INTL. SYMP. ON SUSTAINABLE SECONDARY BATTERY MANUFACTURING AND RECYCLING

Nowadays, improvement of functional materials is a sought after issue, with the aim of combining high-energy consumption and sustainable society. It is known that functionality of materials depends on crystallographic characteristics. Regarding to battery materials, ionic diffusion in bulk becomes easier by increasing specific surface area and improving crystallinity, whose ionic conductivity depends on crystal face. So, crystallographic controls of battery materials should be one of the crucial concerns to realize innovation in next-generation energy applications. Flux method is one of the crystal growth techniques in liquid phase. This technique enables us to achieve various crystallographic characteristics, in terms of crystallinity and morphology, such as size, shape, and also habits. We have studied flux growth of battery materials. So far, lots of unique and functionalized crystals have been grown. For example, polyhedron, cylinder, flower-type LiCoO₂ crystals are representative morphology. Since they have never been grown by other technique, we expected that flux method is a suitable method to improve battery by means of crystallography.
Recently, we are focusing on designing lithium metal phosphates and its derivative, formulated as LiMPO₄ and Li₂MPO₄F (M=Fe, Mn, Ni). Although they show poor conductivity, their electrochemical stability and high energy density are attractive advantages as active materials. We aimed to control crystal facets of LiMPO₄ and Li₂MPO₄F, which exhibits higher conductivity, by using the flux method. As a result, we grew LiMPO₄ and Li₂MPO₄F crystals with idiomorphic, high-crystalline natures. Some of them showed anisotropic morphology along to one direction, which may be typical due to flux method. In the SIPS2018 conference, we will report the flux growths, crystallographic characteristics, battery properties, and growth manners of a series of LiMPO₄ and Li₂MPO₄F.

The development of advanced electrode materials for secondary Li batteries is essential to meet the increased energy demands posed by portable electronic devices and the rapid growth of electrical vehicles and energy storage systems.[1] In order to replace the intercalation reaction-based materials that have capacity limitations, many researchers have focused on new electrode materials reacting through conversion or alloying reactions, which can take up multiple Li-ions per unit formula.[2]
In this study, using ammonium fluoride (NH₄F), we developed a new synthetic route to fabricate metal fluoride (MF_x) nanocomposites for conversion reaction-based high capacity cathodes and nanostructured silicon (Si) for alloying reaction-based high capacity anodes. At first, we discovered that various anhydrous MF_x can be obtained through simple heat treatment of metal precursors with NH₄F under an inert atmosphere. Based on this process, MF_x/mesoporous carbon nanocomposites were successfully synthesized.[3] From the reaction mechanism of this synthetic method, we expected that residual impurities in the raw Si materials, such as SiO₂, could be easily removed using NH₄F. Interestingly, the reaction of raw Si materials with NH₄F not only removed residual SiO₂, but also generated nanopores on Si. When used as electrodes in Li batteries, the MF_x nanocomposites and nanostructured Si showed noticeable improvements in electrochemical performance. It is expected that this study will motivate further research into the synthesis of advanced electrode materials for secondary batteries using NH₄F.

A spent lead acid battery consists of four parts, namely the electrolyte, lead and lead alloy components (for example the battery grid and plate), lead paste (the "redox", otherwise known as active, component of the battery) and organics or plastics with weight percentages of 11-30%, 24-30%, 30-40% and 22-30% respectively [1]. The spent battery paste is arguably the most complex component to recycle. It is complex as it is made up of a multitude of materials including PbSO₄ (~60%), which dominates in spent batteries, PbO₂ (~28%), PbO (~9%), free metallic lead (~3%) and a small but substantial concentration of impurities such as iron, antimony, tin and barium [1,2].
The recovery of Pb from spent lead paste is achieved conventionally through pyrometallurgical process requiring relatively elevated temperature (>900°C) for the decomposition of PbSO₄ [3]. The elevated temperature releases SO₂ gas and lead particulates into the environment, raising serious environmental concerns [4]. Hydro-electro metallurgical processing, which has been developed as an alternative, also consumes high energy and uses toxic acids like HBF₄ or H₂SiF₆ [5]. There is a need for eco-friendly method. In this study, a hydrometallurgical process for complete dissolution of spent lead paste at room temperature has been developed. Post recycling of the dissolved spent lead paste, the residual Pb ions are determined and removed using an eco-friendly biological method.
The complete dissolution of spent lead acid battery paste is achieved in the presence of sodium hydroxide (NaOH), nitric acid (HNO₃) and hydrogen peroxide (H₂O₂). The concentration of Pb ions in the processed water is determined by deploying bacterial cells, Pseudomonas aeruginosa, using differential pulse anodic stripping voltammetry (DPASV). The parameters namely, pH, time, biomass loading and Pb ions concentration were optimized for maximum Pb ions removal by the selected bacterial cells.

Single-Walled Carbon Nanohorns (SWCNHs), are a kind of carbon material with graphene type surface structure characterized by horn shaped graphitic tubules (2-5 nm diameter and 40-50 nm tube length) to form dahlia-like structures. They can be mass produced (tons/year) using a novel proprietary process technology, making them attractive for various industrial applications. SWCNHs can be considered as the next generation of graphene-based materials. Thanks to their particular 3D structure, they do not stack as in the case of 2D graphene-based materials, and keep their original chemical-physical proprieties at the powder state.
Inspired by their unique structure, Nitrogen doped Single-Walled Carbon Nanohorns (N-SWCNHs) were used as a conductive substrate with various post lithium ion batteries active materials such as Sulfur (cathode), Germanium, and Tin (anodes).
The choice of nitrogen doping is motivated by the quest for improved interaction between SWCNHs and the surrounding active material.
N-SWCNHs were used as porous conductive host for encapsulating sulfur, using a simple melt diffusion method. Electrochemical results obtained from N-SWCNHs-Sulfur composite as cathode for lithium sulfur batteries showed high gravimetric capacities of 1650 mAh/g (almost the theoretical capacity), with high sulfur content of 80% by weight. Furthermore, N-SWCNHs were exploited by growing 5-10 nm germanium nanocrystal around the cones of N-SWCNHs. The Ge@N-SWCNHs composite, when used as anode material, provided extremely stable and high gravimetric capacities of 1400 mAh/g at 0.1C after 100 cycles. Similarly, results were obtained for Sn@N-SWCNHs composites, where a strong reducing agent (Lithium Naphthalenide) was used to decorate Sn nanocrystal on the surface of N-SWCNHs. Capacities as high as 735 mAh/g were achieved at 0.1C even after 140 cycles. The detailed results will be presented and discussed at the symposium.

Lithium ion secondary batteries (LIBs) have been widely used as energy-storage systems for a variety of power devices. It is necessary to further develop LIBs toward high-functional devices, such as electric vehicles and mobile electronics. Nowadays, all solid-state LIBs have been of much interest because of high energy densities and high level of safety. All solid-state LIBs provide many advantages in terms of size, flexibility, cost, and performance. However, there are serious problems to be solved toward practical uses. For example, diffusion of lithium ions at the interface between different solid materials is still poor for operating charge/discharge in batteries.
Our group has studied high-quality crystals for applications as energy and environmental materials by using a flux method. Flux method is a nature-mimetic liquid-phase crystal growth technique. It is possible to construct molten reaction field at any temperature with facile setup and give designed crystals shape, including crystal faces, which has never been achieved using other methods like solid state reaction. Recently, we have applied the flux technique to battery materials to create "all-crystal (solid)-state LIBs". We have expected that flux crystal growth gave (I) crystal-shape control of active materials, (II) construction of good interfaces in electrodes among cathodes, solid electrolytes, and anodes. As a result, smooth ionic transportation through bulks and their interfaces would be realized in all-crystal (solid)-state LIBs. Our concept using flux method would provide new aspect to make innovation in all solid state LIBs as next-generation energy storage. The details of interfacial and crystal designs of battery materials will be introduced in the SIPS2018 conference.

Si and Sn are the most promising anodes for Li-ion and Na-ion batteries, respectively. Despite their high capacity upon the formation of Li and Na rich alloys, the main drawback in commercializing these promising electrodes lies in the severe volume expansion and subsequent fracture they experience upon electrochemical cycling. The present talk, hence, focuses on capturing and modeling this severe fracture, by electrochemically cycling Si and Sn films with respect to Li and Na. Scanning electron microscopy can illustrate the extent of fracture and reveal that additional plasticity mechanisms occur in the case of Na-Sn. The experimental data are complemented by a phase field model, which can accurately predict the fracture in patterned Si anodes during lithiation. This is the first rigorous correlation between experiments and modelling in fracture of anodes and paves the way for developing design criteria that predict the onset of fracture initiation based on the anode material and geometric properties.

Modern microelectronic devices such as backup power for computer memories, MicroElectroMechanical Systems (MEMS), medical implants, smart cards, Radio-Frequency Identification (RFID) tags, and remote sensors have necessitated the development of high performance power sources at the microscale. In this context, the development of three-dimensional (3D) microbatteries forms a viable alternative to provide high volumetric energy densities to meet the demands of these devices.[1] The development of nano-architectured electrodes is one of the most promising approaches to realize the 3D paradigm of microbatteries.[2] Among all the potential anode materials, TiO₂ nanotubes (TiO₂-NTs) possess remarkable characteristics for the design of 3D Li-ion microbatteries. Self-organized nanotubular materials allow a good diffusion of Li ions in the porous structures, and the 1D morphology allows an efficient charge transfer along the axis of the tube that results in a good apparent electronic conductivity of the TiO₂-NTs layer, when compared to a film composed of nanoparticles [3,4]. Anatase TiO₂ can accommodate only 0.5 Li⁺ per formula unit, corresponding to a theoretical capacity of 168 mAh g^-1. Hence, several approaches have been investigated to improve the overall performance of TiO₂-NTs for the design of high-performance Li-ion microbatteries. Doping with aliovalent ions like Niobium (Nb⁵⁺) is also a facile strategy to modify the electronic properties of titanium oxide and thereby enhance the electrochemical performance.[5,6]
We report the fabrication of self-supported Nb doped TiO₂-NTs by anodization of Nb/Ti alloys devoid of any carbon additives or binders. An increase in the capacity of the TiO₂-NTs was observed as the Nb doping concentration increased. Such a composition of 10 wt.% Nb doped TiO₂-NTs (Nb10-TiO₂-NTs) showed a first cycle capacity of 200 mAh.g^-1 (0.144 mAh.cm^-2) compared to pristine TiO₂-NTs, which gave a capacity of 115 mAh.g^-1 (0.078 mAh.cm^-2) at C/10. Galvanostatic cycling tests at various C-rates revealed the influence of Nb doping in the TiO₂-NTs. Compared to pristine TiO₂-NTs, the discharge capacities of doped nanotubes are improved and almost doubled when the Nb concentration reaches 10 wt.%. Besides a good cycling behaviour at multiple C-rates, an overall capacity retention of 87 % is achieved after 100 cycles. According to Electrochemical Impedance Spectroscopy measurements, the enhanced electrochemical performance of the Nb-doped TiO₂-NTs is attributed to their higher electronic conductivity.

The recycling of lead-acid batteries (LABs) is currently an energy intensive, inefficient and polluting procedure. An alternative hydrometallurgical recycling route using citric acid(1)(2) has been proven to effectively and efficiently facilitate the extraction of lead from discarded LAB paste material to form an intermediate that can be further processed to be potentially reused again in new LABs.
This citric acid route has been extensively trialled in the laboratory at the University of Cambridge and has recently been through several concurrent iterative experimental trials at a pre-pilot scale at Aurelius Environmental Ltd in Tipton, UK.
The procedure of scaling up any process from the laboratory to pilot and, if successful, to full commercial scale is a journey that is well trodden. The current review paper will seek to describe some of the challenges and successes that has thus far been encountered in scaling up this promising recycling route.
As the author, associates and collaborators attempt to translate what has been shown in the laboratory to a pre-pilot scale, the ultimate aim is to transition to a full pilot scale and beyond in the near future. The progress and future aims of this nascent technology will be outlined and discussed in order to inform and educate a wider audience of this exciting and sustainable recycling method.

As a new generation of supercapacitor, the Li-ion capacitor (LIC) is an advanced energy storage device which consists of an electric double-layer capacitor (EDLC) cathode and a pre-lithiated anode [1,2], between which the ions shuttle during charge and discharge processes. Because of using pre-lithiated and low surface anode materials, the LIC can be charged to a maximum voltage as high as 4.0 V, which is much higher than of EDLCs and comparable to Li-ion batteries (LIBs); therefore, it allows the LIC and LIB to be assembled in one package as a LIB/LIC hybrid energy storage cell.
We have demonstrated a new hybrid energy storage cell that combines the advantages of both the LIB and the LIC [3], thereby avoiding their inherent defects, while bridging the gap between the high energy densities offered by batteries and the high power densities seen in EDLCs. The energy density and power density of the hybrid cell can be designed to meet the requirements by a reasonable distribution of the ratio between LIB and LIC electrode materials in the internal hybrid cell. For example, we show a hybrid LIC consisting of a Li nickel cobalt manganese oxide (NMC)/activated carbon (AC) composite cathode in combination with an ultra-thin Li film (u-Li) pre-loaded hard carbon anode. Additionally, we show that by utilizing three design approaches: dry composite electrode fabrication method, cathode to anode capacity ratio design, and pre-lithiation method using u-Li, we can demonstrate an energy storage device with excellent cycle life, and that can be tailored by composite ratios within the cathode to fit different applications. Shown here is an in-depth look at various composite material ratios, pre-lithiation calculations and hybrid Li-ion battery-capacitor energy storage device creation based on targeting essential energy-power performance characteristics.

The lead-acid battery (LAB) market is forecast to reach $84 billion USD by 2025.¹ Despite intense competition from alternative and emerging energy storage solutions, LABs continue to deliver the most proven, low-cost, safe and affordable option for electrical energy storage. Indeed, LABs are used widely in automobiles (for starting, lighting and ignition), traction and heavy industry (for example electric forklifts and trucks), telecommunications, emergency lighting, renewable energy systems, medical equipment, railway backup systems, oil and gas exploration, and more.

The recycling of LABs via current methods is energy intensive and wasteful. In some parts of the world it produces "smelter smoke", a toxic mixture of sulphur dioxide, nitrogen dioxide and very often lead metal particles. For this reason, although LABs are the world's most successfully recycled commodity product,² and a perfect example of a successful multi-million tonne circular economy, the incumbent recycling processes are in dire need of improvement and technological innovation.

At Aurelius, our aim is to revolutionise the art of recycling through science, ethical practice, sustainability and technology. Our vision is a web of industries, where one stream's waste is another stream's feed-stock: bridging linear and wasteful processes to create circular, energy efficient, non-polluting, zero waste industries. Our stepping stone towards this vision is a technology for the recycling of LAB paste.

Invented in 2006 by Professor Vasant Kumar at the University of Cambridge,^3-5 UK, the technology was licensed exclusively in 2016 to Aurelius for further development, scaling up and commercialisation. Our piloting efforts are funded by two Innovate UK awards and a Horizon 2020 (Phase 2) SME grant. To date, we have raised more than 2 million USD in grant funding, while our annual turnover from the collection, dismantling and processing of more than 10,000 tonnes of LAB scrap per year is also used to fund our technology and innovation.

The patented hydrometallurgical process, branded as Fenix^Pb, brings about a critical improvement to the lead recycling industry.⁶ It enables conversion of spent battery paste to leady oxide (Pb/PbO) without producing or handling an intermediate ingot, and without utilising electrowinning. In fact, our process reduces the carbon footprint by 80-89%; eliminates noxious gases (including sulphur dioxide) at no added cost; reduces slag by more than 90%; and produces energy (this is because a key stage in the process is highly exothermic, releasing rather than consuming energy).

Our leady oxide is also a step-change in lead-acid battery technology. Laboratory tests carried out at the University of Cambridge have shown that batteries produced from our leady oxide have a 30% improved energy density. This innovation is largely due to the particle size; indeed, our advanced leady oxide is a nano-crystalline solid. Moreover, our process delivers a scalable means of controlling accurately the free metallic lead content (%Pb) and ratio between the alpha and beta phases of the oxide - enabling battery manufacturers to fine-tune their batteries' active materials dependant on its properties and applications.

Lithium Sulfur (Li-S) batteries are one of the most promising next generation battery technologies due to their high theoretical energy density, low materials cost, environmental friendliness, and relative safety [1]. Nevertheless, sulfur is an electrically insulating material, which leads to poor electrochemical accessibility and low utilization in the electrode. The polysulfide anions that are generated during cycling are highly soluble in the organic electrolyte solvent. The diffusion of polysulfides to the lithium anode results in low active material utilization, low Coulombic efficiency, and short cycle life of the sulfur electrode. In terms of making the lithium/sulfur batteries suitable for operation, carbon and conducting polymers are the promising conducting material to improving performance.
Ternary composites with porous sulfur/dual-carbon architectures were synthesized by a single-step spray-pyrolysis/sublimation technique, which is an industry-oriented method that features continuous fabrication of products with highly developed porous structures [2]. A double suspension of commercial sulfur and carbon scaffolding particles was dispersed in ethanol/water solution and sprayed at 180°C using a spray pyrolysis system. In the resultant composites, the sulfur particles were subjected to an ultrashort sublimation process, leading to the development of a highly porous surface, and were meanwhile coated with amorphous carbon, obtained through the pyrolysis of the ethanol, which acts as an adhesive interface to bind together the porous sulfur with the scaffolding carbon particles, to form a ternary composite architecture. This material has an effective conducting-carbon/ sulfur-based matrix and interconnected open pores to reduce the diffusion paths of lithium ions, buffer the sulfur volumetric expansion, and absorb electrolyte and polysulfides. Because of the unique structure, the composites show stable cycling performance for 200 cycles and good rate capability of 520 mAh g-1 at 2°C. This advanced spray-pyrolysis/sublimation method is easy to scale up and shows great potential for the commercialization of Li-S batteries.
Sulfur-conducting polymer composites were also investigated to improve the performance of Li-S batteries. A PPy@S@PPy composite with a novel three-layer-3D-structure was synthesised by the oxidative chemical polymerization method and chemical precipitation method. The discharge specific capacity of the PPy@S@PPy composite cathode is 554 mAh g-1 after 50 cycles, representing approximately 68.8% retention of the initial discharge specific capacity of about 801 mAh g-1 [3].
A free-standing sulfur-PPy cathode and a PPy nanofiber coated separator were designed for flexible Li-S batteries. The as-prepared PPy film not only has a rough surface, which can enhance adhesion of the active materials and trap dissolved polysulfides, but also possesses elastic properties, which can accommodate the volume expansion and maintain the integrity of electrode during cycling. On the other hand, the PPy-separator not only acts as a reservoir for soluble lithium polysulfides, but also acts as an upper current collector to accelerate the kinetics of the electrochemical reactions. Moreover, PPy is electrochemically active and could contribute to the capacity of Li-S batteries. Benefiting from the advantages above, the flexible Li-S battery can deliver an initial discharge capacity of 1064 mA h g-1, and retain a capacity of 848 mA h g-1 after 20 cycles at 0.1 C. After repeated bending of 10 times, the capacity remains almost the same. In addition, the soft-packaged Li-S battery could power a device containing 24 white LEDs, both before and after bending, indicating its great potential application in flexible electronics. We believe that this flexible electrode structure may provide guidance for fabricating high energy, flexible electrochemical energy-storage devices [4].

Lead acid batteries have been well established for over 150 years and remain the largest segment of batteries in use. The market continues to grow in the automotive sector in ICVs, HEVs and EVs, e-bikes, small vehicles, energy storage, and back-up UPS. Furthermore it is well supported by a strong recycling infrastructure which is the envy of all other battery technologies. New recycling methods offer opportunities for controlling the morphology and structure of electrode components in order to derive new energy and power benefits from nanotechnology. New materials offer options for long-life electrode grids that are light and corrosion resistant. A doubling of capacity and rate at a lower cost will offer a paradigm shift in creating new markets for lead-acid batteries.

There is a need to develop cost-efficient and high-performance large-scale batteries for intermittent energy sources. In this regard, sodium-ion batteries (SIBs) have emerged as a potential candidate for the use of electrical energy storage systems (ESS), which share similar electrochemical principles to the comparatively high-cost lithium-ion batteries (LIBs). However, high-performance electrode materials are required for the realization of SIBs.
In this presentation, the development of anode materials for SIBs will be discussed. Our group has contributed to a variety of materials such as carbonaceous, intercalation-based metal oxides, conversion-based metal oxides, and alloying materials as anodes for SIBs. The results show that novel carbon-based anodes possess the capability of high energy and power density. The intercalation-based anodes such as TiO2 have also shown good stability over long cycling, thus demonstrating the suitability as anodes for SIBs. Conversion-based metal oxides also show promising electrochemical properties when used as a full sodium-ion cell. Finally, the nano-sized alloying-based SnF2 material was tested as anodes, and the electrochemical results, as well as the reaction mechanism of the material using synchrotron-based X-ray absorption spectroscopy, are measured. All of the above will be discussed in detail during the talk.

Pyrometallurgy lead-acid battery recycling causes pollution and is energy-intensive. This research aims to implement an alternative hydrometallurgical process of recycling lead-acid battery paste, NovoPb, by developing processes to make it economically viable in the current market and to ensure the quality of the newly recycled batteries in a 1 ton capacity pilot plant at Minas Gerais - Brazil.
NovoPb is based on a paste-to-paste route using a biomass source, citric acid. The new intermediary lead compound is calcined at a much lower temperature (340°C) than usual smelted lead (1200°C), saving energy and reducing hazardous gas emissions such as Pb and SOx, to directly generates nanostructured PbO for battery paste.
The process to be deployed in Brazil has as a first challenge the battery scrap characterisation, to measure the use of reagents per ton of scrap, which is not standard protocol in the current pyrometallurgical process. The study of the characterisation forms will be carried out in the laboratory to define the route to be followed in the pilot plant, which will be built by the British partners.
The determination of the optimal reaction conditions will be designed by factorial modelling. The influence of the impurities will be evaluated from a pure standard mixture of the main species that compose the battery paste. The optimization of the pilot process will be carried out by application of artificial neural networks after controlled operation.
This research is part of the Embrapii project of the Vitoria Innovation Center of the Federal Institute of Espirito Santo, in partnership with the University of Cambridge, Innovate UK, Brazilian companies Tudor MG de Baterias, Antares Reciclagem LTDA and the British company, Aurelius Technology.

The demand for energy storage systems (ESS) has increased tremendously in the last decade due to their use in a variety of applications ranging from mid- to large-scale. The most important factors in the development of ESS include high-performance and cost-effective systems. At present, lithium-ion batteries (LIBs) are being used as storage devices but their application is limited to small- to medium-scale. The main reasons to not use LIBs at large-scale are high production cost and limited lithium resources. While searching for alternatives, sodium-ion batteries (SIBs) have emerged as a potential candidate for the use of ESS, which is considered cost-effective and also share similar electrochemical principle to LIBs. However, high-performance cathode and anode materials are urgently required for the commercialization of SIBs.
In the search of high-performance electrode materials, we have prepared several cathode and anode materials for SIBs. I will briefly discuss the preparation and electrochemical properties of the high-performance cathode materials, which include FeF₃.0.5H₂O and olivine-type NaFePO₄, and also discuss the investigated reaction mechanism. The nanocomposite of FeF₃.0.5H₂O and reduced graphene oxide has shown high sodium storage performance where it delivers a capacity of 266 mAh g^-1 while NaFePO₄ has shown excellent cyclability with a capacity retention of 94% after 100 cycles. Further, alloying-based SnF₂ anode material was prepared and the electrochemical properties, as well as reaction mechanism, were systematically investigated. The nanocomposite of SnF₂ and acetylene black has shown promising electrochemical performance where it delivers a high capacity of 563 mAh g^-1. In-situ XRD and synchrotron-based X-ray absorption spectroscopy (XAS) were used to investigate the reaction mechanism of the above-mentioned materials. The details of the investigated reaction mechanism will be discussed in my presentation.

Sulfide-based solid electrolytes have attracted much attention due to their high conductivities, which are far beyond those of oxide-based solid electrolytes. [1,2] However, They (Li₂S-P₂S₅ system, i.e., LPS) have been normally synthesized by solid state synthesis such as mechanical ball milling. These methods require rigorous control of reaction environment as well as high temperature heat treatment and repeated pelletizing steps. In contrast, solution-based synthesis methods can induce chemical reaction among precursor particles (Li₂S and P₂S₅) at low temperatures resulting in the formation of conductive phases of Li₃PS₄ and Li₃P₇S₁₁ with only moderate thermal treatment.[3,4] The method deserves great attention since it simplifies synthesis process, yields products of great purity, and may facilitate the fabrication of composite electrodes with improved interfaces.
In this work, we have developed an efficient method to form a thin solid electrolyte layer directly on Li metal using the liquid coating techniques. The formation of LPS (Li₂S-P₂S₅) based electrolyte is achieved by rational design of the solvent and the Li, P, and S precursor ratios. The solution electrolyte can be directly coated and formed on Li metal through the in-situ formation of the solid electrolyte layer, which does not require the complex synthesis process and high temperature sintering step. Layers of thickness of < 50 um can be fabricated and electrochemical cycling of lithium is achieved. This liquid-phase coating is a simple and straightforward technique for making a thin solid electrolyte and can be applicable to anode surface with complex contours. The new liquid coating technique holds the promise to overcome the limitations of current state solid electrolytes.