A critical current density on stripping is identified that results in dendrite formation on plating and cell failure. When the stripping current density removes Li from the interface faster than it ...can be replenished, voids form in the Li at the interface and accumulate on cycling, increasing the local current density at the interface and ultimately leading to dendrite formation on plating, short circuit and cell death. This occurs even when the overall current density is considerably below the threshold for dendrite formation on plating. For the Li/Li
PS
Cl/Li cell, this is 0.2 and 1.0 mA cm
at 3 and 7 MPa pressure, respectively, compared with a critical current for plating of 2.0 mA cm
at both 3 and 7 MPa. The pressure dependence on stripping indicates that creep rather than Li diffusion is the dominant mechanism transporting Li to the interface. The critical stripping current is a major factor limiting the power density of Li anode solid-state cells. Considerable pressure may be required to achieve even modest power densities in solid-state cells.
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EMUNI, FIS, FZAB, GEOZS, GIS, IJS, IMTLJ, KILJ, KISLJ, MFDPS, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, SBMB, SBNM, UKNU, UL, UM, UPUK, VKSCE, ZAGLJ
All-solid-state batteries potentially offer safe, high-energy-density electrochemical energy storage, yet are plagued with issues surrounding Li microstructural growth and subsequent cell death. We ...use 7Li NMR chemical shift imaging and electron microscopy to track Li microstructural growth in the garnet-type solid electrolyte, Li6.5La3Zr1.5Ta0.5O12. Here, we follow the early stages of Li microstructural growth during galvanostatic cycling, from the formation of Li on the electrode surface to dendritic Li connecting both electrodes in symmetrical cells, and correlate these changes with alterations observed in the voltage profiles during cycling and impedance measurements. During these experiments, we observe transformations at both the stripping and plating interfaces, indicating heterogeneities in both Li removal and deposition. At low current densities, 7Li magnetic resonance imaging detects the formation of Li microstructures in cells before short-circuits are observed and allows changes in the electrochemical profiles to be rationalized.
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IJS, KILJ, NUK, PNG, UL, UM
Hybrid solid electrolytes, composed of 3D ordered bicontinuous conducting ceramic and insulating polymer microchannels are reported. The ceramic channels provide continuous, uninterrupted pathways, ...maintaining high ionic conductivity between the electrodes, while the polymer channels permit improvement of the mechanical properties from that of the ceramic alone, in particular mitigation of the ceramic brittleness. The conductivity of a ceramic electrolyte is usually limited by resistance at the grain boundaries, necessitating dense ceramics. The conductivity of the 3D ordered hybrid is reduced by only the volume fraction occupied by the ceramic, demonstrating that the ceramic channels can be sintered to high density similar to a dense ceramic disk. The hybrid electrolytes are demonstrated using the ceramic lithium ion conductor Li 1.4 Al 0.4 Ge 1.6 (PO 4 ) 3 (LAGP). Structured LAGP 3D scaffolds with empty channels were prepared by negative replication of a 3D printed polymer template. Filling the empty channels with non-conducting polypropylene (PP) or epoxy polymer (epoxy) creates the structured hybrid electrolytes with 3D bicontinuous ceramic and polymer microchannels. Printed templating permits precise control of the ceramic to polymer ratio and the microarchitecture; as demonstrated by the formation of cubic, gyroidal, diamond and spinodal (bijel) structures. The electrical and mechanical properties depend on the microarchitecture, the gyroid filled with epoxy giving the best combination of conductivity and mechanical properties. An ionic conductivity of 1.6 × 10 −4 S cm −1 at room temperature was obtained, reduced from the conductivity of a sintered LAGP pellet only by the volume fraction occupied by the ceramic. The mechanical properties of the gyroid LAGP–epoxy electrolyte demonstrate up to 28% higher compressive failure strain and up to five times the flexural failure strain of a LAGP pellet before rupture. Notably, this demonstrates that ordered ceramic and polymer hybrid electrolytes can have superior mechanical properties without significantly compromising ionic conductivity, which addresses one of the key challenges for all-solid-state batteries.
•A low-cost, high productivity fabrication route was developed for LiCoO2 thin films.•Waspaloy substrates, Ar process gas, a powder target and 600 °C annealing were used.•Films of ∼3 μm thickness ...were deposited at a rate of ∼700–790 nm h−1.•The maximum discharge capacity in an organic liquid electrolyte was 62 µAh cm−2µm−1.•The cells fabricated were able to deliver capacity at rates up to 2 C.
A radio frequency (RF) magnetron sputter deposition process designed for low-cost, high-rate fabrication of LiCoO2 (LCO) thin films was developed and used to fabricate approximately phase pure cathodes with the R3¯m crystal structure, strong (104) preferred orientation and high discharge capacities. Starting from a typical set of processing conditions for LCO films, the values of key deposition and post-deposition parameters were systematically changed to increase the deposition rate, simplify the sputter deposition process and minimize process gas use without compromising the structural properties and electrochemical performance. Cathodes were deposited onto Waspaloy (58Ni-19Cr-14Co-Mo-Ti-Al-Fe wt%) foil current collectors to provide enhanced thermal stability during post-deposition annealing. The best properties were attained using a process pressure of 0.5 Pa, an RF power density of 5.5 W cm−2 and a post-deposition anneal in air at 600 °C for 2 h. A sintered sputter target, oxygen gas flow and substrate heating were not required. This set of conditions resulted in a high deposition rate of ∼700–790 nm h−1, allowing the formation of a relatively thick (∼2.8–3.2 µm) film in 4 h. Furthermore, high maximum specific and areal discharge capacities of 132 mAh g−1 / 62 µAh cm−2µm−1 and 172 μAh cm−2 were attained during galvanostatic cycling at a rate of 0.1 C with an organic liquid electrolyte, which are among the highest values reported. Cycling rate tests showed that the thin-film LCO cathodes could deliver capacity up to a cycling rate of at least 2 C without causing any significant cell damage.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Degradation of lithium ion (Li-ion) cells affects both performance and safety of Li-ion batteries. In order to avoid potential safety hazards, it is crucial to detect the onset and extent of critical ...degradation modes in commercial Li-ion cells. This work demonstrates the application of a diagnostic algorithm to identify and quantify degradation modes of commercial Li-ion pouch cells cycled at − 10°C and a C-rate of 2 C. Rapid loss of active negative electrode material was successfully identified and results were validated using 3-electrode cells, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDX). The positive electrode material was less strongly affected by the tests, as found by the diagnostic algorithm and confirmed with EDX and SEM results.
Nitrogenous solid electrolytes such as lithium phosphorus oxynitride (LiPON) have effectual interfacial compatibility with lithium metal; in part, this has enabled the development of thin-film ...solid-state batteries with excellent long-term cycling performance. However, most known nitrogen-containing solid electrolytes lack the ionic conductivity required for high-power/high-capacity batteries; therefore, the development of new nitrogenous solid electrolytes with increased ionic conductivity is highly desirable. The mechanical milling of lithium nitride (Li3N) with phosphorus pentasulfide (P2S5) has previously been reported to produce amorphous lithium-ion conductors, but the composition of these materials and the reactions occurring during the milling processes were hitherto undetermined. Here, we show that mechanochemically milled Li3N·P2S5 solid electrolytes contain less nitrogen than expected as N2 gas is released during an early stage of the ball milling process. Li3N·P2S5 solid electrolytes are mixtures composed of multiple lithium thiophosphates, lithium sulfide, and red phosphorus. We show that amorphous Li3PS4 is responsible for the ionic conductivity of Li3N·P2S5 electrolytes produced by ball milling.
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IJS, KILJ, NUK, PNG, UL, UM
All-solid-state batteries potentially offer safe, high-energy-density electrochemical energy storage, yet are plagued with issues surrounding Li microstructural growth and subsequent cell death. We ...use
Li NMR chemical shift imaging and electron microscopy to track Li microstructural growth in the garnet-type solid electrolyte, Li
La
Zr
Ta
O
. Here, we follow the early stages of Li microstructural growth during galvanostatic cycling, from the formation of Li on the electrode surface to dendritic Li connecting both electrodes in symmetrical cells, and correlate these changes with alterations observed in the voltage profiles during cycling and impedance measurements. During these experiments, we observe transformations at both the stripping and plating interfaces, indicating heterogeneities in both Li removal and deposition. At low current densities,
Li magnetic resonance imaging detects the formation of Li microstructures in cells before short-circuits are observed and allows changes in the electrochemical profiles to be rationalized.
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IJS, KILJ, NUK, PNG, UL, UM
The potential of all-solid-state batteries with lithium metal anodes to be safer, more energy dense and better performing energy storage devices than current lithium ion batteries has led to a major ...drive in developing solid electrolytes that combine high ionic conductivity with suitable interfacial and mechanical properties. This work analyses the electrochemical and mechanical properties of two ceramic solid electrolytes, Li1.4Al0.4Ge1.6(PO4)3 (LAGP) and Li6.5La3Zr1.5Ta0.5O12 (LLZTO), and their interfacial behaviour with a lithium metal anode. A novel synthetic route to a 3D hybrid solid electrolyte with tuneable properties and a new approach to diagnose cell failure in all-solid-state batteries are presented. A hybrid electrolyte with 3D bicontinuous ordered ceramic and polymer microchannels was successfully synthesised using 3D printing. While the ceramic solid electrolyte channels enable high ionic conduction pathways, the presence of non-conductive polymer channels provides the hybrid with structural stability and resilience to fracture. Full control of the hybrid's parameters such as the choice of ceramic electrolyte, polymer, microarchitecture and ceramic-to-polymer ratio was demonstrated. The LAGP-epoxy hybrid electrolyte with a gyroid microarchitecture achieved the highest ionic conductivity of 1.6 x 10-4 S·cm-1, which is only lowered by the volume of non-conductive polymer present and the channel tortuosity. The favourable combination of the epoxy polymer's fracture strength and the 'easy-to-fill' gyroid channels, improved the hybrid's electrochemical and mechanical performance compared to a LAGP pellet. The variation of the ceramic electrolyte and the microarchitecture influence the hybrid's electrochemical properties, while the polymer volume fraction provides a suitable 3D backbone to increase the hybrid's mechanical stability and cycle life. Despite the sintering challenges of LLZTO, a possible synthetic route to generate LLZTO-epoxy hybrid electrolytes was also demonstrated. Additionally, inhibiting lithium dendrite growth in LLZTO and other solid electrolytes is another vital challenge. Hence, this work also presents a new method to diagnose dendrite growth by combining galvanostatic cycling with ex-situ magnetic resonance imaging. This approach allowed the identification of lithium dendrites in short-circuit cells and monitoring of their location in 3D space at different stages of cycling.
Hybrid solid electrolytes, composed of 3D ordered bicontinuous conducting ceramic and insulating polymer microchannels are reported. The ceramic channels provide continuous, uninterrupted pathways, ...maintaining high ionic conductivity between the electrodes, while the polymer channels permit improvement of the mechanical properties from that of the ceramic alone, in particular mitigation of the ceramic brittleness. The conductivity of a ceramic electrolyte is usually limited by resistance at the grain boundaries, necessitating dense ceramics. The conductivity of the 3D ordered hybrid is reduced by only the volume fraction occupied by the ceramic, demonstrating that the ceramic channels can be sintered to high density similar to a dense ceramic disk. The hybrid electrolytes are demonstrated using the ceramic lithium ion conductor Li
1.4
Al
0.4
Ge
1.6
(PO
4
)
3
(LAGP). Structured LAGP 3D scaffolds with empty channels were prepared by negative replication of a 3D printed polymer template. Filling the empty channels with non-conducting polypropylene (PP) or epoxy polymer (epoxy) creates the structured hybrid electrolytes with 3D bicontinuous ceramic and polymer microchannels. Printed templating permits precise control of the ceramic to polymer ratio and the microarchitecture; as demonstrated by the formation of cubic, gyroidal, diamond and spinodal (bijel) structures. The electrical and mechanical properties depend on the microarchitecture, the gyroid filled with epoxy giving the best combination of conductivity and mechanical properties. An ionic conductivity of 1.6 × 10
−4
S cm
−1
at room temperature was obtained, reduced from the conductivity of a sintered LAGP pellet only by the volume fraction occupied by the ceramic. The mechanical properties of the gyroid LAGP-epoxy electrolyte demonstrate up to 28% higher compressive failure strain and up to five times the flexural failure strain of a LAGP pellet before rupture. Notably, this demonstrates that ordered ceramic and polymer hybrid electrolytes can have superior mechanical properties without significantly compromising ionic conductivity, which addresses one of the key challenges for all-solid-state batteries.
A novel templating method to create 3D bicontinuous structured hybrid electrolytes with improved mechanical properties for all-solid-state lithium batteries.
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