고체용 고분자 전해질에 대한 고찰 | 란저우 첨가제 주식회사

Nature Communications 14권, 기사 번호: 4884(2023) 이 기사 인용

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리튬 이온 배터리(LIB)가 상용 시장에 등장하기 전에는 고체 리튬 금속 배터리(SSLMB)가 유망한 고에너지 전기화학 에너지 저장 시스템으로 여겨졌으나 안전 문제로 인해 1980년대 후반에 거의 폐기되었습니다. 그러나 30년의 개발 끝에 LIB 기술은 이제 흔들의자 화학에 의해 부과된 에너지 함량과 안전 한계에 접근하고 있습니다. 이러한 측면은 학술 및 산업 수준 모두에서 SSLMB 기술에 대한 연구 활동의 부활을 촉발하고 있습니다. 이 관점 기사에서는 초기 개발부터 SSLMB 구현까지 고체 고분자 전해질(SPE)에 대한 개인적인 성찰을 제시하고 주요 이정표를 강조합니다. 특히 1990년대 초 C. Austen Angell이 제안한 결합 및 분리 SPE 개념을 고려하여 SPE의 특성을 논의한다. SPE의 물리화학적, 전기화학적 특성을 개선하기 위한 가능한 해결책도 검토됩니다. 이 기사를 통해 우리는 이상적인 SSLMB를 구축하는 데 누락된 블록을 강조하고 미래 충전용 고에너지 배터리를 위한 혁신적인 전해질 재료에 대한 연구를 활성화하는 것을 목표로 합니다.

1870년 소설 "해저 2만리"에서 Jules Verne은 잠수함 노틸러스(Nautilus)가 고급 배터리 시스템으로 구동된다고 설명하고 Nemo 선장은 "... 나트륨이 있는 세포는 가장 활력이 넘치는 세포로 간주되어야 하며 기전력은 다음과 같습니다. 쥘 베른(Jules Verne)이 제안한 고에너지 배터리 제작 개념은 의심할 바 없이 19세기 후반 시대를 앞선 것이었지만 전기 사용이 만들어내는 경이로움에 대한 당시의 매혹과 일치했습니다. '전기로 모든 것을'은 1900년대 초반 인류의 꿈이었지만 20세기 후반 흔들의자 개념을 기반으로 한 리튬이온전지(LIB)가 발명되면서 현실이 됐다. 전기화학적 에너지를 저장/전달하기 위한 서로 다른 전위를 가진 두 개의 삽입 기반 전극)2,3. 현재 LIB의 전 세계 생산량은 500GWh(기가와트시)를 넘는 대규모 규모에 도달하여 600만 대 이상의 전기 자동차(EV)4의 전원 역할을 하고 있습니다. LIB의 성공은 "모든 것이 전기로 이루어진다"는 초기 가설을 입증하고 에너지를 소비하는 인류 활동의 보다 지속 가능한 개발을 위한 새로운 길을 열어줍니다.

LIB의 생산 능력은 지난 10년 동안 10배 증가했으며5 이 수요는 빠르게 성장하는 EV 부문을 중심으로 향후 10~30년 동안 계속해서 빠르게 증가할 것으로 예상됩니다4. 고성능(예: 에너지 밀도, 안전성, 비용 등) 재충전 가능 배터리에 대한 요구도 시급하며, 특히 현대의 실제 응용 분야(예: 도로 및 비행용 EV, 드론, 고급 로봇공학 등)가 가져오는 엄격한 요구 사항을 고려할 때 더욱 그렇습니다. .), 고유한 안전성과 비에너지(>500Wh kg−1) 및 에너지 밀도(>1000Wh L−1)6를 포함합니다. 불행하게도 오늘날 LIB에 사용되는 비수성 액체 전해질은 유기 탄산염 용매(예: 디메틸 탄산염, 에틸렌 탄산염 등)의 존재로 인해 불안정하고 가연성이 높습니다. 또한, 372mAh g−1의 상대적으로 낮은 비용량을 갖는 흑연 음극도 최신 LIB의 비에너지를 더욱 향상시키는 데 제한 요소입니다6. 이와 관련하여, 고에너지 전극 물질(예: 리튬 금속(Li°), 리튬 합금, 니켈이 풍부한 LiNi1−x−yCoxMnyO2(1−x − y > 0.8))을 결합한 고체 리튬 금속 배터리(SSLMB), 황 등)과 고체 전해질은 현재 LIB 기술의 특정 에너지 밀도 걸림돌을 우회하는 실행 가능한 접근 방식으로 간주됩니다7,8,9.

1 GWh) of SPE-based SSLMBs as power sources for EV and grid storage have been deployed by the Bolloré group since 201013. This is a relevant industrial example of SPE technology capable of providing support for the development of high-performance SSLMBs./p>4 eV for PEO34). The two discs (light gray) on the top and bottom of the SPE membrane represent the blocking electrodes. DC: direct current. c Phase diagram of lithium trifluoromethyl sulfonate (LiCF3SO3)/PEO. The values are taken from ref. 38. The light green and pink areas represent the amorphous phase (abbreviated as AP) region and two-phase region in the PEO-based electrolytes, respectively. PEO(C) and (PEO)3LiCF3SO3(C) denote the crystalline phase of PEO and the salt/polymer complex (i.e., (PEO)3LiCF3SO3), respectively. d Microscopic views of PEO-based SPEs at room (25 °C) and high (>60 °C) temperatures above the melting transition of PEO phases. e Effect of temperature on the ionic conductivity of PEO-based SPEs [(PEO)20LiCF3SO3] and conventional liquid electrolyte solutions (e.g., 1.0 mol kg−1 lithium hexafluorophosphate (LiPF6) per kilogram propylene carbonate). The ionic conductivity values are taken from refs. 39,122./p>4 eV34) for electron jumping between conduction and valence bands (Fig. 2b). Yet, it was not clear whether the transportation of ionic species would be possible at that time. In 1966, Lundberg et al.35 investigated the mixture of metal salts (e.g., potassium iodide) and poly(ethylene oxide) (PEO). They concluded that metal salts interact with PEO and reduce crystallinity. In 1971, M. Armand carried out several ionic conductivity tests with lithium bromide (LiBr)/PEO. From the analysis of the results, he concluded that because of the very high resistance (>1 MΩ) measured at room temperature (ca. 20–30 °C), the utilization of LiBr/PEO for battery applications was not recommended. Two years later, Fenton et al.36 discovered that the mixtures of PEO and low-lattice-energy metal salts (e.g., sodium iodide (NaI), sodium thiocyanate (NaSCN), potassium thiocyanate (KSCN), etc.) become ionically conductive upon warming up the samples (e.g., ionic conductivities for the (PEO)4KSCN complex: 10−7 (40 °C) vs. 10−2 S cm−1 (170 °C)). This key finding rapidly caught the attention of Armand, and he suggested the utilization of these polymeric ionic conductors as solid electrolytes for building solid-state batteries37. These pioneering research works ushered a new direction for developing soft solid electrolytes and circumventing the surface contact issue in solid-state batteries with inorganic solid electrolytes./p>10−3 S cm−1) for operating SPE-based SSLMBs at elevated temperatures (≥80 °C)51,52. In the last decade, the development of molecules with delocalized negative charges has further progressed53,54. For example, Ma et al.54 proposed a delocalized polyanion, i.e., poly[(4-styrenesulfonyl)(trifluoromethyl(S-trifluoromethylsulfonylimino) sulfonyl)imide] (PSsTFSI−), that demonstrates improved lithium-ion conductivity of SPEs for unipolar conduction (i.e., only positive charges are mobile) due only to lithium cation (e.g., at 80 °C, ca. 10−4 S cm−1 for LiPSsTFSI-based electrolyte and ca. 10−5 S cm−1 for lithium poly[(4-styrenesulfonyl)(trifluoromethanesulfonyl)imide] (LiPSTFSI)-based electrolyte54). The polyanion PSsTFSI− could be obtained through the replacement of an oxygen atom in a TFSI-like moiety (i.e., CF3SO2N(−)SO2—) with strong electron-withdrawing trifluoromethanesulfonylimino ( = NSO2CF3) group; thus, the negative charges are further delocalized via five oxygens and two nitrogen atoms. These research works demonstrate an effective strategy for improving the ionic conductivity in coupled SPEs by weakening the interaction between salt anion and lithium ions./p>50 vol%) SPEs or when particular morphologies (e.g., nanowire) of inorganic phases are used56./p>50 wt% of salt in SPEs)17, promoting the metal ions to diffuse through this second conduction path. This demonstrates the ability of PIS-type SPEs to decouple metal-ion motion from polymer dynamics77. Several criteria, such as polymer Tg, salt type, polymer/salt solubility, electrochemical stability, and ionic conductivity78, were also discussed in C. Austen Angell’s early works to understand the physicochemical properties of PIS electrolytes. Among these, the concept of the ionicity of lithium salt is of utter importance. Specifically, ionicity is a measure of the degree of ion dissociation, commonly referring to the effective fraction of ionic species being able to participate in ionic conduction18. Figure 5c displays the Walden-Angell plot for the dependence of equivalent conductivities on the viscosities of electrolytes. With 1.0 M potassium chloride/H2O solution as a reference electrolyte, the regime above the diagonal line refers to the electrolyte materials with super-ionic characters. For PIS-type SPE systems, the lithium salt should possess sufficient ionicity to ensure the high conductivity, i.e., be located in the super-ionic regime in Fig. 5c./p> 4089) via the loose structures (i.e., rigid polymer chains with low packing density), despite their low segmental relaxation rate; segmental motion is necessary for the less-fragile polymers with dense structures (i.e., compact packing of flexible polymer chains), including PEO and other polyethers./p>0.9). This is also a fact in most PIS-type electrolytes since only a small portion of metal ions can be decoupled from the polymer, whereas the rest are still bound to the polymer chains. In the case of the PolyIL-IS systems, the weak coupling between the metal ion and the polymer exists through the anion-bridging co-coordination. The highly coupled metal ion-anion motion also limits the metal-ion transference number to ca. 0.595. In this case, improving the ionicity of the salt could maximize the decoupling motion in PolyIL-IS, although not yet experimentally proved./p>1000 cycles) and stable cycling of these SPE-SSLMBs have been achieved by the research group at Hydro-Québec100. Yet, the main obstacle to large-scale implementation of batteries with vanadium-based positive electrodes lies, at the cell level, in the dissolution of vanadium species during continuous cycling, and at the raw material level, in the uneven geographical distribution of vanadium resources worldwide101./p>6 × 108 km with a decent safety record (only two cases with unexplained runaway reactions). These industrially-relevant examples stimulated industrial and academic laboratories to restart the research activities in lithium metal rechargeable batteries after the initial abandonment of this technology as a consequence of the various fire accidents that occurred in AA-size Li°||molybdenum disulfide cells produced by Moly Energy in the late 1980s24./p>350 °C (LiCF3SO3)]115. A further homologation of the oxygen atom results in the formation of a super lithium sulfonimide salt (Li[CF3SO(NSO2CF3)2], LisTFSI) with a low melting transition approaching the ionic liquid domain (i.e., Tm ≤ 100 °C for typical ionic liquids88, and Tm = 118 °C for LisTFSI116). In this regard, we speculate that the concept of negative charge delocalization could be extended further to accessing liquid lithium salts. From another perspective, one may also replace typical neutral polyether/polyesters with charged polysalts (e.g., polycations, polyanions, or poly(zwitterions)), to regulate the ion-ion interactions and thereby achieving decoupled SPE systems117. For instance, the utilization of imidazole-type poly(zwitterions) could provide ordered subdomains with superionic nature, which allows rapid transport of ionic species even at temperatures close to their Tg values118./p>

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