Challenges and prospects of the role of solid electrolytes in the revitalization of lithium metal batteries

The scientific community is continuously committed to the search for new high energy electrochemical storage devices. In this regard, lithium metal batteries, due to their very high electrochemical energy storage capacity, appear to be a highly appealing choice. Unfortunately, the use of lithium metal as the anode may lead to some safety hazards due to its uneven deposition upon charging, resulting in dendrite growth and eventual shorting of the battery. This issue may be successfully addressed by using intrinsically safer electrolytes capable of establishing a physical barrier at the electrode interface. The most promising candidates are solid electrolytes, either polymeric or inorganic. The main purpose of this review is to describe the present status of worldwide research on these electrolyte materials together with a critical discussion of their transport properties and compatibility with metallic lithium, hoping to provide some general guidelines for the development of innovative and safe lithium metal batterie

How much does size really matter? Exploring the limits of graphene as Li ion battery anode material

Abstract We unravel the role of flake dimensionality on the lithiation/de-lithiation processes and electrochemical performance of anodes based on few-(FLG) and multi-layer graphene (MLG) flakes prepared by liquid phase exfoliation (LPE) of pristine graphite. The flakes are sorted by lateral size (from 380 to 75 nm) and thickness from 20 (MLG) to 2 nm (FLG) exploiting a sedimentation-based separation in centrifugal field and, finally, deposited onto Cu disks for the realization of four binder-free anodes. The electrochemical results show that decreasing lateral size and thickness leads to an increase of the initial specific capacity from ≈590 to ≈1270mAhg −1 . However, an increasing irreversible capacity is also associated to the reduction of flakes' size. We find, in addition, that the preferential Li ions storage by adsorption rather than intercalation in small lateral size

RICERCA DI SISTEMA ELETTRICO. Ricerca di materiali anodici per batterie litio ione operanti in elettroliti organici convenzionali di più elevata energia rispetto a quelle sul mercato

Il rapporto descrive il lavoro svolto per la preparazione e caratterizzazione di anodi per batterie litio ione costituiti da metalli (Si, Sn, Sb) capaci di formare leghe del tipo LixM con il litio secondo la reazione elettrochimicamente reversibile x Li+ + x e- + M LixM dove x può assumere valori pari a 4.4 per Sn e Si e 3 per Sb con capacità teoriche pari a 993 mAh/g, 4200 mAh/g e 660 mAh/g rispettivamente. I problemi degli elettrodi costituiti da leghe metalliche sono essenzialmente dovuti alle variazioni di volume durante i processi di formazione delle leghe che possono raggiungere valori dell’ordine del 300% (Sn), 360 % (Si) e 200 % (Sb). Le variazioni di volume inducono stress meccanici sugli elettrodi che polverizzano progressivamente con rapida perdita di capacità. In letteratura si trovano moltissimi lavori in cui gli stress meccanici sono tamponati preparando elettrodi compositi nei quali le particelle metalliche sono supportate su matrici di varia natura capaci di compensare le variazioni di volume [1]. Sulla base di recenti lavori di letteratura [2-6] durante questa ricerca è stato utilizzato grafene come supporto per le particelle metalliche. Dal punto di vista strutturale il grafene (GNS) corrisponde a grafite completamente esfoliata: array bidimensionale di atomi di carbonio ibridizzati sp2 con uno spessore di un atomo. In quanto tale può essere considerato come il mattone fondamentale per tutte le forme allotropiche dei fullereni (buckyball, carbon nanotubes etc.) [7]. Proprietà fondamentali del grafene sono: (i) elevata area superficiale( 2630 m2/g), (ii) elevatissima conducibilità ( 64 mS cm-1 circa 60 volte quella dei nanotubi). Nel caso oggetto di questa ricerca nei compositi M/grafene, il grafene serve sia come materiale ad elevata conducibilità elettronica, sia come materiale che può intercalare litio ed allo stesso tempo può agire da tampone per minimizzare gli stress meccanici durante i processi di formazione/dissoluzione delle leghe metalliche. La sintesi dei nano compositi grafene-metallo è stata effettuata mediante impregnazione di grafene ossido (GO), preparato in laboratorio, con diversi tipi di sali. I gruppi funzionali (-OH, -COOH, -OOH) presenti sul GO possono ancorare per coordinazione gli ioni metallici che per successiva riduzione danno origine a nanoparticelle [6]. La procedura di preparazione è stata compiuta aggiungendo un sale ad una sospensione di GO in glicole etilenico. La sospensione è stata successivamente trattata con microonde. Il trattamento determina la riduzione del GO a RGO (Reduced Graphene Oxide) e la formazione di metalli ed ossidi metallici. A causa della disposizione casuale dei gruppi funzionali nel GO, le particelle risultanti sono uniformemente distribuite nella matrice di RGO che funziona da tampone per le variazioni di volume. Le polveri così ottenute sono state caratterizzate mediante SEM, TEM, XRD ed utilizzate per la preparazione degli elettrodi con tecnica doctor-blade. I test elettrochimici sono stati condotti in celle a T con Li metallico come contro-elettrodo ed elettrodo di riferimento, fibra di vetro imbevuta con una soluzione 1M di LiPF6 in etilene carbonato/dimetile carbonato 1:1 in peso, (Merck LP30) come separatore. Le capacità specifiche ottenute a velocità di carica e scarica dell’ordine dei 100 mAh/g sono risultate pari a 600, 1000 e 400 per compositi di Sn, Si e Sb, rispettivamente

Students’ Confidence and Interest in Palliative and Bereavement Care: A European Study

As part of a European Erasmus Plus project entitled Death Education for Palliative Psychology, this study assessed the ways in which Master’s Degree students in psychology and the creative arts therapies self-rated their confidence and interest in death education and palliative and bereavement care. In five countries (Austria, Israel, Italy, Poland, Romania), 344 students completed an online questionnaire, and 37 students were interviewed to better understand their views, interest, and confidence. The results revealed some significant differences between countries, and showed that older respondents with previous experience as formal caregivers for end-of-life clients showed greater interest in obtaining practical clinical competence in these fields. A mediation analysis indicated that students’ previous care experiences and past loss experiences were related to students’ current interest in death education and palliative and bereavement care through the mediation of their sense of confidence in this field. The qualitative findings identified five shared themes: life and death, learning about death, the psychological burden, personal experience and robust training, and four key training needs. Overall, students’ interest in studying and working with terminal illness and death are rooted in internal resources, a preliminary sense of confidence, but also external requirements

Ultrahigh Surface Area Three-Dimensional Porous Graphitic Carbon from Conjugated Polymeric Molecular Framework

Porous graphitic carbon is essential for many applications such as energy storage devices, catalysts, and sorbents. However, current graphitic carbons are limited by low conductivity, low surface area, and ineffective pore structure. Here we report a scalable synthesis of porous graphitic carbons using a conjugated polymeric molecular framework as precursor. The multivalent cross-linker and rigid conjugated framework help to maintain micro- and mesoporous structures, while promoting graphitization during carbonization and chemical activation. The above unique design results in a class of highly graphitic carbons at temperature as low as 800 ??C with record-high surface area (4073 m2 g-1), large pore volume (2.26 cm-3), and hierarchical pore architecture. Such carbons simultaneously exhibit electrical conductivity >3 times more than activated carbons, very high electrochemical activity at high mass loading, and high stability, as demonstrated by supercapacitors and lithium-sulfur batteries with excellent performance. Moreover, the synthesis can be readily tuned to make a broad range of graphitic carbons with desired structures and compositions for many applications.clos

Li1.5La1.5MO6 (M = W6+, Te6+) as a new series of lithium-rich double perovskites for all-solid-state lithium-ion batteries

Solid-state batteries are a proposed route to safely achieving high energy densities, yet this architecture faces challenges arising from interfacial issues between the electrode and solid electrolyte. Here we develop a novel family of double perovskites, Li1.5La1.5MO6 (M = W6+, Te6+), where an uncommon lithium-ion distribution enables macroscopic ion diffusion and tailored design of the composition allows us to switch functionality to either a negative electrode or a solid electrolyte. Introduction of tungsten allows reversible lithium-ion intercalation below 1 V, enabling application as an anode (initial specific capacity >200 mAh g-1 with remarkably low volume change of ∼0.2%). By contrast, substitution of tungsten with tellurium induces redox stability, directing the functionality of the perovskite towards a solid-state electrolyte with electrochemical stability up to 5 V and a low activation energy barrier (<0.2 eV) for microscopic lithium-ion diffusion. Characterisation across multiple length- and time-scales allows interrogation of the structure-property relationships in these materials and preliminary examination of a solid-state cell employing both compositions suggests lattice-matching avenues show promise for all-solid-state batteries

INFORME SOBRE LA PARTICIPACION EN LA QUINTA REUNION DE GEOLOGOS DE AMERICA CENTRAL EN MANAGUA. NICARAGUA

Esta nota corresponde a un informe sobre la participación en la quinta Reunión de Geólogos de América Central en Managua, Nicaragua

Graphene/silicon nanocomposite anode with enhanced electrochemical stability for lithium-ion battery applications

A graphene/silicon nanocomposite has been synthesized using a green approach during both synthesis and electrode processing. It has been characterized and tested as anode active material for lithium-ion batteries. The synthesis was performed by dispersing silicon nanoparticles in a carbonaceous matrix, obtained by a dual step reduction process of a previously functionalized graphene oxide substrate which avoids the formation of aggregates of Si particles and partially buffers the huge volume variations associated with Li/Si alloying processes. The graphene oxide matrix functionalization was achieved using low-molecular weight polyacrylic acid and a low-cost and eco-friendly solvent like ethylene glycol. As concerns electrode processing, composite anodes were prepared using high-molecular PolyAcrylic Acid as green binder and using ethanol as non- toxic and cheap solvent, thus avoiding the standard PVDF/NMP system which is, on the other hand, toxic and highly expensive. Furthermore, Vinylene Carbonate (VC) was used as electrolyte additive. Long cycling performance was evaluated at a current of 500 mAg-1 : after 100 cycles the anode showed a discharge capacity retention of about 80%. Analyzing the impedance spectra of the tested cells, the beneficial effect of the VC additive was showed in terms of lower SEI resistance in the long term

A Silicon/Graphene Composite Anode for High-Efficiency Lithium Batteries

Composite anodes based on Si and reduced graphene oxide (RGO) have been prepared using commercial Si nanopowder, graphene oxide (GO) and polyacrilic acid (PAA) as starting materials. A double reduction step, consisting in microwave irradiation at mild power followed by thermal annealing in reducing atmosphere, yielded the composite powder made of Si:reduced graphene oxide (RGO) in the approximate mass ratio 30:70. The charge/discharge properties of the anode materials are determined by the homogeneous dispersion of Si grains between RGO nanosheets, that act as structural buffer for volume changes related to Li-Si reversible alloying and as improved electrical conductor. Electrodes have been prepared using high-molecular weight PAA as binder, which promises better mechanical stability towards silicon volume changes. The electrochemical behavior of the composite anode material has been characterized by galvanostatic cyclations and electrochemical impedance spectroscopy, using LiPF61M in EC:DMC 1:1 electrolyte, also modified by the addition of 5% vinylene carbonate (VC). Several anodes have been investigated, consistently delivering reversible capacities higher than 1000 mAhg- 1, with a mechanism that, after initial lithiation of crystalline Si, mainly involves reversible Li-Si alloying/dealloying between amorphous a-Li and a-LixSi phases. Particularly, when cycled in VC-modified electrolyte the anode exhibits a remarkable cycle life, resulting in a residual capacity of more than 900 mAhg- 1 after 60 cycles at 500 mAg-1 and efficiency values close to unity. Several factors concur in determining this behavior, namely: (i) the efficient Si dispersion in RGO carbonaceous matrix; (ii) the good mechanical properties of PAA binder; (iii) the formation of a stabilized SEI by VC additive in the electrolyte