Promising All-Solid-State Batteries for Future Electric Vehicles

By Yang‐Kook Sun. ACS Energy Letters, 2020

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The global electric vehicle (EV) market has grown sharply over the past decade on the back of technological advances and supportive policies. There were about 7.2 million EVs on the world’s roads in 2019, and this number is predicted to near 140 million within the next decade. Among the various types of secondary batteries, lithium-ion batteries (LIBs) have been a key technology in the success of EVs owing to their high energy densities and long service lives. However, current LIBs are expensive, with limited ability to sufficiently deliver the performance required to advance EV development. In particular, the short driving range achievable with a single charge and long charging times are the main concerns of the broad consumer market. To achieve EV performances comparable to those of internal combustion engine vehicles, many researchers and manufacturers are devoted to developing LIBs with higher power and energy densities. However, this drive to develop more efficient and powerful LIBs has exposed the safety challenges of certain approaches. The tight packing of electrodes and their narrow separation increase the energy densities of LIBs but also increase their risk of explosion. The occasional reports of exploding or combusting LIBs in mobile phones, EVs, and energy storage systems are enough to make the average consumer nervous, possibly damaging market demand for EVs. Hence, safe LIBs are a prerequisite for the further acceleration of EV deployment. The liquid organic electrolyte (LE) is the component of an LIB primarily responsible for any combustion risk because of its high volatility and flammability. In this regard, all-solid-state batteries (ASSBs), in which solid electrolytes (SEs) are used as substitutes for LEs, are increasingly regarded as very promising next-generation battery systems. In addition to being nonflammable, SEs have several advantages over conventional LEs. Current state-of-the-art LIBs have a narrow operating temperature range owing to the LE; at low temperatures (< ∼0 °C) the ionic conductivity of the electrolyte is reduced and performance decreases significantly, whereas, at high temperatures (> ∼60 °C), the high reactivity of LEs accelerates their decomposition and the deterioration of other components, thus causing battery swelling or malfunction. Unlike LEs, the intrinsic solid nature of SEs tolerates a wide operating temperature range (−30 to 100 °C) while delivering reliable performance. Moreover, the energy densities of ASSBs can be greatly increased by directly adopting lithium metal as an anode, as the solid−solid contact between the electrolyte and lithium effectively disrupts the free growth of lithium dendrites, which are the cause of critical safety problems. In addition, SEs acting as rigid physical barriers between the anodes and cathodes enable bipolar electrode configurations, which is advantageous for optimizing energy density and utilizing limited space. Despite several advantages that distinguish them from conventional LE-based batteries, considerable time and effort will be required before ASSBs are market-ready; the technology is still in an early research stage. First, high ionic conductivity, comparable to the level of LEs at operating temperature, is the most important criterion for efficient ASSBs because most SEs demonstrate inherently lower ionic conductivity than liquid electrolytes. Various organic and inorganic materials have been studied as possible substitutes for LEs, and recent research shows great potential. A number of oxideand sulfide-based SEs have demonstrated high ionic conductivities near or even better than those of LEs (∼1−10 mS cm−1). For example, the oxide-based electrolyte, La0.51Li0.34TiO2.94, and sulfide-based electrolytes, Li10GeP2S12 and Li9.54Si1.74P1.44S11.7Cl0.3, achieved ionic conductivities of ∼1, 12, and 25 mS cm−1, respectively. Given these advances, some argue that ionic conductivity, in itself, is not the bottleneck for high-performance ASSBs; however, creative solutions involving highly conductive SEs remain a challenge. Second, reported ASSBs suffer from low Coulombic efficiency, poor power performance, and unstable cycling stability, largely resulting from high interfacial resistance at numerous solid−solid interfaces. Unlike LEs, SEs cannot completely cover the cathode or anode interfaces; consequent interfacial complications arise even at electrolyte−electrolyte interfaces despite the high pressures prevailing during cell assembly. As lithium ions can migrate only through intimate interfaces, the poor wettability of solid electrolytes with other components results in high charge-transfer resistance and thus the rapid deterioration of ASSB performance. The mechanical stresses induced by the continuous and repeated volume

Subfields: Automotive Engineering, Electrical and Electronic Engineering

View Paper: https://www.semanticscholar.org/paper/30728dba192a7f08c606164160fd4550b0125013

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In Automotive Engineering

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  2. Chunsheng Wang
  3. Zonghai Chen
  4. Sergiy Kalnaus
  5. Stephen Harris
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In Electrical and Electronic Engineering

  1. Chunsheng Wang
  2. Jie Xiao
  3. Zonghai Chen
  4. Sergiy Kalnaus
  5. Stephen Harris
  6. B. McCloskey
  7. J. Nanda
  8. N. Dudney

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