Solid-state Li-ion Batteries Research Articles

Influence of Al on the structure and ion transport in garnet-type Li7La3-xAlxZr2O12 solid electrolytes for Li-ion batteries

This work reports on the preparation of garnet-type Al-doped Li7La3-xAlxZr2O12 (x = 0, 0.1, and 0.2) electrolytes for solid-state Li-ion batteries. The undoped and Al-doped cubic phase LLZO has been synthesized by conventional solid-state mixing and annealing at 1000 °C for 2 h. The prepared materials have been characterized by X-ray diffraction, scanning electron microscopy, Fourier-transform infrared spectroscopy, and Raman spectroscopy. The electrical properties were evaluated by impedance spectroscopy at varies temperatures. The ionic conductivities of Li7La3Zr2O12, Li7La2.9Al0.1Zr2O12, and Li7La2.8Al0.2Zr2O12 were determined to be 1.8x10−6, 4.1x10−6, and 6.5x10−6 S cm−1 at 100 °C respectively and their activation energy has been derived as 0.70, 0.69 and 0.73 eV from the Arrhenius plot. The DC conductivities were calculated as 1.6x10−4, 3.3x10−4, and 5.7x10−4 S cm−1 for Li7La3Zr2O12, Li7La2.9Al0.1Zr2O12, and Li7La2.8Al0.2Zr2O12 respectively. Furthermore, the hopping rates, charge carrier concentration, ionic mobility, and diffusion coefficient were also calculated and the results show an increasing trend with increasing temperature.

First-principles simulations to understand the structural and electrolyte properties of idealized Li7.5B10S18X1.5 (X=Cl, Br, I)

Recently, researchers at the University of Waterloo (Canada) and Oak Ridge National Laboratory (Oak Ridge, TN) reported a new family of lithium thioborate halide electrolytes with the composition ${\mathrm{Li}}_{7.5}{\mathrm{B}}_{10}{\mathrm{S}}_{18}{X}_{1.5}$ $(X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I})$ having very impressive ionic room-temperature conductivity of magnitude $\ensuremath{\sigma}=1 \mathrm{mS}/\mathrm{cm}$. The researchers characterized the structures of the three materials in terms of a well-defined thioborate framework with a void structure containing fractionally occupied Li and X sites. The space group of the materials was identified to be monoclinic ($C2/c$, No. 15). We report the results of first-principles simulations of these materials focusing on understanding the idealized ground-state structures, the mechanisms of Li ion migration, and the overall stability of the materials. A systematic search of many possible stoichiometric crystalline configurations found ordered ground-state realizations of the materials for each of the three halides, $X=\mathrm{Cl}, \mathrm{Br}, \mathrm{I}$. Molecular dynamics simulations based on the initially ordered structures at various temperatures show significant Li ion hopping within the void channels of the structures at temperatures as low as T = 400 K. Simulations of possible decomposition products suggest that these electrolytes are also chemically stable. Overall, the simulations are consistent with the experimentally reported findings indicating that these materials are very promising solid electrolytes for possible use in solid-state Li ion batteries.

Argyrodite-type advanced lithium conductors and transport mechanisms beyond paddle-wheel effect

Development of next-generation solid-state Li-ion batteries requires not only electrolytes with high room-temperature (RT) ionic conductivities but also a fundamental understanding of the ionic transport in solids. In spite of considerable work, only a few lithium conductors are known with the highest RT ionic conductivities ~ 0.01 S/cm and the lowest activation energies ~0.2 eV. New design strategy and novel ionic conduction mechanism are needed to expand the pool of high-performance lithium conductors as well as achieve even higher RT ionic conductivities. Here, we theoretically show that lithium conductors with RT ionic conductivity over 0.1 S/cm and low activation energies ~ 0.1 eV can be achieved by incorporating cluster-dynamics into an argyrodite structure. The extraordinary superionic metrics are supported by conduction mechanism characterized as a relay between local and long-range ionic diffusions, as well as correlational dynamics beyond the paddle-wheel effect.

Modeling the effect of electrolyte microstructure on conductivity and solid-state Li-ion battery performance

Solid-state batteries offer the potential to improve safety, cyclability, and energy density of Li-ion batteries. However, their conductivity, stability, and processing limit their use. To this end, the effects of solid electrolyte microstructure on overall battery performance are determined. The conductivities of Al-doped Li7La3Zr2O12 (Al-LLZO), with a range of microstructures, are found using a resistor network model. Varying electrolyte properties are combined with a Li-metal negative electrode and LiCoO2 positive electrode in a 1-D continuum model to predict the effects on performance. Simulations suggest that the ratio of electrolyte conductivity to electrolyte thickness must remain above 10 S m−2 to maintain high energy and power output, particularly at C-rates greater than 10. To maintain conductivity near the grain interior conductivity, a grain size at least 10,000 times larger than grain boundary thickness is needed. Further improvements in grain size, grain boundary thickness, and void fraction beyond typical Al-LLZO microstructures, with the goal of higher conductivities, are predicted to have diminishing returns in overall battery performance, even at more sensitive high C-rates up to 100.

A Review on Green Polymer Binder-based Electrodes and Electrolytes for All Solid-State Li-ion batteries

It is not an exaggerated fact that the whole world relies on the energy storage systems such as Li-ion batteries (LIBs). Li-ion batteries have been widely used in electric vehicles and electronic devices such as laptops, mobile phones, etc. However, the commercial Li-ion batteries have many issues associated with safety and durability including the thermal runaway and the use of toxic solvents during the construction of batteries. In order to highlight the recent developments towards addressing these issues, we have summarized the major impact in replacing the toxic solvents, which are conventionally used to dissolve the binder in the commercial Li-ion batteries, with the aqueous-based binder called green binders. Further, an emphasis has been given on the importance of shifting from flammable liquid electrolytes to non-flammable solid-electrolytes, which essentially suppress the issues such as leakage problems, mechanical failure and fire explosives in LIBs. Even though considerable works have been performed on the development of green-based solid polymer electrolytes, it still needs more effort to overcome the obstacles towards improving the properties of the solid-polymer matrix, which is their low ionic conductivity at low temperatures. Further research in this direction has been highlighted in this review, which involves improving the interfacial contacts in the solid-polymer electrolytes, where the interfacial interaction and conductive mechanisms are yet to be clearly investigated to have the solid-electrolytes with improved electrochemical property.

Pressure-induced interfacial contacts and the deformation in all solid-state Li-ion batteries

In this paper, we use a combination of computational models and experiments to study the effects of stack pressure on interfacial contacts and deformation of solid state electrolytes in an all solid state battery (ASSB). The induced strain distributions in the LiBH 4 –LiNH 2 based all solid-state battery are measured using a combination of in-situ optical microscopy and digital image correlation (DIC) techniques, while the contact strains and stresses are computed using analytical and computational finite element models. The results show that moderate pressure improves the interfacial contacts and battery electrochemical performance characteristics with low induced strains in the electrolyte, while high pressure induces large axial and shear strains that can cause failure by yielding or cracking phenomena, in addition to the degradation of electrochemical performance characteristics. The highest room temperature conductivity of 9 × 10 −5 Scm −1 was obtained at a stack pressure of 0.26 MPa. The implications of the results are discussed for the design and fabrication of robust all solid state batteries with improved performance characteristics. • In-situ strain mapping/computational modeling of contacts and deformation. • Pressure application improves electrode-electrolyte interfacial surface contacts. • Intermediate stack pressures improve ionic conductivity without cracking. • High stack pressures induce large axial/shear strains and cracking of the electrolyte.

Ionic Liquid and Polymer Coated Garnet Solid Electrolytes for High‐Energy Solid‐State Lithium Metal Batteries

An ionic liquid-polymer coated garnet electrolyte was employed for a rechargeable solid-state Li-ion battery. The composite electrolyte can effectively suppress the formation of passivation layers on the garnet surface and reduce the interfacial resistance. The polymer solid-state battery electrolyte combined with a lithium metal anode and LiFePO4 cathode delivers a specific capacity of 120 mAh g−1. More details can be found in article number 2100907, Zhen Liu, Andriy Borodin, and Frank Endres.

Hybrid covalent organic-framework-based electrolytes for optimizing interface resistance in solid-state lithium-ion batteries

High ion conductivity and low electrode-electrolyte interface resistance are intensively pursued topics for the development of solid-state Li-ion batteries with high safety and energy density. Here, we propose a design using keto-enamine covalent organic frameworks (TPBD) and polyethylene oxide (PEO) to prepare a solid-state electrolyte (TPBD-LiPF 6 @PEO), achieving a high ion conductivity of 0.543 mS cm −1 at 25°C and optimizing the electrode-electrolyte interface resistance in Li-ion batteries. Solid-state nuclear magnetic resonance experiments and density functional theory calculations show that the strong interaction between the –C=O site in TPBD and Li + ions promotes the dissociation of LiPF 6 . The assembled LiFePO 4 |TPBD-LiPF 6 @PEO|Li batteries without using liquid electrolytes offer a specific capacity of nearly 140 mAh g −1 at 0.2 C with a columbic efficiency of 99.6% after 200 cycles at 25°C. This strategy for preparing solid-state electrolytes provides practical ideas and suggestions in the development of solid-state energy devices. • The –C=O groups in TPBD frameworks promote the dissociation of LiPF 6 • TPBD reduces the crystallinity of PEO and enhances mechanical strength of the electrolyte • Fast ion conduction is achieved due to the optimized interface resistance • Solid-state Li-ion batteries can operate at 25°C without adding any liquid electrolyte The low conductivity of solid electrolytes and the interface resistance of solid-state batteries have long been scientific problems that plague the development of solid-state Li-ion batteries. Cheng et al. report a fibrous covalent organic framework TPBD that can promote the dissociation of LiPF 6 , combining with flexible PEO to prepare an inorganic/polymer solid electrolyte. The results show that the electrode-electrolyte interface impedance is greatly reduced, realizing the operation of solid-state battery at room temperature without the addition of liquid electrolyte.

Confining nonflammable liquid in solid polymer electrolyte to enable nickel-rich cathode-based 4.2 V high-energy solid-state lithium-metal and lithium-ion batteries

Solid polymer electrolyte (SPE)-based solid-state batteries (SSBs) offer a potential safety, but the integration of practical cathode loading for high-energy density SSBs is a challenge. Herein, we demonstrate a proof of unique design concept of “NonFlammable Liquid-confined in-Solid Polymer Electrolyte” (NFL-SPE) enabling highly loaded (10 mg cm−2) LiNi0.8Co0.1Mn0.1O2 (NCM811) cathode-based 1.5 mAh cm−2-class solid-state 4.2 V Li-metal and Li-ion batteries. in-situ crosslinked semi-interpenetrating polymer network SPE maintains its solid form when limiting the confined NFL amount to 35 wt%. The NFL comprises propylene carbonate, fluorinated linear carbonates, and solid electrolyte interphase-forming additives of lithium bis(phthalate)borate and vinylene carbonate. The critical roles of NFL are to enhance ion conductivity to 2-fold from SPE only and 1000-fold from traditional poly(ethylene) oxide, to permit a facile interfacial wetting to highly loaded NCM811 and to reduce interfacial resistance. A higher discharge capacity of 169 mAh g−1 is achieved with Li/NFL-SPE/NCM811 at 45 °C with improved cycling performance and a suppressed lattice contraction of NCM811 along the c-axis, compared to that with SPE only. Importantly, an unprecedented 1.5 mAh cm−2-class solid-state Li-ion battery is realized by fabricating silicon-graphite/NFL-SPE/NCM811 utilizing silicon (5 wt%)-graphite anode active material and showing stable 50 cycles at 25 °C.

High capacity all-solid-state lithium battery enabled by in situ formation of an ionic conduction path by lithiation of MgH2.

All-solid-state Li batteries have attracted significant attention because of their high energy density and high level of safety. In a solid-state Li-ion battery, the electrodes contain a solid electrolyte that does not contribute directly to the capacity. Therefore, a battery that does not require a solid electrolyte in its electrode mixture should exhibit a higher energy density. In this study, a MgH2 electrode was used as the negative electrode material without a solid electrolyte in its mixture. The resultant battery demonstrated excellent performance because of the formation of an ionic conduction path based on LiH in the electrode mixture. LiH and Mg clearly formed upon lithiation and returned to MgH2 upon delithiation as revealed by TEM-EELS analysis. This mechanism of in situ electrolyte formation enables the development of a solid-state battery with a high energy density.

A high strength asymmetric polymer–inorganic composite solid electrolyte for solid-state Li-ion batteries

All solid-state lithium metal batteries (ASSLMBs) are regarded as one favorable future technology for energy storage. Composite solid-state electrolytes (CSEs) exploit the strengths of both solid polymer electrolytes (SPEs) and inorganic ceramic electrolytes (ICEs), which commonly exhibit enhanced ionic conductivity, as well as excellent cycling stability, and favorable interfacial resistance. However, rational structure design for better CSE/electrodes interface contact is necessary for the future practical applications. Herein, an asymmetrical composite solid electrolyte is constructed by introducing the electro-spun polyacrylonitrile (PAN) into the casting membrane. Oxidation-resistant PAN shows strong adsorption of Li-salt anions, providing long range Li+ transmission path and extended electrochemical window and protections for bottom oxidative polyethylene oxide (PEO) -based layer. Meanwhile, the bottom PEO/garnet Li6.4La3Zr1.4Ta0.6O12 (LLZTO) matrix obtains good ion conductivity and stability to Li metal anode, and successfully protects the antioxidative PAN for possible severe side reactions with anodes. Obtained bilayer CSE shows high ionic conductivity (6.0×10−4 S cm−1 at 60 °C), broad electrochemical window (5.2 V, vs. Li/Li+), and good mechanical properties. The battery displays 159.9 mA h g−1 and remained 153.5 mA h g−1 after 90 cycles at 0.2 C rate and good inhibition to lithium dendrites growth and side reactions. This work indicates that the asymmetric designed CSE film provides a possible directions towards future high energy density ASSLMBs.

Perfect combination: Solid-state electrolytes and silicon anodes?

<h2>Summary</h2> An ongoing challenge for Li-ion batteries with silicon anodes has been the limited battery life that results from volume changes and solid electrolyte interphase growth that occurs during cycling. In a recent issue of <i>Science,</i> Meng and coworkers develop a solid-state Li-ion battery with a carbon-free silicon anode.

Covalent−organic framework-based electrolytes fabricated for solid-state Li-ion batteries

Covalent−organic framework-based electrolytes fabricated for solid-state Li-ion batteries

A compliant and low-expansion 2-phase micro-architectured material, with potential application to solid-state Li-ion batteries

A two-phase 2D lattice material is identified that possesses both a high macroscopic compliance and a low macroscopic coefficient of thermal expansion. The macroscopic effective properties of the lattice are analysed and the features that give high macroscopic compliance and low macroscopic actuation strain are identified. A detailed case study is presented to explore the potential of the lattice for use as a composite cathode in a solid-state Li-ion battery, taking into account the swelling of the active cathode material upon lithiation. A design map is developed to reveal the competition between battery capacity and degradation due to fracture of the composite cathode. The intent is to identify promising battery topologies and compositions by overcoming the usual problems associated with cathode swell during charge and discharge.

First Principles Simulations to Understand the Structural and Electrolyte Properties of Idealized Li7.5B10S18X1.5 (X = Cl, Br, I) Li Superionic Conductors Recently Identified in the Experimental Literature

Recently, researchers at the University of Waterloo (Canada) and Oak Ridge National Laboratory (USA) reported a new family of lithium thioborate halide electrolytes which have the composition Li7.5B10S18X1.5 (X = Cl, Br, I) and which are very impressive ionic conductors with \U0001d782=10-3 S/cm measured at room temperature [1]. The researchers identified the crystal structure of the three materials with the monoclinic space group C2/c (No. 15) having highly disordered Li and X sites. In this presentation, we report the results of first-principles simulations of these materials, focusing on understanding the mechanisms of Li ion migration and the overall stability of the materials. By optimizing many possible stoichiometric crystalline configurations, we found ordered ground state realizations of the materials for the three halides X = Cl, Br, and I. Molecular dynamics simulations based on the initially ordered structures at various temperatures show significant Li ion hopping within the void channels of the structures at temperatures as low as T = 600 K. Simulations of possible decomposition products suggest that these electrolytes are also chemically stable. Overall, the preliminary simulations are consistent with the experimental findings of Ref. [1], indicating that these materials are very promising solid electrolytes for possible use in solid state Li ion batteries.------------------------------------------[1] K. Kaup, A. Assoud, J. Liu, and L. F. Nazar, Fast Li-ion conductivity in superadamantanoid lithium thioborate halides, Angewandte Chimie, 133, 7051-7056 (2020) doi.org/10.002/anie.202013339.------------------------------------------Acknowledgements -- This work was supported by NSF grant DMR-1940324. Computations were performed on the Wake Forest University DEAC cluster, a centrally managed resource with support provided in part by the university.

Computational Investigation of Known and Predicted Li Boracites Li4B7O12Cl and Li4B7S12Cl as Solid Electrolytes Having Possible Applications for Developing All Solid-state Li Ion Batteries

The lithium chloroboracite Li4B7O12Cl with fractionally occupied Li sites located in diffusion channels formed by a rigid B7O12 framework possesses essential features of an ideal Li-ion conductor. Early experimental work in 1977 [1] identified three structural modifications related to a face-centered cubic pattern. The room-temperature α form was suggested to have a rhombohedral distortion, but was not fully characterized. Our first-principles calculations find the optimized structure of the α phase to have a face centered rhombohedral structure with space group R3c (No. 161) and structurally very similar to the higher temperature cubic structures of the ꞵ and ɣ forms apart from the fractional occupancy patterns of the Li configurations. Using the convex hull approach, we estimate α-Li4B7O12Cl to be thermodynamically stable within the composition space of Li2O, B2O3, and LiCl. Our analysis of Li ion mechanisms indicates that a concerted process, involving two host Li sites and a neighboring unoccupied site based on the face-centered cubic structure, provides the most efficient ion transport in Li4B7O12Cl. The room-temperature ionic conductivity calculated from molecular dynamic (MD) simulations is on the order of 10-4 S/cm, showing good agreement with the recent experimental measurement for pure polycrystalline samples of Li4B7O12Cl [2]. The temperature-dependent occupancies of Li sites, as the main structural distinction of the three reported modifications of Li4B7O12Cl, are also observed in the MD simulations performed at various temperatures. We also predict that the Li ion conductivity can be enhanced by substituting S for O to form Li4B7S12Cl, which has the same R3c ground state structure with an expanded lattice. Our preliminary studies show that Li4B7S12Cl has better Li conducting performance than Li4B7O12Cl and therefore also shows promise as a solid-state electrolyte for all-solid-state Li-ion batteries.------------------------------------------[1] W. Jeitschko, T. A. Bither, and P. E. Bierstedt. Crystal structure and ionic conductivity of Li boracites. Acta Crystallographica Section B, 33(9): 2767-2775, 1977.[2] D. Tan, F. Wang, T. Pietsch, M. A. Grasser, T. Doert, and M. Ruck. Low-Temperature Ionothermal Synthesis of Li-Ion Conductive Li4B7O12Cl Solid-State Electrolyte. ACS Applied Energy Materials, 2(7): 5140-5145, 2019.------------------------------------------Acknowledgements -- This work was supported by NSF grant DMR-1940324. Computations were performed on the Wake Forest University DEAC cluster, a centrally managed resource with support provided in part by the university.

First principles calculation of Li2+2xZn1-xSiO4 (x = 0.125–0.5) as solid electrolyte for lithium-ion battery

Li2ZnSiO4 has the structural characteristics of superionic conductor for Li, but the actual measured Li conductivity is not high. Based on first-principles calculations, the Li diffusion properties of varied configurations are studied, in which Li replaces Zn with different concentrations. Particularly, topological analysis is used to obtain the possible Li interstitial sites of Li2ZnSiO4. These interstitial sites can accommodate more lithium ions and increase the concentration of lithium ions. The Li ion conductivity of the Li-doped Li2+2xZn1-xSiO4 with increased lattice Li and interstitial Li is improved dramatically. When x = 0.375, the Li ion conductivity reaches 2.006 mS/cm and the Ehull is 23 meV/atom. The mean square deviation (MSD) and probability density indicate that Li2+2xZn1-xSiO4 (x = 0.125–0.5) is a three-dimensional Li conductor. In addition, the calculation of energy band structures shows the bandgap width of 5.7 eV and 5.8 eV for Li2ZnSiO4 and Li2.5Zn0.75Si4, respectively, indicating that these materials are poor conductors of electron. These characteristics (fast Li diffusion, good phase stability, and poor electronic conductivity) make Li-doped Li2ZnSiO4 one promising solid electrolyte for solid-state Li-ion batteries.

Dynamic behavior of Li depth profiles in solid state Li ion battery under charging and discharging by means of ERD and RBS techniques

Change in Li depth profiles of Ti/NbO/LiPON/LMO/Ti and Ti/LMO/LiPON/NbO/Ti (NbO=Nb2O5, LiPON=Li3.3PO3.8N0.2, LMO = LiMn2O4) batteries prepared on Si substrate on one cycle of charging and discharging has been in-situ measured from both Ti/NbO and Ti/LMO sides by ERD (elastic recoil detection analysis) and RBS (Rutherford backscattering spectroscopy) techniques with 9 MeV O+4 ion beam, in order to understand Li transport between NbO to LMO. It is found that on over-charging of the Ti/NbO/LiPON/LMO/Ti battery Li charged in NbO diffuses into top Ti film, but on the Ti/LMO/ LiPON/NbO battery Li does not diffuse into bottom Ti film, but returns back to LMO, reacts with top Ti film and segregates at the Ti surface. The difference in Li transport in both batteries is discussed in terms of the difference in Fermi levels at the interfaces of LMO/Ti and NbO/Ti on the Si substrate.

Temperature dependences of the double layer capacitance of some solid/liquid and solid/solid electrified interfaces. An experimental study

This study investigates the influence of the temperature on the electrical double layer capacitance (CDL) of various materials, which are essential for fuel cells and solid-state Li-ion batteries. Electrochemical impedance spectroscopy is utilized to measure the CDL of polycrystalline Pt/aqueous electrolytes interfaces, cathode catalyst layers of polymer electrolyte membrane fuel cells (PEMFC), and Au or Li electrodes in contact with a solid-state electrolyte (SSE), a prime example for solid-state ionics. Our results show that within the investigated temperature ranges, the CDL decreases with an increase in the temperature for Pt electrodes in an aqueous acidic electrolyte. However, for SSE and PEMFC cathode catalyst layers, the CDL increases with temperature. The CDL behavior with the temperature of herein presented systems is important for understanding and modeling of the interface processes for renewable energy conversion systems such as fuel cells, water electrolyzers, and batteries.

Editors’ Choice—Quantification of the Impact of Chemo-Mechanical Degradation on the Performance and Cycling Stability of NCM-Based Cathodes in Solid-State Li-Ion Batteries

The use of solid electrolytes in lithium batteries promises to increase their power and energy density, but several challenges still need to be overcome. One critical issue is capacity-fading, commonly ascribed to various degradation reactions in the composite cathode. Chemical, electrochemical as well as chemo-mechanical effects are discussed to be the cause, yet no clear understanding of the mechanism of capacity fading is established. In this work, a model is proposed to interpret the low-frequency impedance of the cathode in terms of lithium diffusion within an ensemble of LiNi1−x−y Co x Mn y O2 (NCM) cathode active material particles with different particle sizes. Additionally, an electrochemical technique is developed to determine the electrochemically active mass in the cathode, based on the estimation of the state-of-charge via open circuit potential-relaxation. Tracking the length of lithium diffusion pathways and active mass over 40 charge-discharge cycles demonstrates that the chemo-mechanical evolution in the composite cathode is the major cause for cell capacity fading. Finally, it is shown that single-crystalline NCM is far more robust against chemo-mechanical degradation compared to polycrystalline NCM and can maintain a high cycling stability.