Failure Analysis Of Lithium Ion Batteries-Dissolution And Deposition Of Transition Metal Ions And Gas Release

Battery failure analysis is a vital important part in both the fundamental investigations and practical development of superior lithium ion batteries for future applications.Battery failure can originate from quit a bunch of factors entangled altogether and the fundamental understandings still need further study.The lack of proper characterization techniques,particularly for quantified analysis,further add to the challenge of corresponding investigations.In this work,we conducted systematic and comprehensive investigations on the LiFePO₄/graphite based battery failure analysis process and developed novel characterization techniques for quantitative analysis,focusing on the prevailing issues related to transition metal ions dissolution-deposition and gas release.The detailed dissolution-deposition and gas release problem mainly in LiMn₂O₄ is systematically investigated.Detailed studies include:?1?Battery failure mechanism on LiFePO₄/graphite based full battery.We developed a standard proceeding method for novel double-side-coated electrodes,the standard error is estimated to be less than 0.5%,which is superior to conventional electrode-wiping method and direct double-side-coated electrode detection method.This novel proceeding strategy builds up a valid foundation for further quantitative analysis.Based on systematical characterizations including electrochemical,morphological,structural,compositional and content measurement,the failure model on cathode,anode and separator can be established respectively.The main reason for capacity decay can be attributed to reversible Li loss.Based on the conservation of Li content,the estimated capacity decay on cathode and anode sides accounts for 33.25%and 66.74%in total capacity loss,respectively.?2?The investigation of transition metal ion dissolution during LiMn₂O₄ battery storage and cycle.We utilized UV-vis spectroscopy to quantify the dissolved Mn concentration in electrolyte,which is further calibrated by ICP.The Mn dissolution behavior from LiMn₂O₄ active powder was studied with different charge/discharge state at 45?,where high voltage charged LiMn₂O₄ demonstrates most efficient Mn dissolution.The dissolved Mn was verified to be mostly?>94%?at Mn²⁺state as probed by sXAS.The cathode/electrolyte interface reaction was investigated by ab initio molecular dynamics?AIMD?method,where Mn₂O₄?110?surface exhibits inferior surface stability compared to LiMn₂O₄?110?surface.The Mn dissolution behavior upon battery cycle was characterized by specially designed in-situ UV-vis cell and the Mn concentration demonstrates increase-balance-increase behavior with charge-discharge process.?3?Investigation on the influence of Mn dissolution-deposition on the cathode/anode properties.We designed LiMn₂O₄/graphite based multi-layer sealed laminated model battery and compared the Mn dissolution-deposition behavior difference at storage 45?and long time cycle.It was verified that the deposited Mn on graphite anode was in 2+state as MnO and MnF₂ instead of metallic Mn⁰.By virtue of systematic characterizations on electrodes and electrolyte with electrochemical, structural,morphological,compositional analysis,Mn dissolution-deposition behavior was found to follow consistent role on both cathode and anode sides in capacity fading,where stored electrolyte>stored electrode>cycled electrode> cycled electrolyte>fresh electrolyte?electrode?.?4?Investigations on the in-situ and operando gas release behavior in liquid electrolyte and solid electrolyte based batteries.By designing specific liquid and solid electrolyte based in-situ cells,we combined cold well,in-situ heater,and mass spectroscopy to build up the integrated differential electrochemical mass spectrometry system?DEMS?.With the newly commissioned DEMS system,we investigated the operando gas release behavior of LiMn₂O₄/Li and LiCoO₂/Li battery with conventional carbonate based liquid electrolyte and LiMn₂O₄/PEO/Li based solid battery.It was found that LiMn₂O₄/Li liquid battery doesn't detect gas release whether the charging cut-off voltage is 4.3 V,4.5 V or 4.8 V.As for LiCoO₂/Li liquid battery charging to 4.8 V,the unmodified LiCoO₂ generates O₂, CO and CO₂ when charged to 4.6 V,while the doped LiCoO₂ has no gas release during the whole charge process.And the LiMn₂O₄/PEO/Li solid battery can cycle in voltage range 3.0-4.2 V and 3.0-4.5 V without gas release.But when LiMn₂O₄/PEO/Li solid battery was charged to high voltage 4.65 V,irreversible battery fade takes place in accompany with CO₂,CO and CH₄ gas release.