Stable Operation of Li-Air Batteries

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1 Stable Operation of Li-Air Batteries Ji-Guang Zhang Pacific Northwest National Laboratory Richland, Washington, U.S.A. The 4th Symposium on Energy Storage: Beyond Lithium Ion June 8, 211 1

2 2 Outline 1. Development of High Capacity Primary Li-air Batteries 2. Stability of Li-air Batteries Using Aqueous Electrolyte & NASICON Glass 3. Stability of Li-air Batteries Using Non-Aqueous Electrolyte 3.1 Reaction Products During Discharge Process 3.2 Reaction Products During Charge Process 4. Summary

3 1. Development of High Capacity Primary Li-air Batteries.8 mil polymer membrane Footprint: 4.6 cm x 4.6 cm; thickness = 3.8 mm Metal mesh.7 mm KB carbon electrode 1 mil separator with binding layer.

3 3 1. Development of High Capacity Primary Li-air Batteries.8 mil polymer membrane Footprint: 4.6 cm x 4.6 cm; thickness = 3.8 mm Metal mesh.7 mm KB carbon electrode 1 mil separator with binding layer.5 mm Li foil Cu mesh mah/g carbon Voltage (V) Operated in ambient air (~2% RH) for 33 days Total weight of the complete battery: g Specific energy: 362 Wh/kg Cell capacity (Ah)

$C/O = 14 and C/O = 1, respectively. e, TEM image of discharged air electrode. f, Selected area electron diffraction pattern (SAED) of the particles: Li 2.$

4 Hierarchically Porous Graphene as a Lithium-Air Battery Electrode a and b, SEM images of asprepared graphene-based air electrodes c and d, Discharged air electrode using FGS with C/O = 14 and C/O = 1, respectively. e, TEM image of discharged air electrode. f, Selected area electron diffraction pattern (SAED) of the particles: Li 2. 4 Jie et al, to be published

5 5 Graphene as a Lithium-Air Battery Electrode Record Capacity of 15, mah/g

6 Li Li + Anode Glass e - Li Li + Load Air Electrode Basic-electrolyte ½ H 2 O LiOH Li + stable coating 2. Stability of Li-air Batteries Using Aqueous Electrolyte & NASICON Glass In Aqueous Electrolyte e - ¼ Final product stays in air electrode Challenges: Stable glass electrolyte at strong acid and alkaline environment Chemical stability Electrochemical stability Single ion conductivity Li+ ½ + ½ H 2 O LiOH 6

7 7 Advantages and Challenges in Li-air Batteries Li/ Reaction in Different Electrolyte With precipitation (Li/electrolyte/carbon) Theoretical voltage Theoretical specific energy based on metal Theoretical specific energy based on reactants (excluding ) Theoretical specific Specific energy based energy based on reaction on full reaction products V Wh/kg Wh/kg Wh/kg Wh/kg Li + ½ ½ Li ** Li H 2 O LiOH. H 2 O Li HCl LiCl +.5H 2 O With no precipitation (Li & electrolyte) Li H 2 O LiOH+1.64H 2 O Li HCl +2.29H 2 O LiCl +2.79H 2 O * ~ * ~ * ~ * ~ * Voltage is a function of ph value: V = ph **J. P. Zheng et al, J. Electrochem. Soc., 158 (1), A43- A46 (211).

8 Voltage in Li-Air Batteries Strongly Depends on ph Value of Aqueous Electrolyte V(x)* = ph (V) Strong acid (HCl) electrolyte (1M, 4.21 V) Voltage (V) Neutral electrolyte (3.855 V) Strong base (LiOH) electrolyte (1M, 3.4V) ph *Xia et al, NATURE CHEMISTRY, VOL 2, SEPTEMBER, 76 (21) 8

) 1k 1.8 μm 塩基性 basic 14. 13. 12. 1. 11.

9 9 Stability of LTAP Glass vs. ph 未処理 pristine LiCl 3 週間 LiCl(aq.) 1k 1.8 μm 塩基性 basic LiOH LiOH 1 週間 LiNO 3 (aq.) LiNO 3 3 週間 H 2 O H 2 O 半年超 HCl HCl 3 週間塩基性 : Li 3 PO 4 の結晶析出 acidic 酸性酸性 : 表面が溶出 Yamamoto et al, presentation in Symposium on Energy Storage Beyond Lithium Ion,ORNL, Oct, 21

10 Limitation of Li-air Batteries in Acid Electrolyte ph Li HCl +2.29H 2 O LiCl +2.79H 2 O mol HCl ph = V Strong acidic (HCl) electrolyte (11. 5 M, 4.33 V) Voltage (V) Neutral electrolyte mol HCl ph = 7 V = V Glass Stability limit: 118 Wh/kg Soluability limit: 1353 Wh/kg HCl (M) Capacity (%) % 8.7% 1% To utilize the full capacity of acid electrolyte based Li-air batteries, ph value of the electrolyte has to be limited to be larger than 4. 1

11 Limitation of Li-air Batteries in Alkaline Electrolyte ph Neutral electrolyte mol LiOH ph = 7 V = V Li H 2 O LiOH+1.64H 2 O Voltage (V) mol LiOH ph = V.5 mol LiOH ph = V 1 mol LiOH ph = V 5.3 LiOH 3.4 V 3.2 Glass Stability limit: 85 Wh/kg Soluability limit: 444 Wh/kg LiOH (M) % Capacity (%) 19.2% 1% To utilize the full capacity of alkaline electrolyte based Li-air batteries, ph value of the electrolyte has to be limited to be less than 1. 11

Electrochemical Stability of NASICON Glass in Aqueous Electrolytes 2 18 EMF / mv 16

5 lg (C1/C2) NASICON solid electrolyte cannot distinguish between H + ions and Li +

Both Li + and H + ion in chamber B participate in the electrochemical process.

12 Electrochemical Stability of NASICON Glass in Aqueous Electrolytes 2 18 EMF / mv LiCl EMF HCl EMF K+ ion in nonaqueous Linear (LiCl EMF) lg (C1/C2) NASICON solid electrolyte cannot distinguish between H + ions and Li + ions, at least on the interface. Both Li + and H + ion in chamber B participate in the electrochemical process. Increase of ph value in chamber B may indicate the reaction of H + with glass electrolyte. See Dr. Fei Ding s poster for more details 12

13 3. Stability of Li-air Batteries Using Non-Aqueous Electrolyte Anode Separator 2Li Air electrode Non-aqueous electrolyte -2 Challenges: Stable non-aqueous electrolyte in oxygen rich environment 2Li + 2e - Load Li 2 2e - Final product stays in air electrode In non-aqueous electrolyte a. 2Li + Li 2 In non-aqueous b. 2Li + electrolyte Li 2 2Li + Li 2 E = 3.1V Schematic of reaction processes in metal-air batteries. 13

14 14 Investigation on the Reaction Products in Li- Batteries - +? 2Li + Li 2 Teflon container In situ analysis in Coin cells holder Mass Spec ---C? GC ---C? Compressed, 2 atm Li/air coin cells filled with 1M LITFSI in PC/EC (low vapor pressure electrolyte ) ex situ analysis X-ray FTIR NMR Developed unique characterization tools

15 Reaction Products During Discharge Process - +? 2Li + Li 2 Teflon container In situ analysis in Mass Spec ---C? GC ---C? Coin cells holder Li/air coin cells with 1M LITFSI in different electrolytes ex situ analysis Compressed, 2 atm X-ray FTIR NMR

16 16 Li 2 Was Not Observed in the Discharge Products When Carbonate Solvents Was Used Intensity (a. u.) 2.8 V 2.7 V 2.6 V 2.5 V 2.4 V 2.2 V 2. V Teflon Li 2 CO 3 Li 2 Li 2 O KB carbon LPDC LEDC Theta (Degree) For all DODs (from 2.8 V to 2. V), nearly no Li 2 and Li 2 O were detected. Lithium alkylcarbonates (LPDC and LEDC) and Li 2 CO 3 are identified to be the primary discharge products.

17 Ether Based Electrolytes Can Lead to the Formation of Li 2 During Discharge 2Li + Li 2 Yes. If the right electrolytes are used Li2O2 Li2O Li2CO3 PC-EC Sebaconitrile Triglyme BDG TEPa Teflon DMSO Carbon 17 See Dr. Wu Xu s poster for more details

18 3.2 Reaction Products During Charge Process ? 2Li + Li 2 Teflon container In situ analysis in Coin cells holder Mass Spec ---C? GC ---C? Li/air coin cells filled with 1M LITFSI in PC/EC ex situ analysis Compressed, 2 atm X-ray FTIR NMR

19 19 What Can be Charged? (f) Li 2 O First cycle charge capacities: Cell voltage (V) (b) Li 2 CO 3 (e) Li 2 (d) LPDC (c) LEDC (a) SP a) SP: 4.1 mah/g b) Li 2 CO 3 : 4.8 mah/g c) LEDC: 99.6 mah/g (331 mah/g, 3.1%) d) LPDC: mah/g (38 mah/g, 49.8%) e) Li 2 : mah/g (1165 mah/g, 92.5%) a) Li 2 O: 63.3 mah/g Test time (hour) Li 2 : Highly chargeable (>92%) LEDC and LPDC: Partially chargeable (~42-69%) and is responsible for apparent recharge-ability reported before. Li 2 O, SP, and LiC 2 O 3 : Not chargeable

20 2 What Are the Charge Products? (GC/MS Analysis).3 (a) SP 4.4 (c) LEDC/SP 5.3 (e) Li 2 /SP 5 Gas composition (%).2.1 Voltage Argon CO/N 2 3 Voltage (V) Gas composition (%) C CO/N 2 Voltage 4 3 Voltage (V) Gas composition (%).2.1 Voltage CO/N 2 C 4 3 Voltage (V) CO H 2 2 O Time (hour) Argon H 2 O Time (hour) H 2 O Argon Time (hour).3 (b) Li 2 CO 3 /SP 4.4 (d) LPDC/SP 5.3 (f) Li 2 O/SP 5 Gas composition (%).2.1 Argon H 2 O Voltage CO/N 2 C 3 2 Voltage (V) Gas composition (%) Argon C CO/N 2 H 2 O Voltage 4 3 Voltage (V) Gas composition (%).2.1 H 2 O C Voltage CO/N 2 Argon 4 3 Voltage (V) Time (hour) Time (hour) Time (hour) a) SP mainly CO with minor C b) Li 2 CO 3 small amount of C and CO c) LEDC large amount of C d) LPDC large amount of C e) Li 2 mainly with minor C f) Li 2 O some C and CO. It cannot be oxidized.

21 Current / ua Charge Efficiency in Different Non-Aqueous Electrolytes in Oxygen-Rich Environment Cyclic voltammograms (1 mv/s) on glass carbon in and Ar saturated LiPF 6 in different non-aqueous solvent 3 2 No OER peak forlipf 6 /PC a) b) solution c) indicates that all the ORR products react with PC -3 LiPF 6 /PC -2 which leads to the products Current / ua E / V (Li/Li + ) ORR OER Ar E / V (Li / Li + ) DME (.1M): Q OER /Q ORR = 97.5% bkgrd Current / ua Current / ua LiPF 6 / EC bkgrd E / V (Li/Li + ) LiPF6 / BDG bkgrd E / V (Li / Li + ) Butyl Diglycol Ether (1.M) Q OER /Q ORR = 96.7% Current / ua 4 No OER peak for LiPF 6 /PC solution indicates that all the ORR -4 products react with PC LiPF 6 / DMC which leads to the products that can that can -8 not be oxidized/recharged bkgrd not be O within the potential 2 range potential 3 4range. 5 E / V (Li/Li + ) oxidized/recharged within the Large Q OER /Q ORR ratio for LiPF 6 /ether solution indicates that most ORR products can be oxidized/recharged within the potential range. See Dr. Yuyan Shao s poster for more details 21

22 22 What Are the Source of Limited Efficiency? --NMR Investigation on Discharged Electrodes The characteristic peak of carbon for Li 2 CO 3 is located at 169 ppm and the peak at 112 ppm is ascribed for Kel- F signal from the two end plugs inside the MAS rotor. Li 2 CO 3 is still found in all electrodes discharged in all different electrolytes. The formation of Li 2 CO 3 during discharge process of a Li-air battery will limit the cycle life of the batteries. Where is Li 2 CO 3 from carbon electrode or electrolyte?

23 Li 2 CO 3 Comes From the Electrolyte C-MAS NMR Study 13 C-labeled air electrode was prepared and discharged in the same electrolyte. IfLi 2 CO 3 comes from the carbon electrode, the 13 C- MAS NMR signal corresponding to Li 2 CO 3 would increase by nearly 9 folds using 99% 13 C labeling since the natural abundance of 13 C is only 1.1% without isotope enrichment. The signal of Li 2 CO 3 in the 13 C-labeled carbon electrode is not larger, but even less, than the corresponding signal in the natural abundance carbon electrode. This result unambiguously reveals that the Li 2 CO 3 is originated not from the carbon electrode but from the electrolyte. Oxygen and/or superoxide radical anions may oxidize the alkyl groups (CH 3 or CH 2 ) or ether bond (C O) into the carbonate groups that in turn form Li 2 CO See Dr. Jian Zhi Hu s poster for more details

24 24 4. Summary 1. Graphene based air electrode exhibits very high capacity (~15, mah/g) due to its dual pore structure and defect activity. 2. Specific energy of Li-air batteries with aqueous electrolyte is strongly limited by the operational ph window of NASICON glass. Electrolyte additives and other approaches which can stabilize ph value of electrolyte is critical for long term operation of aqueous based Li-air batteries. 3. In carbonate electrolytes, the majority of the discharge products in Li-air batteries are lithium alkylcarbonates and Li 2 CO 3. Apparent rechargeability is due to oxidation of Lithium alkylcarbonates which release C and CO. This process is not sustainable. 4. Li 2 can be formed during discharge process when ether based electrolytes were used, Li 2 CO 3 was still observed and need to be minimized. 5. Electrolyte is the key for rechargeable, long term operation of Li-air batteries.

25 Acknowledgments Technical Team: Wu Xu, Jie Xiao, V. Viswanathan, Jianzhi Hu, Vijayakumar Murugesan, Silas A. Towne, Phillip Koech, Donghai Mei, Fei Ding, Zimin Nie, Yuyan Shao, Jian Zhang, Dehong Hu, Deyu Wang, Jun Liu, and Gordon L. Graff Financial support: Defense Advanced Research Program Agency Laboratory Directed R&D Program (Transformational Materials Science Initiative) of PNNL 25

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