JP4852700B2 - Lithium ion secondary battery - Google Patents

Description

The present invention relates to a lithium ion secondary battery having a stable charge / discharge capability using a negative electrode containing graphitic carbon as a negative electrode active material and a non-aqueous electrolyte containing propylene carbonate (PC) as a main component as a solvent. About.

In lithium ion secondary batteries, lithium-containing composite metal oxides such as lithium cobalt composite oxide are mainly used as the active material of the positive electrode, and lithium ion insertion and intercalation of lithium ions between the layers are used as the active material of the negative electrode. Carbon materials such as natural graphite and artificial graphite having a multi-layer structure capable of releasing carbon are mainly used.

The positive and negative electrode plates of a lithium ion secondary battery are prepared by dispersing an active material and a binder resin such as polyvinylidene fluoride (hereinafter abbreviated as “PVDF”) in a solvent such as N-methyl-2-pyrrolidone or water. The slurry is coated on both sides of a current collector such as copper or nickel metal foil, dried to remove the solvent to form a mixture layer, and then formed by compression molding with a roll press. Yes.

Since the organic solvent used in the lithium ion secondary battery needs to have a high dielectric constant in order to ionize the electrolyte, and because it needs to have high ionic conductivity in a wide use temperature range, propylene carbonate ( PC), carbonates such as ethylene carbonate (EC), lactones such as γ-butyrolactone, ethers, ketones, esters and the like. In particular, a mixed solvent in which an acyclic carbonate having a low viscosity such as dimethyl carbonate (DMC), diethyl carbonate (DEC), or methyl ethyl carbonate (MEC) is added to EC is widely used, but these organic compounds are vapors. Since the pressure is low, the battery tends to swell when the battery is left in a high temperature state.

On the other hand, compared to EC, PC has a high vapor pressure and high oxidation potential, so it is difficult to be decomposed. Therefore, it has an excellent effect that the amount of gas generated is small and the battery is difficult to swell, and the freezing point is low. Therefore, it has the advantages of excellent low temperature characteristics and low cost. Therefore, many studies have been conducted on lithium ion secondary batteries using an electrolytic solution containing PC as a main solvent.

Negative electrodes using carbonaceous materials such as graphite and amorphous carbon as the negative electrode active material are widely used as negative electrodes for lithium ion secondary batteries because of their low material cost and excellent cycle life. However, when a negative electrode formed by applying a carbon material to a current collector using PVDF as a binder and a non-aqueous solvent electrolyte containing PC as a main component is used, reductive decomposition of PC during charging As a result, the battery capacity is reduced. In particular, a high-capacity carbonaceous material (natural graphite, artificial graphite) that has been graphitized has a problem that PC is decomposed more violently and charging does not proceed well.

As one means of dealing with this problem, various compounds are added to the non-aqueous solvent electrolyte,
Form a film (SEI: Solid Electrolyte Interface. SEI surface film) on the negative electrode surface,
A means for preventing the negative electrode active material from directly reacting with the organic solvent is employed (Non-Patent Document 1).
). This SEI surface coating is also referred to as a passivation layer.

Further, many methods for coating the carbonaceous powder used as the negative electrode active material with other materials have been proposed. For example, a material such as nylon, polyacrylonitrile, polycaprolactone, and poniphenylene oxide that can transmit lithium ions and has low electronic conductivity is used as a binder for graphite powder, or the surface of the carbon negative electrode is coated (Patent Document 1). It is known to provide a coating layer such as an ion conductive polymer, a water-soluble polymer, an alkali metal salt, an alkali metal oxide, or an alkali metal hydroxide on the surface of the carbon negative electrode (Patent Document 2).

Moreover, what formed the carbon negative electrode by mixing what coat | covered graphite particle itself with another substance with binders, such as PDVF, is known (patent documents 3-8, nonpatent literature 2).

As a binder resin for bonding the active material to the current collector, both the positive electrode and the negative electrode are PV.
DF has been mainly used. However, PVDF has a problem in safety when the temperature rises when the battery is used. Polyacrylonitrile (PAN), polyacrylic acid (PAA) resin (patent documents 9 to 14), polyacrylamide (PAAd) resin (Patent Document 15) has been proposed.

JP 07-201357 A JP-A-11-129992 JP 2002-134171 A Japanese Patent Laid-Open No. 2002-231241 JP 2002-241117 A JP 2002-246020 A JP 2003-163005 A JP 2003-308838 A JP-A-11-135129 Japanese Patent Laid-Open No. 11-238505 JP 11-354125 A JP 11-354126 A JP 2002-373701 A JP 2004-281055 A JP 2005-203370 A Hiroyoshi Nakamura et al., “Inhibition of Decomposition of Electrolyte for Lithium Ion Battery Using Electrolyte Containing Acetate”, Electrochemistry and Industrial Physical Chemistry, Vol. 73, no. 9, pp. 788-790 (September 2005) Kunihiko Eguchi et al. “Reduction of Irreversible Capacity by Amine Polymer Coating on Graphite for Lithium Ion Secondary Battery Negative Electrode”, Electrochemistry and Industrial Physical Chemistry, Vol. 73, no. 6, pp. 429-434 (June 2005)

As a negative electrode material for lithium ion secondary batteries used as power sources for portable electronic devices,
Conventionally, carbon powder has been used. Due to the demand for higher capacity of small batteries, negative electrode materials have also been increased in capacity, and artificial graphite with a high degree of graphitization is currently used as the negative electrode material.

On the other hand, the negative electrode material is also required to be reduced in cost. In particular, a large battery for use in automobiles and the like uses a large amount of negative electrode material. Therefore,
Attempts have been made to use natural graphite, which is cheaper and has a higher degree of graphitization, instead of expensive artificial graphite.

However, when the degree of graphitization of graphitic carbon increases, the reactivity with the electrolyte increases, and the irreversible capacity associated with the decomposition of the electrolyte increases, and the battery performance such as storage characteristics and safety is impaired. . In particular, in automobile applications that are used outdoors, the battery may be exposed to low temperatures. Therefore, the melting point is ethylene carbonate (around 39 ° C) or dimethyl carbonate (0.5
)) The need to use propylene carbonate (-49 ° C), which is much lower, in the electrolyte increases, but graphitic carbon powders with a high degree of graphitization, such as natural graphite, decompose propylene carbonate. It could not be used as a material.

Therefore, many attempts have been made to suppress the reactivity with PC by using a carbon powder having a multi-layer structure in which the surface of graphitic carbon powder having a high graphitization degree is coated with a carbonaceous material having a low graphitization degree. It has been broken. In addition, in order to suppress the decomposition reaction of PC, a special additive is added to the electrolytic solution, the polymer material is preliminarily applied to the carbon material particles, or the surface coating treatment is further performed after the carbon negative electrode is formed. The means to do is also adopted. As described above, when graphite having a high graphitization degree is used as the negative electrode active material and PC is used as the main component of the non-aqueous solvent, various devices are required, which has been a factor in increasing manufacturing costs.

On the other hand, the main role of the binder used for manufacturing the negative electrode plate of the lithium ion secondary battery is
It is the bonding between the carbon particles that are the active material and between the carbon particles and the metal foil of the current collector. However, since the water-soluble resin is an electrically insulating material, if an excessive amount is used, the conductivity deteriorates. Insertion and desorption of lithium ions into the carbon anode do not work. Therefore, the resin used as the binder has a sufficient bonding strength in a small amount, and has an electrolytic solution resistance that does not dissolve in the electrolytic solution,
It must be a resin that can permeate and desorb lithium ions. Further, when carbon particles are uniformly coated with a binder, contact reaction with PC can be avoided, but permeation and desorption of lithium ions become difficult.

The present invention uses a highly crystalline carbon material having a carbon hexagonal network structure developed as a graphite carbon powder, and the graphite carbon powder is directly mixed with a binder without being subjected to a coating treatment. When a negative electrode is formed by coating and drying, a novel binder capable of suppressing the decomposition reaction of PC and covering and desorbing lithium ions is obtained by uniformly coating the graphitic carbon powder with a resin. For the purpose.

The present inventor uses polyacrylic acid, which is an anionic water-soluble polymer conventionally known as a binder, and performs dehydration polycondensation with a cross-linking agent to use PC with high graphitization degree as a negative electrode. It was found that the decomposition of can be suppressed.

That is, the present invention relates to (1) a lithium ion secondary battery having a non-aqueous electrolyte containing a positive electrode, a negative electrode, a separator, and an organic solvent, wherein the negative electrode comprises a graphitic carbon powder having a graphitization degree of 0.8 or more. Water-soluble polyacrylic acid containing a dehydration polycondensate of acrylic acid (PAA) and polyallylamine hydrochloride (PAH), or polyacrylic acid (PAA) and polyacrylamide (P
Lithium which is bound to a negative electrode current collector using a water-soluble polyacrylic acid containing a dehydrated polycondensate of AAd) as a binder, and the organic solvent contains 50% by volume or more of propylene carbonate An ion secondary battery.

The present invention is (2) the lithium ion secondary battery according to (1) above, wherein the organic solvent comprises 90 to 100% by volume of propylene carbonate.

The present invention is also characterized in that (3) the graphitic carbon powder is natural graphite.
1) a lithium ion secondary battery.

The present invention also provides: (4) graphitic carbon powder having a graphitization degree of 0.8 or more and polyacrylic acid (PA
After slurrying A) with distilled water, 0.1 to 5.0% by weight of polyallylamine hydrochloride (PAH) with respect to the amount of PAA was added to form a slurry in which a dehydrated polycondensate was formed. The method for producing a negative electrode for use in the lithium ion secondary battery according to the above (1), characterized by being coated and dried.

The present invention also provides (5) graphitic carbon powder having a graphitization degree of 0.8 or more and polyacrylic acid (PA
After slurrying A) with distilled water, 0.1 to 5.0% by weight of polyacrylamide (PAAd) with respect to the amount of PAA was added to form a dehydrated polycondensate on the current collector. The method for producing a negative electrode used for the lithium ion secondary battery according to the above (1), characterized by being dried.

The use of PAA as a binder is already known as described in the above-mentioned prior art, but the cycle maintenance characteristic when only PAA is used as a binder is 10 cycles, compared with 10 cycles. By using PAA containing a small amount of a dehydration polycondensate of polyallylamine hydrochloride (PAH) as a binder, an effect of improving to about 30 cycles can be obtained. In addition, compared with the case where only PAA is used as a binder, PAA
By using PAA containing a small amount of a dehydration polycondensate of polyacrylamide (PAAd) as a binder, an effect of improving to about 50 cycles can be obtained.

As a factor of the effect by including a small amount of the dehydration polycondensate by PAH or PAAd, the following formula is obtained by the dehydration polycondensation reaction process between the carboxyl group of PAA and the amino group of PAH or the amide group of PAAd. As shown, the amide bond and the imide bond are respectively formed, the surface of the graphitic carbon powder is strengthened by the polymer layer, and the SEI is made thin and uniform so that the solvent PC and the negative electrode active material graphite It can be estimated that this is because the contact reaction with the carbon powder can be suppressed.

The dehydration polycondensation process can be represented by the following formula:
PAA-PHA (amide bond); R-COOH + R-NH ₂ → R-CONH-R + H ₂ O
PAA-PAAd (imide bond); R-COOH + R-CONH ₂ → R-CONHCO-R + H ₂ O
(R = polymer main chain)

On the other hand, when PVDF is used as a binder, since the entire graphitic carbon powder is encased in a network, as shown schematically in FIG. The graphene layer of graphite is exfoliated and charge / discharge reaction is impossible. In contrast, PA having an amide bond or an imide bond
Similarly, in the case of A, as shown in FIG. 1, in order to selectively form a passivation film so as to cover the graphite edge portion of the graphitic carbon powder, solvated molecules are inserted. It is presumed that stable charging / discharging with suppression of the above became possible.

According to the present invention, a graphite material having high crystallinity can be used as a negative electrode active material of a lithium ion secondary battery using a non-aqueous electrolyte containing PC as a main component of a solvent, and a battery having high capacity and high safety. A negative electrode can be obtained.

In the lithium ion secondary battery of the present invention, graphitic carbon powder having a graphitization degree of 0.8 or more is used as the negative electrode active material. The graphitization degree of the graphitic carbon powder is more preferably 0.85 or more. Graphite includes natural graphite, artificial graphite, and quiche graphite. In order to increase the discharge capacity in a practical battery, it is advantageous that the degree of graphitization is as high as possible. However, if it is a small amount (30% by mass or less, preferably 10% by mass or less of the entire graphite carbon powder), artificial graphite or quiche graphite powder can be used in combination with natural graphite powder. These graphitic carbon powders have an average particle size of about 3 to 100 μm, more preferably about 5 to 50 μm. If the particle size is too small, the specific surface area increases, the reaction with the electrolyte increases, and the irreversible capacity may increase.

The degree of graphitization of the graphitic carbon powder is measured from a diffraction pattern such as 002 plane of X-ray diffraction. When the degree of graphitization is less than 0.8, the required charging time of the battery is increased and the rate characteristics are deteriorated. Specific examples of the carbonaceous material having a graphitization degree of 0.8 or more include artificial graphite, graphite, natural graphite, MCMB, pitch-based carbon fiber, etc., fired at 2,000 ° C. or more. Natural graphite is preferred. Here, “graphitization degree” is a numerical value from 0 to 1.
. It refers to a parameter indicating the microstructure of a carbonaceous material having zero. Generally, carbon having a high degree of graphitization has a fine structure close to that of graphite as it is high, and carbon having a low degree of graphitization has a fine structure close to that of coke as it is low.

In the present invention, the graphitic carbon powder suitable for use as the negative electrode active material is 270 mAhr / g or more in terms of electric capacity by a half cell with a charge / discharge rate of 0.2 mA / cm ² when expressed in electric capacity. belongs to. This electric capacity is 300 mAhr / g or more, especially 3
More preferably, it is 30 mAhr / g or more. Such a large electric capacity indicates a highly crystalline carbon material having a developed carbon hexagonal network structure. Most preferably, when lithium ions are intercalated, a composition represented by C ₆ Li, that is, a stage 1 structure containing one lithium atom per six carbon atoms can be formed.

In order to manufacture the secondary battery of the present invention, the graphitic carbon powder and PAA are slurried with distilled water, and the PAH is in weight% (PAH / PAA) of 0.1 to 1.0% with respect to the amount of PAA.
(PAH / PAAd) 0.1 to 1.% by weight of PAAd relative to the amount of PAH or PAA.
A slurry obtained by adding 0% PAAd is applied to a current collector and dried. PAA to PA
It is considered that the polycondensation reaction proceeds spontaneously by adding H or PAAd, and that this binding reaction is promoted by heat treatment. The heat treatment is preferably about 100 to 200 ° C. and about 1 to 2 hours.

When the amount of PAH or PAAd relative to the amount of PAA is less than 0.1 wt%, a dehydration polycondensate is not sufficiently formed, and when it exceeds 1.0 wt%, PAA and PAH or PAAd are polymerized,
An appropriate slurry cannot be obtained, and an electrode cannot be produced. PA in terms of cycle characteristics
The weight percent of PAH or PAAd with respect to the amount of A is more preferably 0.3 to 0.5%.

The formation of the slurry is preferably from room temperature to about 60 ° C. The slurry should be a suitable current collector (rolled copper foil,
A copper electrodeposited copper foil or the like) is coated using a doctor blade method or the like, dried, and then consolidated by roll rolling or the like to produce a negative electrode. If necessary, a suitable conductive agent may be mixed in the slurry to improve conductivity.

The mixing ratio of the graphitic carbon powder and PAA is such that the PAA is 0. 0 with respect to the amount of the graphite carbon powder.
It is preferably 1 to 30% by weight, particularly 0.5 to 10% by weight. If there is too much PAA,
The internal resistance of the electrode increases, which is not preferable. Conversely, when the PAA is too small, it is difficult to obtain an electrode in which the current collector and the graphitic carbon powder are integrally and firmly bound. The solvent for PAA is N-
Methyl pyrrolidone, distilled water or the like may be used.

The proportion of propylene carbonate in the non-aqueous electrolyte is 50% by volume or more, more preferably 90% by volume or more, and even if it is 100% by volume, PC decomposition can be suppressed. Non-aqueous solvents used in combination with propylene carbonate include ethylene carbonate, chloroethylene carbonate, trifluoropropylene carbonate, butylene carbonate, diethyl carbonate, dimethyl carbonate, ethyl methyl carbonate, methyl propyl carbonate, isopropyl methyl carbonate, ethyl propyl carbonate, isopropyl Ethyl carbonate, butylmethyl carbonate, butylethyl carbonate, dipropyl carbonate, 1,2-dimethoxyethane, γ-butyrolactone, tetrahydrofuran, 2-methyltetrahydrofuran, sulfolane, 3-methylsulfolane, 2,4-dimethylsulfolane, 1,3 -Dioxolane, methyl acetate, ethyl acetate, methyl formate, ethyl formate, etc. .

Examples of the lithium salt of the electrolyte include LiClO ₄ , LiPF ₆ , LiBF ₄ , and LiAsF _6.
, LiCl, LiBr and other inorganic salts, LiCF ₃ SO ₃ , LiN (SO ₂ CF ₃ ) ₂ , LiN
Organic salts such as (SO ₂ C ₂ F ₅ ) ₂ , LiC (SO ₂ CF ₃ ) ₃ , LiN (SO ₃ CF ₃ ) _2, etc.
What is commonly used as the electrolyte of the nonaqueous electrolytic solution may be used. Among these, LiP
It is preferred to use F ₆ , LiBF ₄ or LiClO ₄ . The electrolyte is 0.5% in a non-aqueous solvent.
It is preferable to dissolve so as to be -2.0 mol / L. Moreover, although one type of electrolyte is usually used, two or more types can be used in combination if desired.

The lithium secondary battery according to the present invention can be composed of ordinary members except for the above-described negative electrode and non-aqueous electrolyte. As the positive electrode active material, LiCo that can occlude and release lithium ions
It is manufactured using a lithium-containing composite metal oxide such as O ₂ , LiNiO ₂ , LiMnO ₂ , LiMn ₂ O ₄ .

In order to manufacture a positive electrode using these positive electrode active materials, a material obtained by adding a binder, carbon black, and the like to the positive electrode active material may be applied to the current collector, as in the case of the negative electrode. A polyolefin nonwoven fabric or a porous film may be used as the separator for holding the electrolytic solution. The shape of the battery is not particularly limited, and may be any of a cylindrical shape, a square shape, a coin shape, a sheet shape, and the like.

Natural graphite powder (average particle size 3μm) 0.9g and PAA (weight average molecular weight 1,000,000) in a mortar
0.1 g (about 10 wt% with respect to the amount of graphite) was added and slurried with distilled water. Then, 0.5 ml of 10-3M PAH (weight average molecular weight 15,000) aqueous solution in air at room temperature
(About 0.4 wt% with respect to the amount of PAA) was added, and further stirred to prepare a slurry. The obtained slurry was applied to a Ni mesh (100 mesh) as a current collector. Then, the electrode was produced by making it dry for a whole day and night at 80 degreeC in the vacuum with the electrode dryer. The battery was produced in a glove box filled with argon gas (dew point: −100 ° C. or lower).

The electrochemical measurement uses a tripolar beaker cell, the working electrode is a graphite electrode,
PC containing lithium metal as a counter electrode and a reference electrode, and 1 moldm ⁻³ LiClO ₄ as an electrolyte
Solvent was used. The constant current charge / discharge test has a current density of 175 mAg ⁻¹ (C / 2), a potential range of 0
2 V (vs. Li ^/ Li ⁺ ) was performed.

FIG. 2 shows an initial charge / discharge curve. The number 1 in FIG. 2 shows the charge / discharge curve of the first cycle, and the number 2 shows the charge / discharge curve of the second cycle. As reported in the literature at the time of the first charge, a potential flat part (co-insertion reaction of solvated molecules) near 0.8 V was not confirmed, and a potential flat part (0.2% due to intercalation between graphite layers) V or less) can be clearly confirmed. Moreover, it turns out that the charging / discharging behavior of the next cycle is also stable.

Example 1 except that an aqueous solution of PAAd (weight average molecular weight 6,000,000) was used instead of PAH
A battery was produced under the same conditions as in Example 1. FIG. 3 shows an initial charge / discharge curve. The number 1 in FIG. 3 shows the charge / discharge curve of the first cycle, and the number 2 shows the charge / discharge curve of the second cycle. As reported in the literature at the time of the first charge, a potential flat part (co-insertion reaction of solvated molecules) near 0.8 V was not confirmed, and a potential flat part (0.2% due to intercalation between graphite layers) V or less) can be clearly confirmed. Moreover, it turns out that the charging / discharging behavior of the next cycle is also stable.

Comparative Example 1
Polyacrylic acid (PAA) (weight average molecular weight 1,000,000) which is an anionic water-soluble polymer as a binder is 3.5 wt%, 8.5 wt%, 10 wt%, 20 w with respect to natural graphite.
A negative electrode was produced in the same manner as in Example 1 except that a slurry prepared by adding t% each was used.

Comparative Example 2
A negative electrode was produced in the same manner as in Example 1 except that a slurry prepared by adding 10 wt% of PVDF to the amount of natural graphite as a binder was used.

FIG. 4 shows the discharge characteristics of the electrodes of Example 1, Example 2, and Comparative Example 1 obtained from the constant current charge / discharge test. In the case of PAA alone, the SEI coating layer existing at the edge of the graphite particles deteriorates due to the insertion / extraction of lithium accompanying the cycle, and the characteristics deteriorate rapidly after 10 cycles. On the other hand, in the electrode to which PAH or PAAd is added, it is suggested that the former is an amide bond and the latter is an imide bond, and this bond suppresses the deterioration of the SEI coating layer.

FIG. 5 shows initial charge / discharge curves in the case of Comparative Example 1 using a negative electrode using 1 moldm ⁻³ LiClO ₄ / PC as an electrolyte and using PAA as a binder and Comparative Example 2 using a negative electrode using PVDF as a binder. Is shown. From this result, the PVDF electrode shows almost no discharge capacity in the PC electrolyte, whereas the electrode coated with PAA shows EC
It was almost the same as the performance tested in the system electrolyte.

When PAA is used as a binder (Comparative Example 1), the co-insertion does not occur and EC +
Although it is very similar to the charge / discharge curve when using the DEC electrolyte, as reported previously, when PVDF is used as a binder (Comparative Example 2), about 0.8 V (vs.
A potential flat portion is confirmed in Li / Li ⁺ ), and it is estimated that a PC decomposition reaction occurs. Furthermore, it can be confirmed that the graphite layer is destroyed by co-insertion with PC and the discharge reaction is hardly shown.

By using graphitic carbon powder having a high graphitization degree as the negative electrode active material and using PC as the main component of the non-aqueous solvent, a lithium ion secondary battery having stable charge / discharge capability can be provided at low cost.

It is a figure which shows typically the behavior of a solvation molecule | numerator at the time of using PVDF as a binder, and the water-soluble polyacrylic acid containing the dehydration polycondensate of this invention. 3 is a graph showing a charge / discharge curve of the secondary battery of Example 1. FIG. 4 is a graph showing a charge / discharge curve of the secondary battery of Example 2. 4 is a graph showing discharge characteristics of Example 1, Example 2, and Comparative Example 1. 6 is a graph showing initial charge / discharge curves of secondary batteries of Comparative Example 1 and Comparative Example 2.

Claims (5)

In a lithium ion secondary battery having a non-aqueous electrolyte containing a positive electrode, a negative electrode, a separator and an organic solvent,
The negative electrode is a water-soluble polyacrylic acid containing a dehydrated polycondensate of polyacrylic acid (PAA) and polyallylamine hydrochloride (PAH) with a graphitic carbon powder having a graphitization degree of 0.8 or more,
Or water-soluble polyacrylic acid containing a dehydration polycondensate of polyacrylic acid (PAA) and polyacrylamide (PAAd),
A lithium ion secondary battery, wherein the organic solvent contains 50% by volume or more of propylene carbonate. 2. The lithium ion secondary battery according to claim 1, wherein the organic solvent comprises 90 to 100% by volume of propylene carbonate. The lithium ion secondary battery according to claim 1, wherein the graphitic carbon powder is natural graphite. Graphite carbon powder having a graphitization degree of 0.8 or more and polyacrylic acid (PAA) are slurried with distilled water, and 0.1% to 5.0% polyallylamine hydrochloride (% by weight with respect to the amount of PAA) (
The method for producing a negative electrode for use in a lithium ion secondary battery according to claim 1, wherein a slurry in which a dehydrated polycondensate is formed by adding (PAH) is applied to a current collector and dried. Graphite carbon powder having a graphitization degree of 0.8 or more and polyacrylic acid (PAA) are slurried with distilled water, and then 0.1% to 5.0% polyacrylamide (PA by weight with respect to the amount of PAA).
The method for producing a negative electrode for use in a lithium ion secondary battery according to claim 1, wherein the slurry in which Ad) is added to form a dehydrated polycondensate is applied to a current collector and dried.

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