Patent Application
20210066748
The present invention relates to a solid electrolyte for a sodium battery with microstructure approaching a continuous glass and excellent chemical stability with sodium metal or sodium-based alloys and a method of producing the same electrolyte.
In contrast to batteries using liquid electrolytes, solid-state batteries utilize non-flammable, mechanically stable solid-state electrolytes (SEs) that could offer all-solid state batteries with higher energy density, higher safety, and longer life span. Solid-state sodium batteries are promising for large-scale energy storage application due to lower cost than the lithium counterparts.
Solid-state sodium metal batteries (SSMBs) are very promising candidates for grid-scale energy storage applications. To date, however, there are no commercialized SSMBs mainly due to the lack of a high conductivity solid-state electrolyte that is stable with Na metal. So far, the only successful example of a commercialized Na metal battery for grid-scale energy storage involve NAS batteries (Wen et al., “Main Challenges for High Performance NAS Battery: Materials and Interfaces.” Adv Funct Mater 23, 1005-1018 (2013)). Development of Na+-ion SEs mainly include two categories, oxide (e.g. β″-Al2O3 and NASICON-type ceramics) and sulfide (e.g. heat-treated Na3PS4, Na3SbS4) (
Ideal SEs require the combination of several key parameters: high ionic conductivity, chemical compatibility with anode and cathode, excellent mechanical and thermal stability, wide electrochemical window, simple synthesis and film forming process, easy device integration and low cost. Among various SEs, sulfide-based SEs attract significant attention not only due to high ionic conductivity, but also with superb film formability. Sulfide-based SE powders can be well densified even pressing at room temperature, and no sintering process is necessary in contrast to oxide-based SEs. Many high ionic conductivity sulfide-based SEs have been developed (U.S. Pat. No. 9,640,835B2; Kim et al. Small Methods 2017, 1700219) including Na3PS4, cation-doped Na3PS4 (Na3+xP1−xMxS4, M=Si, Ge, Sn; Na3P1−xMxS4, M=As), anion-doped Na3PS4 (Na3PS4−xMx, M=Se; Na3−xPS4-xMx, M=C1, Br), Na3SbS4 and Na10SnP2S12. Some electrolytes show comparable conductivities with liquid electrolytes. As-doped Na3PS4 (Na3P0.62As0.38S4), Cl-doped Na3PS4 (Na2.9375PS3.9375Cl0.0625) and Na3SbS4 show sodium-ion conductivities 1.46×10−3 S cm−1, 1.38×10−3 S cm−1, and 1.05×10−3 S cm−1 at room temperature, respectively.
One of the key challenges of currently existing sulfide-based SEs is poor chemical stability with sodium metals or sodium-based alloys. Therefore, sodium metals or sodium-based alloys are not suitable for use as anodes in solid-state batteries. Theoretical thermodynamic calculations demonstrate that most sulfide electrolytes have a narrow electrochemical window (Y. Zhu, et al. ACS Appl. Mater. Interfaces 2015, 7, 23685-23693; Y. Tian, et al., Energy Environ Sci. 2017, 10, 1150-1166). The undesired reactions between Na metal and solid electrolyte has also been experimentally shown (Wenzel, et al., ACS Appl. Mater. Interfaces 2016, 8, 28216-28224).
In addition to the challenge of chemical instability, the other formidable challenge is short circuit events in all-solid-state metal batteries. Multiple research groups have reported cases where solid electrolytes paired with a Li or Na metal anode experience a short circuit event. A recent study shows the failure mechanism is Griffith-like, and solid state electrolyte without crack, grain boundary or defect on its surface will be ideal electrolyte to suppress short circuit event (Adv. Energy Mater. 2017, 1701003). A solid-state electrolyte that forms a highly dense layer with a microstructure approaching a continuous glass is therefore strongly desired.
In Tatsumisago et al. U.S. Pat. No. 9,537,174B2, “Sulfide solid electrolyte”, a oxysulfide electrolyte was reported with the chemical formula of yLi2S-(100-x-y)P2S5-xP2O5, which is found to (1) show enhanced moisture stability, and (2) crystalline phase in nature.
Amorphous glass is typically processed through melt-quench method, which requires high temperature to melt the electrolyte and adds complexity to producing an electrolyte. Ideally, a glass-forming approach using powders compressed at room temperature is preferred due to low-cost synthetic approach.
Methods, batteries, and electrolytes are discussed herein utilizing a solid-state electrolyte, such as a sodium oxy-sulfide. This new class of sodium-ion conducting solid-state electrolytes that forms a highly dense layer that approaches a continuous glass when powders are compressed at low temperatures, while maintaining a stable low-resistance interface with Na metal or Na-alloy electrodes, are discussed further herein. For example, the electrolytes discussed herein may be mainly amorphous, and/or have a relative density of 95% or greater. These electrolytes may be utilize with a sodium battery with Na metal or Na-alloy electrode(s). Further, these electrolytes may operate 250 hours or longer with a Na metal or Na-based alloy electrode at 0.2 mA/cm2. This new electrolyte is transformative in that it exhibits the benefits of a continuous glass formed by melt processes, but can be formed using low-cost and highly scalable powder slurry methods.
In some embodiments, a method of forming the electrolyte utilizes ball-milling of starting materials comprising at least one sodium sulfide and at least one oxide. For example, ball-milling may be performed at 500 rpm or greater. The resulting materials are pressed at relatively low temperatures and pressure to form the electrolyte. In some cases, the materials may be pressed at temperatures of 100° C. or less and/or at 100-450 MPa.
This oxysulfide electrolyte may have a nominal composition of Na3PS4−xOx (0<x≤2), which can be synthesized by ball milling a mixture of Na2S—P2S5—P2O5 with a molar ratio of 75:(25−y):y (0<y≤20). Examples of starting materials may comprise Na2S, P2S5, and P2O5.
The foregoing has outlined rather broadly various features of the present disclosure in order that the detailed description that follows may be better understood. Additional features and advantages of the disclosure will be described hereinafter.
For a more complete understanding of the present disclosure, and the advantages thereof, reference is now made to the following descriptions to be taken in conjunction with the accompanying drawings describing specific embodiments of the disclosure, wherein:
Refer now to the drawings wherein depicted elements are not necessarily shown to scale and wherein like or similar elements are designated by the same reference numeral through the several views.
Referring to the drawings in general, it will be understood that the illustrations are for the purpose of describing particular implementations of the disclosure and are not intended to be limiting thereto. While most of the terms used herein will be recognizable to those of ordinary skill in the art, it should be understood that when not explicitly defined, terms should be interpreted as adopting a meaning presently accepted by those of ordinary skill in the art.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only, and are not restrictive of the invention, as claimed. In this application, the use of the singular includes the plural, the word “a” or “an” means “at least one”, and the use of “or” means “and/or”, unless specifically stated otherwise. Furthermore, the use of the term “including”, as well as other forms, such as “includes” and “included”, is not limiting. Also, terms such as “element” or “component” encompass both elements or components comprising one unit and elements or components that comprise more than one unit unless specifically stated otherwise.
A solid electrolyte for sodium batteries and corresponding methods for making the solid electrolyte are discussed herein. This solid electrolyte may provide excellent chemical stability with sodium metal and/or may have a microstructure approaching a continuous glass. Further, the methods for making this solid electrolyte simplify the process of making the electrolyte.
This new class of electrolytes is different from others in following aspects: (1) the new electrolytes show enhanced chemical stability with Na metal or Na-based alloy electrodes, not with ambient moisture; and (2) the new electrolyte is mainly amorphous phase instead of crystallized glass phase.
A new family of solid-state electrolytes discussed herein are glassy SEs that combine the advantages of sulfide and oxide SEs to demonstrate the best cycling stability with sodium metal over all other known SEs and the distinctive ability to undergo a room-temperature pressure-induced sintering that creates a nearly fully flawless glassy structure that has robust mechanics and substantial chemical/electrochemical stability. Microstructural analysis reveals a significantly stronger and denser glassy network structure of oxysulfide SEs with more bridging oxygen units compared to the fully ionic and non-network structure of Na3PS4. In some embodiments, these SEs demonstrate very highest energy density (≥1800 Wh kg−1).
In some embodiments, the new SEs involve oxysulfide SEs (Na2S—P2S5—P2O5) existing as a nearly flawless glass using a facile one-step mechanochemical milling method. The ternary electrolyte system discussed further herein has been carefully designed involving the following: first, P2S5 with a low melting point is a strong glass former that appears to facilitate the formation of a structurally defect-free bulk glass, which is crucial to addressing the Na dendrites propagation issue in above pure oxide SEs; second, P2O5 with stronger chemical bonding of P—O compared to that of P—S can form more robust glass network, thereby boosting the mechanical strength and retarding the known electro-/chemical decomposition of pure sulfide SEs; third, Na2S is an outstanding glass modifier to achieve high Na+-ion conductivity. During normal uniaxial cold-pressing, these new oxysulfide SEs were found to spontaneously transform into fully dense and microscopically homogeneous glasses (
In some embodiments, solid-state electrolytes can be synthesized via a one-step ball-milling process. The resulting electrolyte may be any suitable sodium oxy-sulfide, such as Na3PS4−xOx glass where 0<x≤2. In some embodiments, desired amount of starting materials including at least one sulfide or sodium sulfide and at least one oxide (e.g. Na2S, P2S5, and P2O5) with a desired molar ratio are place together in a container with milling balls, and the ball milling may be performed. Ball-milling may be performed at speeds of 500 rpm or greater.
As a nonlimiting example, Na3PS4−xOx electrolytes with 0<x≤2 involve starting materials of Na2S, P2S5, and P2O5 mixed with a molar ratio of 75:(25−y):y where y≠0. Further, 0<y≤20 for the ratio in some cases. For example, a total mass of ˜2 g were placed in a 250 mL stainless steel jar together with stainless steel balls (2×Φ16 mm/20×Φ10 mm or 2×Φ10 mm/20×Φ6 mm) and ball-milled at high rotation speed of 500 rpm for 3˜10 hours.
After synthesis of the starting materials via one-step ball-milling, the resulting materials may optionally be further densified by pressing, such as by pressing at temperatures of 100° C. or less or at room temperature. Additionally, in some embodiments, the pressing may be performed under pressure of 100-450 MPa. In some embodiments, the pressing may be performed at pressures 350-450 MPa. In some embodiments, the pressing may be performed at pressures 250-350 MPa. In some embodiments, the pressing may be performed at pressures 150-250 MPa. In some embodiments, the pressing may be performed at pressures 100-150 MPa. In some embodiments, the pressed electrolyte may have relative densities close to 95% or greater. In some embodiments, the pressed electrolyte may have relative densities close to 100%. As a nonlimiting example, the Na3PS4−xOx (x=1.0) glass electrolytes can be densified into pellets at room temperature under a pressure of 100-450 MPa. Notably, this densification results in samples with relative density close to 100%. Prior art of Na3PS4 glass electrolyte processed at the same condition results in ˜94% relative density [M. Nose et al. J. Mater. Chem. A, 2015, 3, 22061]. In some embodiments, the resulting electrolyte may be mainly amorphous and/or nearly a continuous glass.
In some embodiments, the solid-state electrolyte is a product of ball-milling starting materials including at least one sodium sulfide material and at least one oxide material. As a nonlimiting example, Na2S, P2S5 and P2O5 with the molar percentage of 75:(25−y):y, wherein 0<y≤20 may be utilized. The resulting electrolyte may be Na3PS4−xOx electrolytes with 0<x≤2 in some cases. Further, x may be 0.25 for the Na3PS4−xOx electrolytes. In some embodiments, the starting materials are subjected to a one-step ball-milling approach, such as in a stainless steel jar. Subsequently, the ball-milled materials may then be optionally cold-pressed, such as at room temperature or at temperatures of 100° C. or less, to produce the desired sodium oxy-sulfide solid-state electrolyte. In some embodiments, the solid-state electrolyte produced is mainly amorphous phase with a very small amount of highly-conductive crystalline phase (e.g. Na3PS4). It shall be understood herein that the electrolyte may be referred to as being mainly amorphous when a small amount of crystalline phase is present, such as <1%, or demonstrate properties as discussed further herein in the experimental examples. In some embodiments, the resulting electrolyte may be a nearly continuous glass. The nearly continuous glass may be nearly flawless with very few pores, grain boundaries, or flaws. For example, “pop-in” phenomenon may be absent from nearly flawless glasses or the nearly flawless glass may demonstrate one or more properties as discussed further herein in the experimental examples. In some embodiments, solid-state electrolytes, e.g. Na3PS4−xOx with 0<x≤1 or 0<x≤2 have higher ionic conductivity than pure sulfide glass (x=0). In some embodiments, the solid-state electrolytes discussed above can form very uniform and dense pellet approaching nearly flawless glass that may also be mainly amorphous when pressing the resulting ball-milled powders discussed above. The pressing may be performed at room temperature or temperatures lower than 100° C. In some embodiments, the pressing may occur at room or low temperatures and/or at low pressures. In some embodiments, the pressing may be performed under pressure of 100-450 MPa. In some embodiments, the pressing may be performed at pressures 350-450 MPa. In some embodiments, the pressing may be performed at pressures 250-350 MPa. In some embodiments, the pressing may be performed at pressures 150-250 MPa. In some embodiments, the pressing may be performed at pressures 100-150 MPa. In some embodiments, the pressed electrolyte may have relative densities close to 95% or greater. In some embodiments, the pressed electrolyte may have relative densities close to 100%.
In some embodiments, the solid-state electrolytes discussed above are utilized in a sodium battery. The electrolyte may be utilized with Na metal or Na-based alloy electrode(s). In some embodiments, the electrolyte is suitable for use with a Na metal or Na-based alloy (e.g. Sn, Sb, P, Si, Ge, Bi and etc.) anode. In some embodiments, any suitable Na metal or Na-based alloy (e.g. Sn, Sb, P, Si, Ge, Bi and etc.) cathode may be utilized. In contrast, other prior SSEs demonstrate poor long term stability and degrade in a short time. The electrolyte may be Na3PS4−xOx electrolytes with 0<x≤2 in some cases. Further, x may be 0.25 for the Na3PS4−xOx electrolytes. In some embodiments, the resulting electrolyte may be mainly amorphous and/or nearly a continuous glass. In some embodiments, the electrolytes discussed above can perform 500 hours or longer with Na metal or Na-based alloy at 0.2 mA/cm2. In some embodiments, the electrolytes discussed above can perform 400 hours or longer with Na metal or Na-based alloy at 0.2 mA/cm2. In some embodiments, the electrolytes discussed above can perform 300 hours or longer with Na metal or Na-based alloy at 0.2 mA/cm2. In some embodiments, the electrolytes discussed above can perform 250 hours or longer with Na metal or Na-based alloy at 0.2 mA/cm2. In some embodiments, the solid-state electrolytes discussed above can also be combined with other sulfide electrolytes that are unstable with Na metal or Na-based alloy electrodes. In some embodiments, the new electrolytes discussed above and the other (unstable) sulfide electrolytes form a multiple-layer (e.g. tri-layer) electrolyte. The other sulfide electrolyte may be sandwiched between the new electrolytes in some multiple layer configurations to isolate it from the Na metal or Na-based alloy. In some embodiments, the multiple-layer electrolyte discussed above can also be matched with Na metal or Na-based alloy (e.g. Sn, Sb, P, Si, Ge, Bi and etc.) anode.
The following examples are included to demonstrate particular aspects of the present disclosure. It should be appreciated by those of ordinary skill in the art that the methods described in the examples that follow merely represent illustrative embodiments of the disclosure. Those of ordinary skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments described and still obtain a like or similar result without departing from the spirit and scope of the present disclosure.
Na3PS4−xOx electrolytes were produced according to the nonlimiting examples discussed previously. Among various oxysulfide electrolytes Na3PS4−xOx,
Solid-state nuclear magnetic resonance (NMR) has been shown as a powerful tool for determining Li local environment. To further understand the difference of materials composition, 31P NMR spectra of four Na3PS4−xOx (x=0, 0.25, 0.50 and 1.0) samples was measured as shown in
NaSn alloy is typically believed to be less aggressive than Na metal in terms of chemical reactivity.
In stark contrast, as shown in
The synergistic effects of oxygen additions on the properties of the Na2S—P2S5—P2O5 (Na3PS4−xOx) SEs were examined and systematically characterized on different compositions of x=0.00, 0.25, 0.50, 1.00 that were synthesized via the synthesis process for electrolytes discussed above, which may be referred to as herein as high-energy mechanochemical milling (MCM). The XRD patterns (
P MAS-NMR was used to gain further insights into the glassy phase of these SEs by examining the local structure around the phosphorus glass forming cations. As seen from
FTIR spectroscopy was further applied to explore the chemical bonding of P—S and P—O. The FTIR spectra shown in
A nearly defect-free and mechanically robust SE is a prerequisite for effectively suppressing dendrite penetration. Consequently, the morphological structure and mechanical properties of Na3PS4−xOx SEs were then investigated. For comparison, the widely studied heat-treated (HT-Na3PS4) glass-ceramic SE was also studied. Obvious pores and grain boundaries that are the typical Griffith flaws are clearly observed in the surface and cross-sectional SEM images of pelletized HT-Na3PS4 (
To quantify the mechanical properties of SEs, two critical parameters: Young's elastic modulus E and hardness H were measured using our previously reported nano-indentation technique. Typical loading-displacement curves (
Assuming that Poisson's ratio v is ca. 0.3, the shear modulus G of Na3PS3O glass is ca. 8.0±0.3 GPa, which is sufficient to suppress dendritic penetration of Na metal as predicted by the Monroe and Newman criterion. Thus, the electrolyte can be described as a nearly flawless or defect-free glass.
As described above, the chemical and electrochemical stability of SEs against Na metal anode is critically important for developing high-performance SSMBs. The Na/Na3PS4−xOx SE interface was examined by monitoring the EIS change of Na|Na3PS4−xOx|Na symmetric cells before and after 5 hours of rest at 60° C., as shown in
The obtained EIS spectra from high frequency to middle frequency to low frequency can be fitted into: the bulk resistance and capacitance (Rb+Rgb, Cb+Cgb) of the SEs, the interfacial resistance and capacitance (Ri, Ci) between Na and SEs with the characteristic capacitance of 10−6˜10−7 F, and the charge-transfer resistance and capacitance (Rct, Cct). It is noteworthy of pointing out that the Rct and Ri includes the resistance at two Na|SE interfaces.
To identify the solid electrolyte interphase (SEI) composition that apparently grows with time for the x≠1 glassy SEs, Na metal was detached from the symmetric cells and the surface of SEs was probed by the XPS. Compared to the XPS spectra of the pristine SEs (
The superb formability of the Na3PS3O SE can provide access to fabricate a thin SE layer, the resistance of which could be very low. An ideal SE for SSMBs requires both high ionic conductivity and excellent mechanical and chemical stability. To create such an SE, therefore, a tri-layer architecture with the most ionically conductive Na3PS3.75O0.25 in the middle and the most mechanically and chemically stable Na3PS3O in the outside is designed and shown in the inset of
Before fabricating a full cell, however, the cyclability of the tri-layer SE was studied in a symmetric Na|tri-layer SE|Na cell using gradient-current and constant-current tests, as shown in
In the constant-current mode,
It has been shown above that the Na3PS3O SE can be combined with Na3PS3.75O0.25 to create a stable all-glass separator. In a similar way, using the tri-layer architecture, Na3PS3O can be used for protecting other highly conducting but chemically unstable (vs. Na metal) SEs such as glass-ceramics, e.g. HT-Na3PS4, or ceramics, e.g. Na3SbS4, SEs. An example of this is shown in
The excellent Na—Na3PS3O stability enables the fabrication of SSMBs, of which the one of the most promising is the ambient-temperature Na—S battery with very low cost and high specific energy. On the basis of the above study of tri-layer SEs, a Na—S battery having the architecture of S—Na3PS3.75O0.25|Na3PS3.75O0.25|Na3PS3O|Na was designed and tested at 60° C.
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A new class of oxysulfide glass SEs with combined advantages of sulfide SEs and oxide SEs was successfully synthesized and systematically investigated in both symmetric and full cell configurations. Compared with pure sulfide SEs, oxygen-doped Na3PS4−xOx oxysulfide SEs show much stronger and denser glass networks due to the formation of more oxide and oxysulfide units with BO characteristics. The addition of oxygen also causes these oxysulfide SEs to exhibit the never before seen capability of pressure-induced homogenization of the glassy powder starting materials into continuous near flawless glass microstructure. This dramatically improved formability causes the as-formed homogeneous oxysulfide SEs to have significantly higher mechanical strength and dramatically higher chemical stability towards Na metal. A near flawless tri-layer composite SE with Na3PS3O|Na3PS3.75O0.25|Na3PS3O can not only demonstrate a record critical current density of up to 2.3 mA cm−2 and for a cycling life of up to 500 h among the reported Na metal symmetric cell, but also enable an ambient-temperature Na—S cell to deliver the highest energy density among all known solid-state Na systems to date. These new oxysulfide SEs and the tri-layer composite SEs may provide a very promising avenue of research towards the development of new high energy, safe, low cost and long cycle life Na metal anode-based SSMBs in general and new solid-state Na—S batteries for energy storage devices.
Synthesis of Na3PS4−xOx SEs. Na2S, P2S5, and P2O5 (Sigma-Aldrich, 99%) were used as the raw materials without further purification. The Na3PS4−xOx (x=0.00, 0.25, 0.50 and 1.00) SEs were prepared by high-energy MCM technique. Typically, 2 g mixtures of appropriate amounts of Na2S, P2S5, and P2O5 powders were milled in an argon-protected stainless steel jar containing stainless steel milling balls at 500 rpm for 3 h to obtain the glassy SEs. The Na3PS4 glass-ceramic SE, namely HT-Na3PS4, was obtained by heating the glassy Na3PS4 (x=0.00) under vacuum at 260° C. for 2 h.
Materials Characterizations of Na3PS4−xOx SEs Since Na3PS4−xOx SEs are sensitive to air and moisture, all of the characterizations were conducted under argon protection. Lab-based X-ray diffraction (XRD) and synchrotron XRD patterns were collected using a Rigaku MiniFlex 600 with Cu Kα radiation (λ=1.5418 Å) and Beamline 11-ID-C at Advanced Photon Source with an X-ray wavelength of 0.1173 Å, respectively, to determine the amorphization of raw materials and the possible crystalline phases of Na3PS4−xOx products. The thermal behavior of the SEs powders was examined using differential scanning calorimetry, DSC, TA Instruments Q2000, using nitrogen as the carrier gas. The sample was placed in the Tzero aluminum pan and hermetically crimp-sealed inside the argon-filled glove box. The DSC measurements were carried out at a heating rate of 20° C. min−1 from 50° C. to 400° C. A Renishaw inVia Raman spectrometer employing a 488 nm Ar+ laser and 10 mW of power was used to collect the Raman spectra from 200 to 700 cm−1. SE powders were placed into a small plastic sample holder inside the glove box and covered with transparent tape to prevent exposure to air during data collection. Infrared (IR) spectra were acquired on a Bruker IFS 66 v/s vacuum IR spectrometer in the range of 400-1200 cm−1 using a KBr beamsplitter. During the test, the spectrometer optical bench was held under vacuum to protect the samples from moisture and air. The IR spectra of the samples were taken by diluting the finely ground glass and glass-ceramic powders to ˜2 wt % in finely ground and carefully dried CsI powders and then pressed into small pellets. P Solid-state Magic Angle Spinning Nuclear Magnetic Resonance (MAS NMR) spectra were collected using a JEOL ECA-500 NMR spectrometer. SE powders were packed into an alumina spinner with a sealant in an argon-filled glove box. Spectra were collected using a 4.25 μs, 60° pulse length, and a 200 s recycle delay with the spinning speed of 20 kHz. Chemical shifts were externally referenced to NaH2PO4. The elastic modulus E and hardness H were measured using the same method as reported. Briefly, E and H values were measured using a G200 Keysight nanoindenter with a Berkovich indenter using the Oliver-Pharr method on samples inside an argon-filled glove box to avoid the moisture and air contaminations. Indentations with a maximum indentation load of 1 mN were pressed on different spots of the SE surfaces to ensure the convergence of the measured results. The loading-displacement curves were recorded during the tests. Morphologies of the SEs powders, as well as the surface and cross-section of the densified pellets, were observed using a Gemini LEO 1525 scanning electron microscope (SEM). Nanocrystals embedded in the glassy SE were confirmed using a JEOL 2100F transmission electron microscope (TEM). The X-ray photoelectron spectroscopy (XPS) spectra were collected using a Physical Electronics PHI 5700 on the SEs pellets before and after contacting with Na metal using a monochromatic Mg Kα X-ray source. The XPS signals were corrected relative to the C 1s signal (284.8 eV) and fitted using the XPSPEAK41 software.
Electrochemical Characterizations of SEs The temperature-dependent ionic conductivities of the pelletized SEs were measured from 25° C. to 90° C. using electrochemical impedance spectroscopy (EIS, frequency: 1 MHz-0.1 Hz, amplitude: 5 mV) on a VMP3, Bio-Logic Co. electrochemical workstation. Before the measurement, the SEs powders were cold-pressed in a polyetherether-ketone (PEEK) test cell die (φ=13 mm) under a pressure of 450 MPa and then co-pressed with 20 mg nano-copper powders (Sigma-Aldrich, 40-60 nm, ≥99.5%) as the electrodes under a pressure of 200 MPa. Chemical stability of the SEs towards Na metal was studied by monitoring the impedance change vs. rest time of the symmetric cell Na|SEs|Na, which was assembled by attaching two same pieces of Na metal foils (˜100 μm in thickness) on both sides of the SEs. Cyclic voltammetry of the stainless steel|tri-layer SEs|Na asymmetric cell was carried out using a scanning rate of 0.05 mV/s in a potential range of −0.3 V to +3.0 V. Galvanostatic cycling of Na|tri-layer SEs|Na symmetric cells was conducted at 0.2 mA cm−2 and 0.5 mA cm−2. For the fabrication of tri-layer electrolytes, first, ˜150 mg of Na3PS3.75O0.25 glass or Na3PS4 glass-ceramic SE powders were cold-pressed at 75 MPa; then ˜25 mg of Na3PS3O glass powders were evenly distributed on both sides of as-pressed Na3PS3.75O0.25 glass or Na3PS4 glass ceramic pellet; finally the three layers were co-pressed at 450 MPa and attached with Na metal or stainless steel foils.
Electrochemical Characterizations of Na—S Full Cells Since Na3PS3.75O0.25 is the most conductive among the Na3PS4−xOx SEs and Ketjen black (EC-600JD, AkzoNobel) has a high surface area of 1400 m2 g−1, they were chosen to blend with sulfur to create both fast ionic and electronic pathways for the sulfur active material in the composite cathode. In detail, sulfur (99.5%, Alfa Aesar) and Ketjen black (EC-600JD, AkzoNobel) powders with a weight ratio of 1:1 were ball-milled in an agate jar at a rotation speed of 500 rpm for 20 h to obtain a sulfur/Ketjen black nanocomposite, which was then milled with Na3PS3.75O0.25 electrolyte powders at a rotation speed of 350 rpm for 30 min. The weight ratio of sulfur:Ketjen black:Na3PS3.75O0.25 composite cathode is 2:2:6. To fabricate a Na—S battery, ˜150 mg Na3PS3.75O0.25 electrolyte powders were firstly pressed at 75 MPa into a pellet, of which both sides were then uniformly covered with 20˜25 mg Na3PS3O electrolyte powders and ˜2 mg composite cathode powders. The tri-layer was finally co-pressed at 450 MPa and attached with a piece of Na metal foil onto the Na3PS3O electrolyte side. Galvanostatic tests of the as-fabricated full cells were performed in the potential range of 1.0 to 3.0 V vs. Na/Na+ at different current densities from 0.05 to 0.35 mA cm−2. All the electrochemical tests were conducted at 60° C.
Embodiments described herein are included to demonstrate particular aspects of the present disclosure. It should be appreciated by those of skill in the art that the embodiments described herein merely represent exemplary embodiments of the disclosure. Those of ordinary skill in the art should, in light of the present disclosure, appreciate that many changes can be made in the specific embodiments described, including various combinations of the different elements, components, steps, features, or the like of the embodiments described, and still obtain a like or similar result without departing from the spirit and scope of the present disclosure. From the foregoing description, one of ordinary skill in the art can easily ascertain the essential characteristics of this disclosure, and without departing from the spirit and scope thereof, can make various changes and modifications to adapt the disclosure to various usages and conditions. The embodiments described hereinabove are meant to be illustrative only and should not be taken as limiting of the scope of the disclosure.
This application claims the benefit of U.S. Provisional Patent Application No. 62/616,854 filed on Jan. 12, 2018, which is incorporated herein by reference.
This invention was made with government support under Grant No. DE-AR0000654 from Advanced Research Projects Agency-Energy (ARPA-E) within the U.S. Department of Energy. The government has certain rights in the invention.
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/US19/13465 | 1/14/2019 | WO | 00 |
| Number | Date | Country | |
|---|---|---|---|
| 62616854 | Jan 2018 | US |
