Synthesis of Mg and Mn Doped LiCoO₂and Effects on High Voltage Cycling

Abstract

LiCo 1-2x Mg x Mn x O 2 (0 ≤ x ≤ 0.05) materials were prepared from Co 1-2x Mg x Mn x (OH) 2 (0 ≤ x ≤ 0.05) co-precipitated precursor materials by mixing precursor materials with stoichiometric amounts of Li 2 CO 3 and heating to 900 • C for 10 h. All precursor and lithiated materials were characterized by Scanning Electron Microscopy, X-ray Diffraction (XRD), Inductively Coupled PlasmaOptical Emissions Spectroscopy and electrochemical testing. In situ XRD was performed on LiCo 1-2x Mg x Mn x O 2 (x = 0, 0.02, 0.05) electrodes while cycling to study the effects of substitution on phase transitions and unit cell variations. Increasing Mg/Mn substitution in the material was found to slightly increase the 1 st charge capacity, decrease the 1 st discharge capacity and increase the 1 st cycle irreversible capacity (3.6 V-4.7 V). Cells with even 1% Mg/Mn doping were shown to have markedly improved cycling performance, and results suggest that the improvements stem from suppressing the cell impedance growth, not from the suppression of the O3-O6-O1 phase transitions. Lithium ion (Li-ion) batteries are used to power cell phones, laptops, other portable electronics, electric vehicles and grid storage. With an ever-increasing demand for energy, battery manufacturers and researchers constantly look for ways to increase the energy density while maintaining a long lifetime. LiCoO 2 (LCO) positive electrode materials, proposed by Mizushima et al. in 1980, 1 have been utilized since the commercialization of Li-ion battery technology by Sony in 1991. 2 Significant improvements have been made since then, but commercially available batteries never push LCO electrodes past 4.48 V (vs Li/Li + ), corresponding to the deintercalation/intercalation of ∼0.7 Li (per LCO) or a capacity of ∼190 mAh/g (out of a theoretical capacity of ∼274 mAh/g). In order to unlock more capacity and increase the energy density, the LCO electrodes have to cycle to voltages above 4.5 V (vs Li/Li + ). However, pushing cells with LCO electrodes to an even higher voltage result in a dramatic decrease in long term cycling performance. [3][4][5][6][7][8][9] There are multiple causes for this drop in performance, including structural instability of highly delithiated LCO,[6][7][8]10,11 electrolyte oxidation 5-7,9,10,12,13 and Co dissolution. 3,5,7,8,14,15 To further understand the structural instability that arises from high voltage cycling, X-ray diffraction (XRD) has been instrumental in studying the unit cell lattice parameter changes and phase formations. 10,11,16,17 Theoretical work has also confirmed the majority of these occurrences and helped shed light in understanding phase formation at low lithium content. 18,19 As Li deintercalates from LCO, the material undergoes a series of phase changes. The first is an insulatormetal transition, resulting in a 2-phase region. 10,16 As the material continues to deintercalate, LCO will undergo an order-disorder transition around 0.5 Li.16,18 Both of these transitions occur reversibly and are not detrimental to cycli...

The influence of synthesis temperature on the HT-LiCoO2 crystallographic properties

“…These are in good agreement with the best values for HT-LCO found in the literature, attesting that even low treatment time is enough for the sample to exhibit high electrochemical performance (DAI et al, 2016;LIU et al, 2017).…”

Unveiling Nickel Chemistry in Stabilizing High‐Voltage Cobalt‐Rich Cathodes for Lithium‐Ion Batteries

“…Elevating the upper cutoff voltage in charging is the most straightforward method to further increase the energy density of LCO, but it unfortunately leads to poor cyclability if charged to >4.40 V versus Li/Li + (x ≥ 0.6 in the form of Li 1−x CoO 2 ). What then happen afterward inside LCO are not very clear, but there are theories and practices about mitigating the ill effects, by either i) suppressing irreversible phase transformations in the bulk LCO by bulk doping (e.g., Mg, Cr, Ti, Mn, and Al; Al/La codoping) [15][16][17][18][19][20][21] or ii) suppressing surface instabilities, including formation of spinel-phase and cathode-electrolyte interphase (CEI) by engineering LCO surface via various coating process (e.g., sol-gel process, chemical polymerization or deposition techniques). It is known that oxygen redox (O 2− ↔O 1− ) starts to contribute capacity at these higher voltages, since the O 2p orbitals hybridizes with the Co 3d orbitals in the Co 3+/4+ :t 2g & O 2p resonant band at lower electronic energies.…”

“…This disrupts the cathode-electrolyte interface, and the effluent oxygen will react with liquid electrolyte and burn up this scarce resource (only few gram (electrolyte)/Ah used in practical full cells), leaving voids and reduced transition metals (TM) behind. What then happen afterward inside LCO are not very clear, but there are theories and practices about mitigating the ill effects, by either i) suppressing irreversible phase transformations in the bulk LCO by bulk doping (e.g., Mg, Cr, Ti, Mn, and Al; Al/La codoping) [15][16][17][18][19][20][21] or ii) suppressing surface instabilities, including formation of spinel-phase and cathode-electrolyte interphase (CEI) by engineering LCO surface via various coating process (e.g., sol-gel process, chemical polymerization or deposition techniques). [7,[22][23][24][25] While in practice both approaches improve the performance of LCO, the "bulk-phase" versus "surfacephase" dichotomy of this discussion seems a bit self-contradictory, since if mechanism (i) dominates, method (ii) should not work; and vice versa, if mechanism (ii) dominates, method (i) should not work.…”

A Novel Protective Strategy on High‐Voltage LiCoO2 Cathode for Fast Charging Applications: Li1.6Mg1.6Sn2.8O8 Double Layer Structure via SnO2 Surface Modification

“…SnO 2 is from the surface coating and Mg should be from the Mg‐doped LiCoO 2 . If Mg ions are extracted out of LiCoO 2 and forms undoped LiCoO 2 , the lattice parameters are possible to decrease, since the Mg‐doped LiCoO 2 has a larger lattice …”

“…If Mg ions are extracted out of LiCoO 2 and forms undoped LiCoO 2 , the lattice parameters are possible to decrease, since the Mg-doped LiCoO 2 has a larger lattice. [21,22] Layer-structure LiCoO 2 is going to convert to double layer Li 1.6 Mg 1.6 Sn 2.8 O 8 when reacting with SnO 2 . But with small amount SnO 2 , the reaction product might be different.…”