The latest achievements of lithium battery technology are as follows.
1. Ultra-low concentration electrolyte realizes highly stable lithium metal battery!
The interfacial structure of electrodes is closely related to the electrochemical performance of lithium metal batteries (LMBs). In particular, a high-quality solid-electrode interface (SEI) and a uniform and dense Li deposition/stripping process are crucial to achieving stable LMBs.
By reducing the electrolyte concentration without changing the solvation structure, Guo Xiaodong of Sichuan University, Wu Zhenguo et al. achieved LiF-rich SEI and uniform and dense deposition/stripping process, thus avoiding the high cost and low wettability of high-concentration electrolytes.
In this study, the authors designed a new ether-based electrolyte system.
Among them, tetrahydrofuran (THF), which is cheap, readily available, and low-viscosity, was used as the solvent, and lithium bisfluorosulfonimide (LiFSI), which has high ionic conductivity, was used as the lithium salt. In addition, considering cost and viscosity, D5 (THF:LiFSI=14:5, molar ratio) was diluted to H1 (THF:LiFSI:TTE=14:5:14) with fluoroether (TTE). The results show that the contact ion pair and the aggregated ion pair are only separated into island-like aggregates by the diluent TTE, while the solvation structure of lithium ions in the electrolyte does not change. Therefore, the obtained ultra-low-concentration electrolyte can suppress the inhomogeneous diffusion flux of Li+ while keeping the Li+ solvation structure unchanged, resulting in a more uniform Li deposition and stripping process while maintaining the LiF-rich SEI.
As a result, the H1-matched Li/Cu half-cells are stable for 1000 cycles, and the CE can be maintained at ≈99% at 1 mA cm-2 and 1 mAh cm-2, showing excellent electrochemistry stability. In this electrolyte system, the lithium metal-LiFePO-matched coin cell exhibited excellent cycling performance with no capacity fading over 100 cycles at a positive load of up to 1.79 mAh cm-2. For the ultra-low concentration of electrolyte H2 (THF: LiFSI : TTE=14:5:28), the Li/LiFePO4 pouch battery has a capacity retention value of 98.6% and 91.4% at 0.5 and 1C, respectively. Therefore, this study provides a new perspective for the commercial application of low-cost electrolytes with ultra-low concentration and high concentration effects.
2.Targeted catalyst design for sulfur evolution reaction in high-performance lithium-sulfur batteries.
The sluggish kinetics of the sulfur evolution reaction (SER) due to the high oxidation barrier of Li2S results in low sulfur utilization and poor rate performance in Li-S batteries. However, catalyst designs to address this issue remain elusive because it is difficult to precisely correlate catalytic oxidation capacity with electronic structure.
Yang Quanhong of Tianjin University, Lv Wei of Tsinghua University Shenzhen Graduate School, etc. used layered transition metal oxide NaxTi0.5Co0.5O2 as a model catalyst to explore the above correlations because of its tunable electronic structure and its high performance in Li-S batteries. Good stability in the working potential window.
Specifically, by removing Na+, the partial phase transition can gradually increase the concentration of Co active sites, while reducing the work function with the upward shift of the Fermi level, accelerating the charge transfer on the catalyst surface, thereby improving the Li2S catalysis oxidative activity. In particular, Na0.7Ti0.5Co0.5O2 with both O3 and P3 phases shows the best catalytic activity for the oxidation of Li2S and the lowest overpotential for the activation of Li2S, contributing to the best rate performance and minimal polarization.
Benefiting from the above advantages, the Li-S battery with Na0.7Ti0.5Co0.5O2 catalyst exhibits 615 mAh g-1 even at an ultra-high rate of 5.0 C due to the high utilization of sulfur and improved SER kinetics of high capacity. In conclusion, this work elucidates the relationship between the electronic structure and catalytic activity of Li2S oxidation, which is important for designing high-performance catalysts for Li-S batteries.
3.Over 5000 cycles! Ultra stable/high capacity alkali metal ion battery!
Porous aromatic frameworks (PAFs) have attracted extensive attention in various fields, however, the understanding of their application in energy storage systems is still in its infancy.
A series of fluorene-based PAFs were synthesized by Zhu Guangshan and Wang Hengguo of Northeast Normal University, which were then used as organic anode materials for cation hosts in rechargeable alkali metal ion batteries.
Here, we design and synthesize a series of fluorene-based PAFs with tailored stereostructures with amorphous and rich aromatic frameworks via Friedel-Crafts reaction. Extensive characterization and DFT calculations suggest that more micropore volume, higher specific surface area, and especially more radicals can benefit the redox activity and electrochemical performance of organic frameworks. Benefiting from the synergy of multiple factors, the optimal PAF-202 anode exhibits ultra-high reversible capacity, ultra-stable cyclability, and excellent rate capability for Li-ion batteries.
As a result, as an anode material for Li-ion batteries, the best PAF-202 has an ultra-high reversible capacity of 1152 mAh g-1 at 0.05 A g-1, and at 20 A g-1 after 5000 cycles It has 95% capacity retention and an extraordinary rate capability of 286 mAh g-1 at 10 A g-1. In addition, PAF-202 also showed good sodium/potassium ion storage properties. Taken together, these results will broaden the horizons of designing functionally oriented porous organic polymers as anode materials, while also paving the way for the development of PAF-based organic electrode materials for energy storage systems.
The cross effect of positive and negative electrodes has a significant impact on the performance of lithium metal batteries!
While crossover effects, such as transition metal dissolution, in Li-ion batteries are well understood, there is limited understanding of the effects of crossover chemical species in batteries employing oxide cathodes and lithium metal anodes.
Arumugam Manthiram of the University of Texas at Austin et al. explored the effect of cathode-to-anode and anode-to-cathode crossover in batteries based on high-nickel cathodes, lithium metal anodes, and localized high-concentration electrolytes (LHCE, LiFSI-DME/TTE).
It was found that the high-nickel cathode paired with lithium (NC|Li, NC=LiNi0.94Co0.06O2) showed a 2-3 times higher capacity decay over 200 cycles than the same cathode paired with graphite (NC|Gr), which One point was verified in batteries reassembled with fresh lithium and electrolyte.
Surprisingly, the cathode with more capacity fade also has a thinner CEI, where the higher fade is attributed to the enrichment of sulfur and nitrogen species and depletion of fluorine rather than simple thickness differences. The effect of the positive electrode on the lithium metal negative electrode is equally important. The SEI of lithium metal anode (NC|Li) paired with high nickel cathode is three times thinner than that of lithium paired with lithium (Li|Li), and it is rich in fluorine relative to sulfur and nitrogen.
Additionally, while other crossover species, including TTE decomposed species, formates from DME oxidation, dissolved transition metal ions, and polysulfide shuttles originating from sulfur in LiFSI, were found in these cells, the lithium metal anode has a negative impact on the preferential defluorination of FSI is considered to be the main driver of the crossover effects that alter the electrochemistry. In NC|Li cells, fluorine is first removed from the FSI at the lithium metal anode, while the remaining sulfur and nitrogen cross over to the cathode and are decomposed there.
This continuous scavenging of sulfur and nitrogen apparently stabilizes the Li metal anode, while their presence or corresponding fluorine depletion adversely affects the cathode. Ultimately, this is a worthwhile trade-off for practical batteries with thin lithium metal anodes, which case crossover may be important for the impressive performance seen in lithium metal batteries with LHCE factor. The understanding of this mechanism from this work will provide an opportunity to further tune electrolyte design in pursuit of lithium metal batteries with higher energy density and cycle life.
5.Achieve 99.49% high CE for lithium highly stable non-combustible electrolyte!
In conventional non-flammable electrolytes, there is always a trade-off between non-flammability and battery performance. Previous studies have focused on the reduction of free solvents and the formation of anion-derived solid-electrolyte interfaces. However, the contribution of solvated anions in enhancing electrolyte stability has been overlooked.
Guo Zaiping, University of Adelaide, Lu Jun, Argonne National Laboratory, Li Baohua, Tsinghua University Shenzhen Graduate School, etc. solved this problem by introducing anions into the Li+ stripping sheath by using anions similar to the Gutmann donor number (DN) of the solvent.
To test this hypothesis, the authors chose nitrate anion (NO3−) with a DN of 22.2 kcal mol−1 and a trimethyl phosphate flame retardant (TMP) (DN=23.0 kcal mol−1) as electrolyte components, and combined LiNO3/TMP The solution was added to the carbonate electrolyte. The presence of TMP weakens the electrostatic attraction between Li+ and NO3−, but it is not sufficient to “release” NO3−. Therefore, the interactions among TMP, NO3− and Li+ reach equilibrium, and NO3− is introduced into the solvated structure. In this designed electrolyte, both the coordinating carbonate in the solvated structure and the electrophilicity of TMP molecules are reduced due to the participation of NO3−, which inhibits the solvolysis of Li.
Also, importantly, this electrolyte is non-flammable and has zero auto-ignition time. It also exhibits low viscosity (4.04 mPa s-1) and high ionic conductivity (5.42 mS cm-1). As a result, the reversibility of Li deposition/stripping in Li/Cu cells is improved to 99.49%, which is one of the highest reported values for non-flammable electrolytes. Furthermore, although the mass loadings of lithium iron phosphate (LFP) and ternary (LiNi0.8Co0.1Mn0.1O2, NCM811) cathodes are as high as 14.3 mg cm-2 and 16.7 mg cm-2, respectively, the n/p ratio is <5, and the use of With lean electrolyte, the life of LMB is still significantly extended. The rational design of this electrolyte is universal and thus can be practically extended to other alkali metal batteries.
6.Ultra-long cycle life lithium metal battery, 1000 cycles at 5C!
The exploration of high-performance polymer-based electrolytes will drive the rapid development of next-generation lithium metal batteries.
A self-healing quasi-solid-state mixed electrolyte network (X-PPS-D4) combined with a deep eutectic solvent was prepared by polyaddition reaction, photo-induced free radical cross-linking, and physical mixing.
The study shows that the obtained X-PPS-D4 not only possesses a high ionic conductivity (σ) of 2.03×10-4 S cm-1 at 30°C, but also has a wide electrochemical stability window (0∼5.0 V vs. Li+/ Li). And the presence of dynamic covalent bonds in the electrolyte structure endows it with self-healing ability. In addition, the Li ion transfer number (=0.44) of X-PPS-D4 is enhanced due to the reduced anion mobility, which is confirmed by spectroscopic analysis, NMR studies, and theoretical calculations.
As a result, X-PPS-D4 can support stable long-term (>1300 h) deposition/stripping cycles for Li/Li symmetric cells at a current density of 0.1 mA cm-2 at the test temperature of 30 °C. More importantly, the in situ formation of X-PPS-D4 on the LiFePO4 cathode within the coin cell promotes excellent battery performance, with a specific capacity exceeding 100 mAh g-1 at 5C, and an ultra-long cycle life ( >1000 cycles), in addition to high specific capacity at 1C (>116.1 mA h g-1 after 1000 cycles). In addition, X-PPS-D4 also showed its potential application value in Li/NCM811 batteries.
In conclusion, this study provides new insights into the structure-property relationship of quasi-solid-state hybrid electrolytes with eutectic mixtures and provides an efficient route to develop LMBs for high-performance polymer-based electrolytes.