity is large, and the discharging voltage is high. Is very excellent in characteristics as a battery, for example, is stable.

The LTP used in the present invention can be prepared by a hydrothermal reaction at a low temperature (180 ° C.) where the reaction step is easy, so that a high-purity product can be efficiently mass-produced. it can.

[Brief description of the drawings]

FIG. 1 is a schematic view of a pressurized reactor used for producing LTP.

FIG. 2 is a graph showing an X-ray diffraction pattern of LTP used in the present invention.

FIG. 3 is a schematic diagram showing the structure of a test battery used in this example.

FIG. 4 is a graph showing a charge curve and a discharge curve in Example 1.

FIG. 5 is a graph showing a charge curve and a discharge curve in Example 2.

FIG. 6 is a graph showing a relationship between a discharge capacity and a cycle in Example 2.

FIG. 7 is a graph showing the relationship among discharge capacity, efficiency, and cycle in Example 3.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Stainless steel rod 2 Copper collector 3 Negative electrode 4 Separator 5 Positive electrode 6 Aluminum collector 7 Stainless steel rod 8,8 'Circular cap 10 Glass tube 11,11' Female threaded end 12 Sealed Space 21 Stainless steel pressurized reactor 21a Stainless steel outer shell 21b Teflon lining layer 21c Stainless steel lid 21d Stainless steel spring

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-74457 (JP, A) JP-A-3-81908 (JP, A) JP-A-2-162605 (JP, A) CHEM. SOC. DALTON TRANS. 1989 No. 5pp. 829-835 (58) Fields surveyed (Int. Cl. ⁷ , DB name) H01M 4/58 C01B 25/37 JICST file (JOIS)

Claims (4)

(57) [Claims] 1. A layered titanium phosphate as a material for a negative electrode :
A lithium secondary battery using TiO (OH) (H ₂ PO ₄ ) . 2. The layered titanium phosphate comprises: (a) heating a mixture of tetramethylammonium hydroxide, titanium dioxide and phosphoric acid at a temperature of 150 ° C. or higher; and (b) subjecting the mixture to hydrogen cation exchange. 2. The lithium secondary battery according to claim 1, wherein the lithium secondary battery is obtained by (c) performing a vacuum heat treatment. 3. LiCoO ₂ or L as a positive electrode material
3. The lithium secondary battery according to claim 1, wherein iNiO ₂ is used. 4. An electrolyte according to claim 1, wherein each of the electrolytes is 1 mol of Li in an equivalent solution of ethylene carbonate and dimethyl carbonate (v / v) or an equivalent solution of propylene carbonate and diethyl carbonate (v / v).
The lithium secondary battery according to any one of claims 1 to 3 is intended to include ClO _4.