Conductive polymer binder for silicon negative electrode, manufacturing method therefor, and all-solid-state battery comprising same

Abstract

The present invention relates to a conductive polymer binder for a silicon negative electrode, a manufacturing method therefor, and an all-solid-state battery including same. More specifically, by applying, as a conductive polymer binder, a crosslinked copolymer in which a polystyrene-based copolymer polymer containing an anionic functional group serving as a binder is introduced to a conductive polymer having electronic conductivity, the conductive polymer binder for a silicon negative electrode of the present invention has excellent electronic conductivity even in a low-pressure operating environment and can significantly improve lifespan characteristics while maintaining the shape of an electrode during charging and discharging. In addition, when applied to a silicon negative electrode, the conductive polymer binder of the present invention can improve the rate-limiting characteristics of the battery, can realize an eco-friendly process due to the employment of an aqueous solvent instead of a toxic solvent such as NMP, and can further implement an all-solid-state battery that can operate under low pressure and at high current density.

Description

Conductive polymer binder for silicon anode, method for producing same, and all-solid-state battery comprising same

[0001] The present invention relates to a conductive polymer binder for a silicon negative electrode, a method for producing the same, and an all-solid-state battery including the same.

[0002]

[0003] To commercialize all-solid-state batteries with high energy density, it is essential to have a cathode with high theoretical capacity, electrochemical stability, low-pressure driving technology, and high capacity retention.

[0004] Recently, research has been conducted on the performance of all-solid-state batteries using silicon anodes that do not contain solid electrolytes or conductive materials. If the silicon anode and solid electrolyte form an electrochemically stable interface, the soft nature of the silicon anode, combined with its low ionic and electronic conductivity, can be offset during charging, thereby improving the lifespan of the all-solid-state battery.

[0005] However, these all-solid-state batteries perform at unrealistically high pressures and still exhibit low discharge capacities when operated at low pressures.

[0006] In order to form an all-solid-state battery that surpasses the energy density of liquid electrolytes, the development of a silicon anode is essential, and the high operating pressure of 70 MPa must be reduced to the commercially feasible level of 5 MPa.

[0007] Electronic conductivity is also an electrochemical component that significantly contributes to electrode resistance at low operating pressures. Previously, fluoride polymers and nano-sized conductive agents were used to enhance electronic conductivity in silicon anodes. However, these methods are now being avoided due to process limitations, such as toxicity generated during the process and limitations in the dispersion of conductive agents.

[0008]

[0009] In order to solve the above problems, the purpose of the present invention is to provide a conductive polymer binder for a silicon anode having both excellent electronic conductivity and binder properties.

[0010] In addition, the present invention aims to provide a silicon anode including the conductive polymer binder having excellent electronic conductivity even in a low-pressure driving environment and significantly improved shape retention and lifespan characteristics of the electrode.

[0011] In addition, the present invention aims to provide an all-solid-state battery including the silicon negative electrode of the present invention.

[0012] In addition, the present invention aims to provide a device including the all-solid-state battery of the present invention.

[0013] In addition, the present invention aims to provide a method for manufacturing a conductive polymer binder for a silicon cathode.

[0014]

[0015] The present invention provides a conductive polymer binder for a silicon negative electrode, which comprises a crosslinked copolymer formed by copolymerizing a polystyrene copolymer containing an anionic functional group and a conductive polymer.

[0016] In addition, the present invention provides a silicon negative electrode comprising a negative electrode active material; and a conductive polymer binder according to the present invention.

[0017] In addition, the present invention provides an all-solid-state battery comprising: a positive electrode; a silicon negative electrode according to the present invention; and a solid electrolyte membrane interposed between the positive electrode and the silicon negative electrode.

[0018] In addition, the present invention provides a device comprising an all-solid-state battery according to the present invention, wherein the device is any one selected from a communication device, a transportation device, and an energy storage device.

[0019] In addition, the present invention provides a method for producing a conductive polymer binder for a silicon negative electrode, comprising the step of copolymerizing a polystyrene copolymer containing an anionic functional group and a conductive polymer to obtain a crosslinked copolymer.

[0020]

[0021] The conductive polymer binder for a silicon anode of the present invention uses a crosslinked copolymer in which a polystyrene copolymer containing an anionic functional group acting as a binder is copolymerized with a conductive polymer having electronic conductivity, thereby exhibiting excellent electronic conductivity even in a low-voltage driving environment and significantly improving the life characteristics while maintaining the shape of the electrode during charge and discharge.

[0022] In addition, by applying the conductive polymer binder of the present invention to a silicon negative electrode, the rate characteristics of the battery can be improved, and an all-solid-state battery can be implemented that is environmentally friendly by using a water solvent instead of a toxic solvent such as NMP, and can be operated at low voltage and high current density.

[0023] The effects of the present invention are not limited to those mentioned above. It should be understood that the effects of the present invention encompass all effects inferred from the following description.

[0024]

[0025] Figure 1 is a graph showing the rate characteristics in a high temperature and low pressure environment for a conventional all-solid-state battery including a silicon anode containing a conductive material.

[0026] FIG. 2 is a graph of the electronic conductivity of a silicon electrode for an all-solid-state battery manufactured using the silicon negative electrode of Example 2 and Comparative Example 4 according to the present invention.

[0027] Figure 3 is a graph showing the rate characteristics of an all-solid-state battery using a silicon negative electrode of Example 2 and Comparative Example 4 according to the present invention.

[0028] FIG. 4 is a graph (a) showing the initial charge / discharge results of an all-solid-state battery half-cell manufactured using a silicon negative electrode manufactured in Example 2 and Comparative Examples 6-1 to 6-3 according to the present invention, and a graph (b) showing the life of the all-solid-state battery half-cell after 50 cycles.

[0029] FIG. 5 is a graph showing the rate characteristics of an all-solid-state battery half-cell manufactured using a silicon negative electrode manufactured in Example 2 and Comparative Examples 6-1 to 6-3 according to the present invention.

[0030] FIG. 6 is a graph evaluating the silicon anode peeling force of an all-solid-state battery half-cell manufactured using the silicon anode manufactured in Example 2 and Comparative Examples 6-1 to 6-3 according to the present invention.

[0031] Figure 7 is a graph measured using silicon cathodes manufactured in Example 2 and Comparative Examples 5 to 7 according to the present invention.

[0032] Figure 8 is a graph showing the capacity and coulombic efficiency of an all-solid-state battery manufactured using a silicon negative electrode manufactured in Example 2 and Comparative Examples 5 to 7 according to the present invention after one cycle of charge and discharge.

[0033]

[0034] Hereinafter, the present invention will be described in more detail with one embodiment.

[0035] The present invention relates to a conductive polymer binder for a silicon negative electrode, a method for producing the same, and an all-solid-state battery including the same.

[0036] As previously explained, conventional all-solid-state batteries utilizing silicon anodes have limited rate characteristics due to their low electronic conductivity in low-voltage operating environments. Furthermore, they face challenges in overcoming process limitations, such as the use of fluoride polymer binders, toxic solvents like NMP, and nano-sized conductive materials.

[0037] Accordingly, in order to solve this problem, the present invention applies a crosslinked copolymer in which a polystyrene copolymer containing an anionic functional group acting as a binder to a conductive polymer having electronic conductivity is copolymerized as a conductive polymer binder, thereby enabling excellent electronic conductivity even in a low-voltage driving environment, and significantly improving the lifespan while maintaining the shape of the electrode during charge and discharge.

[0038] By applying a conductive polymer binder with both excellent electronic conductivity and binder properties to a silicon anode, the rate characteristics 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 can be operated at low voltage and high current density.

[0039] Specifically, the present invention provides a conductive polymer binder for a silicon negative electrode comprising a crosslinked copolymer formed by copolymerizing a polystyrene copolymer containing an anionic functional group and a conductive polymer.

[0040] The above anionic functional group may be at least one selected from the group consisting of a carboxylic acid group, a sulfonic acid group, a sulfuric acid group, a phosphoric acid group, and an ammonium group, preferably a carboxylic acid group, a sulfonic acid group, or a mixture thereof, and most preferably a carboxylic acid group.

[0041] The carboxylic acid group may be polyacrylic acid, polymaleic acid, or a mixture thereof, and preferably polymaleic acid. A silanol group (Si-OH) exists on the surface of the silicon anode, which can function as a binder by bonding with the carboxylic acid group (COOH). The polyacrylic acid contains one carboxylic acid group per monomer, and polymaleic acid contains two. Therefore, when the polymaleic acid is applied as a conductive polymer binder for a silicon anode, the binder properties are much better than those of the polyacrylic acid, thereby suppressing cracking of the silicon anode and further improving the electrode life.

[0042] The polystyrene copolymer containing the above anionic functional group may be a copolymer in which a polystyrene polymer and polymaleic acid are copolymerized in a molar ratio of 0.5 to 2:1, preferably in a molar ratio of 0.7 to 1.5:1, more preferably in a molar ratio of 0.8 to 1.2:1, and most preferably in a molar ratio of 1:1.

[0043] At this time, if the content of the polystyrene polymer is less than 0.5 molar ratio, the electronic conductivity may decrease during charging, and the charge transfer resistance may increase due to the discontinuity of the electron transfer path between silicon particles. On the other hand, if the molar ratio exceeds 2, the volume expansion of the silicon negative electrode may occur during charging and discharging, and as the number of charge and discharge cycles increases, the stability of the electrode and the lifespan of the battery may rapidly decrease, and the phenomenon of electrolyte penetration obstruction due to excessive polymer matrix may occur, which may reduce the lithium ion diffusion coefficient and cause the ion transfer path to be blocked.

[0044] Conventional all-solid-state batteries can exhibit high electronic conductivity of Li-Si alloy when the battery is charged and Li ions are sufficiently inserted into the silicon anode. However, due to the volume expansion rate (>300%) during charge and discharge, it is difficult to suppress cracking of the silicon anode using only the conductive polymer. In the present invention, the polymaleic acid copolymerized with the polystyrene polymer acts as a binder to hold the silicon particles together, thereby maintaining the shape of the electrode while suppressing cracking of the electrode, thereby extending the battery life.

[0045] Most preferably, the polystyrene copolymer containing the anionic functional group may be a compound represented by the following chemical formula 1.

[0046] [Chemical Formula 1]

[0047]

[0048] (In the above chemical formula 1, x and y are the polymerization molar ratios of each repeating unit, x is 0.5 to 10, y is 0.5 to 1, and x:y is 0.5:0.5 to 20:1.)

[0049] Preferably, in the above chemical formula 1, x is 0.5 to 2, y is 0.5 to 1, and x:y may be 1:0.5 to 1:1.

[0050] At this time, if x in the chemical formula 1 does not satisfy any one of the ranges of 0.5 to 10 and y in the range of 0.5 to 1, cracks may occur on the surface of the silicon negative electrode or the electronic conductivity of the negative electrode may be insufficient, resulting in a significant reduction in the battery life.

[0051] The above conductive polymer is environmentally friendly because it uses water as a solvent, and has excellent electronic conductivity. Generally, the silicon-based active material contained in the silicon negative electrode exhibits low electronic conductivity if the lithium (Li) ions are not sufficiently lithiated. However, in the present invention, by using the conductive polymer, it can play a role in improving the low electronic conductivity of the silicon-based active material.

[0052] The conductive polymer may be at least one 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, a polythiophene-based polymer.

[0053] The crosslinked 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)-(Carboxylated polystyrene), PEDOT:PSS:CP), poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonate)-poly(acrylic acid)), PEDOT:PSS:PAA), It may be at least one 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-maleic acid), PEDOT:P(SSA-co-MA)).

[0054] 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).

[0055] The above PEDOT:P(SSA-co-MA) may be a compound represented by the following chemical formula 2.

[0056] [Chemical Formula 2]

[0057]

[0058] (In the above chemical formula 2, n and m are the polymerization molar ratios of each repeating unit, 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.)

[0059] Preferably, in the above chemical 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.

[0060] At this time, if n in the chemical formula 2 does not satisfy any one of the ranges of 0.5 to 1 and m in the range of 0.8 to 7.5, when applied to a silicon negative electrode, the rate characteristics of the electrode may deteriorate or a limit in capacity expression may appear in high-rate evaluation.

[0061] Meanwhile, the present invention provides a silicon negative electrode comprising a negative electrode active material; and a conductive polymer binder according to the present invention.

[0062] The above silicon anode is environmentally friendly by including the conductive polymer binder in the anode active material instead of using a conventional fluoride polymer binder, nano-sized carbon black conductive agent, and toxic solvent such as NMP, and uses water as a solvent instead of a polar solvent, and can realize high charge / discharge efficiency and life characteristics even in a low-voltage driving environment due to its excellent electronic conductivity and binder characteristics.

[0063] The silicon anode may comprise 87 to 93 wt% of a negative electrode active material and 7 to 13 wt% of a conductive polymer binder, preferably 88 to 91 wt% of the negative electrode active material and 9 to 12 wt% of a conductive polymer binder, and most preferably 90 wt% of the negative electrode active material and 10 wt% of a conductive polymer binder. In particular, if the content of the conductive polymer binder is less than 7 wt%, the sheet resistance of the electrode may increase, so that the capacity retention rate and coulombic efficiency of the battery may significantly decrease, and on the contrary, if it exceeds 13 wt%, the sheet resistance of the electrode may decrease, but the electronic conductivity of the electrode may become unstable due to the excessive binder content, so that the charge / discharge efficiency may decrease.

[0064] In addition, the present invention provides an all-solid-state battery comprising: a positive electrode; a silicon negative electrode according to the present invention; and a solid electrolyte membrane interposed between the positive electrode and the silicon negative electrode.

[0065] In addition, the present invention provides a device comprising an all-solid-state battery according to the present invention, wherein the device is any one selected from a communication device, a transportation device, and an energy storage device.

[0066] In addition, the present invention provides a method for producing a conductive polymer binder for a silicon negative electrode, comprising the step of copolymerizing a polystyrene copolymer containing an anionic functional group and a conductive polymer to obtain a crosslinked copolymer.

[0067] The anionic functional group may be at least one selected from the group consisting of a carboxylic acid group, a sulfonic acid group, a sulfuric acid group, a phosphoric acid group, and an ammonium group. Preferably, the anionic functional group may be a carboxylic acid group, a sulfonic acid group, or a mixture thereof, and most preferably, a carboxylic acid group.

[0068] The polystyrene copolymer containing the above anionic functional group may be a copolymer in which a polystyrene polymer and polymaleic acid are copolymerized in a molar ratio of 0.5 to 1.8:1, preferably in a molar ratio of 0.8 to 1.4:1, more preferably in a molar ratio of 0.8 to 1.2:1, and most preferably in a molar ratio of 1:1.

[0069] Preferably, the polystyrene copolymer containing the anionic functional group may be a compound represented by the following chemical formula 1.

[0070] [Chemical Formula 1]

[0071]

[0072] (In the above chemical formula 1, x and y are the polymerization molar ratios of each repeating unit, x is 0.5 to 10, y is 0.5 to 1, and x:y is 0.5:0.5 to 20:1.)

[0073] The conductive polymer may be at least one 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, a polythiophene-based polymer.

[0074] 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 at least one 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-maleic acid), PEDOT:P(SSA-co-MA)).

[0075] Preferably, the crosslinked copolymer may be PEDOT:P(SS-co-AA) or PEDOT:P(SSA-co-MA), and most preferably, PEDOT:P(SS-co-AA).

[0076] The above PEDOT:P(SS-co-AA) may be a compound represented by the following chemical formula 2.

[0077] [Chemical Formula 2]

[0078]

[0079] (In the above chemical formula 2, n and m are the polymerization molar ratios of each repeating unit, 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.)

[0080] The step of obtaining the above crosslinked copolymer may include copolymerizing the polystyrene copolymer including 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 characteristics of the battery may deteriorate due to low ionic conductivity and electronic conductivity, and conversely, if the molar ratio exceeds 7.5, a stable interface is not sufficiently formed on the surface of the silicon anode during charging, which may result in low discharge capacity during low-voltage operation.

[0081] The step of obtaining the above crosslinked copolymer may involve crosslinking 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 crosslinked copolymer may not be sufficiently polymerized, and thus the electronic conductivity or binder properties may not be properly expressed.

[0082] The step of obtaining the above crosslinked copolymer may further include mixing a reducing agent into the polystyrene copolymer containing an anionic functional group and the conductive polymer.

[0083] The reducing agent may be Fe2(SO4)3, Na2S2O3 or a mixture thereof.

[0084]

[0085] Hereinafter, the present invention will be described in more detail based on examples, but the present invention is not limited to the following examples.

[0086]

[0087] Example 1 and Comparative Examples 1 to 3: Preparation of conductive polymer binder

[0088] As shown in the following reaction scheme 1 and Table 1, a mixture was prepared by mixing 30.064 g of Fe2(SO4) and 3.353 g of Na2S2O as reducing agents in a mixing vessel with P(SSA-co-MA) polymer (wherein x is 0.5 to 2 and y is 0.5 to 1) and EDOT polymer. Then, the mixture was copolymerized at 25°C for 24 hours to prepare a PEDOT:P(SSA-co-MA) copolymer (wherein n is 1 and m is 2.5) of the following reaction scheme 1. Depending on the molar ratio of PSSA and PMA in the PEDOT:P(SSA-co-MA) copolymer, copolymers of Example 1 and Comparative Examples 1 to 3 were prepared, respectively, as shown in the following Table 1.

[0089] [Reaction Formula 1]

[0090]

[0091]

[0092]

[0093] Example 2 and Comparative Examples 4 to 7: Preparation of silicon cathode

[0094] The conductive polymer binder or PVdF binder prepared in Example 1 and Comparative Examples 1 to 3 was mixed with silicon powder and a binder in an aqueous solvent, as shown in Table 2 below, to prepare a negative electrode slurry, respectively. Next, the negative electrode slurry was applied onto a copper current collector with a blade and vacuum-dried at room temperature for 1 hour. Subsequently, the temperature was increased to 80°C and dried for 11 hours, thereby preparing each silicon negative electrode.

[0095]

[0096]

[0097] Experimental Example 1: Evaluation of the Rate-Dependent Characteristics of All-Solid-State Batteries According to the Use of Conductors

[0098] The rate characteristics of a conventional all-solid-state battery manufactured using a silicon anode containing a conductive material were evaluated under high-temperature and low-pressure environments. The rate characteristics were evaluated by conducting three cycles each of 0.05C-0.1C-0.2C-0.5C-1.0C, based on 1C=3500 mA / g. The results are shown in Figure 1.

[0099] Figure 1 is a graph showing the rate characteristics of a conventional all-solid-state battery comprising a silicon anode containing a conductive agent under high-temperature and low-pressure environments. Referring to Figure 1, it was confirmed that the electrochemical characteristics of a conventional all-solid-state battery containing a conductive agent in a low-pressure environment reached a level similar to that of a high-pressure battery, thereby confirming that the component affecting electrochemical performance is electronic conductivity.

[0100]

[0101] Experimental Example 2: Evaluation of Electronic Conductivity of All-Solid-State Batteries According to Binder Type

[0102] Using the silicon anodes of Example 2 and Comparative Example 4, all-solid-state batteries were manufactured by conventional methods, and the electronic conductivity of the silicon anode according to the insertion and de-insertion of Li ions during charge and discharge was evaluated. The results are shown in Fig. 2.

[0103] Fig. 2 is a graph of the electronic conductivity of the silicon electrode for the 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 had superior electronic conductivity compared to Comparative Example 4 during the insertion and de-insertion of lithium ions during charge and discharge. Through this, it was found that when the conductive polymer binder was used instead of the PVDF binder, superior electronic conductivity could be achieved without a conductive agent.

[0104]

[0105] Experimental Example 3: Evaluation of the Rate Characteristics of All-Solid-State Batteries According to the Type of Binder

[0106] All-solid-state batteries were manufactured using the silicon anodes of Example 2 and Comparative Example 4 using conventional methods, and then 18 charge-discharge cycles were performed to evaluate the rate characteristics of the batteries. The rate characteristics were evaluated by performing 3 cycles each of 0.05C-0.1C-0.2C-0.5C-1.0C based on 1C=3500 mA / g. The results are shown in Fig. 3.

[0107] Fig. 3 is a graph showing the rate characteristics of all-solid-state batteries using the silicon anodes of Example 2 and Comparative Example 4. Referring to Fig. 3, Example 2 showed excellent rate characteristics overall in each section, whereas Comparative Example 4 showed relatively low rate characteristics. Through this, it was found that the conductive polymer binder can improve rate characteristics by simultaneously having excellent electronic conductivity and binder properties.

[0108]

[0109] Experimental Example 4-1: Evaluation of the Lifetime Characteristics of All-Solid-State Batteries According to the PSSA:PMA Ratio

[0110] Half-cells of all-solid-state batteries were manufactured using the silicon anodes manufactured in Example 2 and Comparative Examples 6-1 to 6-3 using conventional methods, and the battery life was evaluated. The life evaluation was performed by performing 50 charge-discharge cycles at 0.2 C (1 C = 3500 mA / g). The results are shown in Fig. 4.

[0111] Fig. 4 is a graph (a) showing the initial charge / discharge results of all-solid-state battery half-cells manufactured using the silicon negative electrodes manufactured in Example 2 and Comparative Examples 6-1 to 6-3, and a graph (b) showing the life of the all-solid-state battery half-cells after 50 cycles. Referring to Fig. 4 (a), the initial charge / discharge graph confirmed that both charge and discharge efficiencies were superior in the case of Example 2 and Comparative Example 6-3 compared to Comparative Examples 6-1 and 6-2.

[0112] In addition, referring to (b) of the above-described Figure 4, in the case of the above-described Example 2, it was confirmed that the life of the battery was maintained at a high level even as the number of cycles increased, and that even after 50 cycles, the capacity of the battery was not significantly reduced and was maintained at a high level of 80% or more.

[0113] On the other hand, in the case of the above Comparative Example 6-3, the discharge capacity was initially excellent, but as the number of cycles increased, the life of the battery decreased, and after 25 cycles, it became worse than that of the above Example 2. In addition, in the case of the above Comparative Examples 6-1 and 6-2, as the number of cycles increased, the life of the battery decreased rapidly, and after 50 cycles, the life of the battery was greatly reduced to less than 50%.

[0114]

[0115] Experimental Example 4-2: Evaluation of Rate Characteristics of All-Solid-State Batteries According to PSSA:PMA Ratio

[0116] Half cells of all-solid-state batteries were manufactured using the silicon negative electrodes manufactured in Example 2 and Comparative Examples 6-1 to 6-3 using a conventional method, and then the rate characteristics of the batteries were evaluated using the same method as in Experimental Example 3. The results are shown in Fig. 5.

[0117] Fig. 5 is a graph showing the rate characteristics of all-solid-state battery half-cells manufactured using the silicon anodes manufactured in Example 2 and Comparative Examples 6-1 to 6-3. Referring to Fig. 5, Example 2 exhibited an excellent capacity retention rate that was equivalent to or superior to that of Comparative Examples 6-1 to 6-3 in each section.

[0118] On the other hand, in the case of Comparative Examples 6-1 and 6-2, it was found that cracks occurred in the electrode due to volume expansion of the silicon anode during charge and discharge because PMA was not included at all, resulting in low capacity retention. In addition, in the case of Comparative Example 6-3, as the electronic conductivity and the content of PMA were sufficiently high, the role of a binder was added, thereby increasing the capacity retention, but the content of PMA was insufficient compared to Example 2, confirming the limitation of the capacity retention.

[0119]

[0120] Experimental Example 4-3: Evaluation of Electrode Peeling Force of All-Solid-State Battery According to PSSA:PMA Ratio

[0121] Using the silicon anodes manufactured in Example 2 and Comparative Examples 6-1 to 6-3, half-cells of all-solid-state batteries were manufactured by a conventional method, and then the peeling strength of the silicon anodes was evaluated. The electrode peeling strength was measured using a universal testing machined (UTM) electrode peeling force measurement method. After fixing the silicon electrode to the substrate, scotch tape (adhesion between the tape and the Si electrode > adhesion between the silicon electrode and the Cu current collector) was attached to the area where the adhesive force was to be measured, and then the force between the silicon electrode and the Cu current collector was measured using the UTM. The results are shown in Fig. 6.

[0122] Fig. 6 is a graph evaluating the silicon anode peeling strength of an all-solid-state battery half-cell manufactured using the silicon anodes manufactured 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 most optimally bonded to the carboxyl group (COOH) of PMA, resulting in excellent binder properties and the highest electrode peeling strength.

[0123] On the other hand, in the case of Comparative Example 6-1, since it did not contain PMA at all, the electrode peeling force was unstable due to the weak binder characteristics. In addition, in the case of Comparative Examples 6-2 and 6-3, as the mixing ratio of PMA increased compared to PSSA, the electrode peeling force increased due to the increase in the number of carboxyl groups (COOH), but it showed a lower value than Example 2. In particular, in the case of Comparative Example 6-1, the electrode peeling force was the lowest, and its value was also 50% or less compared to Example 2.

[0124]

[0125] Experimental Example 5: Evaluation of the electrode surface resistance of an all-solid-state battery according to the mixing ratio of silicon and conductive polymer binder.

[0126] The surface resistance of the upper surface of the silicon anode was evaluated using the silicon anodes manufactured in Example 2 and Comparative Examples 5 to 7. The electrode surface resistance was measured using a surface resistance meter (4-point probe measurement method). The results are shown in Fig. 7.

[0127] Fig. 7 is a graph of sheet resistance measured using the silicon anodes manufactured in Example 2 and Comparative Examples 5 to 7. Referring to Fig. 7, it was confirmed that the sheet resistance value of the electrode decreased as the content of the conductive polymer binder increased to 10 wt% and 15 wt%. In particular, no significant decrease in resistance was observed after 10 wt% of the binder content, and it was confirmed that the addition of more electron-conductive binder may rather have the effect of interfering with the lithium ion transfer path. As shown in Experimental Example 6 described below, it was found that the electron conductivity of the electrode had an optimum point at 10 wt%.

[0128]

[0129] Experimental Example 6: Evaluation of the capacity and coulombic efficiency of an all-solid-state battery according to the mixing ratio of silicon and conductive polymer binder.

[0130] All-solid-state batteries were manufactured using the silicon anodes manufactured in Example 2 and Comparative Examples 5 to 7 by conventional methods, and the capacity and coulombic efficiency of the batteries were evaluated after one cycle of charge and discharge. The coulombic efficiency was measured using a single method of charge capacity (delithiation) / discharge capacity (lithiation). The results are shown in Fig. 8.

[0131] FIG. 8 is a graph showing the capacity and coulombic efficiency of all-solid-state batteries manufactured using the silicon anodes manufactured in Example 2 and Comparative Examples 5 to 7 after one charge-discharge cycle. Referring to FIG. 8, in the case of Example 2 and Comparative Examples 6-1 to 6-3, it was confirmed that the electronic conductivity of the electrode was the 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 included 15 wt% of the conductive polymer binder, the sheet resistance of the electrode was lower, but it was found that the excessive addition of the binder hindered the movement of lithium ions in the silicon anode, resulting in a decrease in the capacity and coulombic efficiency of the battery.

[0132]

[0133] The conductive polymer binder for a silicon anode of the present invention uses a crosslinked copolymer in which a polystyrene copolymer containing an anionic functional group acting as a binder is copolymerized with a conductive polymer having electronic conductivity, thereby exhibiting excellent electronic conductivity even in a low-voltage driving environment and significantly improving the life characteristics while maintaining the shape of the electrode during charge and discharge.

[0134] In addition, by applying the conductive polymer binder of the present invention to a silicon negative electrode, the rate characteristics of the battery can be improved, and an all-solid-state battery can be implemented that is environmentally friendly by using a water solvent instead of a toxic solvent such as NMP, and can be operated at low voltage and high current density.

Claims

1. A conductive polymer binder for a silicon negative electrode comprising a crosslinked copolymer formed using a polystyrene copolymer containing an anionic functional group and a conductive polymer.

2. In paragraph 1, A conductive polymer binder for a silicon negative electrode, wherein the anionic functional group is at least one selected from the group consisting of a carboxylic acid group, a sulfonic acid group, a sulfuric acid group, a phosphoric acid group, and an ammonium group.

3. In paragraph 1, A conductive polymer binder for a silicon negative electrode, wherein the polystyrene copolymer containing the above anionic functional group is a copolymer in which a polystyrene polymer and polymaleic acid are copolymerized in a molar ratio of 1 to 2:

1.

4. In paragraph 3, A conductive polymer binder for a silicon negative electrode, wherein the polystyrene copolymer containing the anionic functional group is a compound represented by the following chemical formula 1. [Chemical Formula 1] (In the above chemical formula 1, x and y are the polymerization molar ratios of each repeating unit, x is 0.5 to 10, y is 0.5 to 1, and x:y is 0.5:0.5 to 20:1.) 5. In paragraph 1, A conductive polymer binder for a silicon anode, wherein the conductive polymer is at least one 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.

6. In paragraph 1, 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)-(carboxylated polystyrene), PEDOT:PSS:CP), poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonate)-poly(acrylic acid)), PEDOT:PSS:PAA), poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonate-co-acrylic acid)) A conductive polymer binder for a silicon anode, comprising at least one 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)(Poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonic acid-co-maleic acid), PEDOT:P(SSA-co-MA)).

7. In paragraph 6, The above cross-linked copolymer is a conductive polymer binder for a silicon anode, which is poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonic acid-co-maleic 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, 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.) 8. A silicon negative electrode comprising a negative electrode active material; and a conductive polymer binder selected from any one of claims 1 to 7.

9. In paragraph 8, A silicon anode comprising 87 to 93 wt% of a negative electrode active material and 7 to 13 wt% of a conductive polymer binder.

10. Bipolar; Silicon cathode of Article 8; and An all-solid-state battery comprising a solid electrolyte membrane interposed between the positive electrode and the silicon negative electrode.

11. A device comprising the all-solid-state battery of clause 10, wherein the device is any one selected from a communication device, a transportation device, and an energy storage device.

12. A method for producing a conductive polymer binder for a silicon negative electrode, comprising the step of copolymerizing a polystyrene copolymer containing an anionic functional group and a conductive polymer to obtain a crosslinked copolymer.

13. In paragraph 12, A method for producing a conductive polymer binder for a silicon negative electrode, wherein the anionic functional group is at least one selected from the group consisting of a carboxylic acid group, a sulfonic acid group, a sulfuric acid group, a phosphoric acid group, and an ammonium group.

14. In paragraph 12, A method for producing a conductive polymer binder for a silicon negative electrode, wherein the polystyrene copolymer containing the above anionic functional group is a copolymer in which a polystyrene polymer and polymaleic acid are copolymerized in a molar ratio of 1 to 2:

1.

15. In paragraph 12, A method for producing a conductive polymer binder for a silicon negative electrode, wherein the polystyrene copolymer containing the above anionic functional group is a compound represented by the following chemical formula 1. [Chemical Formula 1] (In the above chemical formula 1, x and y are the polymerization molar ratios of each repeating unit, x is 0.5 to 10, y is 0.5 to 1, and x:y is 0.5:0.5 to 20:1.) 16. In paragraph 12, A method for manufacturing a conductive polymer binder for a silicon anode, wherein the conductive polymer is at least one 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.

17. In paragraph 12, 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)-(carboxylated polystyrene), PEDOT:PSS:CP), poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonate)-poly(acrylic acid)), PEDOT:PSS:PAA), poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonate-co-acrylic acid)) A method for producing a conductive polymer binder for a silicon anode, wherein the conductive polymer binder is at least one 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)(Poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonic acid-co-maleic acid), PEDOT:P(SSA-co-MA)).

18. In paragraph 17, A method for producing a conductive polymer binder for a silicon anode, wherein the cross-linked copolymer is poly(3,4-ethylenedioxythiophene)-(poly(styrenesulfonic acid-co-maleic 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, 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.) 19. In paragraph 12, A method for producing a conductive polymer binder for a silicon negative electrode, wherein the step of obtaining the crosslinked copolymer comprises copolymerizing a polystyrene-based copolymer including the anionic functional group and a conductive polymer in a molar ratio of 0.5:0.8 to 1:7.

5.

20. In paragraph 12, A method for producing a conductive polymer binder for a silicon negative electrode, wherein the step of obtaining the crosslinked copolymer comprises crosslinking at a temperature of 25 to 30°C for 12 to 24 hours.

Images