Battery Power for All-Electric Road Vehicles John B. Goodenough and M. Helena Braga The University of Texas at Austin, and of Porto, Portugal Modern Society runs on the energy stored in fossil fuels. This dependence is not sustainable Batteries store clean electric power
Outline Introduction to rechargeable batteries Advantages & disadvantages of liquid versus solid electrolytes A transforming dielectric amorphous-oxide electrolyte Status of battery-cell development
Batteries Large-scale batteries contain multiple identical cells Battery cells deliver P dis = I dis V dis for Δt Cell capacity at a constant I dis = dq/dt is ΔΔΔΔ 0 II dddddd dt = QQ(II dddddd ) 0 dddd per unit weight, volume Stored energy density: ΔΔΔΔ 0 PP dddddd dt =<Vdis> Q(Idis)
Components of a Battery Cell Anode( ) M + -Electrolyte Cathode (+) μ A Δl μ C Electrolyte is M + conductor, e - insulator Cell delivers P dis = I dis V dis V oc = (μ A µ C )/e I dis ~ σ M A/Δl (neglecting interface resistance)
Electrolyte E g Restricts V dis µ A LUMO E g µ C ev dis µ A > LUMO or µ C < HOMO require SEI HOMO
Rechargeable Batteries Store P ch P ch reverses reaction inside cell V dis > V oc η dis I dis, V ch = V oc + η ch I ch Storage efficiency: P dis /P ch < 100% Coulomb efficiency: Q(I dis )/Q(I ch ) per cycle Can there be a Q(I dis )/Q(I ch ) > 100%?
Critical Engineering Targets (for powering a competitive all-electric road vehicle) Safety: (i) nonflammable components Cost: Rates: (ii) environmentally friendly materials (i) materials, fabrication, management (ii) charge/discharge cycle life for 150,000 miles (i) (3/4 charge < 10 min.) (ii) T op down to 30 C Range: 300 miles between charges: volumetric <V dis (q)> Q(I dis )
Electrolyte Requirements (Liquids versus Solids) Retain electrode/electrolyte contact during electrode volume change Dendrite-free plating/stripping of alkali-metal anode σ M > 10-2 S cm -1 at 25 C E g > 5 ev matched to μ A and µ C Separators: mechanically robust, chemically inert, thin (< 30 µm), large-area membranes
Aqueous Electrolytes Acidic or Alkaline: H + Electrolyte E g = 1.23 ev: V oc 1.5 V Need large Q(I) of air cathode for large <V dis > Q(I dis )
Organic-Liquid Electrolytes (Carbonates and Ethers) Advantages Li +, Na +, K + ionic conductors σ i 5 10-2 S cm -1 Accommodates electrode volume changes Limitations (carbonates) E g 3 ev not matched to high-voltage V oc LUMO 1.2, HOMO 4.2 ev versus lithium V oc > 3 V with SEI passivation, but limits cycle life LiFePO 4 /Li 4 Ti 5 O 12 for stationary storage (<V(q)> 2 ev)
The Li-Ion Battery Separator Limited safe <V dis > Q(I dis )/volume
Alkali-Metal Wetting a b c d Na-K liquid Na-K liquid immobilized in porous membrane liquid electrolyte immobilized in porous separator liquid electrolyte immobilized in porous separator Cathode Cathode Leigang Xue et al.
Crystalline ceramics: Solid Electrolytes (σ Li at 25 C) oxides: σ Li 10-3 S cm -1, E g > 5 ev sulfides: σ Li 10-2 S cm -1 (E F (Li) E c ) = 3.5 ev Polymers: σ Li 10-4 S cm -1, E g > 5 ev, plastic Amorphous dielectric ceramic: Li + or Na + coexist with electric dipoles σ Li 10-2 S cm -1, E g > 8 ev
Ceramic Garnet Li + Electrolyte Yutao Li Li 7-x Lr 3 Zr 2-x Ta x O 12 not reduced by Li 0 anode 3D interstitial space: Tet bridged by Oct. 10-4 σ Li 10-3 S cm -1 for 0 x 0.5 T op 55 C for thin ceramic film Air exposure gives Li 2 CO 3 on surface
All-Solid-State Li/LiFePO 4 Batteries with Li 2 CO 3 -Free Garnet Electrolyte Photographs of the ceramic based composite membranes: (a) without PEG; (b) with 5 wt% PEG; photographs of PEO LLZTO PEG membrane (the weight ratio of PEO:LLZTO:PEG is 10:85:5) showing the (c) structural integrity after cutting corner; (d e) the self standing and flexibility; (f) SEM image; (g) thermal stability at 140 o C for 30 min.
All-Solid-State Li/LiFePO 4 Pouch Cell at 55 C with PEG, PEO-in-Garnet Electrolyte
Arrhenius Plots of Li + ac conductivity and permittivity at 1000 Hz of a Li-glass M. Helena Braga
Symmetric Li/Li-glass/Li cell (Glass σ Li = 15 10-2 S cm -1 at 25 C) 0.10 10 50 Voltage (V) 0.05 0.00 σ cell = 5-10 ms.cm -1 I = 3 ma.cm -2 9 8 7 6 5 4 3 I (ma) R (Ω) 45 40 35 30 25 20 SS/Cu/Li//Li-glass in matrix//li/cu/ss A = 0.45 cm 2 d = 80 µm -0.05-0.10-2 0 200 400 600 800 1000 1200 1400 time (hours) 2 1 0-1 15 10 5 0 T R 3.1 Ω ~8 Ω 5.7 Ω 0 100 200 300 400 500 600 700 800 900 1000 number of cycles T R 6
Li/Li + -Glass/S + C + Cu a) Li plating S 8 reduction b) c) E F (Li) = 1.39 ev, E F (S 8 ) = 4 ev versus vacuum. Therefore [V OC = E F (Li) E F (S 8 )]/e 2.6 V
Self-Charge, Self Cycling (Found with Li-glass, Na-glass) Cu/Li-glass/Al µ A (Al) µ C (Cu) 2.2 ev; µ A (Li) µ C (Cu) 3.5 ev
Al/Na + -glass + polymer/cu A Relaxation Oscillator
Succinonitrile (SN) -Z'' (Ohm) 16,000 14,000 12,000 10,000 8,000 6,000 4,000 2,000 0 SN mixed with LiClO 4 (5 wt%) σ SN = 8.6 x 10-7 Ω.cm -1 0 4,000 8,000 12,000 16,000 Z' (Ohm) Terahertz vibrational modes of the rigid crystal phase of succinonitrile. D. V. Nickel, S. P. Delaney, H. Bian, J. Zheng, T. M Korter, D. M Mittleman, The journal of physical chemistry. A, 2014 11
Electrochemical Performance of Li- NMO/Li + -glass/li Cell Voltage (V vs Li + /Li 0 ) 5.0 4.5 4.0 3.5 3.0 2.5 23 ma/g 1 120 110 0 50 100 150 200 250 1 110 Specific capacity (mah/g) 1 120 Cycle 1 Cycle 2 Cycle 3 Cycle 25 Cycle 50 Cycle 75 Cycle 90 Cycle 100 Cycle 110 Cycle 120 0 0 10 20 30 40 50 60 70 80 90 100 110 120 Cathode with PVDF and Super P Carbon (8:1:1 and blended with plasticizer (7:3); glass electrolyte in non-woven paper. Specific capacity (mah/g) 300 250 200 150 100 50 Cycle number Charge Discharge 15
Status of Battery-Cell Development Demonstration of new concepts has been completed with coin cells Easy scale-up to pouch-cell size has been made Transition of intellectual property to industry for product development is on-going Reference: Les Nichols, Office of Technology Commercialization, The University of Texas at Austin, lnichols@otc.utexas.edu
Acknowledgement of Support Compete 2020 and FCT PTDC-CTM-ENE-2391-2014