JP2005044704A - Solid electrolyte - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a solid electrolyte with ion conductivity as well as safety improved. <P>SOLUTION: The solid electrolyte is to contain a carbonate group-containing polymer of a branched type and electrolyte salt. With this, its elasticity can be lowered as compared with a conventional one using an organic polymer, and ion is made easier to move. Therefore, the ion conductivity can be improved even without an addition of an inflammable organic solvent. That is, the ion conductivity is improved as the safety is enhanced. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to solid electrolytes for use in various electrochemical devices.

  A liquid electrolyte is generally used from the viewpoint of ion conductivity as an electrolyte constituting an electrochemical device using various ion movements such as a battery, a capacitor, and a sensor. However, a liquid electrolyte has a problem that there is a risk of damage to equipment or parts due to liquid leakage.

  On the other hand, recently, it has been proposed to use a solid electrolyte such as an inorganic crystalline material, inorganic glass, or organic polymer. Such a solid electrolyte can eliminate liquid leakage and can lower the ignitability of the electrolyte as compared with a liquid electrolyte, thereby improving the reliability and safety of the electrochemical device. . Furthermore, in the solid electrolyte using the organic polymer, processability and formability can be improved as compared with the case of using other materials, and the obtained solid electrolyte has flexibility and bending workability. Therefore, development of a solid electrolyte using an organic polymer is expected from the viewpoint of improving the degree of freedom in designing an electrochemical device to which the solid electrolyte is applied.

  As a solid electrolyte using such an organic polymer, a solid electrolyte for a secondary battery in which a specific alkali metal salt is contained in polyethylene oxide is known (for example, see Patent Document 1). Further, a gel electrolyte in which a flammable organic solvent is added to improve ionic conductivity has been studied and put into practical use (see, for example, Patent Document 2). Furthermore, a gel electrolyte using a carbonate group-containing polymer has also been proposed (see, for example, Patent Document 3).

JP 2002-158039 A (page 2-3) JP 2000-82328 A (2nd page) JP 2000-351843 A (page 2-3)

However, a solid electrolyte using an organic polymer in which a specific alkali metal salt is contained in polyethylene oxide is inferior to other materials in terms of ion conductivity. For example, the ionic conductivity at room temperature is as low as about 10 ⁻⁵ S / cm, and it is difficult to apply it to a battery operating at room temperature. Therefore, gel electrolytes that can improve ionic conductivity have been put to practical use or have been proposed, but such electrolytes contain a flammable solvent, so that the electrolyte is in comparison with liquid electrolytes. It is difficult to lower the ignitability of and to improve safety. Therefore, there is a demand for a solid electrolyte that can improve ion conductivity while improving safety.

  An object of the present invention is to improve ion conductivity while improving safety.

The solid electrolyte of the present invention solves the above-mentioned problems by adopting a constitution containing a branched carbonate group-containing polymer represented by the general formula (1) and an electrolyte salt.

（ただし、Ｒ及びＸは炭化水素基、ｍは付加モル数、ｎは分岐数である）
このような構成とすることにより、従来の有機高分子を用いた固体電解質よりも弾性率を低下させることができ、イオンが移動し易くできる。このため、可燃性有機溶媒を添加しなくても、イオン伝導度を向上できる。すなわち、安全性を向上しながら、イオン伝導度も向上できる。
また、一般式（１）の式中、炭化水素基Ｒ及びＸが炭素数２以上７以下である構成とすれば、確実にイオン伝導度を向上できるので好ましい。さらに、炭化水素基Ｒ及びＸが炭素数２以上３以下である構成とすれば、一層確実にイオン伝導度を向上できるので好ましい。

(Where R and X are hydrocarbon groups, m is the number of moles added, and n is the number of branches)
By setting it as such a structure, an elasticity modulus can be reduced rather than the solid electrolyte using the conventional organic polymer, and it can become easy to move ion. For this reason, ionic conductivity can be improved without adding a flammable organic solvent. That is, ionic conductivity can be improved while improving safety.
In addition, in the formula of the general formula (1), it is preferable that the hydrocarbon groups R and X have 2 or more and 7 or less carbon atoms because the ion conductivity can be reliably improved. Furthermore, it is preferable that the hydrocarbon groups R and X have 2 to 3 carbon atoms because the ion conductivity can be improved more reliably.

  In addition, in the formula of the general formula (1), when the number of added moles m is 10 or more and 10,000 or less, the ionic conductivity can be improved with certainty and the characteristics of the solid electrolyte using the organic polymer can be ensured. Since it can hold | maintain, it is preferable. Furthermore, it is preferable that the number of added moles m is 100 or more and 1000 or less because the ion conductivity can be improved more reliably and the characteristics of the solid electrolyte using the organic polymer can be more reliably maintained.

  In addition, in the general formula (1), it is preferable that the number of branches n is 2 or more and 3 or less because a solid electrolyte using an organic polymer that can improve the ionic conductivity can be surely formed. Furthermore, it is preferable that the number of branches n is 3 because a solid electrolyte using an organic polymer that can improve the ionic conductivity more reliably can be formed.

  Further, the lithium secondary battery includes a positive electrode and a negative electrode that reversibly occlude and release lithium, and a solid electrolyte containing lithium ions, and the solid electrolyte includes any one of the above solid electrolytes. By adopting such a configuration, liquid leakage can be eliminated and ion conductivity can be improved. Therefore, the charge / discharge characteristics of the lithium secondary battery can be improved while improving safety.

At this time, the electrolyte salt contained in the solid electrolyte is at least one of LiPF ₆ , LiN (CF ₃ SO ₂ ) ₂ , LiBF ₄ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiI, and LiBr. To do. Furthermore, the electrolyte salt included in the solid electrolyte is preferably at least one of LiN (CF ₃ SO ₂ ) ₂ and LiN (C ₂ F ₅ SO ₂ ) _{2 in view} of the degree of dissociation in the polymer.

  According to the present invention, ionic conductivity can be improved while improving safety.

  Hereinafter, an embodiment of a solid electrolyte to which the present invention is applied and a lithium secondary battery having the solid electrolyte will be described.

The solid electrolyte of this embodiment has a configuration including a branched carbonate group-containing polymer represented by the general formula (1) and an electrolyte salt. Note that the carbonate group refers to a —O— (C═O) —O— structure.

ただし、Ｒ及びＸは炭素数が２以上７以下の炭化水素基、ｍは付加モル数で１０以上１００００以下、ｎは分岐数で２以上３以下である。

However, R and X are hydrocarbon groups having 2 to 7 carbon atoms, m is 10 to 10,000 in terms of added moles, and n is 2 to 3 in number of branches.

  As described above, the hydrocarbon group R in the general formula (1) is a hydrocarbon group having 2 to 7 carbon atoms. For example, ethylene, propylene, butylene, pentylene, dimethyltrimethylene, dimethyltetramethylene, dimethyl And aliphatic hydrocarbon groups such as pentamethylene. If the number of carbon atoms of the hydrocarbon group R exceeds 7, the proportion of the carbonate group occupying a certain weight decreases, and the number of ions, that is, lithium ion coordination sites in this embodiment, decreases. As the number of ion coordination sites decreases, the ionic conductivity decreases. For this reason, when the carbon number of the hydrocarbon group R exceeds 7, the ionic conductivity may not be improved. On the other hand, when the number of carbon atoms of the hydrocarbon group R is smaller than 2, the polymer is easily crystallized, which makes it difficult for ions to move, and the ionic conductivity may not be improved.

  Therefore, the number of carbon atoms of the hydrocarbon group R is not limited to the numerical value of the present embodiment, but can be arbitrarily selected. By setting the number of carbon atoms to 2 or more and 7 or less as in the present embodiment, the ionic conductivity is reliably improved. it can. Furthermore, the ionic conductivity can be improved more reliably by setting the number of carbon atoms of the hydrocarbon group R to 2 or more and 3 or less.

  The added mole number m of the general formula (1) is 10 or more and 10,000 or less as described above. When the added mole number m exceeds 10,000, the molecular weight increases and the molecule becomes too long. Then, as the molecule becomes longer, the molecule becomes difficult to move and the ion becomes difficult to move, so that the ionic conductivity decreases. For this reason, when the added mole number m exceeds 10,000, the ionic conductivity may not be improved. On the other hand, when the added mole number m is smaller than 10, the molecule becomes too short, so that the molecule becomes difficult to move and the ion becomes difficult to move, so that the ionic conductivity decreases. For this reason, even if the added mole number m is smaller than 10, the ionic conductivity may not be improved. In addition, when the number of added moles m is less than 10, the molecule becomes too short, and the properties such as processability, moldability, flexibility and bending workability required for solid electrolytes using organic polymers are impaired. End up.

  Therefore, the number of added moles m is not limited to the numerical value of the present embodiment, and can be arbitrarily selected. However, by setting the number of moles to 10 or more and 10,000 or less as in the present embodiment, the ion conductivity can be reliably improved, The characteristics as a solid electrolyte using an organic polymer can be reliably maintained. Furthermore, by setting the added mole number m to 100 or more and 1000 or less, the ionic conductivity can be improved more reliably and the characteristics as a solid electrolyte using an organic polymer can be more reliably maintained.

  The number of branches n in the general formula (1) is 2 or more and 3 or less as described above. When the number of branches n exceeds 3, and when the number of branches n is less than 2, a solid electrolyte may not be formed. Therefore, the number of branches n is not limited to the numerical value of the present embodiment, but can be arbitrarily selected. However, by setting the branch number to 2 or more and 3 or less as in the present embodiment, the organic polymer can reliably improve the ion conductivity A solid electrolyte using can be formed. Furthermore, by setting the number of branches n to 3, a solid electrolyte using an organic polymer that can improve the ionic conductivity more reliably and reliably can be formed.

  As described above, the hydrocarbon group X of the general formula (1) is a hydrocarbon group having 2 to 7 carbon atoms. Like the hydrocarbon group R, for example, ethylene, propylene, butylene, pentylene, dimethyl And aliphatic hydrocarbon groups such as trimethylene, dimethyltetramethylene and dimethylpentamethylene. When the number of carbon atoms of the hydrocarbon group X exceeds 7, like the hydrocarbon group R, the proportion of the carbonate group occupying a constant weight decreases, and in this embodiment, the coordination possible site of lithium ions decreases. End up. As the number of ion coordination sites decreases, the ionic conductivity decreases. For this reason, when the carbon number of the hydrocarbon group X exceeds 7, the ionic conductivity may not be improved. On the other hand, when the number of carbon atoms of the hydrocarbon group X is smaller than 2, the polymer is easily crystallized, which makes it difficult for ions to move, and the ionic conductivity may not be improved.

  Therefore, similarly to the hydrocarbon group R, the number of carbon atoms of the hydrocarbon group X is not limited to the numerical value of the present embodiment, but can be arbitrarily selected, but by setting it to 2 or more and 7 or less as in the present embodiment. It is possible to improve the ionic conductivity without fail. Furthermore, the ionic conductivity can be more reliably improved by setting the number of carbon atoms of the hydrocarbon group X to 2 or more and 3 or less.

Since the electrolyte salt in the present embodiment is a solid electrolyte constituting a lithium secondary battery, various electrolytes can be used as long as the electrolyte salt can be used for a lithium secondary battery. For example, LiClO ₄ , LiCF ₃ SO ₃ , LiN (CF ₃ SO ₃ ) ₂ , LiN (C ₂ F ₅ SO ₂ ) ₂ , LiBF ₄ , LiPF ₆ , LiI, LiBr, lower aliphatic lithium carboxylate A compound or a mixture thereof can be used. However, considering the degree of dissociation in the polymer, it is desirable to use LiN (CF ₃ SO ₃ ) ₂ or LiN (C ₂ F ₅ SO ₂ ) ₂ .

Furthermore, the solid electrolyte of the present invention includes a branched carbonate group-containing polymer and an inorganic oxide such as a granular inorganic oxide of about several tens of nanometers such as SiO ₂ , TiO ₂ , and ZrO _2. By including at least one kind of oxide, the ionic conductivity can be further improved.

As the positive electrode that reversibly occludes and releases lithium constituting the lithium secondary battery of this embodiment, a layered compound such as lithium cobaltate (LiCoO ₂ ) or lithium nickelate (LiNiO ₂ ), or one or more transition metals is substituted. Or vanadium oxides such as lithium manganate, copper-lithium oxide (Li ₂ CuO ₂ ), LiV ₃ O ₈ , LiFe ₃ O ₄ , V ₂ O ₅ , Cu ₂ V ₂ O ₇ , disulfide compounds And a mixture containing Fe ₂ (MoO ₄ ) _{3 and the} like.

Incidentally, the lithium _{manganate, Li 1 + x Mn 2-} x O 4 ( provided that _{x = 0~0.33), Li 1 +} x Mn 2-xy M y O 4 ( provided that, M is Ni, Co, Cr And at least one metal selected from Cu, Fe, Al, Mg, x = 0 to 0.33, y = 0 to 1.0, ₂ -xy> 0), LiMnO ₃ , LiMn ₂ O ₃ , LiMnO ₂ , LiMn _2−x M _x O ₂ (where M includes at least one metal selected from Co, Ni, Fe, Cr, Zn, Ta, and x = 0.01 to 0.0. 1), Li ₂ Mn ₃ MO ₈ (wherein M includes at least one metal selected from Fe, Co, Ni, Cu, and Zn).

  On the other hand, as a negative electrode that reversibly occludes and releases lithium constituting the lithium secondary battery of this embodiment, a graphitizable material obtained from natural graphite, petroleum coke, coal pitch coke, or the like is heat-treated at a high temperature of 2500 ° C. or higher. Or mesophase carbon, amorphous carbon, carbon fiber, a metal alloying with lithium, or a material having a metal supported on the surface of carbon particles. Specifically, it is a metal or alloy selected from lithium, aluminum, tin, silicon, indium, gallium, magnesium and the like. Furthermore, oxides of these metals can be used as the negative electrode.

  In such a solid electrolyte of the present embodiment, a structure including a branched carbonate group-containing polymer represented by the general formula (1) and an electrolyte salt is used, so that a solid electrolyte using a conventional organic polymer is used. Also, the elastic modulus can be lowered, and ions can be easily moved. For this reason, ionic conductivity can be improved without adding a flammable organic solvent. That is, ionic conductivity can be improved while improving safety.

  Furthermore, by using the lithium secondary battery having the solid electrolyte of the present embodiment, liquid leakage can be eliminated and ion conductivity can be improved, so that charging and discharging of the lithium secondary battery can be performed while improving safety. The characteristics can also be improved.

  Moreover, in this embodiment, although the solid electrolyte used for a lithium secondary battery was shown, the solid electrolyte of this invention is applied to the electrochemical device using not only a lithium secondary battery but the movement of various ions. Can do.

  In addition, the present invention is not limited to a specific application, but can be used in various applications, such as an IC card, a personal computer, a large electronic computer, a notebook computer, a pen input personal computer, a notebook word processor, a mobile phone, a mobile card, a wristwatch, Cameras, electric shavers, cordless phones, fax machines, video cameras, video cameras, electronic notebooks, calculators, electronic notebooks with communication functions, portable photocopiers, LCD TVs, electric tools, vacuum cleaners, game machines with virtual reality, toys , Electric bicycle, walking aid for medical care, wheelchair for medical care, mobile bed for medical care, escalator, elevator, forklift, golf cart, emergency power supply, road conditioner, power storage system, etc. The present invention can be applied to lithium secondary batteries having various configurations. It can also be used for civilian use, military use, space use, etc.

  Hereinafter, an embodiment in which a model of a solid electrolyte to which the present invention is applied and a lithium secondary battery are created and evaluated will be described with reference to FIG. 1 and the like. FIG. 1 is a perspective view showing the configuration of a model of a lithium secondary battery to which the present invention is applied. In this example, sample preparation and evaluation of ion conductivity were performed in an argon atmosphere, viscoelasticity evaluation was performed in a nitrogen atmosphere, and the electrolyte salt concentration was adjusted to 0.05 mol per 1 mol of carbonate groups.

  Here, first, an example of producing a branched polymer, an example of producing an electrode, and a method for evaluating a model of a solid electrolyte or a lithium secondary battery will be described.

The branched polymer was produced according to the description in “Journal of Chemical Society of Japan”, 1993, Vol. 8, p.985-987. That is, 10 mmol of anhydrous potassium carbonate, N, N-dimethylformamide (DMF) or 15 cm ^{3 of} N-methyl-2-pyrrolidone (NMP), 10 mmol of dialcohol, and 5 mmol of alkyl halide are placed in a 50 cm ³ two-necked flask. , After CO ₂ replacement, mount the CO ₂ containing the balloon (volume 500 cm ³⁾ at the top, followed by stirring for 4 hours at 80 ° C.. After the reaction, the reaction mixture was cooled, ether 35 cm ^3, was added 0.5M hydrochloric acid 20 cm ^3, and the layers were separated. The aqueous layer was further extracted twice with ether 10 cm ^3, the organic layer is combined once with 1M aqueous sodium sulfite solution 10 cm ^3, washed twice with saturated brine 10 cm ^3, polycarbonate by drying over anhydrous magnesium sulfate Got. The polycarbonate thus synthesized was mixed with a solution obtained by adding 0.1 g of lithium methoxide to 45 g (0.3 mol) of trimethylolpropane to obtain a branched polycarbonate group-containing polymer.

The electrodes, that is, the positive electrode and the negative electrode were produced as follows. In the production of the positive electrode, cell seed (lithium cobaltate manufactured by Nippon Chemical Industry Co., Ltd.), SP270 (graphite manufactured by Nippon Graphite Co., Ltd.), polyethylene carbonate (manufactured by PAC Polymers Inc.), LiN (CF ₃ SO ₂ ) ₂ (Aldrich) And KF1120 (polyvinylidene fluoride manufactured by Kureha Chemical Industry Co., Ltd.) at a ratio of 70: 10: 5: 10: 5 wt%. This mixture was put into N-methyl-2-pyrrolidone and mixed to prepare a slurry solution. And the produced slurry was apply | coated to the 20-micrometer-thick aluminum foil with the doctor blade method, and it dried. The mixture application amount was 150 g / m ² . The mixture was pressed to a bulk density of 3.0 g / cm ³ and cut to 1 cm × 1 cm to produce a positive electrode.

In the production of the negative electrode, Carbotron PE (amorphous carbon manufactured by Kureha Chemical Industries), polyethylene carbonate (manufactured by PAC Polymers Inc.), LiN (CF ₃ SO ₂ ) ₂ (manufactured by Aldrich), and KF1120 (Kureha Chemical) (Polyvinylidene fluoride manufactured by Kogyo Co., Ltd.) was mixed at a ratio of 80: 10: 5: 5% by weight. This mixture was put into N-methyl-2-pyrrolidone and mixed to prepare a slurry solution. And the produced slurry was apply | coated to the 20-micrometer-thick copper foil with the doctor blade method, and it dried. The mixture application amount was 70 g / m ² . The mixture was pressed to a bulk density of 1.0 g / cm ³ and cut into 1.2 cm × 1.2 cm to produce a negative electrode.

  The model of the lithium secondary battery using the solid electrolyte prepared as described above and the positive electrode and the negative electrode was evaluated by the following evaluation method.

  The molecular weight was measured using gel permeation chromatography (hereinafter abbreviated as GPC).

  The glass transition temperature is measured using a dynamic viscoelasticity evaluation apparatus (DVA-220 manufactured by IT Measurement Control Co., Ltd.), the temperature range is -100 ° C to 100 ° C, the temperature rising rate is 5 ° C min-1, and the measurement frequency is 10 Hz. Under this condition, sinusoidal vibration was applied to the sample and the temperature change of the ratio (δ) of the real part to the imaginary part of the elastic modulus was measured, and the peak temperature of tan δ was defined as the glass transition temperature.

  The ionic conductivity is measured using an alternating current impedance method in which an electrochemical cell is constructed by sandwiching a solid electrolyte between stainless steel electrodes at 25 ° C., and an alternating current is applied between the electrodes to measure the resistance component. Calculation was made from the real impedance intercept of the Cole plot.

The charge / discharge characteristics were evaluated as follows. Using a charger / discharger (TOSCAT3000 manufactured by Toyo System Co., Ltd.), charging / discharging is performed at 25 ° C. and a current density of 0.5 mA / cm ² . In the charging, constant current charging was performed up to 4.2V, and constant voltage charging was performed for 12 hours after the voltage reached 4.2V. In discharging after charging, constant current discharging was performed until the discharge final voltage reached 3.5V. Moreover, the capacity | capacitance obtained by the first discharge was made into the first time discharge capacity. And charging / discharging on such battery charging / discharging conditions was made into 1 cycle, charging / discharging was repeated until it reached to 70% or less of initial discharge capacity, and the frequency | count was made into cycle characteristics.

Furthermore, constant current charging is performed up to 4.2 V at a current density of 1 mA / cm ^2. After the voltage reaches 4.2 V, constant voltage charging is performed for 12 hours. After charging, the voltage is constant until the discharge end voltage reaches 3.5 V. A current discharge was performed. And the capacity | capacitance obtained at this time was compared with the first cycle capacity | capacitance obtained by the charging / discharging cycle on the above-mentioned battery charging / discharging conditions, and the ratio was made into the high-speed charging / discharging characteristic.

(Example 1)
According to the preparation example of the branched polycarbonate group-containing polymer described above, 10 mmol of hexamethylenediol and 5 mmol of 1,4-di (chloromethyl) as the alkyl halide are selected, and the polycarbonate (hereinafter referred to as polymer) is selected using DMF 15 cm ^3. A). Further, according to the above-described production example of the branched polycarbonate group-containing polymer, a branched polycarbonate group-containing polymer (hereinafter referred to as branched polymer A) was obtained using polymer A as a starting material. The molecular weight of the branched polymer A thus obtained was measured by GPC. As a result, the molecular weight was 48,000.

A solution obtained by mixing this branched polymer A and LiBF ₄ as an electrolyte salt in dimethyl carbonate (hereinafter referred to as “solution A”) was applied onto Teflon (registered trademark) and left in argon at 80 ° C. for 12 hours. Thereafter, vacuum drying was performed at 80 ° C. for 12 hours to obtain a solid electrolyte A having a thickness of 100 μm. The glass transition temperature of the solid electrolyte A thus obtained was measured by the above-described method and found to be 15 ° C.

  Further, the obtained membrane-shaped solid electrolyte A was cut out into a disk shape having a diameter of 1 cm, and sandwiched between a pair of stainless steel electrodes, and then the ionic conductivity at 25 ° C. was determined by the above-described method. The conductivity was 0.1 mS / cm.

  Further, the solution A was cast on the positive electrode and the negative electrode prepared by the above-described method, left in argon at 80 ° C. for 12 hours, and then vacuum-dried at 80 ° C. for 12 hours. And these positive electrodes and negative electrodes were piled up, and a load of 0.1 MPa was applied, and they were bonded together by holding at 80 ° C. for 6 hours. Thereafter, as shown in FIG. 1, stainless steel terminals 5 and 7 were attached to the positive electrode 1 and the negative electrode 3, respectively, and inserted into a bag-shaped aluminum laminate film 9.

  When the charge / discharge characteristics of the lithium secondary battery model thus produced were evaluated by the above-described method, the initial discharge capacity was 1.1 mAh and the cycle characteristics were 138 times. Furthermore, the high rate discharge characteristic was 60%.

(Example 2)
A model of a solid electrolyte and a lithium secondary battery was prepared in the same manner as in Example 1 except that LiPF ₆ was used instead of LiBF ₄ used in Example 1 as the electrolyte salt. Measurement and evaluation were performed. As a result, the glass transition temperature was 15 ° C., the ionic conductivity was 0.2 mS / cm, the initial discharge capacity was 1.2 mAh, the cycle characteristics were 138 times, and the high rate discharge characteristics were 60%.

(Example 3)
A solid electrolyte and a lithium secondary battery were exactly the same as in Example 1 except that LiN (CF ₃ SO ₂ ) ₂ (Aldrich) was used as the electrolyte salt instead of LiBF ₄ used in Example 1. And the same measurement and evaluation as in Example 1 were performed. As a result, the glass transition temperature was 18 ° C., the ionic conductivity was 0.3 mS / cm, the initial discharge capacity was 1.2 mAh, the cycle characteristics were 138 times, and the high rate discharge characteristics were 60%.

(Example 4)
According to the preparation example of the branched polycarbonate group-containing polymer described above, 10 mmol of hexamethylene diol is selected as the dialcohol, 5 mmol of hexamethylene diiodo is selected as the alkyl halide, and the polycarbonate (hereinafter referred to as polymer B) is selected using NMP 15 cm ^3. Obtained. Furthermore, according to the above-described production example of the branched polycarbonate group-containing polymer, a branched polycarbonate group-containing polymer (hereinafter referred to as branched polymer B) was obtained using polymer B as a starting material. The molecular weight of the branched polymer B thus obtained was measured by GPC. As a result, the molecular weight was 21,000.

A solution obtained by mixing this branched polymer B and LiN (CF ₃ SO ₂ ) ₂ as an electrolyte salt in dimethyl carbonate (hereinafter referred to as solution B) was applied onto Teflon (registered trademark), and the mixture was applied at 80 ° C. for 12 hours. The solid electrolyte B was left in argon and then vacuum dried at 80 ° C. for 12 hours to obtain a solid electrolyte B having a thickness of 100 μm. The glass transition temperature of the solid electrolyte B thus obtained was measured by the method described above, and it was -20 ° C.

  Further, the obtained membrane-shaped solid electrolyte A was cut out into a disk shape having a diameter of 1 cm, and sandwiched between a pair of stainless steel electrodes, and then the ionic conductivity at 25 ° C. was determined by the above-described method. The conductivity was 0.5 mS / cm.

  Further, the solution B was cast on the positive electrode and the negative electrode prepared by the above-described method, left in argon at 80 ° C. for 12 hours, and then vacuum-dried at 80 ° C. for 12 hours. And these positive electrodes and negative electrodes were overlapped and bonded together by applying a load of 0.1 MPa and holding at 80 ° C. for 6 hours. Thereafter, as shown in FIG. 1, stainless steel terminals 5 and 7 were attached to the positive electrode 1 and the negative electrode 3, respectively, and inserted into a bag-shaped aluminum laminate film 9.

  When the charge / discharge characteristics of the lithium secondary battery model thus produced were evaluated by the above-described method, the initial discharge capacity was 1.2 mAh, and the cycle characteristics were 140 times. Further, the high rate discharge characteristic was 60%.

(Example 5)
Obtained according Preparation Examples of the branched polycarbonate containing polymers described above, hexamethylene diol 10mmol as dialcohols, select hexamethylene dibromo 5mmol as the alkyl halide, polycarbonate with NMP15cm ³ (hereinafter, referred to as polymer C) to It was. As a polymer, a model of a solid electrolyte and a lithium secondary battery was prepared in the same manner as in Example 4 except that polymer C was used instead of polymer B used in Example 4. Measurement and evaluation were performed. As a result, the glass transition temperature was −40 ° C., the ionic conductivity was 0.8 mS / cm, the initial discharge capacity was 1.3 mAh, the cycle characteristics were 140 times, and the high rate discharge characteristics were 65%. .

(Example 6)
According to the preparation example of the branched polycarbonate group-containing polymer described above, 10 mmol of hexamethylene diol as dialcohol and 5 mmol of 1,4-di (chloromethyl) as alkyl halide were selected, and polycarbonate (hereinafter referred to as polymer) was selected using DMF 15 cm ^3. Referred to as D). As a polymer, a model of a solid electrolyte and a lithium secondary battery was prepared in the same manner as in Example 4 except that polymer D was used instead of polymer B used in Example 4. Measurement and evaluation were performed. As a result, the glass transition temperature was −60 ° C., the ionic conductivity was 1.1 mS / cm, the initial discharge capacity was 1.3 mAh, the cycle characteristics were 140 times, and the high rate discharge characteristics were 65%. .

(Comparative Example 1)
A solution (hereinafter referred to as solution E) obtained by mixing polyethylene carbonate (manufactured by PAC Polymers Inc.) having a number average molecular weight of 50,000 and LiN (CF ₃ SO ₂ ) ₂ as an electrolyte salt with dimethyl carbonate is a Teflon (registered trademark). ), And left in argon at 80 ° C. for 12 hours, and then vacuum-dried at 80 ° C. for 12 hours to obtain a solid electrolyte E having a thickness of 100 μm. It was 20 degreeC when the glass transition temperature of the solid electrolyte E obtained in this way was measured by the above-mentioned method.

  Further, the obtained membrane-shaped solid electrolyte E was cut out into a disk shape having a diameter of 1 cm, sandwiched between a pair of stainless steel electrodes, and then the ionic conductivity at 25 ° C. was determined by the above-described method. The conductivity was 0.03 mS / cm.

  Further, the solution E was cast on the positive electrode and the negative electrode prepared by the above-described method, left in argon at 80 ° C. for 12 hours, and then vacuum-dried at 80 ° C. for 12 hours. Then, these positive and negative electrodes were superposed and bonded by applying a load of 0.1 MPa and holding at 80 ° C. for 6 hours. Thereafter, as shown in FIG. 1, stainless steel terminals 5 and 7 were attached to the positive electrode 1 and the negative electrode 3, respectively, and inserted into a bag-shaped aluminum laminate film 9.

  When the charge / discharge characteristics of the lithium secondary battery model thus produced were evaluated by the above-described method, the initial discharge capacity was 0.3 mAh and the cycle characteristics were 30 times. Further, the high rate discharge characteristic was 40%.

The results of evaluation in Examples 1 to 6 and Comparative Example 1 are summarized in Table 1.

このような本実施例での評価の結果から明らかなように、分岐型のポリカーボネート基含有ポリマーを含有する実施例１〜実施例６の固体電解質では、分岐型のポリカーボネート基含有ポリマーを含有していない比較例１の固体電解質に比べて、イオン伝導度が向上している。

As is clear from the results of evaluation in this example, the solid electrolytes of Examples 1 to 6 containing a branched polycarbonate group-containing polymer contain a branched polycarbonate group-containing polymer. Compared with the solid electrolyte of Comparative Example 1 that does not, the ionic conductivity is improved.

  Further, in the models of the lithium secondary batteries of Examples 1 to 6 using the solid electrolyte containing the branched polycarbonate group-containing polymer, a solid electrolyte not containing the branched polycarbonate group-containing polymer was used. Compared with the lithium secondary battery model of Comparative Example 1, the charge / discharge characteristics of the lithium secondary battery such as the initial discharge capacity, cycle characteristics, and high rate discharge characteristics are improved.

  As described above, the solid electrolyte to which the present invention is applied can improve the ion conductivity while improving the safety, and can be used for various electrochemical devices. However, especially in the lithium secondary battery, by using the solid electrolyte to which the present invention is applied, not only can the ion conductivity be improved while improving the safety, but also the charge / discharge characteristics of the secondary battery can be improved. .

It is a perspective view which shows the structure of one Example of the model of the lithium secondary battery formed by applying this invention.

Explanation of symbols

1 Positive electrode 3 Negative electrode 5, 7 Stainless steel terminal 9 Aluminum laminated film

Claims (5)

A solid electrolyte comprising a branched carbonate group-containing polymer represented by the general formula (1) and an electrolyte salt.

(Where R and X are hydrocarbon groups, m is the number of moles added, and n is the number of branches) 2. The solid electrolyte according to claim 1, wherein in the formula of the general formula (1), the hydrocarbon groups R and X have 2 to 7 carbon atoms. 3. The solid electrolyte according to claim 1, wherein, in the formula of the general formula (1), the added mole number m is 10 or more and 10,000 or less. 4. The solid electrolyte according to claim 1, wherein in the formula of the general formula (1), the number n of branches is 2 or more and 3 or less. A lithium secondary battery having a positive electrode and a negative electrode that reversibly store and release lithium, and a solid electrolyte containing lithium ions,
A lithium secondary battery comprising the solid electrolyte according to any one of claims 1 to 4 as the solid electrolyte.

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