Browsing by Author "Lahtinen, Katja"

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Aging mechanisms of NMC811/Si-Graphite Li-ion batteries
(2024-04-15) Laakso, Ekaterina; Efimova, Sofya; Colalongo, Mattia; Kauranen, Pertti; Lahtinen, Katja; Napolitano, Emilio; Ruiz, Vanesa; Moškon, Jozé; Gaberšček, Miran; Park, Juyeon; Seitz, Steffen; Kallio, Tanja
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Electrode degradation processes at various Li-ion batteries’ state-of-health (SoH 100 %, 80 %, 50 %, and 30 %) and cycling temperatures (5 °C, 23 °C, and 45 °C) were investigated. For this purpose, the standard format of Li-ion cylindrical 18,650 batteries with Si-Graphite negative and LiNi0·8Co0·1Mn0·1O2 (NMC811) positive electrodes were cycled with registering battery parameters and the electrochemical impedance spectrum were recorded after every 200 cycles. Once reaching their end-of-life, electrodes from cycled batteries were subjected to post-mortem analysis. NMC811 positive electrode was observed to crack during the charge and discharge processes, suffered by irreversible phase transition, transition metal dissolution, cathode electrolyte interphase growth, and cation mixing. The Si-Graphite negative electrode material was also affected by crack formation, layer exfoliation, solid electrolyte interphase (SEI) recompositing, Li dendrite growth, transition metal contamination, and Si dissolution. Degradation of components leads to an increase of the contact resistance, Li+ diffusion limitations, reduction of active materials participating in Li-ion storage and, as a result, capacity fade that finally rendered the battery utilization unfeasible. Degradation processes can be detected by capacity fade and impedance growth of the full battery. High temperature accelerates electrode degradation processes when low temperature leads to SEI and Li dendrite growth.
Biocarbon from brewery residues as a counter electrode catalyst in dye solar cells
(2021-02-01) Tiihonen, Armi; Siipola, Virpi; Lahtinen, Katja; Pajari, Heikki; Widsten, Petri; Tamminen, Tarja; Kallio, Tanja; Miettunen, Kati
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
We explore biocarbon as a low-cost, abundant, and environmentally friendly replacement for Pt in dye solar cells. We introduce a novel biochar based on brewery residues with good performance and stability potential as a counter electrode in complete dye solar cells, and present the first long-term stability test results of a biocarbon in complete dye solar cells. The hydrothermally carbonized and KOH-activated brewer's spent grain (BSG) offers an extremely high surface area for catalytic reactions (2190 m2/g). Counter electrodes based on this material provide a promising initial performance (efficiency of 3.6 ± 0.2% for biocarbon solar cells compared to 5.3 ± 0.2 for reference cells with Pt catalyst) with current production and the total resistance of solar cells very close to that of Pt based solar cells. In an extended accelerated aging test, the best biocarbon dye solar cell maintained over 86% of its initial efficiency for 3000 h. Moreover, the biocarbon reduced the degradation via loss of electrolyte charge carriers during aging. Based on these results, the activated BSG biocarbon provides a promising alternative for Pt catalysts.
Conjugation with carbon nanotubes improves the performance of mesoporous silicon as Li-ion battery anode
(2020-03-27) Ikonen, Timo; Kalidas, Nathiya; Lahtinen, Katja; Isoniemi, Tommi; Toppari, J. Jussi; Vázquez, Ester; Herrero-Chamorro, M. Antonia; Fierro, José Luis G.; Kallio, Tanja; Lehto, Vesa Pekka
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Carbon nanotubes can be utilized in several ways to enhance the performance of silicon-based anodes. In the present work, thermally carbonized mesoporous silicon (TCPSi) microparticles and single-walled carbon nanotubes (CNTs) are conjugated to create a hybrid material that performs as the Li-ion battery anode better than the physical mixture of TCPSi and CNTs. It is found out that the way the conjugation is done has an essential role in the performance of the anode. The conjugation should be made between negatively charged TCPSi and positively charged CNTs. Based on the electrochemical experiments it is concluded that the positive charges, i.e., excess amine groups of the hybrid material interfere with the diffusion of the lithium cations and thus they should be removed from the anode. Through the saturation of the excess positive amine groups on the CNTs with succinic anhydride, the performance of the hybrid material is even further enhanced.
Cycle Life and Recycling of Positive Electrode Materials in Li-Ion Batteries
(2022) Lahtinen, Katja
School of Chemical Engineering | Doctoral dissertation (article-based)
Li-ion batteries are a primary power source for portable consumer electronics, such as mobile phones and laptops. In addition, they power electric vehicles (EVs) and can be used as a stationary energy storage for renewable energy sources, such as solar and wind power. Lately, the demand for Li-ion batteries has increased rapidly due to the electrification of transportation, and this has induced challenges related to the sustainability of material production. In this thesis, two major factors in improving the sustainability of Li-ion battery positive electrode materials, cycle life and recycling, are investigated. The thesis focuses on understanding, how dopants or impurities affect the positive electrode materials at the different stages of their life from synthesis to recycling. First, adding Mg doping to LiCoO2 in different synthesis stages was investigated. Adding the doping in lithiation step was observed to enhance even Mg distribution to the particles and to improve the morphology, which reduced the increase in the charge transfer resistance and led to the improved cycle life. Precursor doping, on the other hand, induced Mg distribution on the particle surface and decreased the stacking order in the crystal, which decreased the cycle life. Li excess in the samples was observed to decrease the rate capability of all the materials regardless the doping stage but not affect the cyclability of lithiation-doped LiCoO2. In addition to doping with a single element, dual doping of LiCoO2 with Mg and Ti was investigated and compared to the Li excess. The Mg-Ti doping was observed to improve the electrochemical performance of LiCoO2 by enhancing the electric conductivity and suppressing the increase of the charge transfer resistance. Li excess was observed to decrease the cycle life in the voltage range of 3.0–4.2 V. The demand for Li-ion battery raw materials is rapidly increasing alongside the amount of generated waste batteries. In the state-of-art battery recycling processes, all battery parts are recycled at the same process, which leads to impurity metals mixing with the electrode materials. To understand the effect of the metal impurities on the recycling, Li-ion battery waste was recycled using a hydrometallurgical method, and the regenerated chemicals were used in the synthesis of LiCoO2 whose electrochemical performance was then investigated. Cu was observed to be a main impurity in the process, and it decreased the initial capacity of the synthesized materials. However, the regenerated LiCoO2s decreased the increase in impedance, which led to improvements in the rate capability and cycle life. Alternative methods for the state-of-art recycling methods were discussed as well. In this work, a new method to regenerate spent Li-ion battery positive electrode by electrochemical re-lithiation without removing the active material from the current collector was investigated. The effect of doping on the reusability was investigated as well, and Mg-Ti doping was observed to enhance it. The regenerated materials had a slightly poorer cyclability compared to the fresh materials, which was attributed to the decline in the stacking order and the increase in impedance.
In-situ dilatometry and impedance spectroscopy characterization of single walled carbon nanotubes blended LiNi0.6Mn0.2Co0.2O2 electrode with enhanced performance
(2022-04-20) Mousavihashemi, Seyedabolfazl; Lahtinen, Katja; Kallio, Tanja
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Enhancing lithium-ion batteries (LiBs) cycle life is essential from both economic and sustainability perspective. In addition, to make their application in electric vehicles (EVs) even more feasible, the energy and power density have to be enhanced as well. Improvement in the electrical conductivity of battery electrodes can lead to an augmentation in power density and this can be achieved by using highly conductive carbon nanomaterials in the electrode fabrication. On the other hand, cycle life of LiBs is affected by dilation of both positive and negative electrodes during lithium ion (de)-insertion, and this can be also tailored by electrode design. In this work, ozonated long single walled carbon nanotubes (SWCNTs) are utilized to improve electrical conductivity of a LiNi0.6Mn0.2Co0.2O2 (NMC622) positive electrode along with enhancement of the mechanical strength. The enhancement effect of the ozone-treated SWCNTs on the NMC622 positive electrodes is demonstrated by means of electrochemical impedance spectroscopy and in-situ dilatometry. Compared to a conventional conductive carbon containing electrode, the presence of SWCNTs in an NMC622 electrode decreases irreversible height change occurring during a formation cycle from 276 nm to 86 nm and decreases overall electrode height change ∼5.5 times. Furthermore, coulombic and energy efficiencies of the Ozonated SWCNT NMC622 electrodes are improved by 1.2% and 6.4%, respectively, compared to the reference NMC622 electrode after 250 cycles in a three-electrode assembly, showing great potential for SWCNTs to be used in LiBs. Hence, addition of optimized amount of modified SWCNTs is capable of enhancing both power density and cycling stability of LiBs simultaneously.
Kohti korkeampikapasiteettista litiumioniakkua: pii negatiivielektrodina
(2018-05-06) Rimpilä, Ella
Kemiantekniikan korkeakoulu | Bachelor's thesis
Liposomit lääkeaineiden kuljettajina
(2014-12-01) Lahtinen, Katja
Kemiantekniikan korkeakoulu | Bachelor's thesis
Lithium cobalt oxide particles as positive electrode materials in Li-ion batteries
(2017-01-09) Lahtinen, Katja
Kemian tekniikan korkeakoulu | Master's thesis
Li-ion batteries are widely used for portable electronic devices, such as mobile phones and laptop computers. Although they have been successfully commercialized, new applications such as electric vehicles, require higher power and energy density. Therefore, many efforts have been made to improve Li-ion battery cell performance. Lithium cobalt oxide, LiCoO2 is one of the most used positive electrode materials in Li-ion batteries. It was the first positive electrode material used in commercial Li-ion batteries, and has many advantages such as high energy density and excellent cycle life. The disadvantages of lithium cobalt oxide include for example expensive price of cobalt, and thermal instability at high voltages. Since its commercialization in Li-ion batteries, investigations have been widely performed to improve safety, price and rate capability of lithium cobalt oxide. In addition, several other positive electrode materials have been introduced as well. In the literature section of this thesis, the effect of different parameters in lithium cobalt oxide on its electrochemical properties are described. These include preparation process, particle size, phase transitions in the structure upon cycling, stoichiometry, and doping. In addition, the typical Li-ion battery characterization methods and their use in the research are introduced. In the experimental section, the electrochemical properties of three different lithium cobalt oxide materials were investigated. The materials were lithium poor lithium cobalt oxide (LCO12), stoichiometric lithium cobalt oxide (LCO13) and doped lithium cobalt oxide (LCO07). All three materials had the same precursor. The material structural characterization was done with X-ray diffraction (XRD) and scanning electron microscope (SEM). The electrochemical characterization was done using galvanostatic measurements, electrochemical impedance spectroscopy (EIS), and galvanostatic intermittent titration technique (GITT). The doped lithium cobalt oxide had clearly the best rate capability and cycle life properties. The superior rate capability was attributed to the smaller crystal size and the doping. The long cycle life was related to small increase in cell impedance during cycling. Correspondingly, the short cycle life was related to large increase in cell impedance. The long cycle life and small increase in the impedance of the doped material indicate that the material was more stable than the two other materials. Because of this, less side reactions with electrolyte occurred. The diffusion coefficients were determined to be 10-12-10-11 cm2/s for all three materials at states of charge (SoC) of 35-65% and 75-100%. This value was in agreement with values presented in literature. At SoC of 0-10% there were differences in diffusion coefficients. The cause for this was concluded to be caused by either the differences between materials or error in GITT-measurement.
Lithium nickel manganese cobalt oxide as a positive electrode material in lithium ion batteries
(2019-07-31) Pehto, Erkka
Kemian tekniikan korkeakoulu | Master's thesis
Li-ion batteries are the most popular rechargeable batteries due to their high power and energy density, long cycle life, safety and environmental friendliness. Lithium nickel manganese cobalt oxide, LiNixMnyCo1-x-yO2 is an increasingly widely used positive electrode material in Li-ion batteries. Its advantages over other positive electrode materials are its high energy density and long cycle life. It was originally designed to replace lithium cobalt oxide, LiCoO2 in order to decrease the usage of cobalt, which is currently an expensive and often unethically produced material. Lithium nickel manganese cobalt oxide is widely studied and developed into better characteristics. In the literature part of this work, the electrochemistry of Li-ion battery cells is introduced, after which the characteristics of lithium nickel manganese cobalt oxide as the positive material in Li-ion batteries are described. The characteristics include composition, crystal structure and electrochemical performance. Effects of structural modifications, doping, coatings and additives on the electrochemical performance are discussed. In the experimental part, four LiNi0.6Mn0.2Co0.2O2 materials were investigated as the positive electrode material in Li-ion battery cells. Differences between the materials were the secondary particle size of the nickel manganese cobalt oxide precursor and temperature of the lithiation process. Half cells using lithium as the negative electrode and full cells using graphite on the negative electrode were investigated. Structural characterization was performed using X-ray diffraction and scanning electron microscopy. Electrochemical characterization was performed using cyclic voltammetry, electrochemical cycling and electrochemical impedance spectroscopy. Higher lithiation temperature was found to lead to an increase in the secondary particle size and to a higher deviation from the stoichiometric layered lithium-transition metal oxide crystal structure. The material with the lowest deviation from the layered crystal structure had the highest cycle life, and both of the materials with the higher lithiation temperature had faster lithium ion diffusion. All the materials had very similar electrochemical performances. High calendering pressure enhanced the rate capability of the electrodes by increasing electron transfer between the active material particles. The material with the smallest secondary particle size had the lowest discharge capacities at all charging rates. The materials with a larger particle size were found to most likely have a better contact with the current collector on the positive electrode. Charge transfer resistances were growing faster in cells with a 70 % state of charge than in cells with a 30 % state of charge.
Long-term cycling behavior of Mg-doped LiCoO2 materials investigated with the help of laboratory scale X-ray absorption near-edge spectroscopy
(2022-07) Lahtinen, Katja; Labmayr, Maximilian; Mäkelä, Ville; Jiang, Hua; Lahtinen, Jouko; Yao, Lide; Fedorovskaya, Ekaterina O.; Räsänen, Samuli; Huotari, Simo; Kallio, Tanja
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The use of Li-ion batteries is increasing rapidly. Understanding the processes behind active material aging helps to enhance the materials, and therefore, development of new in situ methods for structural studies is important. In addition, understanding the effect of different synthesis methods on the active material properties is necessary to optimize the material cycle life. In this work, the performance of LiCoO2 doped with Mg during the lithiation step is compared to LiCoO2 prepared using an Mg-doped Co3O4 precursor. In situ laboratory-scale X-ray absorption near-edge spectroscopy is used to analyze the Co valence changes in LiCoO2 to understand the electrochemical behavior of the investigated materials. The maximum reachable Co valence state is found to decrease upon aging, a small decrease indicating a good cycle-life, and this is attributed to the enhanced stacking order, better Mg distribution in the lattice, and fine primary particle size in the material. In the synthesis conditions used in this study, Mg doping during the lithiation step is shown to perform better compared to the precursor doping. Overlithiation is shown to reduce the electrochemical performance of nondoped and precursor-doped LiCoO2 materials but not to affect the cyclability of lithiation-doped LiCoO2.
Reuse of LiCoO2 Electrodes Collected from Spent Li-Ion Batteries after Electrochemical Re-Lithiation of the Electrode
(2021-06-08) Lahtinen, Katja; Rautama, Eeva Leena; Jiang, Hua; Räsänen, Samuli; Kallio, Tanja
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
The recycling of used Li-ion batteries is important as the consumption of batteries is increasing every year. However, the recycling of electrode materials is tedious and energy intensive with current methods, and part of the material is lost in the process. In this study, an alternative recycling method is presented to minimize the number of steps needed in the positive electrode recovery process. The electrochemical performance of aged and re-lithiated Mg−Ti-doped LiCoO2 and stoichiometric LiCoO2 was investigated and compared. The results showed that after re-lithiation the structure of original LiCoO2 was restored, the capacity of an aged LiCoO2 reverted close to the capacity of a fresh LiCoO2, and the material could thus be recovered. The re-lithiated Mg−Ti-doped LiCoO2 provided rate capability properties only slightly declined from the rate capability of a fresh material and showed promising cyclability in half-cells.
Role of impurity copper in Li-ion battery recycling to LiCoO2 cathode materials
(2020-02-29) Peng, Chao; Lahtinen, Katja; Medina, Elena; Kauranen, Pertti; Karppinen, Maarit; Kallio, Tanja; Wilson, Benjamin P.; Lundström, Mari
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Copper is a dominating impurity in Co-rich Li(Co,Ni,Mn)O2 battery waste fractions and may exist in similar quantities (e.g. 6 wt%) as Li, Ni and Mn. This paper investigates the behavior of copper from waste batteries up to recycled active materials and the findings highlight that copper contamination is not necessarily detrimental for the active materials in trace amounts, but can rather increase the discharge capacity at high rates. Firstly, industrially crushed battery waste was treated hydrometallurgically to produce Li2CO3 and CoSO4·2H2O precipitates for re-use, before being calcined to prepare fresh LiCoO2 materials. Results suggest that during the hydrometallurgical recycling process, Cu is likely to co-extract along the Co; in the current work both high and low Cu-contaminated CoSO4·2H2O precipitates were obtained and in the former case, formation of CuO as a secondary phase occurred upon calcination. The presence of Cu contamination induced up to ca. 35 mAh/g decrease in the specific capacity, compared to pure LiCoO2. However, a low level of Cu inclusion was found to be advantageous at high discharge rates (4.0C and 5.0C) resulting in a doubling of the capacity (110–120 mAh/g) when compared with pure LiCoO2 (40–60 mAh/g).
Room-Temperature Micropillar Growth of Lithium–Titanate–Carbon Composite Structures by Self-Biased Direct Current Magnetron Sputtering for Lithium Ion Microbatteries
(2019-10-17) Etula, Jarkko; Lahtinen, Katja; Wester, Niklas; Iyer, Ajai; Arstila, Kai; Sajavaara, Timo; Kallio, Tanja; Helmersson, Ulf; Koskinen, Jari
A1 Alkuperäisartikkeli tieteellisessä aikakauslehdessä
Here, an unidentified type of micropillar growth is described at room temperature during conventional direct-current magnetron sputtering (DC-MS) deposition from a Li4Ti5O12+graphite sputter target under negative substrate bias and high operating pressure. These fabricated carbon–Li2O–TiO2 microstructures consisting of various Li4Ti5O12/Li2TiO3/Lix TiO2 crystalline phases are demonstrated as an anode material in Li-ion microbatteries. The described micropillar fabrication method is a low-cost, substrate independent, single-step, room-temperature vacuum process utilizing a mature industrial complementary metal–oxide–semiconductor (CMOS)-compatible technology. Furthermore, tentative consideration is given to the effects of selected deposition parameters and the growth process, as based on extensive physical and chemical characterization. Additional studies are, however, required to understand the exact processes and interactions that form the micropillars. If this facile method is further extended to other similar metal oxide–carbon systems, it could offer alternative low-cost fabrication routes for microporous high-surface area materials in electrochemistry and microelectronics.