JP4306858B2 - Solute for non-aqueous electrolyte battery and non-aqueous electrolyte battery - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a non-aqueous electrolyte battery comprising a positive electrode, a negative electrode, and a non-aqueous electrolyte, and a solute used in the non-aqueous electrolyte in the non-aqueous electrolyte battery. The solute used in the non-aqueous electrolyte is improved. In particular, it is characterized by suppressing the dissociation of the solute at high temperatures and reacting with the electrode, thereby improving the storage characteristics of the nonaqueous electrolyte battery at high temperatures.
[0002]
[Prior art]
In recent years, high-electromotive force non-aqueous electrolyte batteries using a non-aqueous electrolyte and utilizing oxidation and reduction of lithium have come into use as new batteries with high output and high energy density.
[0003]
Here, in such a nonaqueous electrolyte battery, a solute such as lithium hexafluorophosphate LiPF ₆ or lithium perchlorate LiClO _{4 is} generally dissolved in a solvent such as propylene carbonate or dimethyl carbonate as the nonaqueous electrolyte. However, solutes such as lithium perchlorate LiClO ₄ have problems in terms of safety and the like, and at high temperatures, such solutes react with electrodes to cause self-discharge, When the nonaqueous electrolyte battery is charged and stored at a high temperature, there is a problem that the capacity decreases.
[0004]
In recent years, as disclosed in Japanese Patent Application Laid-Open No. 61-214375, lithium tetraphenylborate purified by recrystallization in an organic solvent has been used as a solute of a nonaqueous electrolytic solution. Proposed.
[0005]
However, even when lithium tetraphenylborate is used as the solute of the non-aqueous electrolyte, the solute is easily dissociated in the non-aqueous electrolyte. When the nonaqueous electrolyte battery is stored in a charged state, the capacity is reduced.
[0006]
[Problems to be solved by the invention]
An object of the present invention is to solve the above problems in a non-aqueous electrolyte battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, and as a solute used in the non-aqueous electrolyte at a high temperature. It provides a solute that rarely dissociates and reacts with the electrode, and when such a solute is used in a non-aqueous electrolyte battery and the non-aqueous electrolyte battery is charged and stored at high temperature, the non-aqueous electrolyte An object of the present invention is to prevent a decrease in the capacity of an electrolyte battery and to obtain a nonaqueous electrolyte battery excellent in storage characteristics at high temperatures.
[0007]
[Means for Solving the Problems]
Oite the non-aqueous electrolyte batteries in the first aspect of the present invention, in order to solve the above problems, in the non-aqueous electrolyte battery comprising a positive electrode, a negative electrode and a nonaqueous electrolyte, the negative electrode in the negative electrode As a material, a carbon material is used, and as a solute in the above non-aqueous electrolyte, an alkoxy group is bonded to lithium borate, and at least a part of hydrogen in the alkoxy group is substituted with fluorine. The solute for non-aqueous electrolyte batteries is used.
[0008]
In the solute for a non-aqueous electrolyte battery according to claim 1, the alkoxy group is firmly bonded to boron, and this prevents the solute from being dissociated in the non-aqueous electrolyte, particularly at high temperatures. This solute is stably present in the non-aqueous electrolyte and is less likely to react with the electrode.
[0009]
Further, Oite the alkoxy group described above, the use of which at least part of the hydrogen is substituted with fluorine, the solute is difficult to be reduced, is further inhibited from the solute to react with the negative electrode in charged state It becomes like this.
[0010]
Here, as the nonaqueous electrolyte battery solute at least a part of hydrogen definitive alkoxy group attached to the lithium borate is substituted with fluorine as described above, for example, tetrakis (trifluoromethoxy) lithium borate, At least one hydrogen in an alkoxy group such as lithium tetrakis (2,2,2-trifluoroethoxy) borate, lithium tetrakis (pentafluoroethoxy) borate, lithium bis (trifluoromethoxy) bis (pentafluoroethoxy) borate The part is substituted with fluorine.
[0012]
Here, when the solute for a non-aqueous electrolyte battery described in claim 1 is used as the solute in the non-aqueous electrolyte solution as in the non-aqueous electrolyte battery according to claim 1 of the present invention, the solute is obtained as described above. Dissociation in the non-aqueous electrolyte is suppressed, and in particular, this solute is stably present in the non-aqueous electrolyte even at high temperatures, and this solute is prevented from reacting with the electrode and self-discharging. When the nonaqueous electrolyte battery is stored in a charged state at a high temperature, the capacity is prevented from decreasing, and the storage characteristics at a high temperature are improved.
[0013]
The non-aqueous electrolyte battery of the present invention is characterized by the solute used in the non-aqueous electrolyte as described above, and the solvent used in the non-aqueous electrolyte and the materials constituting the positive electrode and the negative electrode are particularly limited. What is generally used in the nonaqueous electrolyte battery can be used.
[0014]
Here, examples of the solvent used for the non-aqueous electrolyte include cyclic carbonates such as ethylene carbonate, propylene carbonate, vinylene carbonate, and butylene carbonate, and non-cyclic carbonates such as dimethyl carbonate, diethyl carbonate, and methyl ethyl carbonate. Alternatively, solvents such as 1,2-diethoxyethane, 1,2-dimethoxyethane, ethoxymethoxyethane and the like can be used alone or in admixture of two or more. In particular, when a mixed solvent obtained by mixing the above cyclic carbonate and acyclic carbonate is used as the solvent in the non-aqueous electrolyte, the ionic conductivity in the non-aqueous electrolyte is improved and the non-aqueous electrolyte is In the above, the dissociation of the solute is further suppressed, and the storage characteristics at a high temperature are further improved.
[0015]
In the non-aqueous electrolyte battery according to the present invention, a polymer can be impregnated with a non-aqueous electrolyte solution in which the above-described solute is dissolved in the solvent as described above to be used as a gel polymer electrolyte.
[0016]
In the nonaqueous electrolyte battery of the present invention, examples of the positive electrode material constituting the positive electrode include manganese dioxide, lithium-containing manganese oxide, lithium-containing cobalt oxide, lithium-containing vanadium oxide, lithium-containing nickel oxide, Lithium-containing iron oxide, lithium-containing chromium oxide, lithium-containing titanium oxide and the like are used.
[0017]
In the non-aqueous electrolyte battery of the present invention, the negative electrode material constituting the negative electrode may be metal lithium, Li—Al, Li—In, Li—Sn, Li—Pb, Li—Bi, Li—Ga, Li -Sr, Li-Si, Li-Zn, Li-Cd, Li-Ca, Li-Ba, and other lithium alloys; Lithium ion occlusion and release-capable graphite, coke, organic-containing materials such as organic fired bodies, Metal oxides such as SnO ₂ , SnO, TiO, Nb ₂ O _{3 and the} like having a lower potential than the positive electrode material can be used. In particular, as shown in claim 1, when a carbon material is used as the negative electrode material, A non-aqueous electrolyte containing a solute of the above forms a coating with excellent ionic conductivity on the surface of the carbon material, and this coating further suppresses the negative electrode from reacting with the non-aqueous electrolyte. Non-aqueous electrolyte Storage characteristics at high temperature in the pond is remarkably improved.
[0018]
【Example】
Hereinafter, the solute for a nonaqueous electrolyte battery according to the present invention and the nonaqueous electrolyte battery using the solute will be specifically described with reference to examples, and the nonaqueous electrolyte battery in this example is stored at high temperature. It will be clarified by a comparative example that the decrease in capacity in this case is reduced and the storage characteristics at high temperature are improved. In addition, the solute for nonaqueous electrolyte battery and the nonaqueous electrolyte battery according to the present invention are not limited to those shown in the following examples, and can be implemented with appropriate modifications within the scope not changing the gist thereof. is there.
[0019]
( Reference Example 1 )
In Reference Example 1 , a positive electrode and a negative electrode were prepared as follows, and a non-aqueous electrolyte was prepared as follows. As shown in FIG. 1, the diameter was 14 mm, the height was 50 mm, the battery A cylindrical lithium secondary battery with a capacity of 400 mAh was produced.
[0020]
[Production of positive electrode]
In producing the positive electrode, LiCoO ₂ powder was used as a positive electrode material, and this LiCoO ₂ powder and acetylene black powder as a conductive agent were mixed at a weight ratio of 90: 6 to prepare a positive electrode mixture. .
[0021]
Then, a solution in which polyvinylidene fluoride (hereinafter abbreviated as PVdF) as a binder is dissolved in N-methyl-2-pyrrolidone (hereinafter abbreviated as NMP) is added to the positive electrode mixture, The positive electrode mixture and PVdF were made to have a weight ratio of 96: 4, kneaded to prepare a slurry, and this slurry was applied to both surfaces of a positive electrode current collector made of aluminum foil by a doctor blade method. Was vacuum dried at 150 ° C. for 2 hours to produce a positive electrode.
[0022]
[Production of negative electrode]
In producing the negative electrode, natural graphite powder was used as the negative electrode material, and a solution obtained by dissolving PVdF as a binder in NMP was added to the natural graphite powder, so that the weight of the natural graphite powder and PVdF was 96: 4. The slurry is kneaded to prepare a slurry, and this slurry is applied to both surfaces of a copper foil as a negative electrode current collector by a doctor blade method, and this is vacuum-dried at 150 ° C. for 2 hours to obtain a negative electrode. Produced.
[0023]
[Preparation of non-aqueous electrolyte]
In preparing the non-aqueous electrolyte, a 1: 1 volume ratio of ethylene carbonate (hereinafter abbreviated as EC) which is a cyclic carbonate and diethyl carbonate (hereinafter abbreviated as DEC) which is a non-cyclic carbonate. Lithium tetramethoxyborate LiB (OCH ₃ ) ₄ was dissolved at a rate of 1 mol / l in the mixed solvent mixed in step 1 to prepare a non-aqueous electrolyte.
[0024]
[Production of battery]
In producing a battery, as shown in FIG. 1, a polyethylene microporous film is interposed as a separator 3 between the positive electrode 1 and the negative electrode 2 produced as described above, and these are wound in a spiral shape. In the battery can 4, the nonaqueous electrolyte solution is injected into the battery can 4 and sealed, and the positive electrode 1 is connected to the positive electrode lid 5 through the positive electrode lead 1 a, while The negative electrode 2 was connected to the battery can 4 via the negative electrode lead 2a, and the battery can 4 and the positive electrode lid 5 were electrically insulated by the insulating packing 6 to obtain a lithium secondary battery.
[0025]
( Reference Examples 2-7, Examples 1-4, Reference Examples 8-13 )
In the lithium secondary batteries of Reference Examples 2 to 7, Examples 1 to 4, and Reference Examples 8 to 13 , only the solute used in the case of the lithium secondary battery of Reference Example 1 and the preparation of the nonaqueous electrolyte solution. Otherwise, a cylindrical lithium secondary battery was produced in the same manner as in Reference Example 1 above.
[0026]
Here, in Reference Examples 2 to 7, Examples 1 to 4, and Reference Examples 8 to 13 , the solute in the non-aqueous electrolyte solution is LiB (CH ₃ ) in Reference Example 2 as shown in Table 1 below. the (OCH _{3) 3,} and _{LiB (CH 3) 2 (OCH} 3) 2 in reference example 3, the _{LiB (CH 3) 3 (OCH} 3) in reference example 4, in the reference example 5 LiB (OC the ₂ H _{5) 4,} the LiB (OC ₃ H _{7) 4} in reference example 6, the LiB (OC ₄ H _{9) 4} in reference example 7, the LiB (OCF _{3) 4} in example 1, the LiB (OCH ₂ CF _{3) 4} in example 2, the LiB (OC ₂ F _{5) 4} in example 3, example in _{4 LiB (OCF 3) 2 (} OC 2 F 5) 2, In Reference Example 8 , LiB (OC ₆ H ₅ ) ₄ is used. In Reference Example 9 , LiB (OC ₆ H _{4 is used.} CH _{3) 4,} and Reference Example 10 _{LiB (OC 6 H 3 (CH} 3) 2) 4 and the LiB (OC ₆ F _{5) 4} in Reference Example 11, LiB in Reference Example 12 (OC ₆ H ₄ CF ₃ ) ₄ was used as LiB (OC ₆ H ₃ (CF ₃ ) ₂ ) ₄ in Reference Example 13 .
[0027]
(Comparative Examples 1-3)
Also in the lithium secondary batteries of Comparative Examples 1 to 3, only the solute used in the preparation of the non-aqueous electrolyte in the case of the lithium secondary battery of Reference Example 1 above was changed, and for the other cases, the above-mentioned Reference A cylindrical lithium secondary battery was produced in the same manner as in Example 1 .
[0028]
Here, in Comparative Examples 1-3, as shown in Table 1 below, LiPF ₆ in Comparative Example 1, LiB (CH ₃ ) ₄ in Comparative Example 2, In Comparative Example 3, LiB (C ₆ H ₅ ) ₄ was used.
[0029]
Each of the lithium secondary batteries of Reference Examples 1 to 7, Examples 1 to 4, Reference Examples 8 to 13, and Comparative Examples 1 to 3 is charged to 1 V / cm ^{2 with} a charging current of 1 mA / cm ^2. After charging, the battery is discharged at a discharge current of 1 mA / cm ^{2 to} a discharge end voltage of 3 V, the discharge capacity Q0 before storage is measured, and each lithium secondary battery is charged at a charge current of 1 mA / cm ^2. After charging to a voltage of 4.2 V, each lithium secondary battery is stored in a 60 ° C. temperature atmosphere for 1 month, and then discharged to a discharge end voltage of 3 V at a discharge current of 1 mA / cm ² to discharge after storage. The capacity Q1 was measured, the reduction rate of the discharge capacity after storage (capacity reduction rate) was determined by the following formula, and the results are shown in Table 1 below.
Capacity reduction rate (%) = [(Q0−Q1) / Q0] × 100
[0030]
[ Table 1 ]
[0031]
As is clear from these results, each of the lithium secondary batteries of Reference Examples 1 to 7 using a solute in which an alkoxy group is bonded to lithium borate as a solute in the nonaqueous electrolytic solution does not satisfy the requirements of the present invention. Compared to each of the lithium secondary batteries of Comparative Examples 1 to 3 using a low capacity reduction rate when stored for 1 month in a 60 ° C. temperature atmosphere, the storage characteristics at high temperatures were improved. . Further, each of the lithium secondary batteries of Examples 1 to 4 in which at least a portion of the hydrogen definitive alkoxy groups above attached to the lithium borate is substituted with fluorine, hydrogen in the corresponding alkoxy and this induction group The storage characteristics at high temperatures were further improved compared to those in which is not substituted with fluorine.
[0032]
( Examples 5 to 14 )
In the lithium secondary batteries of Examples 5 to 14 , in the preparation of the non-aqueous electrolyte in Reference Example 1 above, the same LiB (OCF ₃ ) ₄ as in Example 1 was used as the solute, The solvent in the aqueous electrolyte was changed as shown in Table 2 below, and a cylindrical lithium secondary battery was produced in the same manner as in Reference Example 1 except that.
[0033]
Here, as a solvent in the nonaqueous electrolytic solution, to use a mixed solvent of a cyclic carbonate and a non-cyclic carbonic ester in Examples 5-8 In Example 5 Propylene carbonate (hereinafter, abbreviated as PC.) and a DEC 1: a mixed solvent obtained by mixing at a volume ratio of butylene carbonate (hereinafter, abbreviated as BC.) in example 6 and the DEC 1: a mixed solvent obtained by mixing at a volume ratio, implemented In Example 7 , a mixed solvent in which EC and dimethyl carbonate (hereinafter abbreviated as DMC) were mixed at a volume ratio of 1: 1. In Example 8 , EC and ethyl methyl carbonate (hereinafter abbreviated as EMC) were used. Were mixed in a volume ratio of 1: 1. On the other hand, only EC in Example 9 , only DEC in Example 10 , only 1,2-dimethoxyethane (hereinafter abbreviated as DME) in Example 11 , and EC and DME in Example 12 were used. In Example 14 , a mixed solvent in which EC and tetrahydrofuran (hereinafter abbreviated as THF) were mixed in a 1: 1 volume ratio was mixed in Example 14 . Is a mixed solvent in which γ-butyrolactone (hereinafter abbreviated as γ-BL) and DEC are mixed at a volume ratio of 1: 1.
[0034]
And also about each lithium secondary battery of these Examples 5-14 , said lithium secondary battery of said reference examples 1-7, Examples 1-4, Reference examples 8-13, and Comparative Examples 1-3. Similarly to the case, the discharge capacity Q0 before storage and the discharge capacity Q1 after storing each lithium secondary battery in a temperature atmosphere at 60 ° C. for 1 month are measured to obtain the above capacity reduction rate. The results are shown in Table 2 below together with the above Example 1.
[0035]
[ Table 2 ]
[0036]
As is apparent from this result, the solute of the non-aqueous electrolyte, with the LiB (OCF _{3) 4} satisfying the requirements of this invention is used, it performed using a mixed solvent of a cyclic carbonate and a non-cyclic carbonate in the solvent Each lithium secondary battery of Examples 1 to 5-8 is 60 ° C. in comparison with each lithium secondary battery of Examples 9 to 14 using a solvent other than a mixed solvent of a cyclic carbonate and an acyclic carbonate. The capacity reduction rate when stored for 1 month in a temperature atmosphere was further reduced, and the storage characteristics at high temperatures were further improved.
[0037]
( Reference Examples 14 and 15 and Comparative Examples 4 and 5)
In the reference example 14 and 15, solute used when the same LiB (OCF _{3) 4} in the example 1 in the non-aqueous electrolytic solution, also as a negative electrode material in the anode, as shown in Table 3 below, reference In Example 14 , lithium metal was used, and in Reference Example 15 , a Li—Al alloy was used. Otherwise, a cylindrical lithium secondary battery was produced in the same manner as in Reference Example 1 above.
[0038]
In Comparative Examples 4 and 5, the same LiPF ₆ as in Comparative Example 1 was used as the solute in the nonaqueous electrolytic solution, and as the negative electrode material in the negative electrode, Comparative Example 4 was used as shown in Table 3 below. In Example 5, a lithium metal was used, and in Comparative Example 5, a Li—Al alloy was used. Otherwise, a cylindrical lithium secondary battery was fabricated in the same manner as in Reference Example 1 above.
[0039]
And also about each lithium secondary battery of these reference examples 14 and 15 and comparative examples 4 and 5, said reference examples 1-7, Examples 1-4, reference examples 8-13, and comparative examples 1-3. Similarly to the case of each lithium secondary battery, the discharge capacity Q0 before storage and the discharge capacity Q1 after storage of each lithium secondary battery in a temperature atmosphere at 60 ° C. for one month are measured, and the above capacity is obtained. The reduction rate was determined, and the results are shown in Table 3 below together with the above Example 1 and Comparative Example 1.
[0040]
[Table 3]
[0041]
As is clear from this result, as shown in Reference Examples 14 and 15 and Comparative Examples 4 and 5, when a lithium metal other than graphite or a Li-Al alloy was used as the negative electrode material, the solute in the nonaqueous electrolyte solution Each of the lithium secondary batteries of Reference Examples 14 and 15 using LiB (OCF ₃ ) ₄ satisfying the requirements of the invention is ₆₀ % as compared with each of the lithium secondary batteries of Comparative Examples 4 and 5 using LIPF ₆ as a solute. The capacity reduction rate when stored for 1 month in a temperature atmosphere of ° C. was low, and the storage characteristics at high temperature were improved.
[0042]
Further, when Example 1 and each of the lithium secondary batteries of Reference Examples 14 and 15 were compared, the lithium secondary battery of Example 1 using graphite as the negative electrode material was different from lithium metal other than graphite or Li— The improvement in storage characteristics at high temperatures was greater than in the lithium secondary batteries of Reference Examples 14 and 15 using an Al alloy.
[0043]
【The invention's effect】
As described above in detail, as a non-aqueous electrolyte battery solute in the present invention, an alkoxy group is coupled to a lithium borate, used as at least a part of hydrogen definitive the alkoxy group is substituted by fluorine Thus, dissociation of the solute in the non-aqueous electrolyte is suppressed, and the solute is stably present in the non-aqueous electrolyte even at a high temperature, and the reaction with the electrode is reduced.
[0044]
And, when the solute for non-aqueous electrolyte battery as described above is used as the solute of the non-aqueous electrolyte battery, it is suppressed that the solute is dissociated in the non-aqueous electrolyte as described above. When the solute is present stably in the non-aqueous electrolyte and the solute reacts with the electrode to prevent self-discharge, and when the non-aqueous electrolyte battery is stored in a charged state at a high temperature, However, the storage capacity at high temperatures was improved.
[Brief description of the drawings]
FIG. 1 is a schematic cross-sectional view showing the internal structure of a lithium secondary battery produced in Examples and Comparative Examples of the present invention.
[Explanation of symbols]
1 Positive electrode 2 Negative electrode

Claims (2)

In a non-aqueous electrolyte battery including a positive electrode, a negative electrode, and a non-aqueous electrolyte, a carbon material is used as a negative electrode material in the negative electrode, and an alkoxy group is bonded to lithium borate as a solute in the non-aqueous electrolyte. becomes non-aqueous electrolyte battery, wherein at least a portion of the hydrogen definitive alkoxy group with solute for non-aqueous electrolyte battery characterized by comprising substituted with fluorine.   2. The nonaqueous electrolyte battery according to claim 1, wherein the carbon material is graphite.