Günümüzde birçok enerji depolama çözümünde, yüksek enerji ve güç yoğunluklarına sahip olmaları nedeni ile Li-iyon polimer tip hücreler tercih edilmektedir. Li-iyon polimer hücrelerde, elektrotlar arasında bulunan seperatör malzeme elektriksel olarak yalıtkan fakat iyonik olarak iletken bir malzemedir. Bu malzemenin yapısı, hücrenin aşırı zorlanma durumlarında özelliğini kaybetmekte ve hücreyi arızalı konuma düşürerek güvenlik problemleri meydana getirmektedir. Hücrelerde geri döndürülemez değişiklilerin meydana geldiği bölgelerden biri elektrot ile seperatör arası katı elektrolit geçişlerinin yaşandığı bölgedir. Bu çalışmada, elektrokimyasal empedans spektroskopi yöntemi ile li-iyon polimer pillerin hücre kinetik parametreleri elde edilmiştir ve hücrelerin zorlanmış dolma ve boşalma durumlarında bu parametrelerin değişimi kuramsal olarak incelenmiştir. Li-iyon polimer pillerde oluşabilecek yanlış doldurma ve boşaltma işlemleri sebebi ile meydana gelen geri döndürülemez etkilerin klasik hücre modelleri tarafından tam olarak yansıtılamadığı görülmüştür. Bu nedenle çalışmada hücre eşdeğer devre modeli arıza durumularına göre geliştirilmiş ve sınıflandırılmış, yeni geliştirilmiş hücre eşdeğer devresi modeli ile pil sağlamlık durumunun daha iyi yansıtılacağı önerilmiştir. Yapılan deneysel çalışma ile, normal dolma ve boşalma durumlarında klasik pil modelinin, sağlamlık durumunun değerlendirmesi için yeterli olduğu görülmüştür. Aşırı dolma ve boşalma durumlarının ve etkilerinin incelendiği deneysel çalışmalar neticesinde klasik modelin durum değerlendirme için yetersiz kaldığı ispat edilmiş ve bu çalışmada önerilen modelin arıza durumlarını daha gerçekçi biçimde yansıttığı görülmüştür. Anahtar Kelimeler: Li-iyon polimer hücre modeli, aşırı şarj, aşırı deşarj, sağlamlık durumu.As much as the batteries involve to our lives in any technologic area as energy storage devices -in our case Li batteries - gain is much importance. Battery state definition is even more important with the complex energy storage solutions. In most cases having a Battery Management System (BMS) integrated with cells is necessary, because of specific applications. One of the main tasks in Battery Management is the determining the battery state by means of charge and health. The battery manufacturers or suppliers have high concern to have a proper battery for the specific application. Charging and discharging of batteries are critical since it is an external intervention to the cell, exciting cell chemistry. When they are not controlled properly there is high risk for battery state of health and the application. The literature reports various different approaches to estimating state of heath (primarily capacity fade). These include the discharge test, which completely discharge a fully cell in order to determine its total capacity; chemistry dependent methods, such as measuring the electrolyte density; ohmic tests such as resistance, conductance or impedance tests perhaps combined with fuzzy logic algorithms. The impedance techniques have been widely used in the last two decades for investigating the kinetic of primary or secondary cells and determining their state of charge or state of health. Electrochemical impedance spectroscopy method is a time consuming but a well proven technique for impedance measurement. In order to have an idea or make a decision on a "Battery State", state of charge and state of health parameters should be obtained. State of function could easily be evaluated after these determinations. However, state of function may differ according to the operating conditions and it is "user defined". Having the accurate value of state of charge and state of health for detecting failure is very important. Changes in state of charge can be defined as reversible changes in a battery. After proper usage and charging of a battery, effective capacity, internal resistance, open circuit voltage and gas production of the battery yield positive trend comparing the initial values. If this parametric changes act as irreversible changes, battery state of health is affected negatively, comparing to the initial state of the battery. Measuring only the cell terminal voltage and esti-mating the cell status is commonly used technique in most applications, bringing us possible faults while easy measurement technique. On contrary to the fact that, it is possible to detect internal short circuit and cell open circuit while it is not possible to detect irreversible changes on self discharge and internal resistance increase or active power loss by only voltage measurement. Therefore generally a small excitation current signal is applied to cell terminals in order to involve impedance to the measurement parameters. This study aims to identify the measurable parametric changes between cell terminals occur during overcharge and overdischarge process of Li-ion polymer batteries. These parametric chances will give the opportunity to detect and evaluate the failure of the battery. In this study, Li-ion polymer cell kinetic parameters were obtained by electrochemical impedance spectroscopy method and changes in these parameters were analyzed theoretically in cases of forced charging and discharging. It was seen that, classical cell models were not sufficient enough to mirror the irreversible effects on Li-ion polymer cells caused by improper charging and discharging procedures. Therefore cell equivalent circuit was improved and classified according to the failure states and it is suggested that the improved model is better reflecting the cell state of health. Experimental studies denote that classical cell model is sufficient and classical method is proper for state of health determination under normal charging and discharging cases. It was proved by experiments concentrated on overcharge and overdischarge characteristics that classical cell model is not sufficient and suggested new model is more realistic for state of health determination. Keywords: Li-ion polymer battery model, over-charge, overdischarge, state of health
