1 | Negative Electrodes for Li-Ion Batteries: Beyond Carbon |
Phoebe K. Allan*,†, Nicolas Louvain‡,§ and Laure Monconduit‡,§,¶,||
*University of Cambridge, University Chemical Laboratory, Lensfield Road, Cambridge, CB2 1EW, UK
†Gonville and Caius College, Trinity Street, Cambridge, CB2 1TA, UK
‡Institut Charles Gerhardt de Montpellier (ICGM) — CNRS, France
§Réseau Français sur le Stockage Electrochimique de l’Energie (RS2E), CNRS FR3459, 33 Rue Saint Leu, 80039 Amiens Cedex, France
¶ALISTORE-ERI European Research Institute, FR CNRS 3104, F-80039 Amiens Cedex 1, France
List of Abbreviations
I.Introduction
II.Lithium Titanates
A.Introduction
B.The Li4Ti5O12 Structure
C.Lithium Insertion Properties
D.Electrochemical Properties
E.Disadvantages of Lithium Titanium Oxide as Electrode
1.The Gassing Problem
F.Improving the Performance of LTO
1.SEI Management
2.Surface Coatings
3.Tailoring Ionic and Electronic Conductivities
G.Critical Perspectives
III.p-Block Element–Based Electrodes
A.Silicon
1.Mechanisms of (De)Lithiation in Silicon Anodes
a.Atomistic-Scale Lithiation Mechanisms
b.Electrode-Scale Lithiation Mechanisms
2.Failure mechanisms in silicon electrodes
a.Volume Expansion on Lithiation
b.Issues Relating to the SEI
3.Improving the Cyclability of Silicon Electrodes
a.Electrode Formulation
b.Nanosizing Electrode Particles
c.Electrode Coating and Electrolyte Additives
d.Association with Inactive Species
B.Other p-block Elements: Antimony, Tin, and Germanium
1.Tin
2.Antimony
3.Germanium
4.Improving the Performance of Tin, Antimony, and Germanium
a.Binary, Ternary Alloys, SnSb, TiSnSb
IV.Summary and Conclusions
V.References
List of Abbreviations
| C/x | charge rate such that the full capacity is reached in x hours |
| CMC | carboxymethyl cellulose |
| CVD | chemical vapor deposition |
| DEC | dimethyl ethyl carbonate |
| DFT | density functional theory |
| DMC | dimethyl carbonate |
| EC | ethylene carbonate |
| FEC | fluroethylcarbonate |
| FIB | focused ion beam |
| GITT | galvanostatic intermittent titration technique |
| LCO | LiCoO2 |
| LIB | lithium-ion battery |
| LMO | LiMn2O4 |
| LTO | Li4Ti5O12 |
| NMR | nuclear magnetic resonance |
| OCV | open-circuit voltage |
| PAA | polyacrylic acid |
| PC | propylene carbonate |
| PDF | pair function distribution |
| PTSI | p-toluenesulfonyl isocyanate |
| PVDF | polyvinylidene fluoride |
| SEI | solid-electrolyte interphase |
| SFG-VS | sum frequency generation vibrational spectroscopy |
| TEM | transmission electron microscopy |
| ToF-SIMS | time-of-flight secondary ion mass spectrometer |
| XPS | X-ray photoelectron spectroscopy |
| XRD | X-ray diffraction |
I.Introduction
Conventional lithium-ion batteries (LIBs) are composed of a layered LiCoOx material cathode and a carbon/graphite anode. Graphite has a layered structure and can be electrochemically reduced in an aprotic organic electrolyte containing lithium salts. Lithium is intercalated between the layers of graphite to form a Li–C alloy. The carbon/graphite anode possesses a theoretical specific capacity of 372 mAh·g−1 according to the following lithium intercalation equation:
Li+ + e− + C6 ↔ LiC6
In the LiCoO2/graphite full-cell system, the overall cell reaction is as follows:
LiCoO2 + Lin-xC ↔ Li1-xCoO2 + LinC
This equation indicates that the cell reaction is a simple migration of lithium ions between positive and negative electrodes. Nevertheless, the lithium intercalation primarily occurs at a voltage below 0.1 V versus Li+/Li, close to the lithium electroplating potential.1 For high discharge rates, and harsh operating conditions, graphite electrode can be polarized to such an extent that reactive lithium metal dendrites may grow on the electrode surface and sporadically cause “soft” short circuiting of the cell.2
New electrode materials that can improve the performance and cycle life of LIB have been extensively explored. As part of this, considerable effort has been directed toward developing alternative negative electrodes that are able to deliver higher capacities and higher energies than graphite electrodes, particularly when charged at high rates.3 The reader is pointed toward several reviews that extensively explore the range of materials proposed by researchers to replace graphite in future batteries.4–6 This chapter describes some of the most promising alternative materials proposed to date: (1) titanates, a material undergoing typical intercalation reactions, and (2) metals and semimetals, which form alloys electrochemically, such as silicon, tin, or antimony.
This study describe how the utilization of advanced characterization tools and theoretical calculations have informed researchers about how these materials behave electrochemically and how improvements in understanding of failure mechanisms of cells are able to suggest directions for improving their electrochemical performance.
II.Lithium Titanates
A.Introduction
Titanium oxides, both those that contain lithium in their starting composition and those that do not, have been proposed as an alternative to carbon/graphite electrodes in LIBs in order to improve specific capacities, high-rate cyclability, and safety.3,7–9 These materials store lithium through intercalation of lithium into the structure and reduction and oxidation of the titanium during lithiation and delithiation, respectively. This intercalation mechanism is analogous to that of metal oxide cathodes such as LiCoO2, but takes place at lower voltages. In a full-cell configuration, lithium removed from the LiCoO2 cathode is inserted into the titanate host; while the cobalt ions are oxidized, the titanium ions are simultaneously reduced. Among lithium titanium oxides, spinel Li4Ti5O12 (LTO) is one of the most studied electrode materials as a potential carbon/graphite replacement in LIBs for power applications such as electric vehicles.8,9 Lithium-free titanium oxides, TiO2, are still considerably investigated as electrode materials,10 while their use in commercial lithium-ion systems might appear unfavorable because of high potential and unlithiated negative.11
LTO is a lithium intercalation compound with an average lithium insertion/deinsertion voltage close to 1.55 V versus Li+/Li.9 This is a relatively high voltage for a negative electrode, and this suggests that lithium dendrites formation and the organic el...