LTO气胀

Mechanism of LTO Gassing and potential solutions Yan Qin, Zonghai Chen, Ilias Belharouak, and K. Amine (PI) Argonne National Laboratory May 9th-13th, 2011 es112 This presentation does not contain any proprietary, confidential, or otherwise restricted information. Overview • Start: 10/01/2010 • End: 09/30/2014 • 15% completed • Barriers addressed – Power fade of Li4Ti5O12 based lithium-ion chemistry – Gassing issues • Total project funding FY 14 – DOE - $1200K – Contractor - $ 0 • Funding received in FY10 – $300K • Funding for FY10 – DOE - $300K Timeline Budget Barriers • EnerDel® • University of Colorado Partners 3  Identify gassing mechanism of Li4Ti5O12 based lithium-ion chemistries.  Identify and develop advanced technologies to eliminate the gassing issue.  Secure sufficient quantities of these advanced materials for further verification in big pouch cells (200 mAh) using either Argonne National Laboratory’s new cell assembling line or with the help of an industrial partner. Objectives of the work Approach  Identify the conditions that lead to aggressive gassing of LTO.  Characterize the gassing from LTO cells.  Identify the real mechanism of gassing and provide possible solution to the LTO gassing 5 Recent Accomplishments and Progress  Identified conditions that lead to aggressive gassing issue o The gassing issue was only limited to chemistries using Li4Ti5O12 anode. o No gassing was observed at fully discharged state. o Gassing was barely observed at room temperature (25oC). o Severe gassing was observed at fully charged state and at elevated temperatures (>=55oC). o Similar phenomena was not observed for cells using carbon anodes.  Proposed preliminary hypothesis on gassing mechanism o Gassing is believed to be generated from the chemical reduction of solvent (carbonates) on surface of Li4+xTi5O12. o The high catalytic activity of titanium oxides might be a promoter to the chemical reduction reaction. o Surface modification was proposed to change the catalytic activity of Li4+xTi5O12. Why Li4Ti5O12 ? 0 40 80 120 160 200 1.0 1.5 2.0 2.5 3.0 1C charge 1C 20C 10C Vo lta ge / V Capacity / mAh g-1 •No volumetric change after lithium insertion. – Zero strain for extreme long term stability. •Specially designed nano-structured material for higher packing density and extremely high rate capability(> 20C). Outstanding electrochemical and safety performance of Li4Ti5O12 /Li1+xMn2-xO4 cells 0 200 400 600 800 1000 70 80 90 100 110 (b) Ca pa ci ty re te nt io n / % Number of cycles Carbon/LMO 5C/5C MSNP-LTO/LMO 5C/5C •Excellent capacity retention at 55oC Li4Ti5O12 MCMB -30 -20 -10 0 0 50 100 150 200 250 MSNP-LTO/LMO Carbon/LMO AS I / O hm c m 2 Temperature / oC •Better low temperature performance 0 10 20 30 40 50 60 0 20 40 60 80 100 120 140 160 0 2 4 6 8 10 12 14 16 (d) Voltage / V Te m pe ra tu re / o C Time / min Cell Temperature Voltage 0 1 2 3 4 5 0 20 40 60 80 100 120 140 160 0 1 2 3 Current / A Te m pe ra tu re / o C Time / min Cell Temperature (a) 100% SOC Nail peneration Current 0 10 20 30 40 50 60 0 100 200 300 400 500 0 2 4 6 8 10 12 14 16 (c) Voltage / V Te m pe ra tu re / o C Time / min Cell Temperature Voltage 0 2 4 6 8 10 12 14 0 20 40 60 80 100 120 140 0 1 2 3 Current / A Te m pe ra tu re / o C Time / min Cell Temperature(b) 100% SOC Nail penetration Current •Unmatched abuse tolerance Carbon/LMO LTO/LMO Higher energy density can be achieved by coupling LTO with high voltage cathodes like LiMn1.5Ni0.5O4. Nail penetration Over- charge Key issue that hinders the deployment of Li4Ti5O12 based chemistry After stored at 63oC & 100% SOC for 1 year Before After stored at 63oC & 100% SOC for 1 year Before •Release large amount of gas after high temperature storage. Li4Ti5O12/Li1+xMn2-xO4 (200 mAh cell) 9 Major gas in the LTO cell is hydrogen 0 20 40 60 80 100 N2C2H4C2H6CH4CO CO2 G as C on ce nt ra tio n, % H2 D001-30 C3H8 C3H6 20 30 40 50 60 70 0 2 4 6 8 10 12 D0 05 -6 0 D0 24 -4 5 D0 01 -3 0 C2H6 CH4 CO CO2 Ab un da nc e, x 1 09 Temperature, oC H2 Amount of H2 in the cell increase with temperature Locating the reaction mechanism (Where does the gas come from in the LTO based Cell?)  H2 is a key component of the gas. Blocking the reaction pathway for H2 might be a solution for the gas issue.  Li4Ti5O12 and Li1+xMn2-xO4 have no source of H element, they will not generate H2 by themselves.  Trace amount of moisture in the electrolyte and electrode has no way to explain the huge amount of gas generated, and that no gas was observed for carbon-based cells.  Electrolyte has H source (carbonates) but is stable at ambient temperature.  The possible mechanism is, Chemical or electrochemical decomposition of the H source (electrolyte) on the electrode surface (metal oxides), serving as the catalysis. 11 CH4 C2H6 C2H4 C3H8 C3H6 C2H2 H2 CO2 CO propylene propane acethylene ethylene ethane methane CO2 CO H2 Products of decompositionProducts of reduction Where the gases come from? Detailed observations on gassing issue Observation for Li4Ti5O12 (LTO)/Li1+XMn2-xO4 (LMO) cells:  Baking Li4Ti5O12  less gas  At completely discharged state (55oC)  no gas  At charged state (55oC)  severe gas  At discharge state (55oC)  no gas  Replacing LMO with NCA or NCM  severe gas at charged state and 55oC  Replacing LTO with carbon anodes  no gas  GC-MS data shows that the gas include H2, CO2, CO, CH4, C2H4, C2H6, C3H6 and C3H8. H2 is the dominated component.  SEM, XRD and electrochemical test of aged electrodes shows no damage to the electrode materials (both LTO and LMO). Quantification of H2 generation using GC-MS (1) A 200 mAh pouch cell using LTO/LMO was charged to 2.8V (fully charged). (2) The pouch cell was then opened and the negative electrode was harvested from the cell. (3) Lithiated LTO recovered from the negative electrode was then mixed with solvent or electrolyte and sealed in a heated reactor. (4) A online gas chromatography (GC) was deployed to detect the evolution of H2 from the mixture. Li7Ti4O12 EC/EMC w/o LiPF6 GC Heated Reactor GC results of reaction between Li7Ti5O12 and solvents w/o LiPF6  Reaction between Li7Ti5O12 and electrolyte (1.2M LiPF6 in EC/EMC=3/7) At 80oC, Li7Ti5O12 : 0.402g = 8.37×10-4 mol; Electrolyte: 25ml H2 produced: ~ 30mL Assume the following reaction: Ti3+ + H+  Ti4+ + ½ H2 In theory, 0.402g Li7Ti5O12 will produce about 28 mL H2 based on above reaction, agreeing quite well with the experimental data.  Reaction between Li7Ti5O12 and solvents (EC/EMC=3/7) plus some residue LiPF6 At 80oC, Li7Ti5O12 : 0.402g = 8.37×10-4 mol; Solvent: 25ml H2 produced: ~ 5mL Might have LiPF6 residue on Li7Ti5O12, resulting in low LiPF6 concentration; not purely solvent. Gas comes from the chemical reduction reaction of solvent by Li7Ti5O12 with the help of LiPF6. Assembling of reaction model to explain experimental observations OO O OH H OO O OH H H H R1 R2 OHO O OHH2 R1 R2 Metal oxide (Li4+xTi5O12) OO O OH H H H R1 R2 Li+ Absorption of solvent on LTO surface. Reduction of hydroxyl group and release H2. Chemical decomposition of solvent. Future work  Understanding the true mechanism is the key to resolve the problem. Following items are key components for the future work. (a) Investigate the reaction kinetics using in situ XANES (X-ray Absorption Near- Edge Structure). (b) Using the kinetics data obtained from XANES to quantify the effectiveness of surface modification agents. (c) Explore additives and “poisoning” agents to supress the catalytic activity of LTO. (d) Explore coating LTO to eliminate the catalytic reactivity at the surface of LTO. Summary  Nano-structured Li4Ti5O12 is a promising anode materials for high power lithium- ion batteries with extremely long life and unmatched tolerance to overcharge and thermal abuses.  Gassing of Li4+xTi5O12 at elevated temperature is the remaining issue that hinders the deployment of this chemistry.  A hypothesis on the gassing reaction was proposed.  More fundamental research is needed to reveal the true mechanism and to completely resolve the problem. Collaborations  EnerDel  Fabrication of 200 mAh LTO/LMO lithium-ion cells to verify the effectiveness of surface modification.  Colorado University  Surface Modification using ALD process Mechanism of LTO Gassing and potential solutions Slide Number 2 Slide Number 3 Slide Number 4 Recent Accomplishments and Progress Why Li4Ti5O12 ? Outstanding electrochemical and safety performance of Li4Ti5O12 /Li1+xMn2-xO4 cells Key issue that hinders the deployment of Li4Ti5O12 based chemistry Slide Number 9 Locating the reaction mechanism�(Where does the gas come from in the LTO based Cell?) Slide Number 11 Detailed observations on gassing issue Quantification of H2 generation using GC-MS GC results of reaction between Li7Ti5O12 and solvents w/o LiPF6 Assembling of reaction model to explain experimental observations Future work Summary Collaborations