CROSS REFERENCE TO RELATED APPLICATIONS

This application is a U.S. National Stage Application of International Application No. PCT/KR2020/017774, filed on Dec. 7, 2020, which claims the benefit under 35 USC 119(a) and 365(b) of Korean Patent Application No. 10-2020-0063029, filed on May 26, 2020, filed on May 26, 2020 in the Korean Intellectual Property Office, the entire disclosure of which is incorporated herein by reference.

TECHNICAL FIELD

The present disclosure relates to management of a battery, particularly a system for predicting a battery lifetime using the charge-discharge characteristics of a battery in a BMS system.

BACKGROUND ART

A lithium-ion battery shows the most excellent performance among secondary batteries that are generally used at present. Since the lithium-ion battery is relatively light and has high energy density in comparison to other secondary batteries, the lithium-ion battery is widely used in various fields including portable products and even large energy storage systems. In particular, with the spread of electrical vehicles, next-generation batteries such as a lithium-sulfur battery, a lithium-air battery, a sodium-magnesium battery, and a solid-state battery are developed to solve the problem with the capacity of a battery for improving mileage and the problem with stability that is a mortal defect. However, there are still many problems in order to generally use such next-generation batteries. Accordingly, the market of lithium-ion battery is expected to expand. In particular, efficient energy use and the problem with stability of the lithium-ion battery are being more spotlighted with the growth of the market of mobile phone and personal mobility (an electric scooter, an electric bicycle, etc.).

In general, the lithium-ion battery is stable for a while in the early stage. However, as the frequency of use increases, the lifetime decreases, the electrolyte is decomposed by an oxidation-reduction reaction and forms a Solid Electrolyte Interface (SEI) layer, which causes the effect of increasing the internal resistance, and the available capacity of the battery decreases. The SEI layer serves as a protective membrane preventing continuous decomposition of the electrolyte, but is a direct reason that causes reduction of irreversible capacity in terms of entropy.

When charge and discharge are repeated with the lifetime reduced, problems such as overcharge, overdischarge, and overcurrent may be generated, depending on circumstances. In particular, with the growth of the market of person mobility, users charge electric scooters, electric bicycles, etc. at home, but fire accidents frequently occur due to overheating and ignition when they charge such devices without considering the lifetime.

When the capacity of the lithium-ion battery drops to 80% or lower from the initial capacity, the lifetime is considered end. It is very important to predict the lifetime of a battery for efficient use of resources and stable management and use of an energy storage system.

Many studies for predicting a lifetime has been conducted.

A “Life prediction apparatus and the life prediction method using the same” has been disclosed in Korean Patent Application Publication No. 10-2010-0019660 (Feb. 19, 2010). The apparatus and system for life prediction of a secondary battery on the basis of a constant voltage period when the battery is charged include: primarily charging a secondary battery within the operation voltage range of the secondary battery; cutting-off when the secondary battery is charged at a specific level of capacity; secondarily charging the battery until a current of specific capacity is reached when the cut-off voltage is reached; measuring the time until the current is reached in the secondary charging; predicting the lifetime of the battery by mapping data of the measurement time and a predetermined reference time; and displaying the predicted lifetime. According to this related art, since a user can check the lifetime of a secondary battery, it is possible to remove the inconvenience that the user cannot use a portable electric device due to discharge of the secondary battery at unexpected time. In particular, it is possible to solve the problem that a user unnecessarily charges the secondary battery without knowing the fact before charging the battery through a charger even when a secondary battery should be replaced.

However, since most devices in the related art use parameters including a time function, there is a defect that the devices cannot cope with use environments that may change at any time. Further, parameters and model estimation device based on temperature (T) cause errors in analysis of the state of a battery due to errors based on boundary conditions, temperature measurement errors, and a slow dynamic characteristic of a temperature change.

Accordingly, there is a strong need for a technology that can accurately predict the remaining lifetime of a battery without uncertain factors.

CITATION LIST

Patent Literature

[Patent Literature 1]

Korean Patent Application Publication No. 10-2010-0019660 (2010.02.19.), titled “Life prediction apparatus and the life prediction method using the same”

SUMMARY OF INVENTION

Technical Problem

An objective of the present disclosure is to provide a prediction system that can predict a battery lifetime in terms of entropy on the basis of not temporal factors, but a voltage/SOC relationship in a battery management system.

Solution to Problem

In order to achieve the objectives of the present disclosure, the present disclosure provides a system for predicting the lifetime of a battery being chargeable and dischargeable using charge-discharge characteristics in a BMS. The battery lifetime predicting system includes: a battery state measurement unit measuring a voltage, a State of Charge (SOC), and a Depth of Discharge (DOD) of a battery while charging and discharging the battery with changing charge current and discharge current; an irreversible energy amount deriving unit deriving an irreversible energy amount (Qir) that is generated when the battery is charged/discharged from the voltage and the SOC using enthalpy and entropy theory; and a remaining lifetime prediction unit predicting a remaining lifetime of the battery from the derived irreversible energy amount (Qir). In particular, the irreversible energy amount deriving unit derives the irreversible energy amount (Qir) using equation

QirQ0=∫(α⁢EC-ED)⁢dSOC,
where Q0is the maximum capacity of the battery, a is an Arrhenius rate constant, and ECand EDare cell voltages at charging and discharging, respectively. Further, the remaining lifetime prediction unit predicts the remaining lifetime of the battery using equation

∑k=1nQir_kmin(mQir_m·∑k=1nQir_k)=NaNp,
where Qir_mis the maximum value of the irreversible energy amount at each cycle, m is the maximum cycle period, Naand NPare the actual number of times of cycles and the predicted number of times of cycles, respectively, and Qir_kis the current irreversible energy amount at a k-th cycle. In particular, the remaining lifetime prediction unit obtains Qir_mand Qir_kfrom the area of a charge/discharge curve at each cycle in a graph showing the relationship between voltage and an SOC of the battery, and the area of the charge/discharge curve at each cycle is obtained by dividing the charge/discharge curve into at least two or more sections and summing up areas of the divided sections. Further, the dividing of the charge/discharge curve at each cycle includes: extracting charging start points (PCS, P*CS), charging knee points (PCK, P*CK), discharging start points (PDS, P*DS), and discharging knee points (PDK, P*DK) at two continuous cycles in the charge/discharge curve; and dividing the charge/discharge curve into: a first section formed by PCS, P*CS, PCK, and P*CK; a second section formed byCS, P*CK, P*DS, and P*DK; and a third section formed by PDS, P*DS, PCK, and P*DK. Further, the charging start points (PCS) and the discharging start points (PDS) are extracted by a change of a current direction, and the charging knee points (PCK) and the discharging knee points (PDK) are extracted on the basis of the amount of a change of voltage for the SOC.

Advantageous Effects of Invention

According to the present disclosure, in order to remove temporal factors in consideration of the actual configuration of a battery management system, the voltage/SOC relationship is examined clearly in terms of entropy and influence by temperature is expressed as V/SOC result, whereby it is possible to estimate the lifetime of a battery without temperature and time components.

