Researchers must find a sustainable way of providing the power our modern lifestyles demand.

Building better batteries

The increasing interest in energy storage for the grid can be attributed to multiple factors, including the capital costs of managing peak demands, the investments needed for grid reliability, and the integration of renewable energy sources. Although existing energy storage is dominated by pumped hydroelectric, there is the recognition that battery systems can offer a number of high-value opportunities, provided that lower costs can be obtained. The battery systems reviewed here include sodium-sulfur batteries that are commercially available for grid applications, redox-flow batteries that offer low cost, and lithium-ion batteries whose development for commercial electronics and electric vehicles is being applied to grid storage.

Electrical Energy Storage for the Grid: A Battery of Choices

Li-ion batteries have transformed portable electronics and will play a key role in the electrification of transport. However, the highest energy storage possible for Li-ion batteries is insufficient for the long-term needs of society, for example, extended-range electric vehicles. To go beyond the horizon of Li-ion batteries is a formidable challenge; there are few options. Here we consider two: Li-air (O(2)) and Li-S. The energy that can be stored in Li-air (based on aqueous or non-aqueous electrolytes) and Li-S cells is compared with Li-ion; the operation of the cells is discussed, as are the significant hurdles that will have to be overcome if such batteries are to succeed. Fundamental scientific advances in understanding the reactions occurring in the cells as well as new materials are key to overcoming these obstacles. The potential benefits of Li-air and Li-S justify the continued research effort that will be needed.

Li-O2 and Li-S batteries with high energy storage.

Each cell of a battery stores electrical energy as chemical energy in two electrodes, a reductant (anode) and an oxidant (cathode), separated by an electrolyte that transfers the ionic component of the chemical reaction inside the cell and forces the electronic component outside the battery. The output on discharge is an external electronic current I at a voltage V for a time Δt. The chemical reaction of a rechargeable battery must be reversible on the application of a charging I and V. Critical parameters of a rechargeable battery are safety, density of energy that can be stored at a specific power input and retrieved at a specific power output, cycle and shelf life, storage efficiency, and cost of fabrication. Conventional ambient-temperature rechargeable batteries have solid electrodes and a liquid electrolyte. The positive electrode (cathode) consists of a host framework into which the mobile (working) cation is inserted reversibly over a finite solid–solution range. The solid–solution range, which is...

The Li-ion rechargeable battery: a perspective.

2.1. Solvents 4307 2.1.1. Propylene Carbonate (PC) 4308 2.1.2. Ethers 4308 2.1.3. Ethylene Carbonate (EC) 4309 2.1.4. Linear Dialkyl Carbonates 4310 2.2. Lithium Salts 4310 2.2.1. Lithium Perchlorate (LiClO4) 4311 2.2.2. Lithium Hexafluoroarsenate (LiAsF6) 4312 2.2.3. Lithium Tetrafluoroborate (LiBF4) 4312 2.2.4. Lithium Trifluoromethanesulfonate (LiTf) 4312 2.2.5. Lithium Bis(trifluoromethanesulfonyl)imide (LiIm) and Its Derivatives 4313

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Nonaqueous liquid electrolytes for lithium-based rechargeable batteries.

Oxygen reduction reactions (ORRs) and oxygen evolution reactions (OERs) on glassy carbon (GC) and gold electrodes were investigated in a neat and Li+-containing room-temperature ionic liquid (RTIL), 1-ethyl-3-methylimidazolium bis(triflouromethanesulfonyl)imide (EMITFSI). The presence of Li+ significantly changes the ORR mechanism. While similar one-electron O2/O2•– reversible couples result on both electrodes in neat EMITFSI, in the presence of added LiTFSI, the initially formed LiO2 decomposes to Li2O2. In addition, the ORR and OER in the Li+-doped solution exhibit strong distinctions between the Au and GC electrodes. The voltammetric data on the Au electrode revealed a highly rechargeable ORR, yielding LiO2 and Li2O2, which underwent multiple cycles without electrode passivation.

Oxygen Electrode Rechargeability in an Ionic Liquid for the Li–Air Battery

Micron-sized Li 4 Ti 5 O 12 was prepared in a single-step solid-state reaction involving TiO 2 and Li 2 CO 3 , and its electrochemical behavior was evaluated in Li and Li-ion cells containing a polyacrylonitrile (PAN)-based solid polymer electrolyte. The usefulness of Li 4 Ti 5 O 12 was demonstrated for three distinctive applications: (i) cathode of a 1.5 V rechargeable Li battery, (ii) auxiliary electrode for investigating the electrochemistry of Li insertion cathode materials, and (iii) anode of a Li-ion cell in conjunction with a high voltage cathode, e.g., cubic spinel LiMn 2 O 4 . The micron-sized Li 4 Ti 5 O 12 exhibited a capacity of 160 mAh/g at C/20-C/30 rates which is about 7% better than the capacity exhibited by this material prepared according to a previously published procedure. More importantly, the micron-sized oxide showed significantly better high rate capability, yielding 25-50% larger capacity at the 3C to 8C rates. Li/solid polymer electrolyte//Li 4 Ti 5 O 12 cells underwent extended, ull-depth, charge/discharge cycling at≥1C rates with virtually no capacity fade. The auxiliary electrode concept was demonstrated in Li (4+x) Ti 5 O 12 (x∼ 1.2)//solid polymer electrolyte//LiMn 2 O 4 cells. At a 1C discharge rate, more than 150 cycles were demonstrate in these cells with a capacity fade rate of about 0.1% per cycle and an end utilization of ∼90 mAh/g for spinel LiMn 2 O 4 . Balanced Li 4 Ti 5 O 12 //solid polymer electrolyte//LiMn 2 O 4 cells of slightly cathode-limited configuration showed full-depth extended cycling capability at a utilization of ∼90 mAh/g for LiMn 2 O 4 at 1C rate and a capacity fade rate of about 0.08% per cycle. The capacity fade in the LiMn 2 O 4 -containing cells appears to come from this cathode. When fully packaged, specific energy of the Li//PAN electrolyte//Li 4 Ti 5 O 12 cell would be about 57 Wh/kg and that of the Li 4 Ti 5 O 12 //PAN electrolyte//LiMn 2 O 4 cell is about 60 Wh/kg.

Preparation of Micron‐Sized Li4Ti5 O 12 and Its Electrochemistry in Polyacrylonitrile Electrolyte‐Based Lithium Cells

Liquid electrolytes typically used in commercial lithium-ion batteries are comprised of lithium hexafluorophosphate in carbonate solvents. This electrolyte undergoes thermal decomposition at moderately elevated temperatures (80-100°C), encountered in the normal operation of these rechargeable power sources, to quantitatively generate highly toxic alkylfluorophosphates. The decomposition occurs via an autocatalytic mechanism initiated by trace impurities of water or alcohol. The thermal decomposition is inhibited in the presence of lithium metal oxides frequently used as the cathode of lithium-ion batteries or Lewis basic additives.

https://iopscience.iop.org/article/10.1149/1.1738551/pdf

Suppression of Toxic Compounds Produced in the Decomposition of Lithium-Ion Battery Electrolytes

Polyacrylonitrile (PAN)-based electrolytes have been prepared by encapsulating Li salt solutions. The conductivity of these electrolytes is governed by a combination of factors including the relative amounts of PAN, EC, PC and the Li salt, and temperature. A conductivity of about 4.5 x 10{sup -3}{Omega}{sup -1} cm{sup -1} at 30 {degrees}C was exhibited by EC-rich electrolytes containing both LiN(SO{sub 2}CF{sub 3}){sub 2} and LiPF{sub 6}. The cationic transference numbers, measured using a dc polarization method coupled with impedance spectroscopy, were found to be between 0.2 and 0.3 for electrolytes containing LiN(CF{sub 3}SO{sub 2}){sub 2} and LiPF{sub 6}. The tensile strength of the electrolytes was observed to increase from 60 to 140 lb/in.{sup 2} upon incorporation of the thermally activated cross-linking agent ethylene glycol dimethacrylate. Cyclic voltammetry on Pt electrodes has shown that these electrolytes have an inherent oxidation stability window extending up to about 5 V versus Li{sup +}/Li. On Al, Ni, and Cu electrodes, however, oxidation was observed at lower potentials because of metal corrosion reactions. Copper was reversibly oxidized at 3.5 V, irrespective of the Li salt present in the electrolyte. On the other hand, the nature of the Li salt influenced the corrosion potentials of Al andmore » Ni. Nickel was found to be stable up to 4.2 V in the presence of LiAsF{sub 6}, whereas it was oxidized at about 3.5 and 4 V when the electrolyte contained LiN(SO{sub 2}CF{sub 3}){sub 2} and LiSO{sub 3}CF{sub 3} showing oxidation at {le}4 V. The electrochemical stability of the electrolytes was further verified in Li/LiMn{sub 2}O{sub 4} cells. 10 refs., 15 figs., 9 tabs.« less

Characterization of some polyacrylonitrile-based electrolytes

Solid polymer electrolytes have been prepared by encapsulating plasticized polymer electrolytes based on poly(tetraethylene glycol diacrylate) into the pores of Celgard{reg_sign} microporous membranes. Electrolyte membranes with thicknesses of {approximately}40 {mu}m have been prepared. The conductivity of the electrolyte is determined by the porosity of the membrane, and a conductivity of {approximately}2 {times} 10{sup {minus}4} {Omega}{sup {minus}1} {center_dot} cm{sup {minus}1} at room temperature has been demonstrated. These electrolytes showed good compatibility with Li and an electrochemical stability window spanning the range of 0.0 to {approximately}4.5 V vs. Li{sup +}/Li. The excellent chemical and electrochemical stabilities enabling the use of the membranes in rechargeable Li batteries have been confirmed by the discharge/charge cycling of Li/solid polymer electrolyte/LiMn{sub 2}O{sub 4} cells at room temperature.

https://iopscience.iop.org/article/10.1149/1.2048517/pdf

K. M. Abraham

Papers

Oxygen Electrode Rechargeability in an Ionic Liquid for the Li–Air Battery

Preparation of Micron‐Sized Li4Ti5 O 12 and Its Electrochemistry in Polyacrylonitrile Electrolyte‐Based Lithium Cells

Suppression of Toxic Compounds Produced in the Decomposition of Lithium-Ion Battery Electrolytes

Characterization of some polyacrylonitrile-based electrolytes

Polymer Electrolytes Reinforced by Celgard® Membranes