Conductive polymer binder for silicon anode, manufacturing method thereof, and all-solid-state battery containing the same

Abstract

The present invention relates to a conductive polymer binder for a silicon anode, a method for manufacturing the same, and an all-solid-state battery including the same. More specifically, the conductive polymer binder for a silicon anode according to the present invention is a cross-linked copolymer in which a polystyrene-based copolymer containing anionic functional groups acting as binders is introduced into a conductive polymer having electronic conductivity. By applying this cross-linked copolymer as the conductive polymer binder, the electronic conductivity is excellent even in a low-voltage operating environment, and the shape of the electrode is maintained during charging and discharging, while simultaneously significantly improving lifespan characteristics. In addition, by applying the conductive polymer binder of the present invention to a silicon anode, the rate capability of the battery can be improved, and an all-solid-state battery can be realized that is environmentally friendly by using a water solvent instead of a toxic solvent such as NMP, and furthermore, can be operated at low pressure and high current density.

Description

Technology Field

[0001] The present invention relates to a conductive polymer binder for a silicon anode, a method for manufacturing the same, and an all-solid-state battery including the same. Background Technology

[0002] For the commercialization of all-solid-state batteries with high energy density, it is essential to possess a cathode with high theoretical capacity, electrochemical stability, low-pressure driving technology, and a high capacity retention rate.

[0003] Recently, research on the performance of all-solid-state batteries using silicon anodes that do not contain solid electrolytes or conductive materials has been conducted. If the silicon anode and the solid electrolyte form an electrochemically stable interface, a stable interface is formed that offsets the low ionic and electronic conductivity caused by the soft nature of the silicon anode during charging, thereby improving the lifespan characteristics of the all-solid-state battery.

[0004] However, these all-solid-state batteries yield performance results at unrealistically high pressures and still exhibit low discharge capacity when operated at low pressures.

[0005] In order to form an all-solid-state battery that surpasses the energy density of liquid electrolytes, the development of silicon anodes is essential, and the high operating pressure of 70 MPa must be lowered to the commercially viable range of 5 MPa.

[0006] In addition, electron conductivity is an electrochemical component that contributes significantly to electrode resistance at low driving pressures. Conventionally, electron conductivity was imparted to silicon anodes using fluoride-based polymers and nanosized conductive materials; however, these methods are being avoided due to process limitations, such as toxicity during the process and dispersion limitations of the conductive materials. Prior art literature

[0007] Korean Registered Patent No. 10-2405605 The problem to be solved

[0008] To solve the above-mentioned problem, the present invention aims to provide a conductive polymer binder for a silicon anode that simultaneously possesses excellent electronic conductivity and binder properties.

[0009] Furthermore, the present invention aims to provide a silicon cathode comprising the conductive polymer binder, which exhibits excellent electronic conductivity even in a low-voltage driving environment and significantly improved electrode shape retention and lifespan characteristics.

[0010] In addition, the present invention aims to provide an all-solid-state battery comprising the silicon anode of the present invention.

[0011] In addition, the present invention aims to provide a device including the all-solid-state battery of the present invention.

[0012] In addition, the present invention aims to provide a method for manufacturing a conductive polymer binder for a silicon anode. means of solving the problem

[0013] The present invention provides a conductive polymer binder for a silicon cathode comprising a cross-linked copolymer formed by copolymerizing a polystyrene-based copolymer containing anionic functional groups and a conductive polymer.

[0014] In addition, the present invention provides a silicon cathode comprising a cathode active material; and a conductive polymer binder according to the present invention.

[0015] In addition, the present invention provides an all-solid-state battery comprising: an anode; a silicon cathode according to the present invention; and a solid electrolyte membrane interposed between the anode and the silicon cathode.

[0016] In addition, the present invention provides a device comprising an all-solid-state battery according to the present invention, wherein the device is one selected from a communication device, a transportation device, and an energy storage device.

[0017] In addition, the present invention provides a method for manufacturing a conductive polymer binder for a silicon anode, comprising the step of copolymerizing a polystyrene-based copolymer containing anionic functional groups and a conductive polymer to obtain a cross-linked copolymer. Effects of the invention

[0018] The conductive polymer binder for the silicon anode of the present invention is a cross-linked copolymer in which a polystyrene-based copolymer containing anionic functional groups acting as binders is copolymerized with a conductive polymer having electronic conductivity. By applying this cross-linked copolymer as the conductive polymer binder, it is possible to have excellent electronic conductivity even in a low-voltage operating environment, maintain the shape of the electrode during charging and discharging, and significantly improve lifespan characteristics.

[0019] In addition, by applying the conductive polymer binder of the present invention to a silicon anode, the rate capability of the battery can be improved, and an all-solid-state battery can be realized that is environmentally friendly by using a water solvent instead of a toxic solvent such as NMP, and furthermore, can be operated at low pressure and high current density.

[0020] The effects of the present invention are not limited to those mentioned above. It should be understood that the effects of the present invention include all effects that can be inferred from the following description. Brief explanation of the drawing

[0021] Figure 1 is a graph showing the rate capability characteristics in high temperature and low pressure environments for a conventional all-solid-state battery containing a silicon anode containing a conductive material. FIG. 2 is a graph of the electronic conductivity of a silicon electrode for an all-solid-state battery manufactured using the silicon cathode of Example 2 and Comparative Example 4 according to the present invention. Figure 3 is a graph showing the rate capability of an all-solid-state battery using the silicon anode of Example 2 and Comparative Example 4 according to the present invention. FIG. 4 is a graph (a) showing the initial charge / discharge results of an all-solid-state battery half-cell manufactured using a silicon cathode manufactured in Example 2 and Comparative Examples 6-1 to 6-3 according to the present invention, and a graph (b) showing the lifespan of an all-solid-state battery half-cell after 50 cycles. FIG. 5 is a graph showing the rate capability of an all-solid-state battery half-cell manufactured using the silicon cathode prepared in Example 2 and Comparative Examples 6-1 to 6-3 according to the present invention. FIG. 6 is a graph evaluating the silicon anode peeling force of an all-solid-state battery half-cell manufactured using the silicon anodes prepared in Example 2 and Comparative Examples 6-1 to 6-3 according to the present invention. FIG. 7 is a graph measured using silicon cathodes prepared in Example 2 and Comparative Examples 5 to 7 according to the present invention. FIG. 8 is a graph showing the capacity and Coulomb efficiency of an all-solid-state battery after one cycle of charge and discharge, manufactured using the silicon cathode prepared in Example 2 and Comparative Examples 5 to 7 according to the present invention. Specific details for implementing the invention

[0022] The present invention will be described in more detail below with reference to one embodiment.

[0023] The present invention relates to a conductive polymer binder for a silicon anode, a method for manufacturing the same, and an all-solid-state battery including the same.

[0024] As previously explained, conventional all-solid-state batteries using silicon anodes had limitations in rate capability due to low electronic conductivity in low-pressure operating environments. In addition, there were problems that required overcoming process limitations, such as the use of fluoride-based polymer binders, toxic solvents like NMP, and nano-sized conductive materials.

[0025] Accordingly, in order to solve these problems, the present invention applies a cross-linked copolymer, in which a polystyrene-based copolymer containing anionic functional groups acting as binders is copolymerized with an electronically conductive polymer, as a conductive polymer binder, thereby providing excellent electronic conductivity even in a low-voltage operating environment and maintaining the shape of the electrode during charging and discharging while significantly improving the lifespan.

[0026] By applying a conductive polymer binder with excellent electronic conductivity and binder properties to a silicon anode, the rate capability of the battery can be improved, and an all-solid-state battery that is eco-friendly by using a water solvent instead of a toxic solvent such as NMP can be realized, and furthermore, can be operated at low pressure and high current density.

[0027] Specifically, the present invention provides a conductive polymer binder for a silicon anode comprising a polystyrene-based copolymer containing anionic functional groups and a cross-linked copolymer formed by copolymerizing a conductive polymer.

[0028] The above anionic functional group may be one or more selected from the group consisting of carboxylic acid groups, sulfonic acid groups, sulfate groups, phosphate groups, and ammonium groups, preferably may be a carboxylic acid group, a sulfonic acid group, or a mixture thereof, and most preferably may be a carboxylic acid group.

[0029] The above carboxylic acid group may be polyacrylic acid, polymaleic acid, or a mixture thereof, and preferably may be polymaleic acid. Silanol groups (Si-OH) are present on the surface of the silicon anode and can function as a binder by bonding with the above carboxylic acid groups (COOH). The above polyacrylic acid contains one carboxylic acid group per monomer, while polymaleic acid contains two. As a result, when the above polymaleic acid is applied as a conductive polymer binder for the silicon anode, the binder properties are much superior to those of the above polyacrylic acid, which can suppress cracking of the silicon anode and further improve the electrode lifespan.

[0030] The polystyrene-based copolymer containing the above-mentioned anionic functional group may be a copolymer in which a polystyrene-based polymer and polymaleic acid are copolymerized in a molar ratio of 0.5 to 2.0:1, preferably 0.7 to 1.5:1, more preferably 0.8 to 1.2:1, and most preferably 1:1.

[0031] At this time, if the content of the polystyrene-based polymer is less than 0.5 molar ratio, the electronic conductivity may decrease during charging, and conversely, if it exceeds 2.0 molar ratio, a large volume expansion of the silicon anode occurs during charging and discharging, and as the number of charge-discharge cycles increases, the stability of the electrode and the lifespan of the battery may rapidly decrease.

[0032] In conventional all-solid-state batteries, the Li-Si alloy can exhibit high electronic conductivity when the battery is charged and sufficient Li ions are inserted into the silicon anode. However, due to the large volume expansion rate (>300%) during charging and discharging, there is a problem in that it is difficult to suppress cracking of the silicon anode using only the conductive polymer. In the present invention, polymaleic acid copolymerized with the polystyrene-based polymer acts as a binder to hold the silicon and silicon particles together, thereby maintaining the shape of the electrode while suppressing electrode cracking and extending battery life.

[0033] Most preferably, the polystyrene copolymer containing the anionic functional group may be a compound represented by the following chemical formula 1.

[0034] [Chemical Formula 1]

[0035]

[0036] (In the above Chemical Formula 1, x and y are the polymerization molar ratios of each repeating unit, where x is 0.5 to 10, y is 0.5 to 1.0, and x:y is 0.5:0.5 to 20:1.)

[0037] Preferably, in the above formula 1, x is 0.5 to 2, y is 0.5 to 1.0, and x:y may be 1:0.5 to 1:1.

[0038] At this time, if either of the ranges of x to 0.5 to 10 and y to 0.5 to 1.0 in the above chemical formula 1 does not satisfy the above range, cracks may occur on the surface of the silicon negative electrode or the electronic conductivity of the negative electrode may be insufficient, which may significantly reduce the battery life.

[0039] The above-mentioned conductive polymer is environmentally friendly as it uses water as a solvent and possesses excellent electronic conductivity. Generally, silicon-based active materials contained in silicon anodes exhibit low electronic conductivity if lithium (Li) ions are not sufficiently lithiated; however, in the present invention, the use of the above-mentioned conductive polymer can serve to reinforce the low electronic conductivity of silicon-based active materials.

[0040] The above-mentioned conductive polymer may be one or more selected from the group consisting of polythiophene-based polymers, polyaniline-based polymers, polypyrrole-based polymers, polyacetylene-based polymers, polyazine-based polymers, polyphenylene-based polymers, and polyselenophene-based polymers. Preferably, the conductive polymer may be a polythiophene-based polymer, a polyaniline-based polymer, or a mixture thereof, and most preferably, it may be a polythiophene-based polymer.

[0041] The cross-linked copolymer according to the present invention is poly(3,4-ethylenedioxythiophene)-(carboxylated polystyrene), PEDOT:CP), poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonate)-(carboxylated polystyrene), PEDOT:PSS:CP), poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonate)-poly(acrylic acid)), PEDOT:PSS:PAA, It may be one or more selected from the group consisting of poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonate-co-acrylic acid), PEDOT:P(SS-co-AA)) and poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonic acid-co-polymaleic acid), PEDOT:P(SSA-co-MA)).

[0042] Preferably, the crosslinked copolymer may be PEDOT:P(SS-co-AA) or PEDOT:P(SSA-co-MA), and most preferably, PEDOT:P(SSA-co-MA).

[0043] The above PEDOT:P(SSA-co-MA) may be a compound represented by the following chemical formula 2.

[0044] [Chemical Formula 2]

[0045]

[0046] (In the above Chemical Formula 2, n and m are the polymerization molar ratios of each repeating unit, where n is 0.5 to 1, m is 0.8 to 7.5, and n:m is 0.5:0.8 to 1:7.5.)

[0047] Preferably, in the above formula 2, n is 0.5 to 1, m is 1 to 2.5, and n:m may be 0.5:1 to 1:2.5.

[0048] At this time, if either of the ranges of n to 0.5 to 1 and m to 0.8 to 7.5 in the above chemical formula 2 does not satisfy the above range, when applied to a silicon anode, the rate capability of the electrode may be reduced or a limit on capacity development may appear in high-rate evaluation.

[0049] Meanwhile, the present invention provides a silicon cathode comprising a cathode active material; and a conductive polymer binder according to the present invention.

[0050] The above silicon anode is environmentally friendly because it uses water as a solvent instead of a polar solvent by including the conductive polymer binder in the anode active material, instead of using conventional fluoride-based polymer binders, nano-sized carbon black conductive materials, and toxic solvents such as NMP, and can achieve high charge / discharge efficiency and lifespan characteristics even in low-voltage operating environments due to excellent electronic conductivity and binder properties.

[0051] The above silicon cathode may comprise 87 to 93 weight% of a cathode active material and 7 to 13 weight% of a conductive polymer binder, preferably 88 to 91 weight% of the cathode active material and 9 to 12 weight% of the conductive polymer binder, and most preferably 90 weight% of the cathode active material and 10 weight% of the conductive polymer binder. In particular, if the content of the conductive polymer binder is less than 7 weight%, the sheet resistance of the electrode is high, which may significantly reduce the capacity retention rate and Coulomb efficiency of the battery; conversely, if it exceeds 13 weight%, the sheet resistance of the electrode is low, but the electronic conductivity of the electrode becomes unstable due to the excessive binder content, which may reduce the charge / discharge efficiency.

[0052] In addition, the present invention provides an all-solid-state battery comprising: an anode; a silicon cathode according to the present invention; and a solid electrolyte membrane interposed between the anode and the silicon cathode.

[0053] In addition, the present invention provides a device comprising an all-solid-state battery according to the present invention, wherein the device is one selected from a communication device, a transportation device, and an energy storage device.

[0054] In addition, the present invention provides a method for manufacturing a conductive polymer binder for a silicon anode, comprising the step of copolymerizing a polystyrene-based copolymer containing anionic functional groups and a conductive polymer to obtain a cross-linked copolymer.

[0055] The above anionic functional group may be one or more selected from the group consisting of carboxylic acid groups, sulfonic acid groups, sulfate groups, phosphate groups, and ammonium groups. Preferably, the above anionic functional group may be a carboxylic acid group, a sulfonic acid group, or a mixture thereof, and most preferably, it may be a carboxylic acid group.

[0056] The polystyrene-based copolymer containing the above-mentioned anionic functional group may be a copolymer in which a polystyrene-based polymer and polymaleic acid are copolymerized in a molar ratio of 0.5 to 1.8:1, preferably 0.8 to 1.4:1, more preferably 0.8 to 1.2:1, and most preferably 1:1.

[0057] Preferably, the polystyrene copolymer containing the anionic functional group may be a compound represented by the following chemical formula 1.

[0058] [Chemical Formula 1]

[0059]

[0060] (In the above Chemical Formula 1, x and y are the polymerization molar ratios of each repeating unit, where x is 0.5 to 10, y is 0.5 to 1.0, and x:y is 0.5:0.5 to 20:1.)

[0061] The conductive polymer may be one or more selected from the group consisting of polythiophene-based polymers, polyaniline-based polymers, polypyrrole-based polymers, polyacetylene-based polymers, polyazine-based polymers, polyphenylene-based polymers, and polyselenophene-based polymers. Preferably, the conductive polymer may be a polythiophene-based polymer, a polyaniline-based polymer, or a mixture thereof, and most preferably, it may be a polythiophene-based polymer.

[0062] The above cross-linked copolymer is poly(3,4-ethylenedioxythiophene)-(carboxylated polystyrene), PEDOT:CP), poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonate)-(carboxylated polystyrene), PEDOT:PSS:CP), poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonate)-poly(acrylic acid)), PEDOT:PSS:PAA, It may be one or more selected from the group consisting of poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonate-co-acrylic acid), PEDOT:P(SS-co-AA)) and poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonic acid-co-polymaleic acid), PEDOT:P(SSA-co-MA)).

[0063] Preferably, the crosslinked copolymer may be PEDOT:P(SS-co-AA) or PEDOT:P(SSA-co-MA), and most preferably, may be PEDOT:P(SS-co-AA).

[0064] The above PEDOT:P(SS-co-AA) may be a compound represented by the following chemical formula 2.

[0065] [Chemical Formula 2]

[0066]

[0067] (In the above Chemical Formula 2, n and m are the polymerization molar ratios of each repeating unit, where n is 0.5 to 1, m is 0.8 to 7.5, and n:m is 0.5:0.8 to 1:7.5.)

[0068] The step of obtaining the cross-linked copolymer may be copolymerized by including the polystyrene-based copolymer containing the anionic functional group and the conductive polymer in a molar ratio of 0.5:0.8 to 1:7.5, preferably 0.5:0.8 to 1:5, and most preferably 0.5:0.8 to 1:2.5. At this time, if the content of the conductive polymer is less than 0.8 molar ratio, the rate capability of the battery may be degraded due to low ionic conductivity and electronic conductivity, and conversely, if it exceeds 7.5 molar ratio, a stable interface is not sufficiently formed on the surface of the silicon negative electrode during charging, which may result in a low discharge capacity when operating at low pressure.

[0069] The step of obtaining the above cross-linked copolymer can be performed by cross-linking at a temperature of 25 to 30°C for 12 to 24 hours. At this time, if either the polymerization temperature or the polymerization time does not satisfy the above range, the cross-linked copolymer may not be sufficiently polymerized, and thus the electronic conductivity or binder properties may not be properly expressed.

[0070] The step of obtaining the above cross-linked copolymer may further mix a reducing agent with a polystyrene-based copolymer containing anionic functional groups and a conductive polymer.

[0071] The above reducing agent may be Fe2(SO4)3, Na2S2O3, or a mixture thereof.

[0072] The present invention will be explained in more detail below based on embodiments, but the present invention is not limited by the following embodiments.

[0073] Example 1 and Comparative Examples 1 to 3: Preparation of conductive polymer binder

[0074] As shown in Reaction Scheme 1 and Table 1 below, a mixture was prepared by mixing 30.064 g of the reducing agent Fe2(SO4) and 33.353 g of Na2S2O with a P(SSA-co-MA) polymer (where x is 0.5 to 2.0 and y is 0.5 to 1.0) and an EDOT polymer in a mixing vessel. Then, the above mixture was copolymerized at 25°C for 24 hours to prepare the PEDOT:P(SSA-co-MA) copolymer of Reaction Scheme 1 below (where n is 1 and m is 2.5). Copolymers of Example 1 and Comparative Examples 1 to 3 were prepared, respectively, according to the molar ratio of PSSA and PMA in the PEDOT:P(SSA-co-MA) copolymer as shown in Table 1 below.

[0075] [Reaction Equation 1]

[0076]

[0077]

[0078] Example 2 and Comparative Examples 4 to 7: Preparation of silicon cathode

[0079] A cathode slurry was prepared by mixing silicon powder and a binder, such as the conductive polymer binder or PVdF binder prepared in Example 1 and Comparative Examples 1 to 3, in a water solvent as shown in Table 2 below. Then, the cathode slurry was applied onto a copper current collector using a blade and vacuum dried at room temperature for 1 hour. Subsequently, the temperature was raised to 80°C and dried for 11 hours to prepare a silicon cathode.

[0080]

[0081] Experimental Example 1: Evaluation of Rate Capability Characteristics of an All-Solid State Battery Using a Conductive Material

[0082] The rate capability characteristics of a conventional all-solid-state battery fabricated using a silicon anode containing a conductive material were evaluated in high temperature and low pressure environments. The rate capability evaluation was performed by conducting 3 cycles each of 0.05C, 0.1C, 0.2C, 0.5C, and 1.0C based on 1C = 3500 mA / g. The results are shown in Figure 1.

[0083] Figure 1 is a graph showing the rate capability characteristics in high temperature and low pressure environments for a conventional all-solid-state battery containing a silicon anode containing a conductive material. Referring to Figure 1, it was confirmed that the electrochemical characteristics of the conventional all-solid-state battery mixed with a conductive material in a low-pressure environment reached a level similar to that of high pressure, and through this, it was confirmed that the component that has a significant influence on electrochemical performance is electronic conductivity.

[0084] Experimental Example 2: Evaluation of Electronic Conductivity of All-Solid State Batteries According to Binder Type

[0085] All-solid-state batteries were each manufactured by a conventional method using the silicon anodes of Example 2 and Comparative Example 4, and the electronic conductivity of the silicon anodes was evaluated according to the insertion and extraction of Li ions during charging and discharging. The results are shown in Figure 2.

[0086] FIG. 2 is a graph of the electronic conductivity of the silicon electrode for an all-solid-state battery manufactured using the silicon anodes of Example 2 and Comparative Example 4. Referring to FIG. 2, it was confirmed that Example 2 exhibits superior electronic conductivity compared to Comparative Example 4 during the lithium ion insertion and extraction processes during charging and discharging. Through this, it was found that excellent electronic conductivity can be achieved without a conductive material when the conductive polymer binder is used instead of the PVDF binder.

[0087] Experimental Example 3: Evaluation of Rate Capability Characteristics of All-Solid State Batteries According to Binder Type

[0088] All-solid-state batteries were prepared using the silicon cathodes of Example 2 and Comparative Example 4 by a conventional method, and the rate capability of the batteries was evaluated by performing 18 charge-discharge cycles. The rate capability evaluation was performed with 3 cycles each at 0.05C, 0.1C, 0.2C, 0.5C, and 1.0C, based on 1C = 3500 mA / g. The results are shown in Figure 3.

[0089] Figure 3 is a graph showing the rate capability of an all-solid-state battery using the silicon anodes of Example 2 and Comparative Example 4. Referring to Figure 3, it was confirmed that Example 2 exhibited excellent rate capability overall in each section, whereas Comparative Example 4 showed relatively low rate capability. Through this, it was found that the conductive polymer binder can improve rate capability by possessing excellent electronic conductivity while simultaneously having binder characteristics.

[0090] Experimental Example 4-1: Evaluation of Lifetime Characteristics of All-Solid State Batteries According to PSSA:PMA Ratio

[0091] Half cells of an all-solid-state battery were prepared by a conventional method using the silicon cathodes prepared in Example 2 and Comparative Examples 6-1 to 6-3 above, and the battery life was evaluated. The life evaluation was performed by conducting 50 cycles of charge and discharge at 0.2 C (1C = 3500 mA / g). The results are shown in Fig. 4.

[0092] FIG. 4 is a graph (a) showing the initial charge-discharge results of an all-solid-state battery half-cell manufactured using the silicon cathode prepared in Example 2 and Comparative Examples 6-1 to 6-3, and a graph (b) showing the lifespan of the all-solid-state battery half-cell after 50 cycles. Referring to FIG. 4 (a), in the initial charge-discharge graph, it was confirmed that the charge and discharge efficiencies of Example 2 and Comparative Example 6-3 were superior to those of Comparative Examples 6-1 and 6-2.

[0093] In addition, referring to Figure 4(b) above, in the case of Example 2, it was confirmed that the battery life was maintained at a high level even as the number of cycles increased, and that the battery capacity remained high at over 80% even after 50 cycles without significantly decreasing.

[0094] On the other hand, in the case of Comparative Example 6-3 above, the discharge capacity was excellent initially, but as the number of cycles increased, the battery life decreased, and after 25 cycles, it deteriorated further than Example 2 above. In addition, in the case of Comparative Examples 6-1 and 6-2 above, the battery life decreased rapidly as the number of cycles increased, and after 50 cycles, the battery life decreased significantly to 50% or less.

[0095] Experimental Example 4-2: Evaluation of Rate Capability Characteristics of All-Solid State Batteries According to PSSA:PMA Ratio

[0096] After manufacturing half-cells of an all-solid-state battery by a conventional method using the silicon cathodes prepared in Example 2 and Comparative Examples 6-1 to 6-3 above, the rate capability characteristics of the battery were evaluated in the same manner as in Experimental Example 3 above. The results are shown in FIG. 5.

[0097] FIG. 5 is a graph showing the rate capability characteristics of all-solid-state battery half-cells manufactured using silicon cathodes prepared in Example 2 and Comparative Examples 6-1 to 6-3. Referring to FIG. 5, Example 2 showed an equivalent or superior capacity retention rate in each section compared to Comparative Examples 6-1 to 6-3.

[0098] On the other hand, in the case of Comparative Examples 6-1 and 6-2 above, it was found that a low capacity retention rate was exhibited because no PMA was included, and cracks occurred in the electrode due to the volume expansion of the silicon anode during charging and discharging. In addition, in the case of Comparative Example 6-3 above, although the capacity retention rate increased as the binding function was added due to sufficiently high electronic conductivity and PMA content, the limit of the capacity retention rate was confirmed because the PMA content was insufficient compared to Example 2.

[0099] Experimental Example 4-3: Evaluation of Electrode Peeling Strength of All-Solid State Batteries According to PSSA:PMA Ratio

[0100] After manufacturing half-cells of an all-solid-state battery by a conventional method using the silicon anodes prepared in Example 2 and Comparative Examples 6-1 to 6-3 above, the peel strength of the silicon anode was evaluated. The electrode peel strength was measured using the electrode peel strength measurement method of a universal testing machine (UTM). After fixing the silicon electrode to the substrate, Scotch tape (adhesion strength between the tape and the Si electrode > adhesion strength between the silicon electrode and the Cu current collector) was attached to the area to be measured for adhesion strength, and the force between the silicon electrode and the Cu current collector was measured using the UTM. The results are shown in Fig. 6.

[0101] FIG. 6 is a graph evaluating the silicon anode peeling force of an all-solid-state battery half-cell manufactured using the silicon anodes prepared in Example 2 and Comparative Examples 6-1 to 6-3. Referring to FIG. 6, in the case of Example 2, the silanol group (Si-OH) present on the surface of the silicon anode was combined with the carboxyl group (COOH) of the PMA in the most optimized state, resulting in excellent binder characteristics and exhibiting the highest electrode peeling force.

[0102] On the other hand, Comparative Example 6-1 did not contain any PMA, resulting in an unstable electrode peeling force due to weak binder characteristics. Additionally, in Comparative Examples 6-2 and 6-3, although the electrode peeling force increased due to the increase in the number of carboxyl groups (COOH) as the mixing ratio of PMA increased compared to PSSA, it showed a lower value compared to Example 2. In particular, Comparative Example 6-1 had the lowest electrode peeling force, and the value was 50% or less compared to Example 2.

[0103] Experimental Example 5: Evaluation of Electrode Sheet Resistance of All-Solid State Battery According to Mixing Ratio of Silicon and Conductive Polymer Binder

[0104] The sheet resistance of the top surface of the silicon cathode was evaluated using the silicon cathode prepared in Example 2 and Comparative Examples 5 to 7 above. The electrode sheet resistance was measured using a surface resistance meter (4-point probe measurement method). The results are shown in Fig. 7.

[0105] Figure 7 is a graph of sheet resistance measured using the silicon cathodes prepared in Example 2 and Comparative Examples 5 to 7. Referring to Figure 7, it was confirmed that the sheet resistance value of the electrode decreases as the content of the conductive polymer binder increases to 10 wt% and 15 wt%. In particular, no significant decrease in resistance was observed after the binder content of 10 wt%, and it was confirmed that the addition of an electron-conducting binder beyond this level could actually have the effect of hindering the lithium ion transport pathway. As shown in Experimental Example 6 described later, it was found that the electron conductivity of the electrode has an optimal point at 10 wt%.

[0106] Experimental Example 6: Evaluation of Capacity and Coulomb Efficiency of All-Solid State Battery According to Mixing Ratio of Silicon and Conductive Polymer Binder

[0107] All-solid-state batteries were manufactured by a conventional method using the silicon anodes prepared in Example 2 and Comparative Examples 5 to 7 above, and the capacity and Coulomb efficiency of the batteries were evaluated after one cycle of charge and discharge. Coulomb efficiency was calculated using the method of charge capacity (delithiation) / discharge capacity (lithiation). The results are shown in Fig. 8.

[0108] FIG. 8 is a graph showing the capacity and Coulomb efficiency of all-solid-state batteries manufactured using silicon anodes prepared in Example 2 and Comparative Examples 5 to 7 after one cycle of charge and discharge. Referring to FIG. 8, it was confirmed that in the case of Example 2 and Comparative Examples 6-1 to 6-3, the electron conductivity of the electrode was best when 10 wt% of the conductive polymer binder was included. In addition, in the case of Comparative Examples 7-1 to 7-4, which contained 15 wt% of the conductive polymer binder, the sheet resistance of the electrode was lower; however, it was found that the excessive addition of the binder hindered the movement of lithium ions within the silicon anode, resulting in a decrease in the capacity and Coulomb efficiency of the battery.

Claims

Claim 1 A conductive polymer binder for a silicon anode comprising a cross-linked copolymer formed by copolymerizing a polystyrene-based copolymer containing anionic functional groups and a conductive polymer, wherein the cross-linked copolymer is poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonic acid-co-polymaleic acid), PEDOT:P(SSA-co-MA)) represented by the following chemical formula 2. [Chemical Formula 2] (In the above Chemical Formula 2, n and m are the polymerization molar ratios of each repeating unit, where n is 0.5 to 1, m is 0.8 to 7.5, and n:m is 0.5:0.8 to 1:7.5.) Claim 2 delete Claim 3 delete Claim 4 delete Claim 5 delete Claim 6 delete Claim 7 delete Claim 8 A silicon cathode comprising a negative electrode active material; and a conductive polymer binder of claim 1. Claim 9 In claim 8, the silicon cathode comprises 87 to 93 weight% of a cathode active material and 7 to 13 weight% of a conductive polymer binder. Claim 10 An all-solid-state battery comprising: a positive electrode; a silicon negative electrode of claim 8; and a solid electrolyte membrane disposed between the positive electrode and the silicon negative electrode. Claim 11 A device comprising the all-solid-state battery of claim 10, wherein the device is one selected from a communication device, a transportation device, and an energy storage device. Claim 12 A method for preparing a conductive polymer binder for a silicon anode, comprising the step of copolymerizing a polystyrene-based copolymer containing anionic functional groups and a conductive polymer to obtain a crosslinked copolymer; wherein the crosslinked copolymer is poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonic acid-co-polymaleic acid), PEDOT:P(SSA-co-MA)) represented by the following chemical formula 2. [Chemical Formula 2] (In the above Chemical Formula 2, n and m are the polymerization molar ratios of each repeating unit, where n is 0.5 to 1, m is 0.8 to 7.5, and n:m is 0.5:0.8 to 1:7.5.) Claim 13 delete Claim 14 delete Claim 15 delete Claim 16 delete Claim 17 delete Claim 18 delete Claim 19 delete Claim 20 A method for manufacturing a conductive polymer binder for a silicon cathode, wherein the step of obtaining the cross-linked copolymer is to cross-link at a temperature of 25 to 30 ℃ for 12 to 24 hours.

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