Investigations of BF3 based compounds as additives, electrolytes and as coating agent for nickel-rich cathode material

Abstract: Adducts with different carbonates as donors were synthesised to introduce BF3 into lithium ion batteries. Therefore, commonly used battery solvents such as dimethyl carbonate (DMC), ethylene carbonate (EC), ethyl methyl carbonate (EMC) and propylene carbonate (PC) were choosen. The BF3 adduct with fluoroethylene carbonate as donor is rapidly decomposing to vinylene carbonate and HF.

The impact of BF3·D (with D = DMC, EC, EMC and PC) as additves was tested in Li[Ni0.33Co0.33Mn0.33O2]/graphite cells. In order to investigate the ability of BF3·D to act as anion receptor initial tests with LiF were carried out, showing the complete conversion to LiBF4. Furthermore, full-cell testing displayed a decreased resistance for cells containing 0.25 wt% additive compared to cells without additive. At slow rates such as C/2 no significant difference of the specific capacity of cells with and without additive was observed. However, the application of high rates up to 5C displayed higher specific capacity for cells containing additive. The ex-situ analysis displayed the incorportation of boron species in both electrodes.

Adding BF3·D to LiX (with X = OCH2CF3, OC(H)(CF3)2 and CO2CF3) the conductivites are increasing significantly up to 5.8 mS·cm−1. Here, according to the concept of weakly coordinating anions the boron centred anions [BFxX4-x]− are lowering the attractions of the ion pairs. NMR studies of the composite electrolytes show the presence of various boron species like BX3, Li[BF3X], Li[BF2X2] and Li[BFX3], which distribute characteristically for each LiX. The electrochemical investigation of the electrolytes in Li[Ni0.33Co0.33Mn0.33O2]/graphite cells exhibit a direct relation between cycling behavior, impedance and boron content on CEI and SEI. The increase of boron content on the surface of the electrodes leads to lower specific capacities, which are increasing in the following order: Li[CO2CF3]/BF3·D < Li[OCH2CF3]/BF3·D < Li[OC(H)(CF3)2]/BF3·D.

The treatment of the Ni-rich cathode material Li1+x[Ni0.85Co0.10Mn0.05]1−xO2 with gaseous BF3 resulted mainly in a LiBF4 coating, whereas the subsequent thermal annealing led to a conversion of LiBF4 to LiF. However, for all coated cathode materials with and without thermal annealing the internal resistances of the full cells were decreased. Apparently, only the lowest applied coating mass of 0.08 wt% without thermal annealing exhibit higher specific capacities after long-term cycling at 45°C than pristine cathode material. Additionally, online electrochemical mass spectrometry studies in half cells showed a reduced CO2 release in the first cycle for cells containing coated cathode material

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• Location: Deutsche Nationalbibliothek Frankfurt am Main
• Extent: Online-Ressource
• Language: Englisch
• Notes: Universität Freiburg, Dissertation, 2021

Classification and Topics

• Classification: Elektrotechnik, Elektronik
• Keyword: Electrolytes ; Lithium ; Nickel ; Investigations ; Lithium-Ionen-Akkumulator

Contributors, Places and Time

• Event: Veröffentlichung
• (where): Freiburg
• (who): Universität
• (when): 2021
• Creator: Eisele, Lea
• Contributor: Krossing, Ingo ; Albert-Ludwigs-Universität Freiburg. Fakultät für Chemie und Pharmazie

Further information

• DOI: 10.6094/UNIFR/175635
• URN: urn:nbn:de:bsz:25-freidok-1756356
• Rights: Kein Open Access; Der Zugriff auf das Objekt ist unbeschränkt möglich.