JP6183830B2 - Non-aqueous electrolyte additive, flame retardant non-aqueous electrolyte, non-aqueous electrolyte secondary battery - Google Patents

Description

The present invention relates to a novel partially fluorinated vinyl phosphate ester compound useful as an additive for a non-aqueous electrolyte, an additive for a non-aqueous electrolyte comprising the compound, a non-aqueous electrolyte containing the additive, and the non-aqueous The present invention relates to a non-aqueous electrolyte secondary battery including an electrolyte.
The non-aqueous electrolyte solution of the present invention has excellent flame retardancy (self-extinguishing property), and the non-aqueous electrolyte secondary battery including the non-aqueous electrolyte solution has a temperature higher than room temperature, particularly 45 ° C. or higher. Excellent charge / discharge characteristics at temperature.

  Lithium batteries are very useful because of their high energy density, and various companies are actively investigating them. By repeating charge and discharge, lithium dissolved in the electrolyte is uniformly distributed on the negative electrode surface. There is a problem in that the lithium deposits locally without growing, and grows in the form of dendrites as a growth nucleus, eventually short-circuits with the positive electrode, causes a short-circuit, and sometimes ignites.

  In addition, examples of non-aqueous compounds used as an electrolyte in non-aqueous electrolyte secondary batteries include carbonate compounds such as ethylene carbonate and propylene carbonate, and organic solvents such as γ-butyrolactone and dimethoxyethane. Since these are very flammable compounds, they may cause fire due to short circuit or runaway overheating during overcharge.

  In order to solve such problems, many techniques for making the electrolyte solution flame-retardant by adding various P (O) group-containing pentavalent phosphorus compounds or phosphate esters to the non-aqueous electrolyte solution have been proposed. (See Patent Documents 1 to 11). For example, Patent Document 10 discloses that an organic electrolyte lithium battery solves the problem of flame retardancy and effectively suppresses swelling of the battery during initial charging and charging / discharging to improve reliability. By adopting the constitutional requirement that the organic electrolyte contains a phosphonate compound represented by a predetermined chemical formula, the reductive decomposition stability is improved and the irreversible capacity at the beginning of the cycle is reduced, Battery charging / discharging efficiency and life characteristics can be improved. Battery thickness after assembly and standard charging does not exceed a certain range, thus improving battery reliability. It is described that

  However, when phosphoric acid esters are added to the electrolyte according to these conventional techniques, the discharge capacity is reduced due to the reaction between the phosphoric acid ester and the negative electrode material. As a result, sufficient discharge capacity cannot be obtained or cycle characteristics are reduced. As a result, the number of cycles that can be used as a secondary battery is reduced (see Non-Patent Document 1).

In addition, non-aqueous electrolyte secondary batteries are used in various applications due to their high energy density, and there are many cases in which they are used at ambient temperature conditions higher than room temperature, such as in-vehicle large batteries. ing.
For this reason, there is an increasing demand for non-aqueous electrolyte secondary batteries in which the deterioration of cycle characteristics is small even when used under environmental temperature conditions higher than room temperature.

  On the other hand, apart from the technology related to the battery as described above, the present inventors have so far developed a method for producing a functional phosphorus compound such as a flame retardant phosphorus compound using a specific catalyst (for example, patents). References 12-22). With this development, it has become possible to efficiently produce various functional phosphorus compounds that have not been known so far and that are new or difficult to synthesize.

JP-A-4-184870 Japanese Patent Laid-Open No. 10-50342 JP-A-11-233141 JP 2003-229173 A JP 2002-280061 A JP 2007-250191 A JP 2009-32454 A JP 2009-224258 A JP 2010-92706 A US2004 / 0142246 A1 US2004 / 0142246 A1 Japanese Patent No. 2775426 Japanese Patent No. 2777985 Japanese Patent No. 2849712 Japanese Patent No. 3041396 Japanese Patent No. 3051928 Japanese Patent No. 3390399 Japanese Patent No. 3572352 Japanese Patent No. 3836459 Japanese Patent No. 3836460 Japanese Patent No. 3951024 Japanese Patent No. 6111127

GS Yuasa Technical Report 2005 Volume 2 Issue 1 Pages 26-31

The present invention, when used as an additive for a non-aqueous electrolyte in a non-aqueous electrolyte secondary battery, imparts excellent flame retardancy to the non-aqueous electrolyte and is not only at room temperature but also at a high temperature such as 45 ° C or higher. The present invention provides a novel partially fluorinated vinyl phosphate ester compound capable of exhibiting excellent cycle characteristics even when a nonaqueous electrolyte secondary battery is used in an environment where Let it be the first problem.
The present invention improves the flame retardancy of the non-aqueous electrolyte, and when applied to a non-aqueous electrolyte of a non-aqueous electrolyte secondary battery used in a high temperature environment such as 45 ° C. or higher, It is a second object to provide an additive for a non-aqueous electrolyte that can exhibit excellent cycle characteristics in a water electrolyte secondary battery.
The present invention exhibits excellent flame retardancy and is excellent in the non-aqueous electrolyte secondary battery even when used in a non-aqueous electrolyte secondary battery used in a high temperature environment such as 45 ° C or higher. It is a third object to provide a non-aqueous electrolyte that can exhibit the cycle characteristics.
It is a fourth object of the present invention to provide a non-aqueous electrolyte secondary battery that exhibits good cycle characteristics even when used in an environment at a high temperature of 45 ° C. or higher.

In order to solve the above problems, the present inventors have examined the use of various functional phosphorus compounds that have been developed as described above as flame retardants and flame retardant additives for non-aqueous electrolytes. In the course of the research, the phosphonate compound (vinyl phosphate ester compound) described in Patent Document 10 was also examined.
As described above, the invention described in Patent Document 10 aims to effectively suppress the swelling of the battery at the time of initial charge and charge / discharge to improve the reliability. In addition, the fact that diethyl vinyl phosphonate (DEVP) was used in the examples as the phosphonate compound represented by the predetermined chemical formula, one or more hydrogen atoms among the alkyl groups in the chemical formula, such as halogen atoms and lower alkyl groups, etc. It is also described that it can be substituted with many exemplified substituents. However, the same document describes a non-aqueous electrolyte that can improve cycle characteristics at a temperature higher than room temperature, and an additive for the non-aqueous electrolyte that can improve the cycle characteristics at such a high temperature. It has not been studied at all, and practical examples using phosphonate compounds substituted with many exemplified substituents are not described at all.
The present inventors have also described vinyl phosphate compounds such as DEVP and phosphate esters having no vinyl group such as (CH ₃ O) ₂ P (O) C ₂ H ₅ and (CH ₃ O) ₃ PO. In the research process, a nonaqueous electrolyte battery containing a vinyl phosphate compound such as DEVP was used at room temperature more than a non-aqueous electrolyte battery containing a phosphate ester having no vinyl group as described above. Thus, although it was found that the cycle characteristics were good, it became clear that the cycle characteristics at a temperature higher than room temperature were greatly lowered with DEVP and the like even with vinyl phosphate compounds.

  The inventors of the present invention further synthesized various phosphorus compounds and conducted extensive studies, and as a result, a specific partially fluorinated vinyl phosphate compound was used as an additive for a non-aqueous electrolyte of a non-aqueous electrolyte secondary battery. Sometimes, when the nonaqueous electrolyte secondary battery is used not only at room temperature but also in a high temperature environment such as 45 ° C. or more, the nonaqueous electrolyte secondary battery is used. The inventors have found a novel partially fluorinated vinyl phosphate ester compound capable of exhibiting excellent cycle characteristics in an electrolyte secondary battery, and have completed the present invention.

According to the present invention, a partially fluorinated vinyl phosphate compound represented by the following formula (i) useful when used as an additive for a non-aqueous electrolyte of a non-aqueous electrolyte secondary battery, comprising this compound Provided are a non-aqueous electrolyte additive, a non-aqueous electrolyte containing the additive, and a non-aqueous electrolyte secondary battery including the non-aqueous electrolyte.
(CF ₃ CH ₂ O) ₂ P (O) CH = CH ₂ (i)

That is, the invention provided by this case is as follows.
(1) A partially fluorinated vinyl phosphate compound represented by the following formula (i).
(CF ₃ CH ₂ O) ₂ P (O) CH = CH ₂ (i)
(2) The additive for non-aqueous electrolytes which consists of the partially fluorinated vinyl phosphate ester compound as described in said (1).
(3) The additive for non-aqueous electrolyte according to (2), which is used for a non-aqueous electrolyte secondary battery used in an environment of 45 ° C. or higher.
(4) A nonaqueous electrolytic solution containing the additive according to (2) or (3).
(5) A non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte according to (4).
(6) The nonaqueous electrolyte secondary battery according to (5), wherein the positive electrode active material is LiCoO ₂ .

The nonaqueous electrolytic solution of the present invention can include the following aspects.
(7) The nonaqueous electrolytic solution according to (4), wherein the additive is added in an amount of 1 to 20 wt%.
(8) The nonaqueous electrolytic solution according to (4) or (7), wherein the additive is added in an amount of 3 to 12 wt%.
(9) The nonaqueous electrolytic solution according to any one of (4), (7), and (8), wherein main components of the organic solvent constituting the nonaqueous electrolytic solution are a cyclic carbonate and a chain carbonate.
(10) The nonaqueous electrolytic solution according to any one of (4) and (7) to (9), wherein the organic solvent is composed of 30 to 70 vol% ethylene carbonate and 70 to 30 vol% dimethyl carbonate.
(11) The nonaqueous electrolytic solution according to any one of (4) and (7) to (10), wherein the electrolyte salt contained is lithium hexafluorophosphate (LiPF ₆ ).

The nonaqueous electrolyte secondary battery of the present invention can include the following aspects.
(12) A non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte according to any one of (7) to (11).
(13) The nonaqueous electrolyte secondary battery according to any one of (5), (6), and (12), wherein the negative electrode active material is Li metal or Li alloy.

  The partially fluorinated vinyl phosphate compound of the present invention has excellent flame retardancy (self-extinguishing) when used as an additive for a non-aqueous electrolyte of a non-aqueous electrolyte secondary battery. When the non-aqueous electrolyte secondary battery is used not only at room temperature but also at a high temperature exceeding the room temperature (for example, 45 ° C. or more, particularly 55 ° C. or more), the non-aqueous electrolyte secondary battery is used. The battery exhibits excellent cycle characteristics (charge / discharge characteristics).

  The additive for a non-aqueous electrolyte of the present invention improves the flame retardancy of the non-aqueous electrolyte and is used not only at room temperature but also at a high temperature exceeding room temperature (for example, 45 ° C. or more, particularly 55 ° C. or more). When applied to the non-aqueous electrolyte of the non-aqueous electrolyte secondary battery used, the non-aqueous electrolyte secondary battery exhibits excellent cycle characteristics.

  The nonaqueous electrolytic solution of the present invention exhibits excellent flame retardancy and is used not only at room temperature but also in an environment where the temperature is higher than room temperature (for example, 45 ° C or higher, particularly 55 ° C or higher). Even when used in a secondary battery, the non-aqueous electrolyte secondary battery exhibits excellent cycle characteristics.

The nonaqueous electrolyte secondary battery of the present invention exhibits good cycle characteristics even when used in an environment where the temperature is high, such as 45 ° C. or higher. It is known that deterioration is accelerated when the temperature exceeds 45 ° C. in a known normal electrolyte system, and it is said that it is necessary to cool by air cooling or the like in large batteries for in-vehicle use. In the non-aqueous electrolyte secondary battery, such cooling can be made unnecessary, simplified, or reduced in cost.

Three types of non-aqueous electrolyte batteries (positive electrode) in which 5 wt% of (a) the additive Me of the comparative example, (b) the additive MeEt of the comparative example, and (c) the additive Et2 of the example were mixed in the base electrolyte, respectively. Active material: LiCoO ₂ , negative electrode active material: Li metal), positive electrode with cycle increase when environmental temperature is changed from 45 ° C to 45 ° C, 55 ° C in the middle of cycle characteristic test under 1.0C condition The drawing which shows the change of the discharge capacity per active material unit weight. (A) The base electrolyte as it is and containing no additive, (b) the base electrolyte mixed with 5 wt% of the comparative example additive Et, and (c) 5 wt% of the example additive Et2 in the base electrolyte. For 3 types of non-aqueous electrolyte batteries (positive electrode active material: LiCoO ₂ , negative electrode active material: Li metal), the ambient temperature was gradually increased from 25 ° C during the cycle characteristic test at 1.0C. The figure which shows the change of the discharge capacity per unit weight of positive electrode active materials with a cycle increase when changing to 45 degreeC, 55 degreeC, 65 degreeC, 75 degreeC, and 65 degreeC. FIG. 3 is a diagram showing a change in coulomb efficiency with an increase in cycle in the same cycle characteristic test as in FIG. 2 for the same three types of batteries (a), (b), and (c) as in FIG. 2. The same three types of batteries as in FIG. 2 (base electrolyte as it is without additives (◯), base electrolyte mixed with 5 wt% of comparative additive Et (□), and examples added to base electrolyte) Drawing which shows change of discharge capacity maintenance rate with (a) cycle increase at environmental temperature of 25 ° C. and (b) change of coulomb efficiency with increase of cycle for mixture of Et2 with 5 wt% (剤)]. FIG. 5 shows (a) a change in discharge capacity retention rate with an increase in cycle at an environmental temperature of 45 ° C. and (b) a change in coulomb efficiency with an increase in cycle for the same three types of batteries as in FIG. 4. FIG. 5 shows (a) a change in discharge capacity retention rate with an increase in cycle and (b) a change in coulomb efficiency with an increase in cycle for the same three types of batteries as in FIG. 4. FIG. 5 shows (a) a change in discharge capacity retention rate with an increase in cycle at an environmental temperature of 65 ° C. and (b) a change in coulomb efficiency with an increase in cycle for the same three types of batteries as in FIG. 4. For the same three types of nonaqueous electrolyte batteries as in FIG. 4, (a) the time point after 30 cycles at an ambient temperature of 25 ° C., (b) the time point after 30 cycles at 45 ° C., (c) at 55 ° C. The drawing which shows the alternating current impedance at the time of 1.0C charge in the time after 40 cycles and (d) the time after 50 cycles at 65 degreeC.

The novel partially fluorinated vinyl phosphate ester compound of the present invention is represented by the following formula (i).
(CF ₃ CH ₂ O) ₂ P (O) CH = CH ₂ (i)
The partially fluorinated vinyl phosphate ester compound may be produced by any production method, but as described in Example 1 described later, in the presence of the catalyst Ni (PMe ₃ ) ₄ , (CF ₃ CH It can be preferably produced by blowing acetylene gas into a solution of ₂ O) ₂ P (O) H.

The partially fluorinated vinyl phosphate compound of the present invention, when added to a non-aqueous electrolyte, imparts excellent flame retardancy, and from room temperature to a non-aqueous electrolyte secondary battery comprising the non-aqueous electrolyte. Can exhibit good cycle characteristics even at high ambient temperatures.
Here, the environmental temperature higher than room temperature is a temperature exceeding 25 ° C, and means 45 ° C or higher, 50 ° C or higher, 55 ° C or higher, and the like. The upper limit of the temperature at which good cycle characteristics are exhibited is not particularly limited, but is usually 80 ° C. or lower, preferably 70 ° C. or lower, more preferably 60 ° C. or lower.
The non-aqueous electrolyte secondary battery of the present invention may be at a high temperature environment temperature for the entire operation period, or is effective even under a high temperature environment for a part of the operation period.

The nonaqueous electrolytic solution of the present invention contains an additive comprising an organic solvent, an electrolyte salt dissolved in the organic solvent, and the partially fluorinated vinyl phosphate compound. The additive can also be referred to as a flame retardant additive for non-aqueous electrolyte, a flame retardant for non-aqueous electrolyte, and the like.
The addition amount of the additive in the non-aqueous electrolyte is set in consideration of the effect of imparting flame retardancy to the non-aqueous electrolyte and the effect of improving the cycle characteristics in a high-temperature environment for the non-aqueous electrolyte secondary battery. . If the amount is too small, it is difficult to obtain the effect. On the other hand, if the amount is too large, the effect may be saturated and adversely affected. The additive amount of the additive in the nonaqueous electrolytic solution is usually 1 to 20 wt%, preferably 2 to 15 wt%, more preferably 3 to 12 wt%, and further preferably 4 to 10 wt%.

The electrolyte salt contained in the non-aqueous electrolyte is not limited, but is lithium hexafluorophosphate (LiPF ₆ ), lithium tetrafluoroborate (LiBF ₄ ), lithium perchlorate (LiClO ₄ ), trifluoromethane. Lithium salts such as lithium sulfonate (LiCF ₃ SO ₃ ) and lithium trifluoromethanesulfonate imide (LiN (CF ₃ SO ₂ ) ₂ ) can be used. Preferably, lithium hexafluorophosphate (LiPF ₆ ) can be used.
The amount of electrolyte salt added to the non-aqueous electrolyte is set so that the conductivity of the non-aqueous electrolyte is sufficiently high and the internal resistance can be kept low, so that the salt does not precipitate at low temperatures. The Usually, it is 0.3-3.0 mol / L, More preferably, it is 0.5-2.0 mol / L.

  As the organic solvent constituting the non-aqueous electrolyte, any known solvent for non-aqueous electrolyte secondary batteries can be used. Examples of such organic solvents include cyclic carbonates such as ethylene carbonate (EC), propylene carbonate, butylene carbonate, and vinylene carbonate, and chain structures such as dimethyl carbonate (DMC), diethyl carbonate, ethyl methyl carbonate, and dipropyl carbonate. Carbonates, aliphatic carboxylic acid esters such as methyl formate, methyl acetate, methyl propionate, ethyl propionate, γ-lactones such as γ-butyrolactone, 1,2-dimethoxyethane, 1,2-diethoxyethane, Examples include chain ethers such as ethoxymethoxyethane, and cyclic ethers such as tetrahydrofuran and 2-methyltetrahydrofuran. These are used alone or in combination. Of these, those containing a mixture of a cyclic carbonate and a chain carbonate as main components are preferred. Suitable mixed solvents of cyclic carbonate and chain carbonate include those whose main components are ethylene carbonate (EC) and dimethyl carbonate (DMC). For example, the organic solvent can be composed of 30 to 70 vol% (preferably 40 to 60 vol%) EC and 70 to 30 vol% (preferably 60 to 40 vol%) DMC.

The non-aqueous electrolyte secondary battery of the present invention includes a positive electrode, a negative electrode, and the like in addition to the non-aqueous electrolyte.
The shape of the battery is not limited at all including a cylindrical shape, a square shape, a coin shape, a button shape, a paper shape, and the like, and various shapes can be adopted.
The active material used for the positive electrode is not limited, but LiCoO ₂ is preferable. The active material used for the negative electrode is not limited, but is preferably a Li metal or a Li alloy. When these preferred positive electrode active materials LiCoO ₂ and negative electrode active materials Li metal or Li alloy are used, at a temperature higher than room temperature than when other positive electrode active materials (LiFePO ₄ , LiMn ₂ O _4, etc.) are used. The cycle characteristics were better. From this, it can be said that the additive of the present invention has a more excellent deterioration suppressing effect under a high environmental temperature with respect to the LiCoO ₂ positive electrode and the Li metal or Li alloy negative electrode.

  Hereinafter, the present invention will be described in more detail based on examples. However, the present invention is not limited to these examples, and various material changes, setting adjustments, and the like are appropriately performed without departing from the gist of the present invention. Can do.

Example 1 <Synthesis of Partially Fluorinated Vinyl Phosphate Compound (CF ₃ CH ₂ O) ₂ P (O) CH═CH ₂ >
In a 50 mL reaction vessel at room temperature under a nitrogen atmosphere, (CF ₃ CH ₂ O) ₂ P (O) H (1 mmol) was added to toluene (5 mL). Subsequently, acetylene gas was added by bubbling, and the reaction vessel was replaced with an acetylene gas atmosphere. Nickel catalyst Ni (PMe ₃ ) ₄ (5 mol% with respect to the reaction substrate) was added and reacted for 5 hours while bubbling acetylene gas. Then, the solvent was removed under reduced pressure, and the residue was subjected to column chromatography (SiO ₂ , SiO ₂ , Purification was performed using hexane / isopropyl alcohol (20/1) (yield 86%).
The analysis results of the purified product were as follows.
HRMS: theoretical value 272.0037, measured value: 272.0036.
¹ H NMR (400 MHz, CDCl ₃ ): δ 6.04-6.48 (m, 3H), 4.33-4.41 (m, 4H).
³¹ P NMR (162 MHz, CDCl ₃ ): δ 20.03.
From these analysis results, it was identified as a partially fluorinated vinyl phosphate compound represented by (CF ₃ CH ₂ O) ₂ P (O) CH═CH ₂ . This compound is a novel compound not registered in CAS or the like.

(Example 2, comparative example) <Battery cycle characteristic test I under a predetermined environmental temperature>
1 mol / L LiPF ₆ dissolved in a mixed solvent of ethylene carbonate (EC) and dimethyl carbonate (DMC) (EC: DMC = 1: 1 (volume ratio)) [Kishida Chemical, Lithium Battery Grade (LBG)] A base electrolyte was used.
As the additive (a) of the comparative example, (CH ₃ O) ₂ P (O) CH═CH ₂ (hereinafter referred to as “Me”) was used, and as the additive (b) of the comparative example, CH ₃ O (C ₂ H ₅ O) P (O) CH═CH ₂ (hereinafter referred to as “MeEt”) and the partially fluorinated vinyl phosphate synthesized in Example 1 as an additive (c) of the Example The compound (CF ₃ CH ₂ O) ₂ P (O) CH═CH ₂ (hereinafter referred to as “Et2”) was used.
Each of the base electrolytes was mixed with 5 wt% of Me, MeEt, Et2 to prepare two types of electrolytes of Comparative Examples (a) and (b) and an electrolyte solution of Example (c).
Using these three types of non-aqueous electrolytes, a positive electrode using 86 wt% of LiCoO ₂ as a positive electrode active material, 7 wt% of acetylene black as a conductive additive, and 7 wt% of polyvinylidene fluoride as a binder, and a negative electrode Three types of non-aqueous electrolyte batteries that are commonly provided with a negative electrode using Li metal as an active material and differ only in the electrolyte were assembled in an argon gas-substituted glove box with less than 1 ppm of water vapor and oxygen.

These three types of non-aqueous electrolyte batteries were subjected to charge / discharge cycle characteristics tests under the condition of 1.0C, changing the environmental temperature from 25 ° C to 45 ° C and 55 ° C sequentially.
FIGS. 1A, 1B, and 1C show the change in discharge capacity per unit weight of the positive electrode active material as the number of cycles increases for each battery.
At room temperature of 25 ° C., the non-aqueous electrolyte battery (c) containing the additive Et2 of the example has a smaller capacity decrease due to the increase in the number of cycles than the additive MeEt-containing battery (b) of the comparative example. The additive Me-containing battery (a) was not so different. However, after changing the environmental temperature to 45 ° C. or 55 ° C., the non-aqueous electrolyte battery (c) containing the additive Et2 of Example is compared with the batteries (a) and (b) of Comparative Examples. It can be seen that the capacity decrease with the increase in the cycle is remarkably small, and the capacity retention rate at an ambient temperature of 45 ° C. or higher, which is higher than the room temperature, is remarkably excellent.

(Example 3, comparative example) <Battery cycle characteristic test II under a predetermined environmental temperature>
As the additive of the comparative example, (C ₂ H ₅ O) ₂ P (O) CH═CH ₂ (DEVP, hereinafter referred to as “Et”) and the additive Et2 of the example were prepared.
The base electrolyte as it is (a) containing no additive, the base electrolyte mixed with 5 wt% of the comparative example additive Et (b), and the base electrolyte containing the example additive Et2 Three types of non-aqueous electrolytes, 5 wt% mixed (c), were prepared.
Using these three types of non-aqueous electrolytes (a), (b), and (c), except for the electrolyte solution, three types of non-aqueous electrolyte batteries differing only in the electrolyte solution were obtained in the same manner as in Example 2 above. Assembled.
For these three types of non-aqueous electrolyte batteries, the environmental temperature was changed from 25 ° C to 45 ° C, 55 ° C, 65 ° C, 75 ° C and 65 ° C under 1.0C conditions, and charge / discharge cycle characteristics tests were conducted. (However, as for (b), since the discharge capacity decreased at the stage of 75 ° C., the subsequent change to 65 ° C. was not performed.) At that time, for each battery, (a) a time point after 30 cycles at 25 ° C., (b) a time point after 30 cycles at 45 ° C., (c) a time point after 40 cycles at 55 ° C., ( d) The AC impedance at the time of 1.0 C charging was measured at the time after 50 cycles at 65 ° C.

<< Changes in discharge capacity and coulombic efficiency due to cycle increase and environmental temperature change >>
FIGS. 2A, 2B, and 2C show changes in discharge capacity per unit weight of the positive electrode active material associated with an increase in the number of cycles and environmental temperature changes for each battery. The battery (b) containing the comparative example additive Et has a larger capacity decrease with the increase of the cycle when the environmental temperature is 45 ° C. or higher than the battery (a) of the comparative example containing no additive. On the other hand, the battery (c) containing the additive Et2 of Example has a comparative battery (a) containing no additive after the environmental temperature is changed to 45 ° C, 55 ° C, 65 ° C and 75 ° C. ) And comparative example additive Et-containing battery (b), the capacity decrease with the increase in the cycle is remarkably small, and the capacity retention rate at an ambient temperature of 45 ° C. or higher, which is higher than room temperature, is remarkable. It turns out that it is excellent.
FIGS. 3A, 3B, and 3C show changes in coulomb efficiency (= discharge capacity / charge capacity) accompanying cycle increase and environmental temperature change for each battery. Coulomb efficiency is preferably as close to 1 as possible, and when it is less than 1, it means that a decomposition reaction other than the battery reaction occurs during charging. In the comparative example battery (a) containing no additive and the comparative example additive Et-containing battery (b), the coulomb efficiency was greatly reduced even at an environmental temperature of 45 ° C. On the other hand, the battery (c) containing the example additive Et2 has a remarkably small decrease in the coulomb efficiency at the environmental temperature of 45 ° C. and 55 ° C., and rapidly decreases once at 65 ° C. It was seen to recover.
From these results of FIGS. 2 and 3, the battery (c) containing the example additive Et2 has a high coulomb efficiency and a high capacity retention rate at an environmental temperature of 45 ° C. or higher. It can be said that it is a desirable battery to use.

<< Changes in discharge capacity maintenance ratio and coulomb efficiency with increasing cycle at each ambient temperature >>
FIGS. 4 to 7 show that the environmental temperature of the comparative battery (◯) containing no additive, the battery containing the comparative additive Et (□), and the battery containing the example additive Et2 (◇) is 25. (A) Discharge capacity maintenance rate with increasing cycle at = ° C. (FIG. 4), 45 ° C. (FIG. 5), 55 ° C. (FIG. 6), 65 ° C. (FIG. 7) The change in the discharge capacity in the first cycle] and (b) the change in coulomb efficiency (= discharge capacity / charge capacity) with an increase in the cycle are shown. This means the number of cycles counted since the environmental temperature was changed.) Similar to FIGS. 2 and 3, as seen from FIGS. 4 to 7, the battery (◇) containing Example additive Et2 has a good discharge capacity maintenance rate and coulomb efficiency at a high temperature of 45 ° C. or higher. I understand.

<< AC impedance (EIS) during charging at each ambient temperature >>
8A to 8D, for each of the three types of batteries, (a) a time point after 30 cycles at 25 ° C., (b) a time point after 30 cycles at 45 ° C., (c The results of measuring AC impedance (electrochemical impedance, EIS) during 1.0C charging at the time point after 40 cycles at 55 ° C. and (d) the time point after 50 cycles at 65 ° C. are shown. The battery containing the additive Et2 in Example (◇) has an AC impedance higher than that of the battery (Comparative Example) containing no additive and the battery containing the additive Et (Comparative Example) (□) at an environmental temperature of 25 ° C. Since it is somewhat large, it cannot be said that the cycle characteristics in a 25 ° C. (room temperature) environment are necessarily better than the batteries of the comparative examples (◯, □). However, the AC impedance during charging of the battery containing the additive Et2 of Example (◇) is lower than that of the comparative battery (◯, □) at 45 ° C or higher, and especially at 55 ° C or 65 ° C, It is clearly smaller than the battery (◯, □) and is dramatically better than the comparative example at about 45 ° C. as a boundary. Considering the results of Example 1 and Example 2 above, the additive Et2 of the example has the effect of removing deterioration factors such as an increase in interfacial charge transfer resistance at the electrolyte interface of the active material when the environmental temperature rises. You can think that you are playing.

(Example 4) <Flame retardance evaluation experiment of non-aqueous electrolyte>
Three types of non-aqueous electrolytes 0.5% without additive, 5% by weight of the additive Et2 of the example, and 10% by weight of the additive Et2 of the example were added to the base electrolyte 0.5% mL was prepared.
A commercially available glass filter fiber was cut into strips having a width of 15 mm and a length of 40 mm, and immersed in each electrolyte solution placed in a petri dish for 1 minute. Then, it took out from the liquid, moved to another petri dish to remove excess electrolyte, and left in the atmosphere for 1 minute. The glass filter impregnated with the electrolytic solution in this way was fixed with one end as a free end and the other end fixed so that the length direction was horizontal. Flame ignited with a lighter for 3 seconds from one end, and the time and flame rate ((length from one end to the position where the fire reached / filter length) x 100) after the fire source was removed and extinguished Sex was evaluated. The results are shown in Table 1.
In addition, although the ignition experiment with the lighter was performed on the additive Et2 itself of the example, the example additive Et2 itself was not ignited.
As is clear from the above experiment, it was found that the additive Et2 of the present invention has an excellent flame retardant effect or flame retardant effect with respect to the non-aqueous electrolyte.

Claims (4)

A non-aqueous electrolyte solution comprising a non-aqueous electrolyte solution containing 3 to 12 wt% of an additive composed of a partially fluorinated vinyl phosphate ester compound represented by the following formula (i) and used in an environment of 45 ° C. or higher Secondary battery.
(CF ₃ CH ₂ O) ₂ P (O) CH = CH ₂ (i) The nonaqueous electrolyte secondary battery according to claim 1, wherein the positive electrode active material is LiCoO ₂ .   The non-aqueous electrolyte secondary battery according to claim 1, wherein the negative electrode active material is Li metal or Li alloy. The non-aqueous electrolyte secondary battery according to any one of claims 1 to 3 , wherein an organic solvent constituting the non-aqueous electrolyte is 30 to 70 vol% ethylene carbonate and 70 to 30 vol% dimethyl carbonate.

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