In situ surface protection for enhancing stability and performance of conversion-type cathodes

Abstract

Lithium and lithium-ion batteries (LBs and LIBs) are the most popular battery systems for electrochemical energy storage technologies. Commercial LIBs utilize intercalation-type cathode materials, mostly nickel (Ni)-based and cobalt (Co)-based cathodes, showing specific capacities of up to ∼200 mA h/g (theoretical capacity below 300 mA h/g), which limit the specific energy of batteries, and are additionally expensive and toxic. An EPA study showed that the Ni-and Co-containing batteries that use solvent-based electrode processing have the highest potential for negative environmental impacts. 1 These impacts include resource depletion, global warming, ecological toxicity, and human health impacts with the largest contributing processes include those associated with the production, processing, and use of cobalt and nickel metal compounds, which may cause adverse respiratory, pulmonary, and neurological effects in those exposed. 1 The study suggested cathode material substitution and solvent-less electrode processing to reduce these impacts. 1 The uneven distribution of Co in the earth crust 2 and the insufficient use of suitable personal protection equipment in many Co mining developing countries 3,4 created a major concern. For example, Amnesty International findings of major exploitations of children in Co mines and the related child sickness and deaths 3,4 demonstrate some of the most horrific examples of child labor, which international community should not tolerate and certainly should not encourage through growing market demands for Co. The growing Co contained-electronic waste ABSTRACTThe use of in situ formed protective layer on conversion cathodes was introduced as a cheap and simple strategy to shield these materials from undesirable interactions with liquid electrolytes.Conversion-type cathodes have been viewed as promising candidates to replace Ni-and Co-based intercalation-type cathodes for next-generation lithium (Li) and Li-ion batteries with higher specific energy, lower cost, and potentially longer cycle life. Typically, in conversion reactions two or three Li ions may be stored per just one atom of chalcogen (e.g., S or Se) or transition metal (e.g., Fe or Cu used in halides). Unfortunately, in conversion chemistries the active materials or intermediate charge/discharge products suffer from various unfavorable interactions and dissolution in organic electrolytes. In this mini-review article, we discuss the current interfacial challenges and focus on the protective layers in situ formed on the cathode surface to effectively shield conversion materials from undesirable interactions with liquid electrolytes. We further explore the mechanisms and current progress of forming such protective layers by using various salts, solvents, and additives together with the insight from molecular modeling. Finally, we discuss future opportunities and perspectives of in situ surface protection.Keywords: Li; S; F; coating; energy storage Review DiSCUSSiON POiNTS• Conversion-type cathodes have been viewed as promi...

A carbonate-free, sulfone-based electrolyte for high-voltage Li-ion batteries

“…S15), the experiments in this work (Fig. S7), and previous studies with other solvents [25]. This will drive anion decomposition at higher potentials, potentially resulting in formation of an inorganic SEI prior to Li cointercalation and the onset of exfoliation.…”

Review on modeling of the anode solid electrolyte interphase (SEI) for lithium-ion batteries

“…Similarly, H-transfer reactions are often coupled with electrolyte oxidation, so the oxidation potential is lower than the calculated HOMO. [18][19][20] Nevertheless, the LUMO of most electrolyte components are higher than the lithiated graphite (~0.1 eV) and lithium metal (0 eV) voltage, and hence reduction of electrolyte on the anode is expected. In comparison to the SEI on the cathode, the SEI on the anode is more unstable due to the evident reduction reactions and the larger volume expansion of anode materials.…”

3D Honeycomb Architecture Enables a High‐Rate and Long‐Life Iron (III) Fluoride–Lithium Battery

“…According to above results, compared to conventional intercalation cathodes including lithium iron phosphate (LiFePO 4 , LFP), Ni‐rich layered oxides (LiNi 0.8 Co 0.1 Mn 0.1 O 2 , NCM), and lithium cobalt oxide (LiCoO 2 , LCO), FeF 3 cathode based on one‐electron reaction is very promising due to low cost Fe resources, higher specific capacity, super rate capability, and excellent cycling performance without voltage fading with cycles. In Figure g,h, the practically achievable specific energies and volumetric energy densities of FeF 3 ‐Li cells are calculated and compared to the cells based on conventional intercalation cathodes (details of the calculations and assumptions are similar to previous reports and provided in the Supporting Information). Only considering the one‐electron reaction, the FeF 3 ‐Li cell offers achievable specific energy and volumetric energy density of 582 Wh kg −1 and 1330 Wh L −1 , respectively, which are much higher than those of current commercial Li‐ion batteries based on intercalation‐type LFP, Ni‐, Co‐based cathodes and graphite anode.…”

“…Recently, battery materials including FeF 3 , FeF 2 , CuF 2 , and elemental sulfur based on conversion reactions have attracted great attention for both Li and Na batteries because of their much higher theoretical capacities originating from multiple electron transfer per redox center and reversibility . Compared to lithium–sulfur batteries, metal fluoride–lithium batteries with relatively higher operating voltage are more competitive in both gravimetric and volumetric energy densities . Compared to Ni and Co, Fe and Cu are low‐cost, more abundant in the Earth's crust, and friendlier to the environment, which are beneficial for future large‐scale applications .…”