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Electrochemical capacity of Ni mass when subjected to various conditions, and the relation to changes in the nickel hydroxide phase and crystallite size

Hedlund, Magnus LU (2016) KOO920 20152
Centre for Analysis and Synthesis
Abstract
The electrochemical capacity of the nickel mass in the positive electrode when subjected to various conditions, and the relation to changes in the nickel hydroxide phases and crystallite size was studied in this thesis work.
The various conditions being: two different electrolytes, KOH and KOH/LiOH, different temperature during charging and different charge times.
The nickel mass was made into monopockets to subject it to these conditions and register the capacity of the mass in a computer, which was connected to the charging station.
From the monopocket analysis it could be seen that for most samples the capacity increased with increasing charge time.
When the monopocket tests were done, the testing electrodes were cut open to analyse... (More)
The electrochemical capacity of the nickel mass in the positive electrode when subjected to various conditions, and the relation to changes in the nickel hydroxide phases and crystallite size was studied in this thesis work.
The various conditions being: two different electrolytes, KOH and KOH/LiOH, different temperature during charging and different charge times.
The nickel mass was made into monopockets to subject it to these conditions and register the capacity of the mass in a computer, which was connected to the charging station.
From the monopocket analysis it could be seen that for most samples the capacity increased with increasing charge time.
When the monopocket tests were done, the testing electrodes were cut open to analyse them in an X-ray diffractometer (XRD) to see what nickel hydroxide phases were present in the samples.
The analyses showed that the electrolyte with LiOH added to it was more prone to form γ-phase and generated smaller crystallite sizes than the electrolyte without this addition.
When comparing the monopocket results and the results from the XRD, it could be seen that the samples with KOH as electrolyte that had lower capacity than expected also had larger amounts of γ-phase. This implies that there was some loss of contact in the active material due to the swelling connected with the γ-phase.
When cycling the monopockets further than the standard three times, it was found that the samples that used pure KOH as electrolyte still had γ-phase residues left even after the twentieth cycle whilst the samples with LiOH added to the electrolyte had no γ-phase left.
The temperature testing gave a bit inconclusive results but the electrolyte with LiOH additions was clearly superior during these tests, which was no surprise as it has been found to improve the performance of the positive electrode at higher temperatures. (Less)
Popular Abstract (Swedish)
Examensarbetet undersökte den elektrokemiska kapaciteten för nickelmassan i den positiva elektroden när den blev utsatt för olika förhållande och dess relation till ändringar i nickelhydroxidfaser och kristallitstorlek.
De olika förhållandena var: två olika elektrolyter, KOH och KOH/LiOH, olika temperaturer under laddning och olika laddningstider.
Nickelmassan gjordes till enfickor, en liten testelektrod, för att utsätta den för de olika förhållandena och dess kapacitet blev registrerad på en dator, som var kopplad till laddningsstationen.
Från enficksanalysen kunde man se att de flesta provernas kapacitet ökade med ökad laddningstid.
När enfickstesterna var klara, klipptes testelektroderna upp för att kunna analysera dem i en... (More)
Examensarbetet undersökte den elektrokemiska kapaciteten för nickelmassan i den positiva elektroden när den blev utsatt för olika förhållande och dess relation till ändringar i nickelhydroxidfaser och kristallitstorlek.
De olika förhållandena var: två olika elektrolyter, KOH och KOH/LiOH, olika temperaturer under laddning och olika laddningstider.
Nickelmassan gjordes till enfickor, en liten testelektrod, för att utsätta den för de olika förhållandena och dess kapacitet blev registrerad på en dator, som var kopplad till laddningsstationen.
Från enficksanalysen kunde man se att de flesta provernas kapacitet ökade med ökad laddningstid.
När enfickstesterna var klara, klipptes testelektroderna upp för att kunna analysera dem i en röntgendiffraktometer för att se vilka nickelhydroxidfaser som fanns i proverna. Resultaten från röntgendiffraktometern användes även för att räkna ut kristallitstorleken.
Analysen visade att elektrolyten med LiOH tillsatt var mer benägen att bilda γ-fas och genererade mindre kristallitstorlekar än vad elektrolyten utan denna tillsats gjorde.
Vid jämförelse mellan enficksresultaten och resultaten från röntgendiffraktometern visade det sig att proverna med elektrolyten KOH som hade lägre kapacitet än förväntat också hade större mängder av γ-fas. Detta indikerar att det var en viss förlust av kontakt i det aktiva matrialet på grund av uppsvällningen kopplad till γ-fasen.
När enfickorna kördes tjugo cykler istället för de tre cykler som var standard, upptäcktes det att proverna som använde ren KOH som elektrolyt hade rester av γ-fas kvar även efter den tjugonde cykeln medan proverna med LiOH tillsatt till elektrolyten inte hade någon γ-fas kvar.
Temperaturförsöket gav ganska otydliga eller inkonsekventa resultat, men elektrolyten med LiOH tillsatsen var klart överlägsen under dessa försök, vilket inte var så konstigt då tidigare studier hade konstaterat att denna tillsats ökade prestandan av den positiva elektroden vid höga temperaturer. Även om resultaten var otydliga hade proverna en fallande kapacitet med ökad temperatur.

Detta arbete genomfördes på och åt batteriföretaget SAFT i Oskarshamn för att få en inblick i hur deras batterier beter sig under olika förhållanden. Då det inte är säkert att batterierna förvaras i den miljö som SAFT rekommenderar är det bra att få reda på hur funktionen påverkas av t.ex. temperaturen. (Less)
Please use this url to cite or link to this publication:
author
Hedlund, Magnus LU
supervisor
organization
course
KOO920 20152
year
type
H2 - Master's Degree (Two Years)
subject
keywords
materials chemistry, materialkemi
language
English
id
8870854
date added to LUP
2016-04-21 10:54:55
date last changed
2016-04-21 10:54:55
@misc{8870854,
  abstract     = {The electrochemical capacity of the nickel mass in the positive electrode when subjected to various conditions, and the relation to changes in the nickel hydroxide phases and crystallite size was studied in this thesis work.
The various conditions being: two different electrolytes, KOH and KOH/LiOH, different temperature during charging and different charge times.
The nickel mass was made into monopockets to subject it to these conditions and register the capacity of the mass in a computer, which was connected to the charging station.
From the monopocket analysis it could be seen that for most samples the capacity increased with increasing charge time.
When the monopocket tests were done, the testing electrodes were cut open to analyse them in an X-ray diffractometer (XRD) to see what nickel hydroxide phases were present in the samples.
The analyses showed that the electrolyte with LiOH added to it was more prone to form γ-phase and generated smaller crystallite sizes than the electrolyte without this addition. 
When comparing the monopocket results and the results from the XRD, it could be seen that the samples with KOH as electrolyte that had lower capacity than expected also had larger amounts of γ-phase. This implies that there was some loss of contact in the active material due to the swelling connected with the γ-phase.
When cycling the monopockets further than the standard three times, it was found that the samples that used pure KOH as electrolyte still had γ-phase residues left even after the twentieth cycle whilst the samples with LiOH added to the electrolyte had no γ-phase left. 
The temperature testing gave a bit inconclusive results but the electrolyte with LiOH additions was clearly superior during these tests, which was no surprise as it has been found to improve the performance of the positive electrode at higher temperatures.},
  author       = {Hedlund, Magnus},
  keyword      = {materials chemistry,materialkemi},
  language     = {eng},
  note         = {Student Paper},
  title        = {Electrochemical capacity of Ni mass when subjected to various conditions, and the relation to changes in the nickel hydroxide phase and crystallite size},
  year         = {2016},
}