Intercalation Compounds

Intercalation Compounds: ... solving the problem of dendrite growth. ... used in the first marketed rechargeable lithium battery (Exxon)...

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Laurea Magistrale in Scienza dei Materiali

Materiali Inorganici Funzionali

Intercalation Compounds:

Functional materials with high efficiency energy storage and conversion for batteries

Prof. Antonella Glisenti - Dip. Scienze Chimiche - Università degli Studi di Padova

Bibliography 1. J.-M.Tarascon et al Nature 414 (2001) 359 2. Y. Wang et al. Adv. Mater 20 (2008) 2251 3. B. Peng et al. Coord. Chem. Rev. 253 (2009) 2805 4. Broussely et al Electrochem. Acta. 45 (1999) 3

COMPARISON AMONG SYSTEMS

ENERGY CONTENT OF SYSTEMS Specific energy = Wh/kg (gravimetric) Energy density = Wh/L (volumetric) RATE CAPABILITY Specific power = W/kg Power density = W/L. RAGONE DIAGRAMS  FC = high-energy systems  Supercapacitors = high-power Systems  Batteries = intermediate power and energy

Why Li?

Secondary/rechargeable

 lithium-ion (Li-ion)  magnesium-ion  nickel/metal hydride (Ni-MH),

Schematic diagram showing energy densities and how they correlate with periodic table

 highest capacity is 26,590mAh/g from H to H+ in the electrode process of hydrogen fuel cells  Li = lightest metal (specific gravity 0.53 g/cm3), good energy carrier, theoretical capacity up to 3860mAh/g  Similarly, magnesium is another alternative lightweight element.  Good transportation properties of ions with small radius

Comparison of the different battery technologies in terms of volumetric and gravimetric energy density.

1. high electrochemical capacity 2. high energy density 3. no memory effect 4. long cycle life Anode:carbon material (graphite) Cathode: lithium metal oxide (LiCoO2, LiMn2O4, LiFePO4, etc.) Electrolyte: LiPF6 in ethylene carbonate–diethylcarbonate.

- Li intercalates into the carbon layer to form LixC alloy (theoretical

specific capacity = 372 mA h g-1 (C6Li), potential < 0.5 V vs Li+/Li The practical performance of carbonaceous materials strongly depends on their crystallinity, microstructure and morphology.

+ Lithiated transition metal oxide (LiCoO2, voltage approaching 4 V, specific energy 1017 W h/kg)

Further advancements Limited capacity Lack of shape flexibility Safety problems.

Battery charging Li ions de-intercalated from the cathode, pass across the electrolyte, and intercalated between the graphite layers in the anode to form LixC alloys. Battery discharging Reverses the process

The Early Days 1. 1962: The first paper on lithium battery Electrochemical Society Fall Meeting - Chilton and (Lockheed Missile and Space Co.) “Lithium Nonaqueous Secondary Batteries” for long life battery of satellites

Cook

cycle

2. 1972 – The concept of electrochemical intercalation and its potential use were clearly defined

3. 1972 – Exxon: large project using TiS2 as the positive electrode – Li perchlorate in dioxolane as the electrolyte Li metal as anode – 4. 1972 Bell Labs: Heavier chalcogenides (higher capacities and voltages) Oxide instead of chalcogenides 5. End of 1980s early 1990s Li substitution by Li+ (Murphy and Sacrosati) – To compensate for the increase of potential of the negative electrode: more oxidizing species for positive electrode)

Voltage versus capacity for positive- and negative-electrode materials presently used or under serious considerations for the next generation of rechargeable Li-based cells. The output voltage values for Li-ion cells or Li-metal cells are represented. Note the huge difference in capacity between Li metal and the other negative electrodes, which is the reason why there is still great interest in solving the problem of dendrite growth.

1. Corrosion 2. Dendrits 3. Volume/shape modification 4. Stability vs time

Schematic representation and principles of Li batteries. a, Rechargeable Li-metal battery b, Rechargeable Li-ion battery

operating

A different approach: non liquid electrolytes Replacing the liquid electrolyte by a dry polymer electrolyte (LiSPE) Technology restricted to large and not portable devices (temperatures up to 80°C required) Pure (dry) polymer consisting of chains, through which the Li ions (red) move assisted by the motion of polymer chains. Li-Hybrid Polymer Electrolyte Battery (Li-HPE) –A hybrid (gel) network consisting of a semicrystalline polymer, whose amorphous regions are swollen in a liquid electrolyte, while the crystalline regions enhance the mechanical stability. Membrane based A poly-olefin membrane in which the liquid electrolyte is held by capillaries.

The Early Days 7. 1991. Sony Corporation – The first cell C/LiCoO2 Li-ion cell with a potential exceeding 3.6 V and gravimetric energy density = 120-150 W h/kg

CATHODE MATERIALS  Layered TiS2: the most popular.  high drain capability  good reversibility  used in the first marketed rechargeable lithium battery (Exxon)  Layered NiPS2  Layered NbSe3 (at the development stage)  Layered MoS2 (until the beginning of mass production)  Metal Oxides MoO3 (1971) WO3  Mizushima and Goodenough: LixCoO2, LixMiO2 (1980)  LiMn2O4 a competitive material especially attractive for its potential low cost

LiCoO2, LiNiO2, and LiMn2O4  layered or tunneled structures = Li ions reversible intercalation-deintercalation  high stability to air and moisture  potential higher than 3V

LiCoO2  voltage approaching 4V  specific energy = 1017Wh/kg.

Crystal structure: Li-ion layers and CoO6 layers. The unit structure of the latter is an octahedron in which one Co atom is coordinated by six O atoms.

Crystal structures of LiCoO2. a = b = 2.9557(4) Å c = 14.532(3) Å; α=β=90◦ and γ=120◦; space group, R−3m;

SYNTHESIS:

 Solid state reaction  Wet chemistry methods complexation, …)

PERFORMANCE:    

(sol-gel,

4.1-4.2 V vs Li/Li+ Reversible specific capacity = 137-140 mAh/g Theoretical specific capacity= 238 mAh/g Excellent ciclability at RT for 0.5 < x < 1

DISVANTAGES:  expensive  toxic

Phospho-olivines and derived as cathodes LiFePO4  high lithium intercalation voltage (~3.5 V relative to lithium metal),

 high theoretical capacity (170 mA h g–1),

 low cost  ease of synthesis  stability when used with common organic electrolyte systems LOW ELECTRONIC CONDUCTIVITY COATING OR CO-SINTERING WITH C (additional processes, loss of energy density – inert additive as much as 30%) SELECTIVE DOPING

LiFePO4

 low toxicity  low cost  high thermal and chemical/electrochemical stability

Crystal structure:

Li ion, FeO6 irregular octahedron and PO4 tetrahedron (covalent). The six-coordinate Fe–O octahedron shares O atoms with a four-coordinate P–O tetrahedron to form a tunneled structure, and Li atoms lie inside the channels.

Crystal structures of LiFePO4: a = 10.3290(3) Å, b = 6.0065(2) Å, and c = 4.6908(2) Å; space group, Pnma;

Doped-phospho-olivines as Li storage electrodes Materials were synthesized as powders and densified compacts using the solid-state reaction of Li2CO3, NH4H2PO4, and FeC2O4⋅2H2O,with the dopant (Mg2+,Al3+,Ti4+,Zr4+,Nb5+ or W6+) being added as a metal alkoxide. Final firing was done at 600–850 °C

 Crystallite size of 50–200 nm and an aggregate structure.  The surface area measured from the BET isotherm was found to be ~30 m2 g–1 Morphologies of undoped (sx) and doped (dx) powders

Ordered-olivine structure of LiFePO4

Doped-phospho-olivines as Li storage electrodes

 Controlled cation nonstoichiometry combined with solidsolution doping by metals supervalent to Li increases the electronic conductivity of LiFePO4 by a factor 108

Absolute values >10–3 Scm–1 over the temperature range –20 °C to +150 °C of interest for battery applications.

Un-doped

NANOSIZED MATERIALS Huge surface area

Short distance for mass and charge diffusion: nanorods Freedom for volume change with lithiuminsertion

MnO2 Good electrochemical performance

Low cost Environmental friendliness But: Low levels of power density (far from theoretical) Practical rechargeability? spinel

Metal oxides as cathode materials for rechargeable Li-ion battery: MnO2 Nanocrystals of α, β and γ-MnO2, where manganese lies in the octahedral site of oxygen

Nanostructure of β-MnO2 (rutile structure) = low capacity and poor cycling stability : rapid convertion to LiMn2O4 spinel upon Li intercalation = unfavorable electrochemical performance However: remarkably high Li intercalation capacity (284 mAh/g)  and  - MnO2: good electrochemical performance

Metal oxides as cathode materials for rechargeable Li-ion battery: MnO2 Synthesis: KMnO4 and fumaric acid on templant 10 KMnO4 + 3 HOOCCH = CHCOOH + 10 H3O+  10 MnO2 + 18 H2O + 6 CO2 + 3 H2C2O4

TEM SEM

Discharge capacity of bulk MnO2 always less than 120 mAh /g

The cell: Cathode = MnO2 + C + binder Anode = Li foil Electrolyte LiClO4 1M in propylene carbonate

Metal oxides as cathode materials for rechargeable Li-ion battery: V2O5

V2O5  Layered structure  Moderate electrical conductivity  Low diffusion coefficient of Li ions  Increasing surface area  Shorting the diffusion distance Nanotechnology  Higher contact area (inner and outer wall surfaces, open ends)  Electrolyte-filler channels  Polycarbonate membranes (CH2Cl2)

Effect of nanomaterial shape: nanotube and films the nanotube array possesses a high Li+intercalation capacity of 300 mAh/g, (twice that of the film). Although the capacities of both the nanotube array and the film decrease during cycling, they reach stabilized capacities within 10 cycles. The stabilized capacity of the nanotube is approximately 160 mAh/g and remains 30% higher than the stabilized capacity of the film.

V2O5 nanotubes after cycling

V2O5 nanorods: the effect of synthesis procedure on electrochemical properties: Electrodeposition and sol-gel

Electrodeposition

Sol-gel

Vanadia nanorods grown by electrochemical deposition are single crystal, with vanadia layers parallel to the nanorod axis. 1. Such structure is extremely favorable to Li+ intercalation and extraction: 2. Such structure permits the most freedom for dimension change that accompanies intercalation and extraction reactions. Sol-gel vanadia films are polycrystalline and consist of platelet vanadia grains with [001] perpendicular to the substrate surface Li+ diffusion through grain boundaries, oxidation and reduction reactions at the surface of individual crystal grains, and diffusion inside individual grains.

Effect of nanomaterial shape Nanorod array electrodes have significantly higher current density and energy storage density than sol-gel-derived V2O5 films. Chronopotentiograms of nanorod arrays (left) and sol-gel (right) measured with various fixed current density Nanorods can intercalate a higher concentration of Li+ than that in sol-gel films in a given current density. For a given Li+ intercalation capacity, (Li0.7V2O5), nanorod arrays possess 5 times larger current density than that of sol-gel films, and similarly for a given current density, such as 0.7A/g, nanorod arrays can store 5 times higher Li than that in sol-gel films.

NANOSIZED COATING ON CATHODE MATERIALS Most cathode materials are typically ceramic materials with low electronic conductivity To improve the electrochemical kinetics:  increasing the ceramic conductivity

 embedding the cathode within an electronically conducting network Thin enough, on the nanoscale, so that ions can across it

 Capable of avoiding interface reactions .

Carbon Oxides Polymers

RuO2 AS AN OXIDIC NANOSCALE INTERCONNECT Synthesis: LiFePO4 + RuO4/pentane slowly from -78°C to RT

 Incomplete carbon network parts are repaired  RuO2 arrangement is percolating but porous, a large number of active triplephase (RuO2, LiFePO4, liquid electrolyte) contacts were formed, (easyer Li insertion).  The C-LiFePO4/RuO2 composite retains the morphology and structure of the C-LiFePO4

3D ARCHITECTURED COMPOSITE STRUCTURES

Ni-V2O5 nH2O nanocable arrays 1, Ni nanorod arrays prepared through the template-based electrochemical deposition; 2. a coating of V2O5 nH2O was applied over the Ni nanorods solgel

The Ni core nanorod is covered completely and uniformly by a V2O5nH2O shell of average thickness = 40 nm. Energy density and power density > than those of film electrode by at least 1 order of magnitude. Li+ IC capacity of nanocable arrays 10 times > than that of single-crystal V2O5 nanorod arrays and 20 times > than that of film.

Voltage versus capacity for positive- and negative-electrode materials presently used or under serious considerations for the next generation of rechargeable Li-based cells. The output voltage values for Li-ion cells or Li-metal cells are represented. Note the huge difference in capacity between Li metal and the other negative electrodes, which is the reason why there is still great interest in solving the problem of dendrite growth.

LixC-ANODE

Graphite intercalation compounds  Intercalation of graphite: penetration of guest species between the carbon layers with the consequent expansion in the c-axis direction;

Carbon alternatives Li transition-metal nitrides

 large, stable and reversible capacity (600 mA h g–1) displayed by Li3–xCoxN.  Performances of the other newly reported Libased nitrides unfortunately display inferior electrochemical performances  The use of Li3–xCoxN is constrained by the restrictive manufacturing requirements for handling such moisture-sensitive negative electrodes.:

Carbon alternatives

Buffer matrix to compensate for the expansion of the reactants  1997 Fuji - STALION An amorphous tin composite oxide (ATCO) as negative electrode. specific capacity twice that of graphite. 1. oxide decomposition by Li through an initial irreversible process to form intimately mixed Li2O and metallic Sn, 2. Li alloying reaction to form nanodomains of Li4.4Sn embedded within the Li2O matrix.  poor long-term cyclability,  huge and irreversible capacity loss during the first cycle

Carbon alternatives Low expanding alloys  Intermetallic alloys such as Cu6Sn5, InSb and Cu2Sb that show a strong structural relationship to their lithiated products, Li2CuSn and Li3Sb for the Sn and Sb compounds, respectively. Ternary LixIn1–ySb system (0
ANODE MATERIALS FOR RECHARGEABLE Li-ION BATTERY Metals and semiconductors that can store lithium:

Al, Si, Sn and Bi Silicon can form Li4.2Si, (highest known theoretical charge capacity of 4200mAh/g (vs. 372mAh/g for graphite LiC6.); Volume of Si anode changes by 400% upon Li intercalation/deintercalation. (poor cycling capacity - pulverization and capacity fading in just a few electrochemical cycles) Wilson and Dahn: Carbon-containing nanodispersed reversible specific capacity = 500mAh/g. Holzapfel: Si/graphite composites 1000 mAh/g

Si:

Nest-like Silicon Nanospheres for HighCapacity Lithium Storage

Synthesis via a solvothermal route Ma from NaSi + NH4Br with Py + dimethoxyethane (DME) as the solvent. Cotton bag with LaNi5 alloy packed in was put in a 25 mL Teflon-lined autoclave at 80°C 24h

et al.

Two steps. 1. The silicon crystal nucleuses gradually grew into nanocrystals and then assembled on the surface of the cotton fibers to form ultrathin nanofibers and sheet-like nanostructures 2. The formation of the nest-like Si hollow spheres involves a gas-bubble nucleation step around the cottonfiber bags. The hydrogen absorption reaction provides a driving force that makes the reaction of NaSi and NH4Br TEM images of the samples obtained after move to the right direction

heating for a) 5 min, b) 12 h, c) 36 h and 48 h.

Ma et al. Nest-like Si nanospheres (90–110nm ø – surface area = 386 m2/g) composed of ultrathin Si nanowires with diameters of 5–10 nm = high-rate capacity and cycling performance.

a–c) SEM and d) TEM images of nest-like Si nanospheres. e) SEM, f) TEM, and g) TEM images of coil-like Si nanospheres. XRD of a) nest-like, b) coil-like Si nanospheres c) commercial Si

fcc Si Broadening of the peaks for nest-like and coil-like Si nanospheres

Specific discharge capacities of the nestlike Si nanospheres, coil-like Si nanospheres and commercial Si particles

 superior lithium-storage capacity,  high-rate capability  long cycling properties potential application as anode

High-Rate, Long-Life Ni–Sn Nanostructured Electrodes for Lithium-Ion Batteries

Ni3Sn4 intermetallic nanoalloy electrodeposited on a nanoarchitectured Cu substrate. The nanoarchitectured Cu current collector was obtained by growing a 3D array of Cu nanorods onto a Cu foil by electrodeposition through a porous alumina membrane that was subsequently dissolved. SEM image = uniformly distributed Cu rods of about 200 nm diameter,

The synthesis was completed by coating the above-described Cu nanorod array with Ni3Sn4 particles achieved by electrodeposition in aqueous solution, formed by NiCl2 + SnCl2 + K4P2O7 + glycine + NH4OH

Ni3Sn4 intermetallic nanoalloy electrodeposited on a nanoarchitectured Cu substrate. High specific capacity (500mAh/g) over 200 charge/discharge cycles without any significant decay.

an efficient way of improving the electrochemical response of lithiumalloy electrodes is that of optimizing their morphology, especially in terms of particle size and interparticle space. This may be obtained by the refinement of preparation methods,

Nano-sized transitionmetal oxides as negative-electrode materials for lithium-ion batteries

for FeO and NiO, the reversible capacity continuously decayed, whereas for Co oxides the capacity remained constant

Performance strongly depend on particle size

For each metal oxide system there is an optimum precursor particle size, producing the best state of division of the metal particles and hence the best electrochemical performance. For example, 100% capacity retention after 100 cycles was achieved using 2-m CoO particles.

The mechanism of the reaction with Li of these MO is not based on reversible insertion/deinsertion of lithium into host structures. This difference is due to  these materials (CoO for instance) crystallize in a rock-salt structure that does not contain any available empty sites for Li ions,  none of the 3d metals considered forms alloys with Li.

CoO

CoO reacts with Li: Co

Starting electrode

This leads to the formation of metallic Co and Li2O nanoparticles that are presumably smaller than the X-ray coherence length, as there are no diffraction peaks.

Fully lithiated electrode

Optimal size for formation/decomposition of Li2O – best electrochemical performance.

High rate capabilities Fe3O4-based Cu nano-architectured electrodes for lithium-ion battery applications

Synthesis: Step 1. cathodic electrodeposition from an electrolytic bath of CuSO4 ·5H2O, (NH4)2SO4 - alumina oxide membrane Step 2. Copper nanopillars covered with Fe3O4 by means of an electrodeposition from an alkaline aqueous solution (pH=12.3) consisting of NaOH, Fe2(SO4)3 ·5H2O,

The electrochemical cell and the nanostructured current collector. Diagram of the nanostructured current collector expected to be obtained at the end of the electrolysis, before and after removal of the AAO membrane. Top view of the Cu current collector obtained after electrolysis and membrane removal. Cross-sectional views of Cu-nanostructured current collector before (left) and after (right) Fe3O4 deposits.

Substrate Cu

XRD patterns and scanning electron micrographs of as-prepared copper nanopillar Fe3O4 assemblies.

120 sec deposition time

150 sec deposition time

XRD: metallic copper, Fe3O4 phase with no preferred orientation. 1. Small and shapeless polycrystalline Fe3O4 grains cover the entire surface of the Cu nanorods. 2. With increasing electroplating time, the round islands at the tip of each nanorod become much more bulky, but no change is observed in the morphology of the grains.  For deposition times < than 230 s, the Cu nanorod was not fully covered with Fe3O4, whereas a coalescence effect is observed for long deposition times

180 sec deposition time

230 sec 300 sec deposition time deposition time

Capacity retention of a Fe3O4 film electrodeposited onto nano-architectured copper substrate for 150 s Excellent rate capability observed for all of the nano-architectured electrodes compared with the Fe3O4 powder cell Full capacity for numerous cycles (SEM = no peeling or other morphology changes of either the Fe3O4 or Cu nanorods

Benefit of having a nanostructured current collector as opposed to a planar one in terms of power density,