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Supporting Information
Instantaneous surface Li3PO4 coating and Al-Ti doping and their effect on the performance of LiNi0.5Mn1.5O4 cathode materials
Valeriu Mereacre,*
,†Nicole Bohn,
†Pirmin Stüble,
†,‡Lukas Pfaffmann,
†and Joachim R. Binder
††Institute for Applied Materials - Energy Storage Systems, Karlsruhe Institute of Technology, D-76344,
Eggenstein-Leopoldshafen, Germany
‡Helmholtz Institute Ulm, D-89081, Ulm, Germany
Email: [email protected]
Experimental Material preparation
The pristine LNMO was prepared by a co-precipitation method as reported1. In a typical synthesis route, 0.185 mol of analytical reagent grade LiCH3COO2H2O, 0.090 mol Ni(CH3COO)24H2O, and
0.270 mol Mn(CH3COO)24H2O were dissolved in 300 ml of water. The solution was transferred into a 1
L continuously stirred tank reactor. Separately, 0.451 mol of H2C2O42H2O were dissolved in 450 ml of
water. Under temperature of 50 oC and constant stirring (400 rpm) of the Li-Ni-Mn solution, 30 g of solid PEG6000 was added. After 10 minutes, when PEG6000 dissolved completely, the oxalic acid aqueous solution was started to be pumped (10 ml/min) into the continuously stirred tank reactor. At the beginning of the reaction the solution was clear, but after ~ 10 min a light green suspension began to form. After the oxalic acid solution was completely pumped, the reaction mixture was stirred for additional 20 minutes. Then, the water in the obtained suspension was evaporated at 90 oC over the night to afford a green viscous precursor (~ 85 g). The resultant mixture was calcined in air at 450 oC for 4 h and then at 900 oС for 24 h, and cooled down to room temperature with the heating and cooling rate s of 4 oC/min to obtain LiMn1.5Ni0.5O4, which is labelled as LNMO. Brunauer-Emmett-Teller surface area is 0.3 m2g-1.
The reference compound, LNMO+800°C was obtained by calcining pristine LNMO in air at 800 °С using the following program: 250 °C for 2 h and then heated at 800 °С for 10 h, and cooled down to room temperature with the heating and cooling rate of 4 °C/min.
1. V. Mereacre, N. Bohn, M. Müller, S. Indris, T. Bergfeldt and J. R. Binder, Materials Research Bulletin, 2021, 134, 111095.
Preparation of Li-Al-Ti-PO4 coating solution
Reagent-grade aluminum nitrate (Al(NO3)39H2O), titanium isopropoxide (Ti(C12H28O4)), H3PO4 (85%),
and lithium acetate (LiOOCCH32H2O) were used as aluminium, titan, phosphate and lithium sources.
0.257 g of Al(NO3)39H2O and 0.265 g LiOOCCH32H2O were dissolved in 10 ml water. Separately,
0.780 g Ti(C12H28O4) and 0.61 g H3PO4 were dissolved in 30 ml H2O2 (30%). Under magnetic stirring of
the second solution, the first one was added. The obtained mixture was stirred until a clear Li-Al-Ti-PO4
solution was obtained (~2-3 minutes). Material coating
In a round bottom flask (300 ml) with 1 g LNMO, under stirring, 20 ml H2O2 (30%) was added. After ~30
seconds, 0.3 ml Li-Al-Ti-PO4 solution was added. During the first 60 minutes the reaction was relatively
silent, but after this time, the reaction started to be very violent and in one minute was ended. After additional 30 minutes of stirring, the reaction mixture was decanted, the obtained powder washed with 100 ml water and dried during of one hour in oven at 100 °C. The obtained dry powder was calcined in air at 800 °С using the same program as for the reference compound: 250 °C for 2 h and then heated at
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800 °С for 10 h, and cooled down to room temperature with the heating and cooling rate of 4 °C/min. The quantity of the Li1.3Al0.3Ti1.7(PO4)3 expected to be coated on the surface of LNMO particles is around 0.5
percent. The obtained sample was labelled as LNMO+LP(0.5%)+800°C. The samples LNMO+LP(5%)+800°C and LNMO+LP(10%)+800°C were obtained by the same procedure using 3.0 and 6.0 ml Li-Al-Ti-PO4 solution, respectively.
Note: it should be mentioned, that if the reaction is heated at ~50°C, then it takes not 60 minutes, but ~4-5 minutes until the coating process is finished.
Coating preparation
The remained Li-Al-Ti-PO4 coating solution, ~ 30 ml, was used to prepare Li1.3Al0.3Ti1.7(PO4)3 in
crystalline form. Under stirring the solution was heated on a hot plate at about 100 oC until the water and hydrogen peroxide was evaporated and a dry powder was obtained. A fine crystalline powder was obtained by calcination at 800 oC in air and labelled as LATP-800. The calcination program was the same
as for the reference and coated samples.
Powder X-ray diffraction and scanning electron microscope
Powder X-ray diffraction (XRD) was carried out using a ST OE diffractometer equipped with a Cu target X-ray tube and a diffracted beam monochromator. The scattering angle (2θ) was of 10–80° at 0.03° intervals with a dwell time of 10 s per point. A scanning electron microscop (SEM, Zeiss Supra 55) was used to elucidate the morphology of precursor, coating material, and coated samples. Before measurement the samples were prepared by mounting the powder on adhesive carbon tape. The energy dispersive X-ray spectroscopy (EDS) was carried out using EDS Detector Apollo 40 SSD, EDAX Inc., USA with the acceleration voltage of 7 kV.
Electrochemical measurements
Electrochemical measurements were carried out via galvanostatic charge/discharge cycling using 2032 coin cells with lithium metal as the anode on an on a BT2000 battery cycler (Arbin Instruments). During electrode preparation, the slurry was a mixture of 80 wt % active material, 10 wt % Super -S carbon black (Timcal) and 10 wt % PVDF (Polyvinylidene fluoride) with NMP (1 -Methyl-2-pyrrolidinone) as solvent. Electrodes were prepared by coating the slurry on an Al foil with a 200 μm notch bar spreader and dried in air at 80 °C for 20 minutes, then at 100 oC for 16 hours in vacuum. Usual cathode loadings were in the
range of 4.0 –5.0 mgcm-2; an electrode diameter of 12 mm was used. Before use the cathode disks were
pressed in a hydraulic press to 6 kN and dried additionally for 30 minutes in a vacuum oven at 100 °C. The electrolyte was 1.0 M LiPF6 solution in 1:1 v/v ethylene carbonate:diethyl carbonate (EC:DEC). As
anode a lithium metal foil was used. As separators were used one Celgard 2320 (Celgard) on the lithium and one on the positive electrode, and one GFC microfiber separator in the middle. Coin cells (2032) were assembled in a dry Ar-filled glove box. For every cell 200 l electrolyte was used. Cycling was performed at a temperature of 23°C. A voltage window of 3.5–5.0 V vs. Li+/Li was applied.
X-ray Photoelectron Spectroscopy
XPS spectra were acquired using a Thermo Scientific K-alpha spectrometer (Thermo Fisher Scientific GmbH, Dreieich, Germany). The samples were analyzed using a micro focused, monochromatic Al Kα X - ray source (1486.6 eV, 400 μm spot size). The spectra were recorded with a concentric hemispherical analyzer at a pass energy of 50 eV.
S3 Further results
Figure S1. SEM with EDS of the LNMO+LP(5.0%)+800°C
Figure S2. XRD of LATP+800°C.
Figure S3. XPS spectra of the oxides (Mn 3s, Ni 3p, Al 2p, Ti 2p and P 2p core levels) for pristine LNMO (top) and LNMO+LP(0.5%)+800°C (bottom).
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Figure S4. Raman spectra of the uncoated and coated (5 wt.%) LNMO powders, both heat-treated at 800°C.
Figure S5. Full rate capability test for three samples: LNMO, LNMO+800°C and LNMO+LP(0.5%)+800°C.
Figure S6. Differential capacity versus potential (dQ/dV versus V) between 3.5 and 5 V (from 5th to 100th cycle).
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Figure S7. A zoomed portion of the dQ/dV for the redox couple Ni3+/Ni4+ after 100 cycles
Table S1. Results of the Rietveld refinement. The values of the parameters indicated by zero were smaller than the esd and therefore not included into the final refinements.
Diffraction pattern Rwp lattice par. a
Al-occupancy Phase fractions [%] [%] LNMO [Ang.] on 8a-site [%]
x(LNMO) x(Rocksalt) x(γ-Li3PO4)
LNMO+800°C 3.1 8.1782(3) 0 95.7(6) 4.1(5) 0 LNMO+LP(0.5%)+800°C 3.3 8.1808(4) 0 97.2(8) 2.8(9) 0 LNMO+LP(5%)+800°C 2.8 8.1954(4) 8(1) 96.9(5) 3.1(3) 0 LNMO+LP(10%)+800°C 2.8 8.2625(3) 76(1) 93.0(5) 0.2(2) 6.8(4)
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Figure S8. Enlarged SEM diagrams of LNMO coated with 0.5 wt.% (top) and 5 wt.% Li-Al-Ti-PO4
