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NEI Expands Selection of Materials for Lithium-ion & Sodium-ion Batteries

January 13, 2022

Somerset, New Jersey (USA) – Today, NEI Corporation announced customers can now order from an expanded selection of cathode, anode, and solid electrolyte materials for both lithium-ion and sodium-ion batteries. The company, which is a leader in the development, manufacture, and supply of specialty materials, has been a go-to organization for producing and delivering custom powders and dispersions of particles in liquids and polymers, as well as electrodes cast on metal foil.

NEI offers a variety of battery materials, with a particular forte in producing specialty materials with compositions and particle morphologies that are not commonplace. In addition, NEI has expertise in producing composite particles that have a surface coating. Off-the-shelf products are sold under the tradename NANOMYTE®.

“We want our customers to easily access high quality and consistent battery materials so they can focus on their core mission,” said Dr. Ganesh Skandan, CEO of NEI Corporation. “The NEI team stands ready, willing, and able to produce and supply materials that our customers want, in any quantity needed, for them to pursue their commercialization efforts.”

Particle Size Distribution graph of Na0.44MnO2+x , which is typical of most of NEI's sodium based cathode/anode powders

Particle size distribution (PSD) of Na0.44MnO2+x , which is typical of most of NEI’s sodium based cathode/anode powders.

NEI has been routinely supplying increasing quantities of simple metal oxide compositions such as Na0.44MnO2+x and Na0.7MnO2+x with a narrow particle size distribution. The portfolio of sodium-ion compositions now includes more complex materials, such as sodium iron phosphate (NaFePO4), sodium nickel phosphate (NaNiPO4), sodium titanium phosphate (NaTi2(PO4)3), sodium chromium oxide (NaCrO2), and others. The average aggregate particle size (D50) for most compositions can be tailored to be in the range of 1 – 2 µm, with the primary particles being much smaller. The particle structure can be further tuned to include a surface coating of carbon or a conducting polymer, such as polyaniline, PANI, or an ionically conducting ceramic material. Some of the materials have been tested and validated in-house using half-cell configuration (i.e., sodium metal anode). For example, Na0.44MnO2+x has a second cycle charge and discharge capacity that is > 105 mAh/g.

Second cycle charge/discharge profile of Na0.44MnO2+x cathode powder

In addition to engineering the particle morphology, all sodium-based cathode and anode materials can be supplied as cast electrodes on a current collector of choice. Customers can specify the active material, binder content, amount of conducting carbon and active material per unit area (in case of cathode and anode).

NEI Corporation has built a reputation for supplying consistent and high-quality solid electrolyte materials – oxide materials, such as Al-doped lithium lanthanum zirconium oxide (LLZO) and tantalum-doped LLZO (LLZTO), phosphate compounds, such as LATP or LAGP, and a variety of sulfide-based materials. While the average particle size (D50) for these standard powders is in the 3 – 5 microns range, customers can request a smaller D50.

Cole-Cole plot of sintered LAGP pellet

Cole-Cole plot of sintered LAGP pellet

The ionic conductivity of the oxide materials, measured in-house using Electrochemical Impedance Spectroscopy in a test cell shown in the inset of the picture (left), is in the range of 1 x 10-4 S/cm to 5 x 10-4 S/cm, and that of sulfides can be as high as 1 x 10-3 S/cm.

A recent and exciting development has been the offering of composite solid electrolyte materials in the form of either a polymer-based dispersion or cast membrane. Customers can choose any oxide ceramic solid electrolyte and a base polymer or co-polymer from PEO, PVDF, PVDF-HFP, and PAN. The type of lithium salt in the polymer can be selected from LiTFSI, LiClO4, LiFSI, and LiBOB.

In addition to increasing the suite of materials being offered, NEI has developed new materials synthesis capabilities, which serve as demonstration stations for exploring new compositions that are difficult to produce using conventional processing. A case in point is precursor materials obtained from recovered nickel, cobalt and manganese salts from recycled lithium-ion batteries. The solution-precipitation setup, installed at NEI, serves as a test-bed to determine processing parameters for materials such as NMC532 and NMC622, or any mixed metal oxide for that matter.

There is also increasing interest in cathode materials that are fluorinated and/or contain vanadium, which as multiple valence states and can lead to high capacities. To this end, NEI has produced LiFeSO4F and LiVPO4F with a high degree of crystallinity and phase purity.

Overall, the introduction of these new materials and processes will provide new capabilities to lithium battery developers and manufacturers to enable practical solid-state batteries. Dr. Skandan adds, “It is exciting for the team at NEI to tread on uncharted waters and explore synthesis and processing of new materials, and particularly using newly developed processes. We welcome the opportunity to serve the needs of the Battery community.”

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About NEI: Founded in 1997, NEI develops, manufactures, and sells advanced materials for a broad range of industrial customers around the world. The company’s core competencies are in designing, developing, and producing products that meet the specific application needs of its customers. More importantly, NEI is a solutions provider, working closely with customers to produce and implement materials for their applications. NEI’s products, which are sold under the registered trademark NANOMYTE®, are backed by a suite of issued and pending patents. NEI’s products include:  Lithium-ion Battery Materials, Na-ion Battery Materials, Functional & Protective Coatings, and Specialty Nanoparticle-based products. NEI also offers associated materials characterization and testing services.

For more information, give us a call or email us.

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Solid Electrolytes: Are we there yet?

Solid Electrolytes for Lithium-ion and Lithium-Sulfur Batteries: A Safer Solution

Lithium-ion batteries have provided a lightweight energy-storage solution that has enabled many of today’s high-tech devices – from smartphones to electric cars. Although these batteries are generally safe, fire and explosion concerns have caused the industry to seek solutions. The importance of safety has been highlighted by several rare, yet highly publicized battery hazards such as the explosion in a Japan Airlines 787 Dreamliner’s cargo hold in 2013 and Samsung’s Galaxy Note 7 catching fire, which resulted in the recall of more than 1 million smartphones in 2016. The combustion is mainly due to leakage of the liquid electrolyte, or short-circuit of the electrodes caused by the failure of the polymer gel separator, which also contains liquid.[1] For this reason, it is desirable to replace liquid components used in existing lithium-ion batteries with all solid materials.[2] This would not only solve the safety issue, but would also provide several other significant advantages, such as greater energy storage ability (pound for pound at the battery pack level), no dendrite formation (tiny, fingerlike metallic projections called dendrites that can grow through the electrolyte layer and lead to short-circuits), chemical and electrochemical stability over a wide voltage window (0 – 6V), and exceptionally long cycle life (>50,000 cycles)[3].

Solid state electrolytes can be broadly classified into three categories: (1) inorganic electrolytes, (2) solid polymer electrolytes (SPE), and (3) composite electrolytes. As the performance of batteries depends on the diffusion of lithium ions within the electrolyte, solid electrolytes need to have high ionic conductivity and negligible electronic conductivity. A summary is given here of the three classes of solid electrolyte materials. The data presented here is based on materials produced and measurements performed at NEI Corporation as part of NEI’s R&D program.

Inorganic Electrolytes

Inorganic solid state electrolytes present high lithium ionic conductivity at temperatures below their melting point. The highest room temperature conductivity reported for any inorganic solid electrolyte is 2.5 × 10−2 S/cm for Li9.54Si1.74P1.44S11.7Cl0.3,[4] which is comparable to the conductivity of a liquid electrolyte. Besides having impressive conductivity values, inorganic electrolytes are single ion conductors, allowing the lithium transference number to approach unity. These characteristics, and the absence of leakage and pollution, make the inorganic electrolyte a highly appealing electrolyte material for lithium-ion and lithium-sulfur batteries. Inorganic electrolytes can be either crystalline or amorphous (glass), or have mixed phases (glass-ceramic).

Sulfur Based Solid Electrolytes (Thio-LiSICONS)

One of the early crystalline lithium ion conductors was based on an oxide compound of lithium zinc germanium, Li14ZnGe4O16, which was reported by Hong.[5] This type of crystalline ion conductor is referred to as LISICON (lithium superconductor). Although the ionic conductivity of Li14ZnGe4O16 reaches 0.125 S/cm at 300°C, it is only 10-7 S/cm at room temperature. Efforts to improve the ionic conductivity of LISICON-type ion conductors have resulted in the replacement of oxygen by sulfur in the framework. Since the radius of S2- is greater than O2-, and S2- has better polarization capability than O2-, the substitution weakens the interaction between the crystal lattice and Li+ ions, thus fostering Li+ ion transport. The incorporation of sulfides in the form of partial sulfide substitution (e.g., oxy-sulfide[6]  compounds) or full sulfide substitution[7] can raise the room temperature conductivity of the electrolyte to about ~10-3 S/cm. An example of the highly conductive sulfur substituted LISICON ion conductor is , Lithium Germanium Phosphorous Sulfide (LGPS). Li10GeP2S12 is a superionic conducting solid that conducts lithium ions at room temperature with conductivity in the range of 10-4 S/cm to 10-2 S/cm, depending on material form (powder, pellet, or sintered pellet) and measurement conditions.

Since germanium is an expensive rare earth element, a similar material was synthesized replacing germanium with much less expensive tin, yielding a crystalline LISICON type ion conductor, Li10SnP2S12, Lithium Tin Phosphorous Sulfide (LSPS), which has conductivity slightly lower than that of LGPS, but is much more affordable. Basic characteristics of the Lithium Tin Phosphorous Sulfide powder produced at NEI Corporation are listed here. The solid electrolyte is phase pure and has Li-ion conductivity in the range of 10-4 to 10-2 S/cm (approaching that of liquid electrolytes) depending upon material/pellet processing conditions, and electrochemically stable up to 6V.

More recently, Li9.54Si1.74P1.44S11.7Cl0.3 and Li9.6P3S12 have been reported. Exceptional room temperature conductivity (2.5 x 10-2 S/cm for Li9.54Si1.74P1.44S11.7Cl0.3) as well as high stability (∼0 V versus Li metal for Li9.6P3S12) were achieved1. NEI has successfully produced the following sulfur based solid electrolytes: (LSPS – Li10SnP2S12, LGPS – Li10GeP2S12, β-LPS – Li3PS4, LPSCl – Li6PS5Cl, LSPSCl – Li9.54Si1.74P1.44S11.7Cl0.3, and LPS – Li9.6P3S12) in bulk quantities (gram to kilogram scale).

Oxide Based Garnet-Type Solid Electrolytes

Garnet-type lithium solid electrolytes have a general formula of Li5La3M2O12 where M can be Ta or Nb. These were first reported in 2005[8] and have been intensively studied in recent years. The most attractive property of this class of crystalline solid electrolyte is its excellent chemical stability against lithium metal and also against moisture, in addition to its high ionic conductivity. These materials can be handled in a dry room. An example of the Garnet-type solid electrolyte is Li6BaLa2Ta2O12, which displays a room temperature conductivity of 4 x 10-5 S/cm and a low grain boundary resistance.[9] When the Garnet-type solid electrolyte Li5La3M2O12 was partially substituted at the M site by Y or In, conductivity was further improved. For example, the composition Li5.5La3Nb1.75In0.25O12 showed an enhanced conductivity of 1.8 x 10-4 S/cm at 50 °C with a low activation energy of 49.2 kJ/mol.[10] Another composition, Li6.5La3Nb1.25Y0.75O12, showed a high conductivity of 2.7 x 10-4 S/cm at 25 °C.[11]

Most recently, a Garnet-type Lithium Lanthanum Zirconate (LLZO – Li7La3Zr2O12) has quickly become a promising solid electrolyte for all solid-state lithium and lithium ion batteries because of its high conductivity (> 10−4 S/cm) at room temperature, excellent thermal performance, and stability versus Li metal and oxygen. The material shows great potential to offer high energy density and minimize battery safety concerns to meet many applications in large energy storage systems such as electric vehicles and aerospace. LLZO exists in tetragonal and cubic crystal structures, with the cubic phase displaying about two orders of magnitude higher ionic conductivity than that of tetragonal phase. The cubic phase is stabilized by doping with Al or Ga.

Al or Ga-doped LLZO (Li6.24La3Zr2Al0.24O11.98 and Li6.24La3Zr2Ga0.24O11.98) have been synthesized at NEI Corporation in various batch sizes. Both the materials are fairly phase pure, crystallized in cubic phase (see PXRD pattern) and have room temperature conductivity in the order of 10-4 – 10-5 S/cm, depending upon the pellet processing and annealing condition (see the impedance plot below). Negligible electronic conductivity, large band gap (~6 eV) and wide electrochemical stability window (0 – 6V), are attractive properties for this material.[12]

Oxide Based Perovskite-Type Solid Electrolytes

Lithium Lanthanum Titanate (LLTO), Li0.5La0.5TiO3, with Perovskite structure has been considered to be a promising solid electrolyte material for lithium-ion and lithium-oxygen batteries due to numerous outstanding advantages, such as: (i) high lithium conductivity at room temperature, (ii) high lithium diffusion coefficient, (iii) low electronic conductivity, and (iv) electrochemical stability window larger than 4 V. NEI has prepared LLTO and various metal doped LLTO (e.g., Al-doped LLTO), and analyzed the crystal structure, particle size, and conductivity.

 

 

 

 

There are two challenges that LLTO electrolyte faces: grain boundary resistance and instability against lithium metal. Although the bulk conductivity of LLTO can reach 10-3 S/cm at room temperature, the grain boundary conductivity is relatively low (10-5 S/cm).[13]

Phosphate Based LISICON-Type Solid Electrolytes

Lithium Aluminum Titanium Phosphate (LATP) is a phosphate based LISICON (Lithium Super Ionic Conductor) with the general molecular formula Li1+xAlxTi2-x(PO4)3, which shows high ionic conductivity of ~10-3 S/cm for x = 0.3 composition. It is electrochemically stable above 1.8 V and thermally stable up to 1000 °C. Phosphate based LISICON type materials have applications in batteries, fuel cells, gas sensors, catalysis, and low thermal expansion ceramics. NEI has synthesized LATP compositions and its sodium analogs (NaSICON) and studied the conductivity.[14]

Sulfide Based Glassy and Glass-Ceramic Solid Electrolytes

Sulfur based glassy and glass-ceramic solid electrolytes, such as Li2S–SiS2[15] and Li2S–P2S5,[16] can achieve ionic conductivity of 10-5 S/cm to 10-3 S/cm due to the high polarizability of sulfur ions. A general composition of the Li2S–P2S5 system can be represented by x Li2S + (1-x) P2S5, where x is the molar fraction. The Li2S–P2S5 system varies widely in crystal form, crystal content, and the resulting ionic conductivity, depending on the composition and processing method. Usually, the grain-boundaries around crystal domains in Li2S–P2S5 glass–ceramics are surrounded by amorphous phases. Therefore, these glass-ceramic solid electrolytes often have lower grain boundary resistance than in polycrystalline systems, which results in improvement in the observed total conductivity.

The composition of x Li2S + (1-x) P2S5 when x = 0.75, or Li3PS4, represents the most stable chemical in the Li2S−P2S5 system. The crystal domains of Li3PS4 exist in either γ or b phase – among these b phase is the more ionically conductive material. β-Li3PS4 (β-LPS) is a “superionic” solid that conducts lithium ions at room temperature. β-LPS synthesized at NEI is phase pure and has a Li-ion conductivity of 10-4 – 10-5 S/cm, depending upon material/pellet processing conditions. The material is electrochemically stable versus lithium over a wide voltage window (0 – 5V).

Although the best of the inorganic solid electrolytes have demonstrated high ionic conductivity comparable to liquid electrolytes, several limitations have to be overcome before they can be widely used as solid electrolyte. First, bulk conductivity is usually higher than grain boundary conductivity, which makes the total conductivity smaller than the intrinsic bulk conductivity, unless the material is sintered at high temperature and pressure. A related and often asked question is that if sintering is not an economically viable method, what processing alternatives are available to utilize these highly ionic conducting powders? Second, a critical issue for the development of high power, solid-state lithium batteries is the high resistance at the electrode/solid electrolyte interface. Inorganic solid electrolytes are generally not flexible enough to handle the stress developed as a result of volumetric expansion/contraction of the electrodes. Therefore, how to create and maintain a favorable interface between the electrode and solid electrolyte is a challenge. Polymer electrolytes when used alone, or in combination with inorganic electrolytes, have the potential to address both of these issues pertaining to inorganic solid electrolytes.

Solid Polymer Electrolytes (SPE)

The most common solid polymer electrolytes (SPE) for rechargeable solid-state lithium batteries are composed of low lattice energy lithium salts (e.g., LiClO4, LiN(CF3SO2)2, LiCF3SO3, or LiBC4O8) dissolved in polyether-containing polymers such as poly(ethylene oxide), poly(propylene oxide), or poly(ethylene glycol). Other polymers have also been studied, such as polyphosphazenes, which have oligoethyleneoxy side chains to facilitate lithium ion conduction and reduce glass transition temperature (Tg). Since solid polymer electrolytes are flexible and can be easily made into free standing membranes, they have been predominantly used as solid electrolytes in a variety of electrochemical devices. A traditional dry, PEO-based electrolyte has a severe drawback in that its conductivity only becomes sufficient at elevated temperatures (above 60 °C). PEO is a semi-crystalline material where PEO crystalline and amorphous domains co-exist. It has been widely accepted that ion transport occurs in the amorphous region. PEO crystals melt above 60 °C and a jump of conductivity is observed above the melting point. To overcome this limitation, polymer gel electrolytes were developed. These are crosslinked polymer networks with liquid electrolyte imbibed to boost the room temperature ionic conductivity, which generally exceeds 1×10-3 S/cm. However, the liquid electrolyte in gel polymer electrolytes still poses safety issues, and the polymer gel has inferior mechanical properties. For these reasons, there is renewed interest in developing truly dry polymer electrolyte systems and some systems have room temperature conductivity values approaching 10-4 S/cm. We discuss only the 100% solid polymer electrolyte here.

One of the polymers developed at NEI Corporation using the copolymer strategy is H-polymer. As a 100% solid material, H-polymer combines the benefits of high room temperature lithium-ion conductivity (5 x 10-5 S/cm) with good mechanical properties of a solid polymer. H-polymer is a PEO-based copolymer with PEO segments in the polymer backbone that has four orders of magnitude higher room temperature conductivity than that of pure PEO. The significant improvement of room temperature conductivity is due to the amorphous nature of PEO segments in the copolymer. H-polymer can be used as a separator, or as a conductive binder for active cathode and anode materials.

Another series of copolymers that shows good room temperature conductivity has been reported in the literature.[17] These are POEA-g-PDMS or POEM-g-PDMS copolymers, which are graft copolymers made of grafted PEO chains and grafted PDMS (poly(dimethylsiloxane)) chains. The oligomeric nature of PEO segments prevents it from crystallizing and the low Tg PDMS segments make the polymer a rubbery flexible ionic conductor, where the conductivity reaches in the range of 10-5 S/cm to 10-4 S/cm at room temperature.

Composite Electrolytes

Composite electrolytes are SPEs with sub-micron or nano- sized inorganic particles dispersed in the polymer matrix. Adding inorganic particles induces a favorable interaction between the ceramic surface states and the anions of both the lithium salt and PEO segments, thereby promoting lithium-ion transport and inhibiting polymer crystallite formation. This results in enhanced ionic conductivity, promoting interfacial stability at Li/Li+ interface, suppressing the growth of dendrites, improving mechanical properties, and increasing Li+ transference number. It has been found that particle size is important and nanoparticles are more effective than larger particles. One to two orders of magnitude enhancement in room temperature ionic conductivity can be realized with the addition of ceramic nanoparticles in an SPE host, compared to the undispersed system, along with improvements in the physical, mechanical and electrochemical properties. A few of the ceramic nanoparticles that have been investigated that demonstrated a significant improvement in conductivity are Al2O3, SiO2, TiO2, ZrO2, and BaTiO3.

Most of the systems studied involve inert ceramic particles and PEO with lithium salt. NEI Corporation has explored producing composite electrolytes using active ionic conductive inorganic particles in a conductive polymer host. For example, by incorporating LLZO in H-polymer, we were able to fabricate mechanically sturdy electrolyte membranes/separators with conductivity approaching 10-4 S/cm.

Opportunity for New Materials Development

Market-driven interest in developing practical solid electrolyte materials for use in Lithium-ion and Lithium-sulfur batteries has created opportunities for producing materials with new compositions, chemistry and morphology. Being able to process the material in a usable form is the key to enabling commercial utilization of the solid electrolyte materials. Combining the attributes of inorganic and organic solid electrolyte materials offers a path to high ionic conductivity materials wherein the high ionic conductivity of inorganic electrolytes is combined with the processing advantages and superior mechanical properties of solid polymer electrolytes.

About NEI Corporation

NEI Corporation is an applications-driven company that develops and produces advanced materials. NEI Corporation offers specialty cathode and anode materials (both powders and coated electrodes), and solid state electrolytes for use in lithium-ion and lithium-sulfur batteries. NEI produces battery materials through a scalable and economical synthesis process, which is adaptable to different materials compositions and particle morphologies. The company also offers battery materials development and cell-level testing services.

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References:

[1] http://www.nydailynews.com/news/scientists-solve-mystery-flaming-laptops-article-1.445634

[2] https://chargedevs.com/newswire/japanese-researchers-use-superionic-conductors-as-electrolytes-for-solid-state-batteries/

[3] https://www.excellatron.com/advantage.htm

[4] Y. Kato, S. Hori, T. Saito, K. Suzuki, M. Hirayama, A. Mitsui, M. Yonemura, H. Iba, and R. Kanno, Nature Energy, 2016, 3, 438-446, and references therein

[5] H. Y.-P. Hong, Mater. Res. Bull., 1978, 13, 117.

[6] S. Kondo, K. Takada, and Y. Yamaura, Solid State Ionics, 1992, 53-56, 1183.

[7] J. H. Kennedy and Y. Yang, J. Solid State Chem., 1987, 69, 252.

[8] V. Thangadurai, and W. J. Weppner, J. Am. Ceram. Soc., 2005, 88, 411–418.

[9] V. Thangadurai, and W. J. Weppner, Adv. Funct. Mater., 2005, 15, 107–112.

[10] V. Thangadurai, and W. J. Weppner, J. Solid State Chem., 2006, 179, 974–984.

[11] S. Narayanan, F. Ramezanipour, and V. Thangadurai, J. Phys. Chem.C 2012, 116, 20154.

[12] T. Thompson et al, Energy Letters, 2017, 2, 462-468.

[13] C. W. Ban, and G. M. Choi, Solid State Ionics, 2001, 140, 285–292.

[14] N. Anantharamulu et al, J. Mater. Sci. 2011, 46, 2821.

[15] N. Machida, and T. Shigematsu, Chem. Lett. 2004, 33, 376–377.

[16] M. Tatsumisago, Solid State Ionics, 2004, 175, 13–18.

[17] Q. Hu, A. Caputo, D. R. Sadoway, J. Vis. Exp., 2013, 78, 50067.