KR20210101850A - All-Solid-State Renewable Lithium-Organic Battery Comprising Single-Ion Conducting Polymer Electrolytes - Google Patents

Abstract

The present invention relates to an all-solid-state lithium-organic battery, and more specifically, to an all-solid-state renewable lithium-organic battery comprising a single ion conductive polymer electrolyte. The all-solid-state renewable lithium-organic battery according to an embodiment of the present invention is characterized by using a solid electrolyte comprising polymer nanoparticles having lithium ions bonded to a surface thereof. In the all-solid-state lithium-organic battery according to an embodiment of the present invention, an initial discharge capacity of 352 mAh g^-1, which is close to the theoretical capacity of 397 mAh g^-1 of P4VC, has been obtained, and high electrochemical stability and excellent charge/discharge rate (794 mA g^-1) have been shown.

Description

All-Solid-State Renewable Lithium-Organic Battery Comprising Single-Ion Conducting Polymer Electrolytes

The present invention relates to an all-solid-state lithium-organic battery, and more particularly, to an all-solid-state renewable lithium-organic battery comprising a single ion conductive polymer electrolyte.

As lithium batteries are used in all aspects of modern life, the demand for next-generation battery technology is increasing. In addition to technical issues such as high discharge capacity, high energy density, long cycle life and fast charging time ^[1,2] , concerns have been raised about environmental factors including the toxicity of cathode materials. ^[7-9]

Until recently, most research has focused on molecular design of redox-active organic materials that can control electrical and electrochemical properties. ^[4,9-11] These organic materials include not only conjugated quinones with low band-gap energy, but also ^[4,9,12-14] , N-hetero capable of multiple oxidation-reduction reactions. aromatic molecules ^[7,15] and organic radicals with fast charge transfer rates ^[16] are included. Among a wide range of organic electrode materials, quinone-based materials have attracted particular attention due to their wide range of chemical structures. Nevertheless, the dissolution of oxidation-reduction intermediates in liquid electrolytes remained an unresolved problem for a long time, which is closely related to the poor cycle stability of batteries. ^[17]

Therefore, much effort has been devoted to chemical or physical restraint as a strategy for inhibiting the dissolution of organic active materials. ^[18] Polymer-based active materials have emerged as the only solution because the diffusion rate is slower than that of small organic molecules. ^[19] Due to these efforts, long-term stability of more than 1000 cycles and ^{high discharge capacity of 300 mAh g -1} or more have been recently demonstrated in some organic cathode active materials. ^[14,19,20] Nevertheless, the high solubility of organics in liquid electrolytes remains an important disadvantage of most lithium-organic batteries.

In this regard, the use of solid or semi-solid polyelectrolytes has been regarded as a practical way to avoid loss of active material. ^{[21,22] For} this purpose, inorganic electrolytes (solid oxide and sulfide-based electrolytes) are promising candidates because they exhibit high conductivity despite being solid. ^[23,24] However, despite the excellent charge transfer rate of inorganic electrolytes with intrinsic single-ion conduction properties ^{[25], the} high cost, high density, lack of flexibility, and limited processability of materials allow the fabrication of next-generation batteries with various morphological configurations. remains a fatal flaw in ^[26]

Polyelectrolytes based on polyethylene oxide (PEO) doped with lithium salts have received considerable attention over the past several decades because they exhibit higher lithium ion conductivity than other polyelectrolytes. ^[27-30] However, despite efforts in this field, the reported ionic conductivities are generally in the ^{range of 10 -7} -10 ^-4 S cm ^-1 at room temperature, and their mechanical properties are very sensitive to temperature ^{[29,31,32] ]} Not suitable for practical applications. Therefore, most of the polyelectrolytes that have been successful in cell experiments are gel polyelectrolytes containing an excess of liquid additives. ^{[33,34] In} any case, lithium-organic batteries exhibiting long-term cycle characteristics when using solid or semi-solid electrolytes have not yet been achieved, and a factor in these results is the dissolution or diffusion of oxidation-reduction intermediates at the molecular level. because this happens ^[34,35]

Another important hurdle for lithium-organic batteries is their limited rate performance. This is because the charge transfer rate of the organic electrode material is inherently inferior to that of the inorganic material. ^[36,37] This problem becomes more serious when a solid electrolyte having a large charge transfer resistance at the electrolyte-electrode interface and an organic electrode material are combined. ^{[37] In} addition, in the case of the salt-doped PEO-based electrolyte, the lithium transition number is generally lower than 0.3, resulting in significant polarization at high current densities. ^[38] Single ion conductive polymer electrolytes can solve this problem, but single ion conductive polymers have a conductivity that is several orders of magnitude lower than double ion conductive polymers. ^[39-46]

Undoubtedly, the development of new solid electrolytes with high conductivity and lithium transition number will lead to radical development of lithium-organic battery technology. Nevertheless, this topic has not received much attention and there are few examples of high-performance all-solid-state lithium-organic batteries. All-solid-state lithium-organic batteries exhibiting mechanical stability, high discharge capacity and excellent charge/discharge rate performance remain very difficult tasks.

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An object to be solved by the present invention is to provide a new solid electrolyte for a secondary battery.

Another object to be solved by the present invention is to provide a novel high-performance all-solid-state lithium-organic battery having mechanical stability, high discharge capacity, and excellent charge/discharge rate.

Another problem to be solved by the present invention is to provide a new particle used in a solid electrolyte for a secondary battery.

Terms

In the present invention, 'nano' means 1 to 999 nanometers.

Summary of the invention

In order to solve the above problems, the present invention

Provided is an electrolyte for a secondary battery comprising polymer nanoparticles having lithium ions bonded to a surface thereof.

In the present invention, the polymer nanoparticles may be nanoparticles having an anion so that lithium ions can be bound, and preferably polymer nanoparticles having an anion functional group to which lithium ions can be bound to the surface of the polymer nanoparticles. can be

In the present invention, the polymer nanoparticles may be core-shell-shaped polymer nanoparticles having a plurality of anionic functional groups capable of binding to lithium ions on the surface.

In the present invention, the anionic functional group to which lithium ions can be bound in the polymer nanoparticles is not particularly limited as long as lithium ions can be bound and dissociated during the charging/discharging process of the battery, but preferably electrons are delocalized. An anionic functional group capable of easily binding and dissociating lithium ions is preferred.

In one embodiment of the present invention, the anionic functional group may be represented by the following formula (1).

(1)

(One)

In a preferred embodiment of the present invention, the core-shell-shaped polymer nanoparticles to which lithium ions can be bound may include a crosslinked polystyrene core and a shell represented by the following Chemical Formula (2).

Here, n is a repeating unit, and may be an integer of 10 to 100,000.

In the present invention, the polymer nanoparticles to which lithium ions are bonded to the surface are 10 wt% or more, preferably 20 wt% or more, more preferably 30 wt% or more, even more preferably 40 wt% or more of the electrolyte. It may be included, and most preferably, it may be used in an amount of 40 to 60% by weight. If the content of the nanoparticles is excessive, the aggregation of nanoparticles may interfere with the ion conductive pathway and cause a sharp decrease in conductivity.

In the present invention, the electrolyte may include a material capable of transporting ^{Li +} ions in the charging/discharging process so as to solve the decrease in conductivity due to aggregation of nanoparticles.

^{In the present invention, the material capable of transporting Li +} ions in the charging/discharging process is preferably selected from organic materials so that the entire electrolyte forms an organic electrolyte together with the polymer nanoparticles to which lithium ions are bonded.

In the practice of the present invention, the organic material may be made of Li ⁺ succinonitrile (SN: succinonitrile) having ion conductivity and excellent thermal stability.

In the present invention, the polymer nanoparticles to which lithium ions are bonded to the surface may have a diameter of 500 nm or less, preferably 300 nm or less, more preferably 100 nm or less so as to have a high surface area.

In the practice of the present invention, when the electrolyte is composed of polymer nanoparticles bound to lithium ions on the surface and succinonitrile, the polymer nanoparticles bound to lithium ions on the surface are 30 nm to prevent crystallization of succinonitrile. Hereinafter, it is preferable to use nanoparticles having a diameter of more preferably 25 nm or less, and most preferably 20 nm or less.

In one aspect, the present invention provides an electrolyte including polymer nanoparticles having lithium ions bonded to a surface thereof, and a secondary battery including a positive electrode and a negative electrode.

In the present invention, the polymer nanoparticles bound to the surface with lithium ions are single ion conductive polymers that only move lithium ions bound to the surface of the polymer nanoparticles during charging and discharging and the polymer nanoparticles having an anion do not move. can

In the present invention, the positive electrode preferably uses an active material having an anion as an intermediate in order to prevent elution of the positive electrode active material during the oxidation-reduction process.

Although not limited in theory, the electrolyte according to the present invention, including single ion conductive polymer nanoparticles, dissociates and moves lithium ions from the polymer nanoparticles having lithium ions bonded to the surface during the charging and discharging process, Polymer nanoparticles remain, and thus, when active materials having an anion are used in the oxidation-reduction process, it is possible to prevent elution from the electrode due to the repulsive force between the ions.

In the present invention, the positive active material may be used with special limitations as long as it has an anion in the oxidation-reduction process.

In the practice of the present invention, P4VC based on polyvinyl catechol obtained from nature may be used as the cathode active material to provide an eco-friendly battery.

In a preferred embodiment of the present invention, the positive electrode active material may be adsorbed to the porous gas diffusion current collector to prevent elution from the positive electrode.

The present invention in one aspect,

It provides nanoparticles having a functional group represented by the following formula (3).

(3)

(3)

In the present invention, the nanoparticles may be organic nanoparticles, preferably core-shell nanoparticles having a shell represented by the following formula (2).

Here, n is a repeating unit and may be an integer of 10 to 100,000.

In the present invention, the nanoparticles preferably have a cross-linked polystyrene core so that an electrolyte including the same can have improved mechanical properties.

The present invention proposes an all-solid-state lithium-organic battery comprising an electrolyte based on a solid-state single ion conductive polymer and a cathode active material based on polyvinyl catechol (P4VC), which can be obtained from nature.

All-solid lithium according to the invention the organic cell is a single-ion conductive polymer nanoparticles at room temperature by combining the correct size (surface ^{area) 0.2 x 10 -3 S cm -1} , from 90 ℃ 10 ^-3 S cm ^-1 in the high Conductivity was obtained, as well as a high storage modulus of 20 MPa, which was stable even at a high temperature of 90 °C.

The all-solid-state lithium-organic battery according to the present invention provided an environmentally friendly battery by using P4VC synthesized using naturally abundant caffeic acid for the positive electrode.

The all-solid-state lithium-organic battery according to the present invention was able to obtain an initial discharge capacity of 352 mAh g ^{-1 close to the theoretical capacity of 397 mAh g -1} of P4VC, and exhibited high electrochemical stability and excellent charge/discharge rate (794 mA g ^{- 1} ) was shown.

1 is (a) the synthesis route of ^{x-PS/PSTFSI-Li +} nanoparticles through emulsion polymerization and two-step chemical transformation. (b) FT-IR spectra of x-PS/PSS ^- Na ⁺ , x-PS/PS-SO ₂ Cl and x-PS/PSTFSI ^- Li ^{+ .}
Figure 2 is (a) x-PS/PSTFSI ^- Li ⁺ nanoparticles having a diameter of 20, 40, 200 nm (scale bar: 500 nm). TEM micrographs of nanoparticles with diameters of 40 nm and 200 nm are shown. (b) Bright-field TEM image and 20 nm x-PS/PSTFSI ^- elemental mapping of Li ⁺ nanoparticles: C (carbon), N (nitrogen), O (oxygen), F (fluorine), S (sulfur) ..
Figure 3 shows (a) the ionic conductivity of 50 wt% single-ion nanoparticle electrolyte as a function of nanoparticle size compared to homopolymer, (b) DSC thermograms, and (c) rheological properties of nanoparticles. (d) Rheological properties and (e) ionic conductivity of single ion nanoparticle electrolytes comprising 20 nm nanoparticles at different loadings. (f) Correlation between conductivity and mechanical properties of various single-ion polyelectrolytes reported in the literature compared to this study. Results obtained by hybridizing inorganic fillers are shaded in green.
FIG. 4 is a fabrication diagram of a lithium-organic half-cell manufactured by combining a lithium foil, a single ion nanoparticle electrolyte, and a P4VC positive electrode.
FIG. 5 is (a) constant current charge/discharge voltage profile of lithium foil/single ion nanoparticle electrolyte/P4VC positive electrode measured at ^{39.7 mAh g −1} and 25 ^{o C. FIG.} (b) Discharge capacity and coulombic efficiency of lithium cells based on single-ion nanoparticle electrolytes compared to SN electrolytes (1 M LiTFSI-SN) at ^{25 °C.}
6 shows (a) rate performance of lithium half-cells containing single-ion nanoparticle electrolytes and SN electrolytes measured at ^{25 °C.} (b) Impedance spectra of Li/single-ion nanoparticle electrolyte/P4VC and Li/SN electrolyte/P4VC cells. (c) Long cycle life of lithium cells based on single ion nanoparticle electrolyte and P4VC positive electrode for 500 cycles at ^{794 mA g −1} and 25 ^{o C.} (d) Linear scanning potential voltammograms of single-ion nanoparticle electrolytes at ^{1 mV s −1} and 25 ^o C compared to SN electrolytes. (e) Polarization experiment of Li/single-ion nanoparticle electrolyte/Li symmetric cell at DV = 0.2 V, 60 ^{o C.} Nyquist plots of the cells before and after the polarization experiment are inserted.
7 is a zeta potential measurement diagram of x-PS/PSTFSI-Li+ nanoparticles of different sizes.
8 is a synthetic procedure of P4VC and a 1H nuclear magnetic resonance spectrum (1H NMR in DMSO), and characteristic 1H NMR peaks are indicated in the spectrum.
9 is a cyclic voltammetry analysis of an SN electrolyte and a single ion nanoparticle electrolyte under various scanning rates.
10 is a Li plating / stripping test of SN electrolyte and single ion nanoparticle electrolyte under 0.1 mA cm ^-2 and 60 ^{o C conditions.}

Hereinafter, the present invention will be described in detail through examples. The following examples are not intended to limit the present invention, but to illustrate the present invention.

Figure 1 (a) shows the synthesis route of single ion conductive polymer nanoparticles. By emulsion polymerization of styrene and divinylstyrene in the presence of an excess of sodium styrene sulfonate, polymer nanoparticles (x-PS/PSS ^- Na ⁺ ) having a crosslinked polystyrene (PS) core and polystyrene sulfonate (PSS) shell structure can be obtained. Following nanoparticle synthesis, the sodium sulfonate group is substituted with a sulfonyl chloride group (x-PS/PS-SO ₂ Cl) and sulfonyl(trifluoromethanesulfonyl)imide. As a result, by replacing the cation of the polymer nanoparticles _{having a CF 3} (SO ₂ )N ^{- anion on the surface with Li +} (x-PS/PSTFSILi ^- Li ⁺ ), Li ⁺ conduction properties are provided.

The substitution reaction at the nanoparticle surface was confirmed by Fourier transform infrared spectroscopy (FT-IR). As can be seen in Figure 1(b), in the two-step surface modification process, _{the CH 2} stretching vibration of the PS main chain corresponding to ^{2800-3010 cm -1} does not change, and the peaks corresponding to the C = C bond of the aromatic ring structure are 1430. It is observed at -1680 cm ^{-1 .} When attaching the SO ₂ Cl group, the symmetric stretching vibration of S=O is blue shifted because the ^{electronegative substituent stabilizes S=O rather than S +} -O ^-. After the surface of the nanoparticles was modified with _CF-3 (SO ₂ )N ^- Li ^{+ , the asymmetric vibration peak of sulfonyl chloride observed at 1376 cm -1} disappeared, and other S=O peaks also shifted red. Also it occurs at a stretching vibration 1052cm ^-1 to 1185 cm ^-1 and for the CF, which means that the sulfonamide has been successfully introduced to the surface of the nanoparticles.

CF ₃ (SO ₂ )N ⁻ is expected to be bulky and to promote dissociation of ^{Li + due to electron delocalization. [40,44] In} addition, since the oxidation-reduction intermediate of the organic positive electrode active material has a negative charge, it may have an electrostatic repulsive force with the nanoparticle surface, which may delay dissolution of the active material in the electrolyte. Since the ^{degree of dissociation of Li +} and lithium ion conductivity can be affected by the surface area of the nanoparticles, x-PS/PSTFSI ^- Li ⁺ nanoparticles having three different sizes were prepared by controlling the molar ratio of the reagents.

The morphology and size of x-PS/PSTFSI ^- Li ⁺ nanoparticles were investigated by scanning electron microscopy (SEM) and transmission electron microscopy (TEM). As can be seen from the SEM image of Fig. 2(a), the three different sized nanoparticle samples all had a uniform size distribution. TEM images also show that the nanoparticles in these samples are spherical with sizes of approximately 20, 40, and 200 nm. The core-shell morphology of x-PS/PSTFSI ^- Li ⁺ nanoparticles was described by electron energy loss spectroscopy (EELS). A representative image of x-PS/PSTFSI ^- Li ⁺ nanoparticles at 20 nm is shown in Fig. 2(b), in which certain atom-rich regions appear bright. As can be seen from the carbon phase, the core mainly contains PS chains, but the shell structure composed of PSTFSI chains showed a mapping image that could be expected due to oxygen, fluorine, nitrogen and sulfur atoms of ^TFSI-anions. The thickness of the shell was observed to be 3-4 nm.

The zeta potential and electrophoretic mobility of x-PS/PSTFSI ^- Li ^{+ nanoparticles having different sizes were measured using a Zetasizer.} To exclude aggregation of nanoparticles, a diluted nanoparticle solution (0.04 wt% in ethanol solvent) was prepared. As shown in FIG. 7 , the x-PS/PSTFSI ^- Li ⁺ nanoparticles have negative surface charges with zeta potentials of -32, -31, and -42 mV for nanoparticles with a diameter of 20, 40, and 200 nm. From each electrophoretic mobility measurement, the Li ⁺ concentration of ^{x-PS/PSTFSI -} Li ^{+ was calculated according to Kohlrausch's law. [47] In} this case, the Li ⁺ concentration on the surface of the nanoparticles could be calculated with reference to an infinite dilute solution of LiTFSI. We estimate that the size of the nanoparticles is not a decisive factor in determining the ^{Li + concentration, and that the Li +} concentration is in the range of 1.2-1.4 mol L ^{-1 for the electrolyte containing 50 wt% of the nanoparticles. In the case of PSTFSI -} Li ⁺ homopolymer (Mw=1000 kg mol ^-1 ), a linear single ion conductive polymer, it was calculated to have a Li ^{+ concentration of 3.1 mol L -1} at the same concentration of 50 wt%.

Nevertheless, the size of the nanoparticles was a decisive factor in improving ^{the Li + conductivity of the solid polymer.} We prepared a single-ion NP electrolyte by mixing succinonitrile (SN) and x-PS/PSTFSI ^- Li ^{+ nanoparticles.} SN is a solid with high Li ⁺ conductivity in the semi-solid phase and good thermal stability. ^{[48,49] Ion conductivity data of a single ion nanoparticle electrolyte containing x-PS/PSTFSI-} Li ⁺ nanoparticles with a diameter of 20, 40, and 200 nm at a concentration of 50 wt% is shown in FIG. 3(a). have. ^{The use of small nanoparticles improved the Li +} conductivity while suppressing the crystallinity of SN and resulted in the highest conductivity of ^{0.2 x 10 -3} S cm ^{-1 at room temperature.} Also, the conductivity increased to ^{10 -3} S cm ^{-1 at 90 °C.} In contrast, the conductivity of single ion nanoparticle electrolytes containing 40 nm and 200 nm nanoparticles was low and a sharp decrease in conductivity was observed upon cooling. This phenomenon is due to the lower surface area of the larger nanoparticles, which cannot completely interfere with the crystallinity of the SN and reduces the possibility of intermolecular interactions.

A similar electrolyte containing a ^{linear PSTFSI -} Li ⁺ homopolymer at a concentration of 50 wt % also exhibited limited SN crystallinity due to a ^{significantly higher Li +} concentration (3.1 mol L ^{-1 ).} However, the conductivity was twice that of the single ion nanoparticle electrolyte containing 20 nm nanoparticles over the entire temperature range. ^{These observations imply that the transport of Li+} along the surface of the close-packed nanoparticles is much more efficient than that of the randomly coiled homopolymer, due to the less tortuous ion conduction path. Our approach is particularly noteworthy, given that the majority of literature on single ion-conducting polymers concerns linear polymer chains. ^{[39-41,44,45,50,51]}

Different thermal properties of the electrolyte were confirmed by differential scanning calorimetry as shown in Fig. 3(b). Crystallinity of SN was not observed in single ion nanoparticle electrolytes containing 20 nm nanoparticles. Significant inhibition of the crystallinity of SN was also observed for electrolytes containing linear PSTFSI ^- Li ^{+ homopolymer.} However, in the case of single-ion nanoparticle electrolytes containing 40 nm and 200 nm nanoparticles, crystallization of SN occurred and the degree of crystallinity depended on the size of the nanoparticles.

In addition to the improved ionic conductivity, the single-ion nanoparticle electrolyte containing 20 nm nanoparticles exhibits excellent mechanical properties in the temperature range of 25-90 ° C, as shown in FIG. It is the result. ^{[52] In} the case of an electrolyte containing 20 nm and 40 nm nanoparticles, the elasticity of the electrolyte does not change up to 90 °C, but in the case of an electrolyte having 200 nm nanoparticles, the storage modulus of the electrolyte during the melting transition of SN is rapidly reduced, and in this regard, it can be seen that the high degree of agreement between FIGS. 3(a) and 3(b). Interestingly, all single-ion nanoparticle electrolytes exhibit improved mechanical properties when compared to linear homopolymers, which can be rationalized due to the densely packed morphology of nanoparticles in the electrolyte membrane. This finding emphasizes that the excellent ion transport properties and mechanical stability of single ion conductive polymer electrolytes can be simultaneously improved through the rational design of functional nanoparticles.

Since the single ion nanoparticle electrolyte was prepared by simple hybridization of SN and nanoparticles, ionic conductivity and mechanical properties were added by adjusting ^{the Li + concentration by changing the loading amount of nanoparticles and controlling the packing density of nanoparticles.} can be controlled with Figure 3(d) shows representative frequency-dependent storage moduli of single ion nanoparticle cleavage containing different amounts of 20 nm nanoparticles at ^{25 °C.} As the loading of nanoparticles increases, the electrolyte membrane becomes more elastic (increasing the G'/G'' ratio), and the elasticity is not affected by temperatures up to 90 °C. The improvement of the storage modulus was relatively small when the amount of nanoparticles was increased from 50 wt% to 60 wt%, but showed a decrease in the order when the loading amount was decreased to 40 wt%. This behavior is formed when the close-packing of nanoparticles is 50 wt% and indicates that the high mechanical strength obtained at higher nanoparticle concentration is dominated by the cross-linked PS core. Based on similar bulk mass densities of SN and x-PS/PSTFSI ^- Li ⁺ nanoparticles, close-packing of nanoparticles is expected to be ~74 wt%. However, in the presence of amorphous SN, the actual volume occupied by the polymer nanoparticles will be larger than predicted based on the weight fraction as the ^{PSTFSI -} Li ^{+ chains expand.}

3(e) shows the temperature-dependent ionic conductivity of single-ion nanoparticle electrolytes with different loadings of nanoparticles. When the content of nanoparticles is increased to 60 wt %, the volume fraction of the conductive phase is reduced and the aggregation of excessive nanoparticles interferes with the ion conductive pathway, resulting in a sharp decrease in conductivity. It was also ^{found that crystallization of SN due to the low Li +} concentration was not completely inhibited at 40 wt% nanoparticle loading.

Comparing the literature values for a representative single-ion electrolyte with the conductivity-storage modulus plot of the single-ion nanoparticle electrolyte (Fig. 3(f)), it shows an important development of this study in the solid electrolyte field. ^{[41-46] In} particular, although single-ion nanoparticle electrolytes are all organic, ^{they exhibit improved Li +} ion transport properties and superior mechanical properties compared to organic-inorganic hybrids. ^{[43,53,54] In} cell performance, we focused on a 50 wt% single-ion nanoparticle electrolyte of 20 nm nanoparticles with optimal properties as described. To evaluate the cell performance of single-ion nanoparticle electrolytes combined with organic electrode materials, a vinyl catechol-based P4VC cathode active material synthesized through reversible addition fragmentation transfer (RAFT) polymerization was synthesized. ^{[55] The} synthesis procedure and ¹ H nuclear magnetic resonance ( ¹ H NMR) spectrum are shown in FIG. 8 . By optimizing the molecular weight of P4VC to 3 kg mol ^-1 to obtain small globules, the molecular diffusion into the electrolyte was suppressed while essentially ensuring ^{fast Li + transport in the insulating polymer.}

An organic positive electrode was prepared by infiltrating P4VC into a porous gas diffusion current collector at a loading of 0.4 mg cm ^{-2 .} The theoretical capacity of P4VC was calculated as ^{397 mAh g −1} under the assumption that both redox active sites participate in the electrochemical reaction. A lithium-organic half-cell was fabricated by assembling a lithium foil, a single ion nanoparticle electrolyte, and a P4VC positive electrode as shown in FIG. 4 .

As can be seen in FIG. 5( b ), the battery can deliver initial discharge and charge capacities of ^{269 and 352 mAh g −1 , respectively, with a coulombic efficiency (QE) of 76%.} Poor QE can be attributed to solid-electrolyte interface (SEI) formation due to parasitic reactions on the lithium metal surface. ^{[57] The} low QE is also due to the irreversible structural transition of P4VC where the -OH group is not completely oxidized to the -OLi group. ^{[56] The} QE value increases rapidly to >90% within the first 5 cycles, giving a discharge capacity of 278 mAh g-1 (70% of the theoretical capacity). With continuous cycling, the capacity after 40 cycles ^{reaches a stable value at 165 mAh g -1} and has a high QE value of over 99%. After 100 cycles, the battery shows a reversible discharge capacity of ^{about 137 mAh g -1 .} These results are in sharp contrast to the case of lithium batteries with SN electrolyte (1 M LiTFSI-SN). Here, the capacity decreases rapidly to low QE values within tens of cycles, indicating the formation of a permanent and uncontrollable SEI.

An additional feature of lithium-organic cells comprising a single ion nanoparticle electrolyte and a P4VC positive electrode was improved charge-discharge rate performance. The discharge capacities according to different charge/discharge rates of 79.4, 119.1, 198.5, 397 and 794 mA g ^{-1 are shown in FIG. 6(a) .} Interestingly, the battery can provide a stable discharge capacity of over ^{100 mAh g -1} at a high current density of ^{794 mA g -1} , and upon further cycling at a low rate of ^{39.7 mA g -1 , the original capacity was restored.} can be checked In contrast, the rate performance of lithium cells based on SN electrolytes is poor and a rapid capacity loss is observed at increased current density. Also, it shows a capacity that is not restored even after returning the battery to a low charge/discharge rate.

_{It should be noted that the improved rate performance is closely related to the high lithium diffusion coefficient (D Li+} ) and low polarization in the anode when evaluated by cyclic voltammetry at various scan rates. As can be seen in Fig. 6(b), the D _Li+ value of the single-ion nanoparticle electrolyte was estimated to be 3-5 times higher than that of the SN electrolyte for both the negative and positive peaks using the Randles-Sevcik equation. ^[4] CV is provided in FIG. 9 .

Lithium-organic cells made with single-ion nanoparticle electrolyte and P4VC positive electrode also showed long cycle life at high charge/discharge rates. Representative data for a lithium cell cycled at 794 mA g ⁻¹ is shown in FIG. 6(c). ^{A stable and high discharge capacity of 100 mAh g -1} was obtained even after 500 cycles, and the capacity reduction was nominally 0% from 60 cycles to 500 cycles. A photograph of a single ion nanoparticle electrolyte that exhibits high conductivity, is thermally stable, and is mechanically stable is inset in FIG. 6(c), and the oxidation-reduction mechanism of P4VC is also shown.

Due to the covalent tethering of anions on the nanoparticle surface, anion depletion is fundamentally prevented in single-ion nanoparticle electrolytes, which is measured by the linear scanning potential method (stainless steel: working electrode, lithium foil: counter electrode, reference electrode). Provides a stable electrochemical window up to 6.0 V versus Li ^{+ /Li.} (Fig. 6(d)) The voltammogram of the SN electrolyte is also shown for comparison. The electrochemical stability of single-ion nanoparticle electrolytes at high anode voltages represents a potential application for high-voltage lithium batteries.

_{The t Li+} values of single ion nanoparticle electrolytes were evaluated by polarization experiments. At DV = 0.2 V and 60 ^o C, the initial and steady-state currents were 3.35 μA and 2.93 μA, respectively. (FIG. 6(e)) As can be seen in the inset image of FIG. 6(e), the t _Li+ value was calculated to be 0.87 by combining the electrochemical impedance measurements before and after the polarization experiment. ^[58] The value of t _Li+ is not the theoretical value of 1, which is due to the local movement of single-ion nanoparticles in the amorphous SN matrix.

In addition, a constant current Li plating/stripping test of a symmetrical battery was performed at 60 °C and ^{a constant current density of 0.1 mA cm -2} (Fig. 10). Stable overpotentials were observed over several tens of hours for a battery based on a single-ion nanoparticle electrolyte. became In contrast, the cell containing the SN electrolyte rapidly increased the overpotential within a few hours, resulting in a short circuit of the cell. It was speculated that the dense alignment of x-PS/PSTFSI ^- Li ⁺ on the lithium metal surface effectively inhibited the growth of lithium dendrites, enabling the safe operation of lithium metal-based batteries. The results of this study may provide a new platform for fast-charging, eco-friendly and reliable energy storage technology.

3. Conclusion

The all-solid-state lithium-organic battery investigated in this study provided several advantageous features, including improved electrochemical stability, good charge-discharge rate performance and long cycle life. The key to this success lies in the efforts to synthesize the electrolyte (single ion nanoparticle electrolyte with controlled nanoparticle size and packing density) and electrode active material (polyvinyl catechol with optimized molecular weight). Hybridization of single ion conductive nanoparticles with SN provided ^{high conductivity of the order of 10 −3} S cm ⁻¹ , a high lithium transition number of 0.87, and excellent mechanical strength of over 10 MPa over a wide temperature range. Surprisingly, the lithium battery with single ion nanoparticle electrolyte exhibited a stable discharge capacity of over ^{100 mAh g -1} at a high current density of ^{794 mA g -1 for 500 cycles.} Advantageously, single-ion nanoparticle electrolytes essentially avoid depletion of anions and provide a high-density array of charged nanoparticles at the electrolyte/electrode interface. Therefore, the results of this study highlight the great potential of single-ion nanoparticle electrolytes for the safe operation of lithium metal batteries even at high temperatures.

4. Experiment

Materials:

Styrene (> 99.9%), sodium dodecyl sulfate (SDS, > 99.9%), sodium styrene sulfonate (> 90%), sodium polystyrene sulfonate (> 90%), potassium persulfate (KPS, > 99.0%), N,N - dimethylformamide (DMF, 99.8%), anhydrous acetonitrile (99.8%), 4-dimethylaminopyridine (DMAP, 99.0%), triethylamine (TEA, > 99.0%), sodium bicarbonate (> 99.5%), hydrochloric acid (HCl, 11M), dioxane (> 99.5%), lithium perchlorate (99.99%), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI, 98.0%), succinonitrile (99.0%), and multi-walled CNTs were purchased from Sigma-Aldrich. Divinylbenzene (DIB, > 50%), oxalyl chloride (> 98.0%), trifluoromethylsulfonamide (TFSA, > 98.0%) were obtained from Tokyo Chemical Industry Co., Ltd. was purchased from Super P (> 99%), N-methyl-2-pyrrolidinone (NMP, 99.5%), 3,4-Dihydroxycinnamic acid (caffeic acid, > 98%), chlorotriethylsilane (TESCl, 99.8%), 2-(dodecylthiocarbonothioylthio) -2-methylpropionic acid (TTCA, chain transfer agent, >98%, HPLC) was purchased from Alfa Aesar. n-hexane (95%), tetrahydrofuran (THF, 99.5%), and Azobis(isobutyronitrile) (AIBN, 98%) were purchased from SAMCHUN.

x-PS/PSTFSI ^- Li ⁺ synthesis of :

Here, the synthesis procedure of 20 nm nanoparticles is described as a representative example. After dispersing 28.8 mmol of styrene, 7.7 mmol of DIB and 1.7 mmol of SDS in 100 mL of distilled water, 0.14 mmol of KPS was added. After stirring the mixture at 70 °C for 30 minutes, 6.6 mmol of sodium styrene sulfonate and 0.07 mmol of KPS were further added. After stirring for 15 minutes, 43.6 mmol of sodium styrene sulfonate was added for 1 hour, and polymerization was continued at 70° C. for 16 hours. -SO ₃ ^{nanoparticle-a} Na ⁺ surface using oxalyl chloride / DMF in acetonitrile solvent in anhydrous conditions were modified to -SO ₂ Cl. TFSI ^- and mixed with the surface to obtain the modified nanoparticles, 0 ℃ the DMAP and 2 g of nanoparticles, 1.5 g of TFSA, 4 mL of TEA and 0.5 g of, in acetonitrile solvent conditions. After 16 hours of reaction, x-PS/PSTFSI ^- Li ⁺ nanoparticles were obtained by cation exchange with excess lithium perchlorate at 60 °C.

Synthesis Details of Single Ion Conductive Nanoparticles :

Single ion conductive nanoparticles were synthesized by emulsion polymerization followed by two-step surface modification. Here, only the synthesis procedure of 20 nm nanoparticles as a representative sample is described.

1) Styrene 3.0 g (28.8 mmol), DIB 1.0 g (7.7 mmol), and SDS 0.5 g were dispersed in 100 mL of distilled water, and then KPS aqueous solution (a solution of 40 mg KPS (0.14 mmol) in 2.5 mL of distilled water) was added. dropped drop by drop. After stirring the mixture at 70 °C for 30 minutes, sodium styrene sulfonate aqueous solution (1.37 g (6.6 mmol) sodium styrene sulfonate dissolved in 7.5 mL distilled water) was added, and KPS solution (20 mg (0.07 in 2.5 mL of distilled water) was added. mmol) KPS solution) was further added. After stirring for 15 minutes, an aqueous solution in which an excess of 9 g (43.6 mmol) of sodium styrene sulfonate was dissolved in 50 mL of distilled water was added dropwise over 1 hour. Thereafter, an aqueous KPS solution (a solution of 40 mg (0.14 mmol) of KPS dissolved in 2.5 mL distilled water) was added thereto. -SO ₃ ^- Na ⁺ in order to obtain nanoparticles having a shell and a crosslinked core of polymerized surface was continued for 16 hours at 70 ℃. Different nanoparticles of various diameters were prepared by controlling the concentrations of the above-mentioned reagents. 2) -SO ₃ nanoparticle ^- Na ⁺ surface were first modified by -SO ₂ Cl. 1.0 mL of oxalyl chloride and 0.05 mL of DMF were added to 20 mL of anhydrous acetonitrile, and the mixture was stirred for 5 hours. After slowly adding 2 g of the prepared nanoparticles to the mixture, the mixture was stirred at room temperature for one day. 3) After slowly cooling the resulting mixture to 0 °C, a solution of 1.5 g of TFSA, 4 mL TEA, and 0.5 g DMAP in 15 mL of anhydrous acetonitrile is slowly dropped into the nanoparticle mixture at 0 °C. After 16 hours of reaction, the product was purified by centrifugation at 20,000 rpm using methanol and distilled water.

Synthesis of P4VC :

0.11 mol of caffeic acid and 50 mL of TEA were uniformly mixed with 150 mL of DMF solvent at 25 °C. ^{The mixture was heated to 100 °} C for 1 hour and cooled to 0 °C to obtain 4-vinyl catechol. After preparing bis(triethylsilyl)-protected 4-vinylcatechol, RAFT polymerization was performed using dioxane, AIBN, and TTCA. By removing the RAFT end group and hydrolyzing the capping moiety, P4VC with controlled molecular weight was obtained.

Synthesis details of Poly(4-vinyl catechol) (P4VC) :

1) At a temperature of 25 °C, 20 g (0.11 mol) of caffeic acid and 50 mL of TEA were uniformly mixed in 150 mL of DMF for 10 minutes. The mixture was heated at 100 °C for 1 hour and then cooled to 0 °C to obtain 4-vinyl catechol. 2) After carefully dropping 37 mL of TESCI into the reactor, it was stirred at 0 °C for 2 hours. After the temperature of the reactor returned to room temperature, the reaction was continued for 12 hours, and then the resulting mixture was diluted with n-hexane, _{and washed repeatedly with HCl aqueous solution, NaHCO 3} aqueous solution and distilled water. The product was obtained using a rotary evaporator, and purified by silica gel column using n-hexane as an eluent. The product was vacuum dried to obtain 25 g of bis(triethylsilyl)-protected 4-vinylcatechol (TES2VC). 3) The obtained TES2VC was polymerized using RAFT polymerization. 3 g (8.2 mmol) of TES2VC, 120 mg (0.33 mmol) of TTCA, 22 mg (0.13 mmol) of AIBN and 0.9 mL of dioxane were mixed in a Schlenk flask, and the freeze-pump-thaw process was repeated three times. . In this process, dioxane was used after activation by passing it through basic aluminum oxide. After placing the flask in a 75 ^° C water bath, the reaction was continued for 24 hours. Thereafter, the product was dissolved in n-hexane and purified by repeated precipitation in methanol. 2.76 g of polymer and 1.08 g (6.6 mmol) of AIBN dried in vacuum at 60° C. were dissolved in 40 mL of dioxane to remove the RAFT end. After repeating the freeze-pump-thaw process three times, the reactor ^{was placed in a water bath at 70 o} C, and the product was concentrated using a rotary concentration evaporator and precipitated in methol several times. The molecular weight distribution of the polymer was determined to have a polydispersity index of 1.12 through size exclusion chromatography using a PS standard in THF eluent. The degree of polymerization of the polymer ^{was calculated through end group analysis of 1} H nuclear magnetic resonance ( ¹ H NMR, Bruker 300 and 500). 4) After dissolving 2 g of a polymer in 100 mL of THF, it was reacted with 2.5 mL of 11 M HCl aqueous solution at 25 °C overnight. The crude product was diluted with ethyl acetate, washed with NaHCO ₃ aqueous solution, and washed repeatedly with distilled water. After the organic layer was concentrated, it was repeatedly precipitated in n-hexane to obtain 510 mg of P4VC.

Fabrication of P4VC Anode :

To prepare a P4VC anode, first, synthesized P4VC (3K), Super P, and multi-walled CNT were mixed using a mortar. To obtain a homogeneous slurry, a solution of polyvinylidene difluoride (PVDF, Solvay) dissolved in NMP at 4 wt% was added to the mixture and mixed homogeneously. In this process, the mass ratios of P4VC (3K), Super P, multi-walled CNT and P4VC were 20:30:10:40, respectively. After preparing a slurry of appropriate viscosity, the slurry was cast on porous GDL (210 μm, TGP-G-303, Toray) instead of aluminum foil using a doctor blade technique. The prepared positive electrode was dried at 60° C. for 24 hours, and then further vacuum dried. All anodes were cut to a diameter of 10 mm using a disk cutter (MTI).

Preparation of Single Ion Nanoparticle Electrolytes :

After dispersing pre-prepared single ion nanoparticles and SN in methanol in an Ar environment, solvent casting was performed. The resulting film was placed in a stainless steel mold (1.2 cm in diameter and 250 μm in thickness) and pressurized at 70° C. to prepare an electrolyte membrane of the same thickness.

Preparation of Control Electrolyte (SN Electrolyte):

LiTFSI-SN liquid electrolyte, a control of single ion nanoparticle electrolyte, was prepared by dissolving 1 M LiTFSI in SN. Since LiTFSI-SN is a liquid electrolyte, it was impregnated in Celgard 2400 overnight and then used for the production of half cells.

Preparation of half cell:

To prepare a half-cell, a coin-type (CR2032, MTI) battery was prepared by assembling a lithium foil, an electrolyte, and a P4VC positive electrode in a glove box filled with high-purity Ar. In this procedure, a small amount of EMC/TEGDME (EMC; 99%, Sigma-Aldrich, TEGDME; >99%, Sigma-Aldrich) mixed solvent without lithium salt was used to wet the negative electrode surface.

Characterization of Single Ion Conductive Nanoparticles and Single Ion Nanoparticle Electrolytes:

FT-IR spectroscopy was performed using KBr pellets. (Two IR spectrometer, PerkinElmer) Zeta potential and electrophoretic mobility were measured using a Zetasizer (Malvern Zetasizer, Malvern Panalytical). A transmission electron microscope equipped with electron energy loss spectroscopy (TEM, JEOL JEM-2200FS operated at 200 keV) and a scanning electron microscope (SEM, XL30S FEG) were combined to investigate the morphology and size of core-shell structured nanoparticles. The thermal properties of single ion nanoparticle electrolytes were measured using differential scanning calorimetry (DSC, Q20, TA Instruments) at a heating/cooling rate ^{of 10 o} C min ^{-1 .} Using a stress control rheometer (DHR-2, TA Instruments) and a geometry of 0.8 cm in diameter, the rheological properties of the polymer electrolyte membrane were measured by repeated heating/cooling at a rate of 1 ^o C min ^{-1 at 0.5 rad s -1 .} . The frequency scan experiment was performed in the range ^{of 0.1 rad s -1} to 100 rad s ^-1. All rheological measurements were performed at a spacing of 0.5 mm and a diameter of 0.8 cm with a small strain of 0.1%.

Electrochemical characterization:

To evaluate the ion transport properties of single-ion nanoparticle electrolytes, electrochemical impedance experiments were performed using a stainless steel symmetrical cell. (VersaSTAT3, Princeton Applied Research) The electrochemical stability of single-ion nanoparticle electrolytes ^{was investigated using a lithium foil, electrolyte, and stainless steel sandwich cell at 1 mV s −1} and 25° C. by linear scanning potential method. The applied potential window was 0-6 V. Was performed at a constant current Li plating / stripping test using a lithium battery from the symmetrical electrochemical stability point of view of a single ion nanoparticles electrolyte in contact with the lithium metal conditions experiment 60 ℃, 0.1 mA cm ^-2, the time of charge and discharge cycle was 1 It was time. In addition, in _{order to calculate t Li+} using a symmetric battery, a polarization experiment was performed at ΔV = 0.2 V and 60 ^{o C conditions.} For the evaluation of battery performance, cyclic voltammetry analysis and constant current charging/discharging experiments were performed on the half-cell in a potential window of 1.5-4.0 V using a cycler (WBCS3000, Wonatech).

Claims (21)

An electrolyte for a secondary battery comprising polymer nanoparticles to which lithium ions are bound. According to claim 1,
The polymer nanoparticles are electrolytes for secondary batteries, characterized in that lithium ions are bonded to the surface. According to claim 1,
The polymer nanoparticles are electrolytes for secondary batteries, characterized in that they have an anionic functional group to which lithium ions are bound. According to claim 1,
The polymer nanoparticles are electrolyte for a secondary battery, characterized in that the core-shell shape. According to claim 1,
The polymer nanoparticle is an electrolyte for a secondary battery, characterized in that it has an anionic functional group represented by the following formula (1).

The electrolyte for a secondary battery according to claim 1, wherein the polymer nanoparticles are in a core-shell type having a shell represented by the following formula (2).

Here, n is a repeating unit and may be a natural number of 10 to 100,000. According to claim 1,
The electrolyte is an electrolyte for a secondary battery, characterized in that it contains less than or equal to 60% by weight of the polymer nanoparticles bonded to lithium ions on the surface. According to claim 1,
The electrolyte is an electrolyte for a secondary battery, characterized in that the organic electrolyte. According to claim 1,
The electrolyte is an electrolyte for a secondary battery, characterized in that the single ionic electrolyte. According to claim 1,
The electrolyte is an electrolyte for a secondary battery, characterized in that the polymer nanoparticles are bonded to the surface of lithium ions, and ^{an organic material capable of transporting Li + ions.} 11. The method of claim 10,
The electrolyte for a secondary battery, characterized in that the material capable of transporting ^{Li + ions is succinonitrile.} According to claim 1,
The electrolyte is an electrolyte for a secondary battery, characterized in that it consists of 40 to 60% by weight of polymer nanoparticles bonded to the surface of lithium ions and 40 to 60% by weight of succinonitrile. According to claim 1,
The electrolyte for a secondary battery, characterized in that the size of the polymer nanoparticles to which lithium ions are bonded to the surface is 30 nm or less. A secondary battery comprising the electrolyte according to any one of claims 1 to 13. 15. The method of claim 14,
The secondary battery is a secondary battery, characterized in that at least one electrode forms anions in the oxidation-reduction process. 15. The method of claim 14,
In the secondary battery, at least one electrode comprises poly(4-vinylcatechol). 17. The method of claim 16,
The electrode is a secondary battery, characterized in that poly (4-vinyl catechol) is bonded to a porous gas diffusion current collector. Nanoparticles having a functional group represented by the following formula (3).

(3) 19. The method of claim 18,
Nanoparticles, characterized in that the particles are polymer nanoparticles. 19. The method of claim 18,
The polymer nanoparticles are nanoparticles, characterized in that the core-shell type nanoparticles having a shell represented by the following formula (2).

Here, n is a repeating unit, and an integer from 10 to 100,000. 18. The method of claim 17,
The polymer nanoparticles are nanoparticles, characterized in that having a cross-linked polystyrene core.

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