Jason Zhang Pacific Northwest National Laboratory Richland, WA Presentation in METS 2012 Taipei, Taiwan Nov , HIGH ENERGY BATTERIES FOR ELECTRIC VEHICLE APPLICATIONS

1.Nano-structured Materials for Li-ion batteries 1.1 High capacity anode 1.2 High voltage cathode 2. Energy Storage beyond Li-ions 2.1 Highly Stable Li-S batteries 2.2 High Capacity Li-air batteries 2.3 Li-Metal Batteries 3. Summary 2 Outline

Tarascon & Armand, Nature , Nano-structured Electrodes for Li-Ion Batteries TiO 2 Si LiNi 0.5 Mn 1.5 O 4 LiMnPO 4

4 1.1 High Capacity Anodes Self Assembly of Nano-transition Metal Oxide/Graphene Composite The self-assembled structure composed of ordered “super-lattice” nanocomposite with alternating layers of graphene nanosheets and metal oxides Direct manufacturing of electrodes and batteries without binders and other additives. Nanosynthesis: TiO 2, SnO 2, and other cathode materials Self-assembly with graphene

5 High Performance Nano-TiO 2 /Graphene Composite C/5 1C Best rate capability reported on anatase TiO 2 with only 2.5wt% graphene. Excellent cycling stability: ~ 170 mAh/g at 1C (PHEV constant output).

Conductive Rigid Skeleton Supported Silicon as High-Performance Li-ion Battery Anodes Use conductive B 4 C as nano-/micro- millers to synthesize nano Si (< 10 nm ). Use rigid skeleton to support in-situ generated nano-Si. Use conductive carbon to coat the rigid skeleton supported silicon to form Si/Core/graphite (SCG) which can improve the structural integrity and conductivity of silicon anode. a) Si + Graphite Graphite Si B4CB4C b) c) 6 High energy ball milling Planetary ball milling B4CB4C

The ratio of Si, Core material and graphite are important to the electrochemical performance. Si:Core:graphite = 4:3:3 is the optimized ratio. Ball milling time is also important to the electrochemical performance. 8 hr milling is good for HEBM and PBM. Effects of Composition and Synthesis Condition on the Electrochemical Performances of Si Anodes 7

8 1.2 High Voltage Cathodes LiMnPO 4 Synthesized in Molten Hydrocarbon Has Preferred Growth Orientation Pure phase of LiMnPO 4 was obtained after 550ºC calcination. As-prepared LiMnPO 4 nanoplates are well dispersed without stacking. LiMnPO 4 nanoplates consists of a porous structure formed by self-assembled nanorods aligned in a preferred orientation with high specific surface area of 37.3m 2 /g.  Oleic acid was used as a surfactant and paraffin acts as a non-polar solvent that facilitate thermodynamically preferred crystal growth without agglomeration.

9 High Performance LiMnPO 4 Synthesized in Molten Hydrocarbon Specific capacity of 168mAh/g was achieved which is close to the theoretical capacity of LiMnPO 4. Flat voltage plateau at ~ 4.1 V indicates the phase transition between LiMnPO 4 and MnPO 4. At 1C and 2C rate (PHEV constant output) capacity retention is 120 mAh/g and 100 mAh/g, respectively. Ragone plot indicates that the discharge power density is close in LiMnPO 4 and LiFePO 4 when fully charged at C/25; At low power (< 30 W/kg), energy density of LiMnPO 4 becomes comparable or higher than LiFePO 4. constant charge rate at C/25

10 a bc def ghi Annealed LiNi 0.5 Mn 1.5 O 4 Annealed LiNi 0.45 Mn 1.5 Cr O 4 LiNi 0.5 Mn 1.5 O 4 The relative content between ordered and disordered phase can be tuned by changing synthesis condition. Doping significantly improve the performance of high voltage spinel 1.2 High Voltage Cathode: LiNi 0.45 Cr 0.05 Mn 1.5 O 4 Cr-substituted spinel Cr-substituted spinel LiNi 0.45 Cr 0.05 Mn 1.5 O 4 exhibit stable cycling and excellent rate performance.

11 Conventional Electrolytes are Stable up to 5.2 V Cutoff voltage ≤ 5.2 V: Very similar long cycling performance for the three carbonate mixtures. Cutoff voltage = 5.3 V: EC-DMC is still stable but EC-DEC degrades fast. Rate capability: EC-DMC and EC-EMC is similarly but EC-DEC is poorer.

Li-Metal Batteries Energy Storage beyond Li-ions Comparison of Specific Energy of Various Batteries

Highly Stable Li-S Batteries Potential: 3-4x improvement over Li-ion Barrier: Li 2 S deposition on Li metal

14 Optimization of mesoporous carbon structures (a)MC. (b)MC with pores completely filled with sulfur. (c)MC with pores partially filled with sulfur.

15 Self-breathing Conductive Polymer to Encapsulate Sulfur polymer hollow nanowire S/polymer composite Composite discharged to 1V Composite recharged to 3V At C/10, initial discharge capacity is 755 mAh/g with an activation process in the following cycles. Even after 500 cycles at 1C the capacity retention reaches 76%.

2.2. High Capacity Li-Air Batteries 2Li + + 2e − + O 2 ↔ Li 2 O 2 (2.96 V) Alkaline: O 2 + 2H 2 O + 4e − ↔ 4OH − (3.43 V) Acid: O 2 + 4e − + 4H + ↔ 2H 2 O (4.26 V) Aqueous Li-air Batteries Non-Aqueous Li-air Batteries 16

mAh/g carbon Zhang et al, J. Power Sources 195:4332–4337 (2010). High Capacity Primary Li-air Batteries

18 Hierarchically Porous Graphene as a Lithium-Air Battery Electrode a and b, SEM images of as- prepared graphene-based air electrodes c and d, Discharged air electrode using FGS with C/O = 14 and C/O = 100, respectively. e, TEM image of discharged air electrode. f, Selected area electron diffraction pattern (SAED) of the particles: Li 2 O 2. Xiao et al. Nano Lett., 2011, 11 (11), pp 5071–5078.

19 Graphene as a Lithium-Air Battery Electrode  Record Capacity of 15,000 mAh/g

20 Rechargeable Li-metal batteries are considered the “holy grail” of energy storage systems due to the high energy density. However, Li dendrite growth in these batteries has prevented their practical applications inspect of intensive works in this field during the last 40 years.  Dendrite-free Li metal deposition is needed for rechargeable Li-metal batteries, Li-S batteries, Li-air batteries. Classical Li dendrite growth (Chianelli, Exxon, 1976) GM estimate on HE NMC/Li metal system: 540 Wh/kg, 1050 Wh/L in cell level (2012) 2.3 Li-Metal Batteries

21 20 µm a b c d e Effect of CsPF 6 Additive on The Morphology of Li Deposition Control electrolyte: 1 M LiPF 6 in PC. CsPF 6 concentration in the electrolyte: (a) 0 M, (b) M, (c) M, (d) 0.01 M, and (e) 0.05 M.  Cs + additive can effectively suppress Li dendrite growth.

22 Effect of Current Density on Li Deposition 20 µm b a d c Electrolyte: 1 M LiPF 6 in PC with 0.05 M CsPF 6 as additive. Current density (mA cm -2 ): (a) 0.1, (b) 0.2, (c) 0.5, and (d) 1.0.  SHES mechanism is effective at different current densities.

23 Morphology Changes During Long Term Cycling of Li Electrode in Li/LTO Cells 20 µm b a Surface morphologies of Li electrodes after 100 cycles in coin cells of Li|Li 4 Ti 5 O 12 system containing electrolytes without (a) and with (b) Cs + -additive.  SHES mechanism is effective during long term cycling.

24  Columbic efficiency: 99.97%  Cycling stability: Only 3.3% capacity fade in 660 cycles Excellent Long Term Stability of Li-Metal Batteries Using Cs + Additive Cell: Li/Li 4 Ti 5 O 12 1 M LiPF 6 in PC with 0.05 M CsPF 6

25 Summary 1.Si electrode prepared by a cost effective method (ball milling)  822 mAh/g and a capacity retention of ~ 94% in 100 cycles. 2. High voltage, highly stable cathode  Retain more than 80% capacity after 500 cycles. 3. Highly stable Li-S batteries  mAh/g after 400 cycles. 4. High capacity Li-air batteries  Li-air batteries operate in ambient air for 33 days with a specific energy of ~362 Wh/kg for the complete battery.  Graphene based air electrode (~ 15,000 mAh/g). 5. Dendrite-Free Li-Metal Batteries  Novel additives (Cs, Rb, etc.) based on the SHES mechanism can effectively suppress Li dendrite growth on Li metal batteries.  ~99.97% Coulombic efficiency and ~4.2% capacity fade in 610 cycles for Li-metal batteries.

Acknowledgments Technical Team: Wu Xu, Jie Xiao, Xiaolin Li, Yuyan Shao, V. Viswanathan, Jianzhi Hu, Vijayakumar Murugesan, Silas A. Towne, Phillip Koech, Donghai Mei, Fei Ding, Zimin Nie, Yuliang Cao, Yufan Xiao, Eduard Nasybulin, Jian Zhang, Dehong Hu, Gordon L. Graff, and Jun Liu Financial support: DOE/EERE/Office of Vehicle Technology Laboratory Directed R&D Program of PNNL