7TH INTL. SYMP. ON SUSTAINABLE SECONDARY BATTERY MANUFACTURING AND RECYCLING

The invention of ¹⁴C-based solid state diamond power-cells offers unique opportunities for demonstrating a circular economy in relation to fissile energy production; and closed-loop recycling of these ¹⁴C Diamond Betavoltaic Batteries (C14-DBB). The extremely long half-life of the radioisotope ¹⁴C on a human time scale, 5730 ± 40 years, means that the power output of a C14-DBB is constant from any practical power engineering perspective. The durability of a diamond crystal on geological time scales is quite long and is the result of strong covalent bonds between carbon atoms. ¹⁴C as a beta emitter has a maximum decay energy of 156 keV and a weighted mean energy of 49.5 keV, insufficient to break the covalent bonds and therefore preserving integrity of the crystal over the entire “discharge” period/half-life of the C14-DBB.
Whether as back-up cells for real-time clocks (RTC), volatile memory, infrastructural health monitoring, medical implants, or any other use case, this class of betavoltaics will outlive any foreseeable engineering application they are used in. An examination of the socio-economic, ecological, and regulatory interplay in relation to the use and life cycle of a ¹⁴C-based diamond is meant to demonstrate the applicability of closed-loop circular economy as applied to the nuclear sector as a first of a kind demonstrator of how fissile energy production can operate in a closed-loop circular economy, not just as a means of producing energy with a significant waste stream, but a holistically integrated cycle. As a part of this cycle we demonstrate the utility of harvesting feedstock for radiovoltaics. In the next step we demonstrate the incentive to collect and recycle ¹⁴C-based C14-DBB’s thus completing a closed-loop economic cycle wherein the derivative waste stream from fissile energy production is reutilised and recycled. Though this approach is not a panacea solution for how to deal with the end state waste from fissile energy production, it is our hope that this first demonstration will evince new investigations along similar lines to make maximum use of every part of the process thus converting the entire value chain to a wholly integrated and cyclical ‘value constellation’ relating to fissile energy production.
In this work, we specifically present a novel process flow to identify and recover C14-DBB’s from Waste Electrical and Electronic (WEE) appliances repurposing the ¹⁴C-diamond into new C14-DBBs. The process uses machine vision to detect C14-DBBs on Printed Circuit Boards (PCB) using inspection cameras, and fiducial marks from the SMD assembly process to calculate the exact location of the C14-DBB on the PCB. It is then recovered using selective hot air de-soldering. Electrical contacts and package are removed in a nitric acid bath to expose the C14-DBB and recover it in a controlled environment. The ¹⁴C-diamond is packaged inside a layer of non-active ¹²C-diamond, so no radioactivity is exposed at any point in the recycling process. It is inspected using surface analysis techniques before new ohmic contacts are applied and an electrical check is performed using a flying probe tester. The recovered diamond is finally repackaged as a repurposed C14-DBB device, and valuable metals are recovered from the nitric acid solution for re-used after electro-filtration and purification.

The study of surfaces and interfaces is one of the main fields of material science. This domain requires specific techniques of surface analysis such as X-ray Photoelectron Spectroscopy (XPS), Auger Electron Spectroscopy (AES), Secondary Ion Mass spectrometry (TOF-SIMS) or Scanning Probe Microscopies (AFM – STM). In this field, redox processes and surface and interface phenomena (usually linked) occurring in Li(Na, Mg, K….) batteries during cycling (including liquid or solid electrolyte) play a key role for their performances as well. Solid Electrolyte Interphase (SEI) formed upon cycling leads to a double-edged problematic: its formation lowers the coulombic efficiency and causes irreversible capacity loss, but it also passivates the electrode from the electrolyte and prevents further aging processes.
Several systems were considered in this keynote to illustrate the relevance of such surface analyses in the understanding of redox phenomena in batteries:
 First is the study of Full cells as Li4Ti5O12(LTO)/LiNi3/5Co1/5Mn1/5O2 (NMC) and LTO/LiMn2O4 (LMO). The interactions between the two electrodes during cycling are investigated, especially the deposition and insertion of metallic compounds within the LTO electrode, which can directly influence on the stability of the cells and their electrochemical performances. More specifically, we focus this presentation on the results obtained by Time-of-Flight Secondary Ion Mass Spectrometry (ToF-SIMS) which could give in-depth elemental and molecular information about the interfacial layers through sputter-depth-profiling experiments. Thanks to a high sensitivity and 2 D and 3D imaging capability, it will be particularly useful to follow the deposition of low amounts of metallic species and especially manganese within the SEI layer. Moreover, the evolution of the SEI chemical composition and spatial distribution upon cycling is also reported to better understand the protective role of the SEI.

 Secondly, innovative K-ion batteries were considered; potassium is a promising alternative to lithium as K i) is much more abundant than lithium in the earth's crust and concomitantly much cheaper ; ii) has a low redox potential in non-aqueous solvent so that high voltage is expected and iii) has the lowest Lewis acidity and desolvation energy (compared to Na+ and Li+), which should lead to higher ionic conductivity and faster electrode/electrolyte interface diffusion kinetics so that high power potassium-ion batteries (KIBs) are expected.
However, for the practical use of KIBs, high energy density cathode materials are required. In that direction, polyanionic compounds offer various structural frameworks working at high voltage. Among them, KVPO4F showed reversible capacity up to 105 mAh.g-1 with an average discharge potential of 4.3 V vs. K+/K with excellent rate performance. However, the exact electrochemical redox processes of KxVPO4F remains to be better understood, especially above 4.5 V (i.e. from x=0.5 to x=0), to further improve its electrochemical performance.To fill this gap, the carbon-coating impact of the KVPO4F material on the electrolyte reactivity and the polarization will first be presented. Then, the vanadium average oxidation state of KxVPO4F-C was followed upon charge/discharge in half cell using X-ray photoelectron spectroscopy. Importantly, it will be shown that the obtained results not only validate the occurrence of a redox process from x=0.5 to x=0 but also provide the extent of this process, which was never reported before. Also, a severe electrolyte degradation issue above 4.5 V was observed.
IPREM-UPPA (FRANCE) Contributors : N.Gauthier, C. Courrèges, L. Madec, L.Caracciolo

The expansion of the electric vehicle market is expected to lead to the rapid growth of the lithium-ion battery market [1]. Accordingly, the amount of scrap is also expected to increase, so various attempts are being made to recover valuable metals (nickel, cobalt, etc.) from the scrap [2]. The methods include the pyrometallurgical process, hydrometallurgical process, and direct recycling process, and comparison of each process is also being discussed [3]. However, process development, such as mutual complement of the process, continues. We have investigated the continuous pilot testing of a solvent extraction process to recover nickel and cobalt from secondary battery scrap for the production of high purity nickel sulfate and cobalt sulfate for secondary batteries.
The solvent extraction process is composed of three different solvent extraction processes, and each solvent extraction process is generally composed of extraction, scrubbing, and stripping step. The continuous process was operated for about 200 hours, and the steady state of the process was confirmed through pH observation and quantitative analysis of components, and stability of the process was secured through continuous operation.

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