Gallium-Doped Li 7 La 3 Zr 2 O 12 Garnet-Type Electrolytes with High Lithium-Ion Conductivity

209

204

SSEs) because of their nonflammability and mechanical strength to block dendritic Li growth. [5,6] Among the many SSEs studied, [7][8][9][10][11][12][13][14] the cubic garnet phase SSEs [15][16][17][18][19][20][21] are more attractive because of their excellent chemical stability, [22,23] high ionic conductivities, [15,16,[24][25][26] and wide electrochemical potential window. [27][28][29] One of the major challenges for the application of the garnet-based solid-state Li metal batteries is the poor interfacial contact between garnet SSEs and electrode materials. [24,30,31] Direct contact between Li metal foil and garnet pellets normally results in poor contact and large interfacial resistance. By adding a polymer interface [32,33] or applying pressure, [34,35] the Li and garnet interface can be improved marginally, but still has high resistance. The poor wettability of molten Li against garnet substrates also makes it unfeasible to directly coat Li metal on garnet SSEs. In the previous work, [36][37][38][39][40] the wettability of garnet pellets against molten Li was significantly improved by coating a modification layer on the garnet surface, and the interfacial resistance was decreased from more than 1000 Ω cm 2 to as low as 1-20 Ω cm 2 . [36,37] However, for large-scale practical applications, this additional surface modification step under high vacuum is time-consuming and an additional cost. Therefore, a lower cost and more effective method is still strongly desired to solve the interfacial problem between Li metal anode and garnet SSEs for practical solid-state Li metal batteries.Fundamentally, the poor wetting between molten Li metal and garnet pellets is due to the large difference in surface energy. Our previous strategy introduces new interfaces that have better wettability against molten Li, but another strategy is to tune the surface energy of molten Li itself to match with the garnet SSEs. This wetting issue between liquid metals and ceramic substrates has been extensively studied for multiple applications, such as metal-ceramic joining by brazing and fabricating metal matrix composites. [41][42][43] To improve the wettability between liquid metals and ceramic substrates, alloying elements were normally added to tune the surface energy of the liquid metals and significantly decrease the contact angle on ceramic substrates. [41,43,44] Recently, with the rise in solid-state Li metal batteries, the metal-ceramic contact has become a critical challenge toward the development of high energy density and safe energy storage devices.The high theoretical specific capacity of lithium (Li) metal and the nonflammability of solid-state electrolytes (SSEs) make the solid-state Li metal battery a promising option to develop safe batteries with high energy density. To make the switch from liquid to solid-state electrolyte, the high interfacial resistance resulting from the poor solid-solid contacts between Li metal and SSEs needs to be addressed. Herein, a one-step soldering technique to quickly coat molten Li onto ...

mentioning

confidence: 99%

Universal Soldering of Lithium and Sodium Alloys on Various Substrates for Batteries

Wang

Zhang

et al. 2017

209

204

“…As chemical shift is a sensitive probe of local chemical environment, it is observed the chemical shift decreases from 1.05 to 0.87 ppm with Si addition from 0 to 0.15 (shown in Figure 4b), which directly indicates an evolution of local chemical environment of 7 Li. [30,31] The ratio of t1-long/t1-short is shown in Figure 4c. Similar conclusion can also be made by the broadening of 7 Li spectra as Si content increases.…”

Section: Resultsmentioning

confidence: 99%

Si‐Doping Mediated Phase Control from β‐ to γ‐Form Li₃VO₄ toward Smoothing Li Insertion/Extraction

Liao

Wen

Xia

et al. 2017

Self Cite

power density, high energy density, and environmental friendly. [1,2] Tremendous attempts are made to further improve the energy density of LIBs for new applications as electrical vehicles and hybrid electrical vehicles, which mainly focus on seeking new electrode materials. [3][4][5] It is well recognized that the key for commercialization of LIBs is the discovery and application of insertion anode, graphite. However, in the last three decades, few insertion anode alternatives are available with good promise of commercial requirements and higher energy than graphite, which becomes a bottleneck for the development of next generation LIBs. Besides of graphite and Li 4 Ti 5 O 12 , Li 3 VO 4 is first proposed as a new promising insertion anode in 2013. [6] It shows a theoretical capacity of 394 mA h g −1 when inserted 2 mole Li per formula, higher than graphite and nearly two times that of Li 4 Ti 5 O 12 . The potential plateau of Li 3 VO 4 (1.0-1.5 V) falls in between graphite and Li 4 Ti 5 O 12 , which ensures the energy density as well as safety of battery system. What is more, after continuous research efforts in the following 3 years, its available capacity can be further increased to the level of 400-500 mA h g −1 based on 2 < x < 3 in Li 3+x VO 4 , revealing a promising perspective for application in high energy LIBs. [7,8] However, Li 3 VO 4 is still faced with the challenges of low electrical conductivity, inferior rate performance and cycle life. [9,10] The current reported works on Li 3 VO 4 are mainly focused on decreasing the particle size to improve its reaction activity by exploring different synthesis methods, [11][12][13][14] or enhancing its conductivity by carbon coating or compositing. [15][16][17][18][19] These efforts are indeed helpful to improve the capacity and rate performances, but they did not alter the intrinsic structure properties of Li 3 VO 4 , thus can hardly relieve the complex multistep insertion/extraction electrode process. The slow electrode kinetics associated with the multistep reaction mechanism remains a big issue needed to be solved.With an analogue structure to Li 3 PO 4 , Li 3 VO 4 also possesses low temperature phase (named as β form) and high temperature phase (named as γ form). [20,21] In view of an active electrode material, the γ phase which possesses a higher ionic conductivity may be more preferable for Li 3 VO 4 in LIB application. Unfortunately, the γ phase Li 3 VO 4 is only stable at high temperature and it would transform to β phase spontaneously when cooling down. Up to now, all the reported Li 3 VO 4 for The γ phase Li 3 VO 4 which possesses higher ionic conductivity is more preferable for lithium ion batteries, but it is only stable at high temperature and would convert to low temperature β phase spontaneously when cooling down. Here, the phase control of Li 3 VO 4 to stabilize its γ phase in room temperature is successfully mediated by introducing proper Si-doping, and for the first time the electrochemical performances of γ-Li 3 VO 4 is investigated. It is...

“…Li atoms occupy two crystallographic sites in the interstices of the structure (Li1: tetrahedral 24d, Li2: distorted octahedral 96h). Significant improvements were reported for Al-doped LLZO (2.40 × 10 −4 S cm −1 ), [59] Gadoped LLZO (1.46 × 10 −3 S cm −1 , Figure 2c), [60] Fe-doped LLZO (1.10 × 10 −3 S cm −1 ), [61] Ge-doped LLZO (7.63 × 10 −4 S cm −1 ), [62] Ta-doped LLZO (9.28 × 10 −4 S cm −1 ), [63] Nb-doped LLZO (8.0 × 10 −4 S cm −1 ), [64] and W-doped LLZO (6.60 × 10 −4 S cm −1 ). [56] The motion of Li + ions is of a fully collective nature or synchronous in the tetragonal LLZO, while an asynchronous mechanism of single-ion jumps inducing collective motion takes place in the cubic LLZO.…”

Section: Garnet-type Ssesmentioning

confidence: 87%

Interfacial Incompatibility and Internal Stresses in All‐Solid‐State Lithium Ion Batteries

Liu

et al. 2019

The continuous depletion of fossil fuels, the increase of oil prices, and the need to decrease CO 2 emissions have stimulated intensive research on developing alternative renewable and clean energy sources. [1] Among these alternative energy sources, rechargeable Li-ion batteries (LIBs) are one of the promising candidates. To date, the LIBs basically consisting of a positive electrode (cathode), an electrolyte, and a negative electrode (anode) have widespread applications, such as portable electronic devices, pure electric vehicles (PEVs), and hybrid electric vehicles (HEVs). [2] The state-of-the-art electrolytes are usually the lithium salts (LiPF 6 , LiBF 4 , and LiCF 3 SO 3 ) dissolved in organic solvents, i.e., ethylene carbonate, propylene carbonate, polyethylene oxide, and dimethyl carbonate, [3] which exhibit excellent wetting of the electrodes and produce a fast transfer of Li + ions upon charging and discharging. However, they suffer from flammability, poor electrochemical stability, limited temperature range of operation, and low power density. [4] There is an ever-increasing demand for batteries with a higher energy and power density, although current LIBs offer volumetric and gravimetric energy densities up to 770 Wh L −1 and 260 Wh kg −1 , respectively. [5] To improve the energy/power density of LIBs, one way is to adopt high-potential cathode materials such as LiNi 0.5 Mn 1.5 O 4 (LNMO). The high-voltage plateau of LNMO (≈4.7 V vs Li/Li + ) makes its energy density 20-30% higher than the energy density of commercial LiCoO 2 and LiFePO 4 . [6] However, successful commercialization of the LNMO is restricted in high-energy LIBs due to electrolyte decomposition and side reaction of the cathodes and liquid electrolytes when operating at high voltages. [7,8] The other way to improve the energy/power density is to replace the conventional graphite anode with Li metal. The Li metal, with a low anode potential (−3.04 V vs standard hydrogen electrode) and high specific capacity (3862 mAh g −1 for the Li anode versus 372 mAh g −1 for the graphite anode), [9][10][11] has been considered as the "Holy Grail" of battery technologies. When paired with sulfur and oxygen, the theoretical energy density of Li-S (≈2567 Wh kg −1 ) and Li-O 2 (≈3505 Wh kg −1 ) batteries is far higher than the theoretical energy density of conventional LIBs (≈387 Wh kg −1 ). [12][13][14][15] When Li metal approaches the liquid electrolytes, however, unstable Li/electrolyte interface Rechargeable Li-ion batteries (LIBs) are electrochemical storage device widely applied in electric vehicles, mobile electronic devices, etc. However, traditional LIBs containing liquid electrolytes suffer from flammability, poor electrochemical stability, and limited operational temperature range. Replacement of the liquid electrolytes with inorganic solid-state electrolytes (SSEs) would solve this problem. However, several critical issues, such as poor interfacial compatibility, low ionic conductivity at ambient temperatures, etc., need to be surmounted befor...