JPH0613108A - Nonaqueous electrolyte battery - Google Patents

Abstract

PURPOSE:To provide an excellent nonaqueous electrolyte battery which has no danger such as burst and fire during trouble in short by using solution that lithium salt is dissolved in phosphagen derivative or solution that lithium salt is dissolved in solvent that nonprotic organic solvent is further added to phosphagen derivative, as electrolyte. CONSTITUTION:In a nonaqueous electrolyte battery which is formed with a positive plate, a negative plate possible to occlude and emit lithium and nonaqueous electrolyte containing lithium ions, solution that lithium salt is dissolved in phosphagen derivative with the viscocity of 300cP or less at 25 deg.C or solution that lithium salt is dissolved in solvent that nonprotic organic solvent is further added to phosphagen derivative with the viscocity of 500cP or less at 25 deg.C is used as the electrolyte.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-aqueous electrolyte battery, and more particularly to a non-aqueous electrolyte which eliminates the risk of rupture and ignition at the time of short circuit, and at the same time achieves excellent battery performance such as high voltage and high discharge capacity. Regarding batteries.

[0002]

2. Description of the Related Art Non-aqueous electrolyte batteries have the characteristics of high voltage and high energy density and show excellent self-discharging property. In recent years, in particular, memory backup for AV / information devices such as personal computers and VTRs and those It has received a great deal of attention as a battery for driving power supplies. Nicad batteries are the mainstream as secondary batteries used for these applications, but various alternatives to non-aqueous electrolyte batteries have been tried as alternatives to the Nicad batteries, and some of them have been commercialized. Has been done.

Alkali metals, especially lithium metal and lithium alloys are often used as the material for forming the negative electrode of the above non-aqueous electrolyte battery. However, since they react violently with the aqueous electrolyte solution, for example, non-proton is used as the electrolyte. Non-aqueous electrolyte batteries based on organic solvents such as organic solvents have been used.

[0004]

Although the non-aqueous electrolyte battery has high performance as described above, it has a problem in safety. That is, the alkali metal used in the negative electrode of the non-aqueous electrolyte battery, especially lithium metal and lithium alloys, etc. are very highly active against water, for example, when the sealing of the battery is incomplete and water enters, the above-mentioned negative electrode material. And water may react with each other to generate hydrogen or ignite.

Lithium metal has a low melting point (about 170
Therefore, if a large current suddenly flows, such as during a short circuit,
It is feared that the battery will generate heat abnormally, which will cause a very dangerous situation such as melting of the battery. Furthermore,
As the battery heats up, the electrolyte based on the organic solvent is vaporized or decomposed, so that gas is generated, and there is a high risk that the gas may rupture or ignite the battery.

For example, an AA-type cylindrical battery is prepared by using a positive electrode made of an inorganic compound, a negative electrode made of lithium metal, and a solution prepared by dissolving a lithium salt in an organic solvent such as an aprotic organic solvent as an electrolytic solution. When external short-circuited, 150 ℃
The above heat generation is observed, and as a result, the battery may rupture and eventually ignite.

Therefore, as a method of ensuring the safety of the non-aqueous electrolyte battery, for example, in the case of a cylindrical battery, when the temperature rises and the internal pressure of the battery rises when the battery is short-circuited or overcharged, the safety valve is activated. At the same time, it has been proposed to provide the battery with a mechanism for preventing an excessive current of a predetermined current or more from flowing into the battery by breaking the electrode terminals.

However, not all such mechanisms are reliable, and if they do not work well, there is a concern that excessive heat will generate a large amount of heat, resulting in a dangerous state.
It is hard to say that sufficient safety is still secured.

From this point of view, a lead battery or a nicad battery which is an aqueous electrolyte battery is fundamentally devised and improved by fundamentally devising and improving the battery material, not by the safety measure by providing the incidental parts such as the safety valve as described above. It is expected that a non-aqueous electrolyte battery that exhibits the same level of safety as the above will appear.

The present invention has been made in view of the above circumstances.
An object of the present invention is to provide a non-aqueous electrolyte battery that suppresses vaporization and decomposition of an electrolytic solution at a relatively low temperature, at the same time reduces the risk of ignition and ignition, and has excellent battery performance.

[0011]

Means for Solving the Problems and Actions The inventors of the present invention have conducted extensive studies in order to achieve the above-mentioned object, and as a result, a positive electrode, a negative electrode capable of occluding / releasing lithium, and a non-aqueous electrolyte containing lithium ions were prepared. In the provided non-aqueous electrolyte battery, a solution in which a lithium salt is dissolved in a phosphazene derivative having a viscosity at 25 ° C. of 300 cP or less is used as the electrolyte, and the viscosity at 25 ° C. of 500 cP or less is used as the electrolyte. By using a solution in which a lithium salt is dissolved in a solvent prepared by adding an aprotic organic solvent to a phosphazene derivative, it is possible to suppress vaporization and decomposition of the electrolytic solution at a relatively low temperature, and at the same time reduce the risk of ignition and ignition. It is possible to obtain a non-aqueous electrolyte battery having excellent battery performance such as high voltage, high discharge capacity, and large current discharge property,
It was also found that when the phosphazene derivative and the aprotic solvent are mixed, the protic organic solvent coexists with the phosphazene derivative, so that it becomes difficult to burn and the rupture and ignition can be suppressed.

In other words, from the viewpoint of fundamentally ensuring the safety of the non-aqueous electrolyte battery, it is difficult to cause vaporization or decomposition at a temperature of 200 ° C. or lower, and if the negative electrode material, such as lithium, is melted, ignition occurs inside the battery. Focusing on inorganic polymer materials as a solvent that does not burn, and has conductivity equivalent to that of existing electrolytes, various searches were conducted, and a phosphazene derivative whose basic skeleton consisted of nitrogen and phosphorus was used as a constituent material of the electrolytic solution. It has been found that the above is very promising, and the present invention has been completed.

Conventionally, application of a phosphazene compound to a battery material has been an example of an all-solid battery using polyphosphazene (such as methoxyethoxyethoxypolyphosphazene and oligoethyleneoxypolyphosphazene) as a solid electrolyte. Although the combustion effect can be expected very much, the ionic conductivity is 1 compared to the usual liquid electrolyte.
/ 1000 to 1/10000, which is considerably low, and is limited to use at a limited low discharge current, and it is difficult to achieve excellent cycle characteristics. It is a new finding by the present inventor that the liquid phosphazene derivative is used as a constituent substance of the electrolytic solution as described above, and the conductivity and the excellent cycle characteristics equivalent to those of a normal liquid electrolyte are achieved.

Therefore, the present invention provides a non-aqueous electrolyte battery comprising a positive electrode, a negative electrode capable of occluding and releasing lithium, and a non-aqueous electrolyte containing lithium ions, wherein the electrolyte has a viscosity of 25 ° C. 300 cP (centipoise)
A solution obtained by dissolving a lithium salt in the following phosphazene derivative or a solution obtained by dissolving a lithium salt in a solvent obtained by further adding an aprotic organic solvent to the phosphazene derivative having a viscosity of 500 cP or less at 25 ° C. is used.

The present invention will be described in more detail below. As described above, the electrolyte of the non-aqueous electrolyte battery of the present invention is 25
A solution obtained by dissolving a lithium salt in a phosphazene derivative having a viscosity of 300 cP or less at 25 ° C or a solution of a lithium salt dissolved in a phosphazene derivative having a viscosity of 500 cP or less at 25 ° C and further adding an aprotic organic solvent is used. is there.

Here, as the phosphazene derivative which is the electrolyte solvent, for example, chlorine of (NPCl ₂ ) _n is substituted with various substituents R (NPR ₂ ) _n (where n is 3 to 15). A cyclic phosphazene derivative represented, having a chain bond of phosphoric acid and nitrogen in the basic skeleton, and having a side chain group R added to phosphorus, for example (R ₃ (P = N) _m -PR ₄ ) (however,
m is 1 to 20 and R is a monovalent organic group, or is selected from O and C).

In this case, the substituent or the side chain group R is a monovalent organic group, and by appropriately selecting R, a solvent having an appropriate viscosity that can be used as an electrolytic solution and a solubility suitable for mixing. Can be synthesized. Although the dissolution mechanism of the lithium salt in the phosphazene solvent is still unknown,
The phosphazene derivative is desired to have a solution form having a relatively low viscosity and a structure capable of favorably dissolving a lithium salt. For this reason, it is advantageous that the substituent or the side chain group R contains an ether bond, and such R is an alkoxy group such as an ethoxy group, a propoxy group, a butoxy group, a methoxyethoxyethoxy group, or an alkoxy-substituted alkoxy group. Further, it is also possible to replace hydrogen in the above substituents or side chain groups with a halogen element such as fluorine or boron.

For example, a cyclic phosphazene derivative (N
The phosphazene derivative in which R is a propoxy group in PR ₂ ) ₃ has a viscosity of 60 cP at 25 ° C. and can be a suitable solvent as an electrolytic solution, and the solubility of a lithium salt is about 0.5 per 1 kg of the phosphazene derivative. It can be used up to a mole, and can exhibit extremely good lithium ion conductivity comparable to general organic solvent-based electrolytes.

On the other hand, in a chain type phosphazene derivative having a chain bond of phosphorus and nitrogen in the basic skeleton, one having a propoxy group added to both ends of the P = NP structure has a structure of 25
The viscosity at ℃ can be reduced to about 30 cP,
That is, lower viscosity can be achieved as compared with the above-mentioned cyclic type, and at the same time, solubility of lithium salt up to about 1 mol per 1 kg of phosphazene derivative can be obtained. From the above, it is preferable to use a chain type phosphazene derivative as the electrolyte.

The above phosphazene derivative has a viscosity of 300 at 25 ° C. when an aprotic organic solvent is not used.
Centipoise (cP) or less, particularly 100 cP or less is used. When the viscosity of the phosphazene derivative exceeds 300 cP, the lithium salt becomes difficult to dissolve, and the positive electrode material,
At the same time that the wettability to the separator is reduced, the ionic conductivity is significantly reduced due to an increase in the viscous resistance of the solution, and the performance becomes insufficient when used at a temperature below the freezing point.

In the present invention, a mixture of the above phosphazene derivative and an aprotic organic solvent may be used as an electrolyte solution solvent. In this case, the aprotic organic solvent is not particularly limited, but for example, ether compounds such as 1,2-dimethoxyethane, tetrahydrofuran and propylene carbonate, ester compounds and the like are preferably used.

The phosphazene derivative used here may be the same as described above, but the viscosity at 25 ° C. is 500 cP or less, particularly 300 cP or less. If the viscosity exceeds 500 cP, the viscosity becomes high even after mixing with the aprotic organic solvent, and thus it becomes difficult to achieve optimum ionic conductivity as a non-aqueous electrolyte battery.

The proportion of the phosphazene derivative to be mixed with the aprotic solvent is preferably 50% or more and 90% or less in terms of volume fraction with respect to the entire mixed solvent. If the proportion of the phosphazene derivative is less than 50%, the effect of suppressing battery rupture and ignition may not be sufficient. On the other hand, if this ratio exceeds 90%, the viscosity of the solution increases as it becomes closer to the case where the phosphazene derivative is used alone. Therefore, when a phosphazene derivative having a viscosity at 25 ° C. of more than 300 cP is used, a large current discharge is generated. It becomes difficult to obtain lithium ion conductivity suitable for the above, and the performance may be insufficient when used at a low temperature below the freezing point.

The lithium salt used as the lithium ion source, that is, the lithium salt dissolved in the phosphazene derivative alone solvent or the mixed solvent of the phosphazene derivative and the aprotic solvent is not particularly limited, but LiC
lO ₄ , LiBF ₄ , LiPF ₆ , LiCF ₃ SO ₃ and L
One or two or more selected from iAsF ₆ are preferably used. The amount of the lithium salt added is preferably 0.2 to 1 mol with respect to 1 kg of the solvent.

As the positive electrode material of the battery, V ₂ O ₅ , V
It is possible to use metal oxides such as ₆ O ₁₃ , MnO ₂ , MoO ₃ , and LiCoO ₂ , metal sulfides such as TiS ₂ and MoS ₂ , and conductive polymers such as polyaniline.

The negative electrode material contains lithium. Specifically, lithium metal, an alloy of lithium and aluminum, indium, lead, zinc, etc., a carbon material such as lithium-doped graphite, etc. may be used. it can.

In the non-aqueous electrolyte battery of the present invention, a separator may be interposed between the positive and negative electrodes to prevent a short circuit of current due to contact between both electrodes. Examples of the separator include materials that can surely prevent contact between both electrodes, and that allow or include an electrolytic solution, such as polytetrafluoroethylene, polypropylene, synthetic resin non-woven fabric such as polyethylene, and thin film. I can, but
Particularly, a microporous film made of polypropylene or polyethylene having a thickness of about 20 to 50 μm is preferably used.

As the other constituent members of the battery of the present invention, those normally used can be used without any trouble. In addition, the form of the battery is not particularly limited, and various forms such as a coin type, a button type, a paper type, a prismatic type or a spiral type cylindrical battery can be adopted.

[0029]

EXAMPLES The present invention will be specifically described below by showing Examples and Comparative Examples, but the present invention is not limited to the following Examples.

[Examples 1 to 3, Comparative Examples 1 and 2] Chemical formula L
Using vanadium oxide represented by iV ₃ O ₈ as a positive electrode active material, 10 parts of acetylene black as a conduction aid and 10 parts of Teflon binder as a binder were added to 100 parts of LiV ₃ O ₈ and an organic solvent was added. After kneading with (50/50 volume% mixed solvent of ethyl acetate and ethanol), roll-rolling was performed to prepare a thin layer positive electrode sheet having a thickness of 100 μm and a width of 40 mm.

Next, using an aluminum foil having a thickness of 25 μm as a current collector, the current collector whose surface was coated with a conductive adhesive was sandwiched between the two positive electrode sheets, and a thickness of 25 μm was applied to the current collector.
A lithium metal foil having a thickness of 150 μm was superposed and rolled up with a separator made of a polypropylene microporous film having a thickness of m, and rolled up to form a spiral structure electrode. At this time, the positive electrode length was about 260 mm.

This spiral structure electrode was housed in an AA type container, and LiP was added to each of the five kinds of electrolytic solution solvents shown in Table 1.
An electrolyte in which F ₆ was dissolved at a concentration of 0.5 mol / kg was injected and sealed, and 5 types of AA-type lithium batteries were assembled, 10 each.

Here, phosphazene-No. Which is the phosphazene derivative used as the solvent for the electrolytic solution. 1 is a chlorine of (NPCl ₂ ) _n (where n is 3 to 5) having a cyclic structure,
It was obtained by substituting with an OCH ₂ CH ₂ CH ₃ group. Phosphazene No. 2, in having a chain structure _{^{(R 1 3 P = N-}} P (O) R 2 2), R 1 is -OC
The H ₂ CF ₃ group and the one in which R ² is a —OC ₂ H ₅ group were used. In addition, phosphazene No. Nos. 3 and 4 are Nos. (NPCl ₂ ) _n having the same cyclic structure as 1 (where n is 3 to
Chlorine _{5) -CH 2 CF 2 CF 3} , and -OCH ₂ CF ₂
It was obtained by substituting with a CF ₂ CF ₂ CF ₂ H group.

The initial battery characteristics (voltage, internal resistance) of the five types of batteries manufactured as described above were evaluated,
In addition, charge / discharge cycle performance, high rate discharge property (current dependency of discharge capacity), and safety were evaluated by the following evaluation methods. The results are shown in Table 1.

(Evaluation Method) Charge / Discharge Cycle Characteristics Upper limit voltage 3.0 V, lower limit voltage 2.0 V, discharge current 100
Charging and discharging were repeated up to 50 cycles under the conditions of mA and charging current of 50 mA, and the capacity retention ratio to the initial value at that time was examined, and the average value of three batteries was shown.

High- rate discharge property 5 cycles of charge and discharge were performed, and after charging to 3.0 V,
First discharge at 50mA, recharge, then 500m
A was discharged. Do this for every two batteries,
The discharge capacity at each current value was obtained, and the capacity retention rate was obtained from (discharge capacity at discharge at 500 mA) / (discharge capacity at discharge at 500 mA).

Safety After charging and discharging for 5 cycles and charging to 3.0V,
Both the positive and negative electrodes were connected with lead wires, short-circuited externally, and the appearance of the battery and the presence or absence of burst ignition were checked using 5 batteries.

[0038]

[Table 1]

As shown in Table 1, the conventional battery using the organic solvent as the electrolyte solvent (Comparative Example 2) causes liquid leakage, rupture, and ignition at the time of short circuit, whereas it has an appropriate viscosity. Batteries using the phosphazene derivative as the electrolyte solvent (Examples 1 to 3) are extremely safe with no abnormality at the time of short circuit, and regarding battery performance, compared with conventional batteries using an organic solvent. It turns out that it is not inferior.

In particular, in Example 2 using the phosphazene derivative having a chain structure, it is recognized that the internal resistance is low and the battery performance is the best.

Further, a battery using a phosphazene derivative having a viscosity of more than 300 cP as an electrolyte solvent (Comparative Example 1).
No abnormalities such as ignition were observed at the time of short circuit as in Examples 1 to 3, but since the solvent viscosity was too high, the discharge capacity under large current was considerably reduced and the cycle performance tended to be poor.

[Examples 4 to 7, Comparative Example 3] Examples 1 to 3
A positive electrode material and a negative electrode material similar to the above, and an electrolyte in which LiPF ₆ is dissolved in each of the five kinds of electrolytic solution solvents shown in Table 2 at a concentration of 0.5 mol / kg are used and have the same structure as in Examples 1 to 3. Ten batteries were assembled for each type of the electrolyte solvent.

Here, as the phosphazene derivative, in Examples 4 to 6, chlorine of (NPCl ₂ ) _n (where n is 3 to 5) having a cyclic structure is substituted with a —OCH ₂ CH ₂ CH ₃ group. R in which with those obtained, having a chain structure in example _{^{7 (R 1 3 P = N}} -P (O) R 2 2) by
Those in which ¹ is a —CH ₂ CF ₃ group and R ² is a —OC ₂ H ₅ group were used.

As the aprotic solvent to be mixed with the phosphazene derivative, 1,2-dimethoxyethane was selected and the mixing ratio with the phosphazene derivative was changed to prepare an electrolytic solvent solution. The electrolyte solvent used in Comparative Example 3 consisted only of an aprotic solvent, and a mixture of 1,2-dimethoxyethane and propylene carbonate was used.

The same evaluation as in Example 1 was carried out on the five types of batteries produced as described above. The results are also shown in Table 2.

[0046]

[Table 2]

As shown in Table 2, a battery using an electrolytic solution solvent containing only an aprotic organic solvent (Comparative Example 3).
Causes liquid leakage, rupture, and ignition at the time of short circuit, whereas batteries using a mixture of a phosphazene derivative and an aprotic organic solvent as an electrolyte solvent (Examples 4 to 7)
It is clear that there is no abnormality at all even when a short circuit occurs, and it is very safe, and the battery performance is not inferior to the conventional battery using the organic solvent.

In particular, when comparing Example 6 and Example 7 having the same mixing ratio with the aprotic solvent, Example 7 using a phosphazene derivative having a chain structure has a cyclic structure. It is recognized that an electrolytic solvent having a lower viscosity than that of Example 6 in which the above is used can be obtained, and that a more excellent level of battery performance can be achieved.

[0049]

INDUSTRIAL APPLICABILITY The non-aqueous electrolyte battery of the present invention uses, as an electrolyte, a solution in which a lithium salt is dissolved in a phosphazene derivative or a solution in which a lithium salt is dissolved in a solvent in which an aprotic organic solvent is further added to the phosphazene derivative. Therefore, even if an abnormality such as a short circuit occurs, there is no risk of rupture or ignition, and excellent battery performance can be achieved.

Claims (3)

[Claims] 1. A non-aqueous electrolyte battery comprising a positive electrode, a negative electrode capable of inserting and extracting lithium, and a non-aqueous electrolyte containing lithium ions, wherein the electrolyte is 25 ° C.
A non-aqueous electrolyte battery comprising a solution of a lithium salt dissolved in a phosphazene derivative having a viscosity of 300 cP or less. 2. The battery according to claim 1, wherein a solution in which a lithium salt is dissolved in a solvent obtained by adding an aprotic organic solvent to a phosphazene derivative having a viscosity of 500 cP or less at 25 ° C. is used as the electrolyte. Characteristic non-aqueous electrolyte battery. 3. The battery according to claim 1, wherein the phosphazene derivative is (NPR ₂ ) _n (wherein R is a monovalent organic group, and n is 3 to 15), or a cyclic phosphazene derivative. R having a chain bond of nitrogen and nitrogen in the skeleton
₃ (P = N) _m -PR ₄ (wherein m is 1 to 20 and R is selected from a monovalent organic group, O or C) and is a chain-type phosphazene derivative. And a non-aqueous electrolyte battery.