► Effect of LiNO3 on the Li anode and cathode of Li/S battery is studied, respectively. ► LiNO3 participates in the formation of a stable passivation film on the Li anode surface. ► LiNO3 may be ...reduced irreversibly on the cathode, affecting Li/S battery performance. ► Discharge mechanism of Li/S battery is explained from the viewpoint of phase transition.
In this work we study the effect of LiNO3 on the Li anode and sulfur cathode, respectively, of Li/S battery by using a Li/Li symmetric cell and a liquid Li/Li2S9 cell. On the Li anode, LiNO3 participates in the formation of a stable passivation film, and the resulting passivation film grows infinitely with the consumption of LiNO3. The passivation film formed with LiNO3 is known to effectively suppress the redox shuttle of the dissolved lithium polysulfides on Li anode. On the cathode, LiNO3 undergoes a large and irreversible reduction starting at 1.6V in the first discharge, and the irreversible reduction disappears in the subsequent cycles. Moreover, the insoluble reduction products of LiNO3 on the cathode adversely affect the redox reversibility of sulfur cathode. These results indicate that both the Li anode and sulfur cathode consume LiNO3, and that the best benefit of LiNO3 to Li/S battery occurs at the potentials higher than 1.6V. By limiting the irreversible reduction of LiNO3 on the cathode, we have shown that the Li/S cell with a 0.2m LiNO3 as the co-salt can provide a stable capacity of ∼500mAhg−1.
Lithium/sulfur (Li/S) battery has a 3–5 fold higher theoretical energy density than state-of-art lithium-ion batteries, and research has been ongoing for more than three decades. However, the ...commercialization of Li/S battery still cannot be realized due to many problematic issues, including short cycle life, low cycling efficiency, poor safety and a high self-discharge rate. All these issues are related to the dissolution of lithium polysulfide (PS), the series of sulfur reduction intermediates, in liquid electrolyte and to resulting parasitic reactions with the lithium anode and electrolyte components. On the other hand, the dissolution of PS is essential for the performance of a Li/S cell. Without dissolution of PS, the Li/S cell cannot operate progressively due to the non-conductive nature of elemental sulfur and its reduction products. In this review article, we start with the fundamental chemistry of elemental sulfur in order to discuss the problems and solutions of liquid electrolyte Li/S battery.
► Discuss the real problems of Li/S cells from the fundamental chemistry of Li/S battery. ► Review the current efforts on the research and development of Li/S battery. ► Discuss the drawback of the current efforts. ► Suggest the effective approach for the performance improvement of Li/S battery.
Lithium nitrate (LiNO3) is the most studied additive and co-salt for the electrolyte of lithium-sulfur (Li–S) batteries, its known function is to suppress the redox shuttle of soluble lithium ...polysulfide (PS, Li2Sn), which reflects as an increase in the battery’s coulombic efficiency and cycling stability, as well as a reduced self-discharge rate. The current understanding on this function is that LiNO3 reacts with Li to form a robust surface layer that consequently protects the Li anode from reacting with the dissolved PS. However, little is known on the sulfur cathode except that LiNO3 reduces and adversely affects the battery’s performance when the battery is discharged to lower than 1.7 V. In this paper we report a new finding on the role of LiNO3 in enabling the stable cycling of the sulfur cathode. We show that LiNO3 is capable of catalyzing the conversion of high soluble PS to slightly soluble elemental sulfur near the end of charging process, and that the combination of a soluble nitrate in the electrolyte and an insoluble nitrate in the sulfur cathode leads to synergetic improvement. In addition, a possible mechanism is proposed for the catalysis of LiNO3 on the conversion of PS to elemental sulfur.
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•Role of LiNO3 in Li–S batteries is reinvestigated with focus on sulfur cathode.•Nitrate anion catalyzes the conversion of polysulfide to elemental sulfur.•A catalysis mechanism of nitrate anion on the Li2Sn to S8 conversion is proposed.•Combination of a soluble nitrate and an insoluble nitrate leads to synergetic improvement.
Fast‐charging is highly demanded for applications requiring short charging time. However, fast‐charging triggers serious problems, leading to decline in charge acceptance and energy efficiency, ...accelerated capacity degradation, and safety risk. In this work, a three‐electrode coin cell with a Li metal reference electrode is designed to individually record the potential of two electrodes, and measure the impedance of each electrode by using a power‐optimized graphite‐LiNi0.80Co0.15Al0.05O2 electrode couple. It is shown that regardless of the state‐of‐charge the Li‐ion cell's impedance is contributed predominantly by the cathode, and that the cathode's impedance is dominated by the charge‐transfer resistance. In consistence with the impedance results, polarization of the Li‐ion cell is dominated by the cathode. It is surprised to find that no Li plating occurs on the graphite anode even if the charging rate is increased to 10 C (1 C = 1.30 mA cm−2). The results of this work indicate that low overall impedance with a high cathode‐to‐anode impedance ratio is the key to enabling safe fast‐charging, and that fast‐charging Li‐ion batteries without Li plating on the graphite anode is possible if the cathode and graphite anode are optimistically engineered.
A three‐electrode Li‐ion coin cell with a Li reference electrode enables to simultaneously record the cell's voltage and electrodes’ potentials, and individually measure the cell's and electrodes’ impedances. A health graphite‐LiNi0.80Co0.15Al0.05O2 Li‐ion cell shows much higher impedance of the cathode than the anode, which makes it possible to safely charge Li‐ion cells up to 10C without Li plating on the graphite anode.
Pre-lithiation is an indispensable step for making hybrid lithium-ion capacitors (LICs), its high cost and process complexity have greatly hindered the commercialization of LICs. Aiming to eliminate ...the pre-lithiation step, we propose an in-situ lithiation concept by introducing a Li+ ion source material into the positive electrode to enable the lithiation to be completed in the formation cycle. In this paper we start with the fundamental principle of LICs to discuss the requirements for Li+ ion source materials and demonstrate this concept by employing Li-rich Li2CuO2 as the Li+ ion source material, natural graphite and activated carbon (AC) as the negative and positive electrode materials. It is shown that the LICs made such behave as a pure capacitor with ability to deliver the same level of specific capacity and specific capacitance, i.e., 56 mAh g−1 and 143 F g−1 vs. the mass of AC in the voltage range between 2.8 V and 4.2 V, as those obtained from the counterpart Li/AC half-cell. The present concept is also applicable to other LICs with the negative electrode required to be pre-lithiated.
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•Discussed the superiority of hybrid LIC to symmetric EDLC in view of working principle.•Eliminated pre-lithiation step for making of LICs by using a Li+ ion source material.•Discussed requirements for the Li+ ion source materials.•Demonstrated a proof-of-concept LIC using Li2CuO2 as the Li+ ion source material.
Sulfurized polyacrylonitrile (SPAN) is one of the most important sulfurized carbon materials that can potentially be coupled with the carbonaceous anode to fabricate a safe and low cost "all carbon" ...lithium-ion battery. However, its chemical structure and electrochemical properties have been poorly understood. In this discussion, we analyze the previously published data in combination with our own results to propose a more reasonable chemical structure that consists of short -Sx- chains covalently bonded onto cyclized, partially dehydrogenated, and ribbon-like polyacrylonitrile backbones. The proposed structure fits all previous structural characterizations and explains many unique electrochemical phenomena that were observed from the Li/SPAN cells but have not been understood clearly.
Long charging time for Li‐ion batteries is a critical obstacle for the widespread adoption of electric vehicles, especially when compared with the rapid refueling of traditional internal combustion ...engine vehicles. Fast charging results in accelerated performance degradation and low energy efficiency for Li‐ion batteries. The batteries adopted in the present electric vehicle market are mainly based on chemistry consisting of a graphite anode and a layered lithium transition‐metal oxide cathode. The fast‐charging capability of such batteries is limited by Li plating on the graphite anode and structural instability of the layered lithium transition‐metal oxide cathode. In this Minireview, the challenges and possible solutions to these fast charge problems are reviewed at both the materials and cell levels.
Getting in the fast lane? Fast charging results in accelerated performance degradation and low energy efficiency, which is primarily attributed to Li plating on graphite anodes, structural instability of the layered cathode materials, and electrolyte depletion. Mechanisms and possible solutions to the fast charging problems of Li‐ion batteries are critically reviewed.
► A new direction for improving Li/S batteries by in situ protecting Li anode. ► LiNO
3 promotes formation of a highly protective passivation film on Li surface. ► Li/Li
2S
x
liquid cell offers ...better capacity retention than conventional Li/S cells. ► LiNO
3 increases specific capacity and cycling efficiency of Li/S cells.
In this work we introduce a new direction for the performance improvement of rechargeable lithium/sulfur batteries by employing an electrolyte that promotes Li anode passivation in lithium polysulfide solutions. To examine our concept, we assemble and characterize Li/Li
2S
9 liquid cells by using a porous carbon electrode as the current collector and a 0.25
m Li
2S
9 solution as the catholyte. Results show that Li/Li
2S
9 liquid cells are superior to conventional Li/S cells in specific capacity and capacity retention. We also find that use of LiNO
3 as a co-salt in the Li
2S
9 catholyte significantly increases the cell's Coulombic efficiency. More importantly, the cells with LiNO
3 have a ∼2.5
V voltage plateau before the end of charging and demonstrate a steep voltage rise at the end of charging. The former is indicative of the formation of elemental sulfur from soluble lithium polysulfides on the carbon electrode, and the latter provides a distinct signal for full charging. Electrochemical analyses on Li plating and stripping in Li
2S
9 catholyte solutions indicate that LiNO
3 participates in the formation of a highly protective passivation film on the Li metal surface, which effectively prevents the Li anode from chemical reaction with polysulfide anions in the electrolyte and meanwhile prevents polysulfide anions from electrochemical reduction on the Li surface.
Adhesion of Li plating to electrode substrate and chemical stability of plated Li against electrolyte components are two essential factors affecting the cycling performance of Li metal in a ...rechargeable Li battery. Poor adhesion results in high contact resistance and further the formation of dead Li. Aiming to improve the adhesion of Li plating to Cu substrate, we plate a very thin tin layer as the primer for Li plating on the Cu substrate. By this way, Li metal is first reacted with tin to form a Li-Sn alloy, and then Li is cycled on resultant Li-Sn alloy so that the Li-Sn alloy functions as an “electric glue” to electrically connect the Li plating and Cu substrate. Attributed to the strong affinity between Li and Li-Sn alloy, the pre-plated tin layer is shown not only to enhance the adhesion of the plated Li to electrode substrate but also to improve the morphology of Li plating. Using a 1.0 m (molality) LiPF6 1:4 (wt.) fluoroethylene carbonate/ethylmethyl carbonate electrolyte, in this paper the effect of the tin primer layer on the Li cycling performance in a Li/Cu cell and a Cu/LiNi0.85Co0.10Al0.05O2 cell is demonstrated and discussed.
A pre-plated tin primer layer significantly enhances Li adhesion to electrode substrate and consequently improves the Li cycling performance. Display omitted
•A Sn-plated Cu foil is prepared as the electrode substrate for efficient Li electrodeposition.•Li cycling performance is improved from the view of Li adhesion to electrode substrate.•Tin primer layer significantly enhances the adhesion of Li deposit to electrode substrate.•The effect of tin primer layer on Li electrodeposition is evaluated in a “Li-free” cell.
Lithium (Li) metal has been regarded as the ultimate anode material for high-energy-density rechargeable batteries due to its high specific capacity and low reduction potential. However, the ...application of Li metal in rechargeable batteries was hampered by two major problems: dendritic deposition and inferior cycling efficiency. In this minireview, the mechanisms relating to these two major problems and relative solutions are reviewed by starting with the intrinsic natures of Li metal. In addition, limitations of the electrochemical characterization methods currently used for evaluation of Li cycling performances are discussed, and possible directions for future research are suggested.
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