A lithium primary battery soc estimation method based on open circuit voltage-charge state characteristic curve

Abstract

A lithium primary battery SOC estimation method based on open circuit voltage-charge state characteristic curve, the method comprises the following steps: selecting a lithium primary battery system, establishing the first relationship curve of the open circuit voltage of the lithium primary battery of the system and the battery charge state under different discharge rates; a fitting model is established according to the first relationship curve; the discharge rate is selected as the parameter variable factor, the established fitting model is modeled through matlab, and the correlation model based on the open circuit voltage, discharge rate and battery charge state of the lithium primary battery is established; the current state of the battery is calculated by uploading the battery open circuit voltage and discharge rate value in the correlation model. The present application provides a lithium primary battery charge state rapid estimation method. In practical engineering application, for the case of no BMS system for monitoring the lithium primary battery power consumption, it is of practical significance to judge the remaining capacity of lithium primary battery and improve the reliability, safety and prevent safety accidents of lithium primary battery due to overdischarge.

Description

Technical Field

[0001] This invention belongs to the field of lithium primary battery technology, specifically relating to a method for estimating the state of charge (SOC) of lithium primary batteries based on the open-circuit voltage-charge characteristic curve. Background Technology

[0002] A lithium primary battery is a single-use battery that uses metallic lithium or lithium alloys as the negative electrode and cannot be repeatedly charged and discharged. Once the battery is depleted, it cannot be used. Based on the physical states of the electrolyte and the positive electrode material, lithium primary batteries have several different types, mainly including: solid positive electrode-organic electrolyte batteries, liquid positive electrode-liquid electrolyte batteries, and solid positive electrode-solid electrolyte batteries.

[0003] Lithium-ion primary batteries are characterized by high energy density, high operating voltage, wide operating temperature range, excellent storage performance, and convenient portability, making them one of the preferred power sources for military and civilian equipment. However, because lithium-ion primary batteries cannot be repeatedly charged and discharged, their charge level decreases as they discharge. Therefore, predicting the remaining capacity of lithium-ion primary batteries is crucial for users. Continuing to use them after their capacity is depleted will lead to over-discharge, which can cause gas leakage, electrolyte leakage, and in severe cases, even combustion or explosion, damaging the user, the surrounding environment, and equipment. Thus, the state of charge (SOC) of a lithium-ion primary battery (the ratio of its current energy output to its full capacity) is a very important indicator. In practical use, timely and effective monitoring of the battery's SOC and proper management and control are essential for the safety and reliability of lithium-ion primary battery operation.

[0004] Accurate battery SOC estimation is one of the core technologies in power management systems. It cannot be directly measured by a single sensor; it requires calculation through the measurement of other physical quantities and the application of specific mathematical models and algorithms. For example, using the ampere-hour integration method requires precise recording of the battery's discharge current and time during previous use. The amount of discharge is calculated by integrating the current and time, and then the remaining battery capacity is determined. This method provides relatively accurate calculation of battery charge, but it requires a dedicated power management unit (PMU) to accurately measure relevant discharge parameters such as current and time during battery use. However, in practical use, lithium primary batteries are not always equipped with a PMU to monitor battery discharge parameters in real time, considering factors such as battery size, system complexity, user needs, discharge methods, and cost. Sometimes, multiple, intermittent discharges may occur.

[0005] Therefore, for a specific lithium primary battery system, it is of great practical significance to predict the state of charge of the lithium primary battery quickly and effectively based on the currently testable parameters of the battery, to predict the subsequent discharge capacity of the lithium primary battery, and to ensure the safety and reliability of the subsequent discharge process. Summary of the Invention

[0006] To address the above problems, this invention provides a method for estimating the state of charge (SOC) of a lithium primary battery based on the open-circuit voltage-charge characteristic curve. The method includes the following steps:

[0007] Establish the first relationship curve between the open-circuit voltage and the battery charge of a lithium primary battery;

[0008] A fitting model is established based on the first relationship curve;

[0009] A correlation model is established using MATLAB based on the fitted model.

[0010] The current battery charge is calculated by uploading the battery open-circuit voltage and discharge rate to the associated model.

[0011] Preferably, establishing the first relationship curve between the open-circuit voltage and the battery charge of the lithium primary battery includes the following steps:

[0012] Selected lithium primary battery system;

[0013] Prepare the lithium primary battery for this system;

[0014] Measure the open-circuit voltage of the lithium primary battery;

[0015] The lithium primary battery is discharged.

[0016] Calculate the charge of the lithium primary battery;

[0017] A first relationship curve is established based on the open-circuit voltage and the battery charge.

[0018] Preferably, calculating the charge capacity of the lithium primary battery includes the following steps:

[0019] Get the battery charge expression;

[0020] The expression for obtaining the discharge capacity;

[0021] The battery charge is calculated based on the battery charge expression and the discharge capacity expression.

[0022] Preferably, the battery charge expression is:

[0023]

[0024] Where SOC represents the battery charge, Q Y-XQi represents the discharge capacity, Qi represents the discharge capacity set value, and n represents the number of discharges.

[0025] Preferably, the expression for the discharge capacity is:

[0026]

[0027] Among them, Q Y-X Qi represents the discharge capacity, Qi represents the discharge capacity set value, and n represents the number of discharges.

[0028] Preferably, establishing an association model based on the fitted model includes the following steps:

[0029] Obtain the discharge rate, open-circuit voltage, and battery charge.

[0030] The discharge rate is used as a parameter factor;

[0031] Based on the discharge rate, the open-circuit voltage, and the charge, a correlation model among the three is established using MATLAB.

[0032] Preferably, the expression of the association model is:

[0033] f(x,y)=p00+p10*x+p01*y+p11*x*y+p02*y^2;

[0034] Where f(x,y) represents the charge of the lithium primary battery, x represents the discharge rate, y represents the open circuit voltage, p00 = 65.88, p10 = -0.5825, p01 = 35.32, p11 = 0.4284, p02 = -9.95.

[0035] The SOC estimation method for lithium primary batteries based on the open-circuit voltage-charge characteristic curve provided in this application has the following advantages:

[0036] The SOC estimation method for lithium primary batteries based on the open-circuit voltage-charge characteristic curve provided by this invention has practical significance in engineering applications, especially in situations where there is no BMS system to monitor the power consumption of lithium primary batteries. It helps to determine the remaining capacity of lithium primary batteries, improve the reliability and safety of actual battery applications, and prevent safety accidents caused by over-discharge of lithium primary batteries. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0038] Figure 1 This invention provides a method for estimating the state of charge (SOC) of a lithium primary battery based on the open-circuit voltage-charge characteristic curve, which includes the first relationship curve of open-circuit voltage-charge of a lithium primary battery at room temperature and a 0.1C rate discharge, and a fitting model diagram.

[0039] Figure 2 This invention provides a method for estimating the state of charge (SOC) of a lithium primary battery based on the open-circuit voltage-charge characteristic curve, which includes the first relationship curve of open-circuit voltage-charge of a lithium primary battery at room temperature and a 0.2C rate discharge, and a fitting model diagram.

[0040] Figure 3 This invention provides a method for estimating the state of charge (SOC) of a lithium primary battery based on the open-circuit voltage-charge characteristic curve, which includes the first relationship curve of open-circuit voltage-charge of a lithium primary battery at room temperature and a 0.5C rate discharge, and a fitting model diagram.

[0041] Figure 4 This is a correlation model diagram between discharge rate, open circuit voltage, and charge in a lithium primary battery SOC estimation method based on open circuit voltage-charge characteristic curve provided by an embodiment of the present invention. Detailed Implementation

[0042] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0043] In this application embodiment, the present invention provides a method for estimating the state of charge (SOC) of a lithium primary battery based on the open-circuit voltage-charge characteristic curve, the method comprising the following steps:

[0044] S1: Establish the first relationship curve between the open-circuit voltage and the battery charge of the lithium primary battery;

[0045] In this embodiment of the application, establishing the first relationship curve between the open-circuit voltage and the battery charge of the lithium primary battery includes the following steps:

[0046] Selected lithium primary battery system;

[0047] Prepare a certain number of lithium primary batteries of the selected system;

[0048] Measure the open-circuit voltage of the lithium primary battery;

[0049] The lithium primary battery is periodically discharged at a certain discharge rate and at a certain temperature.

[0050] The charge of the lithium primary battery is calculated according to the expression for the charge of a lithium primary battery;

[0051] A first relationship curve is established based on the open-circuit voltage and the battery charge.

[0052] In this embodiment of the application, calculating the charge capacity of the lithium primary battery includes the following steps:

[0053] Get the battery charge expression;

[0054] The expression for obtaining the discharge capacity;

[0055] The battery charge is calculated based on the battery charge expression and the discharge capacity expression.

[0056] In this embodiment, the selected lithium primary battery system is a lithium-metal oxide battery system. A certain number of aged individual cells to be assembled into a group are selected and numbered as YX (where X represents the number of battery samples). A four-probe internal resistance tester is used to test the open-circuit voltage of the selected individual cells under certain temperature conditions, and the test data is recorded as the open-circuit voltage data before the first discharge. The selected individual cells are discharged for the first time at different rates under certain temperature conditions. The discharge capacity is set as Qi, where i is the number of discharges, and the first discharge capacity is recorded as Q1. The first discharge ends when the battery discharge capacity reaches the set Q1. After a certain interval, a second discharge is performed at the same rate as the first discharge under certain temperature conditions. Before the second discharge, the open-circuit voltage of the selected individual cells is tested and recorded as the open-circuit voltage before the second discharge. The second discharge capacity is recorded as Q2. This process is repeated until the capacity of the lithium primary battery is Qn, and the battery is completely discharged. The discharge is marked by the battery voltage reaching the cutoff voltage, which varies depending on the battery system. The final discharge ends when the battery voltage reaches the set cutoff voltage, and the total number of discharges is recorded as n.

[0057] In this embodiment, the full capacity of the lithium primary battery is denoted as Q. Y-X Where X is the number of battery samples, and the total capacity of a single battery is the sum of the capacities after n discharges, that is, the expression for the discharge capacity is formula (1):

[0058]

[0059] Among them, Q Y-X Qi represents the discharge capacity of a sample battery, where Qi represents the set discharge capacity value and n represents the number of discharge cycles.

[0060] If the battery charge is 100% before the first discharge, then the expression for the charge of the lithium primary battery is formula (2):

[0061]

[0062] Where SOC represents the battery's charge capacity, Q Y-X Qi represents the battery's discharge capacity, also known as the battery's total capacity. Qi represents the set discharge capacity value, and n represents the number of discharge cycles.

[0063] In actual operation, Q1 = Q2 = Q3 = ... Qi ... = Q(n-1), based on the set value of Q1 and the total capacity Q of the lithium primary battery. Y-X The size of the single cell, the final discharge capacity Qn≤Q1=Q2=Q3=…Qi…=Q(n-1).

[0064] S2: Establish a relationship curve between open-circuit voltage and SOC based on the open-circuit voltage measured in S1 and the calculated SOC value, and establish a fitting model based on the first relationship curve;

[0065] S3: Using the discharge rate as a parameter, and based on the fitting model described in S2, establish a correlation model between open-circuit voltage, charge, and parameter using MATLAB;

[0066] In this embodiment of the application, the expression of the association model is:

[0067] f(x,y)=p00+p10*x+p01*y+p11*x*y+p02*y^2;

[0068] Where f(x,y) represents the charge of the lithium primary battery, x represents the discharge rate, y represents the open circuit voltage, p00 = 65.88, p10 = -0.5825, p01 = 35.32, p11 = 0.4284, p02 = -9.95.

[0069] S4: Obtain the open-circuit voltage and discharge rate of the lithium primary battery;

[0070] S5: Upload the battery open-circuit voltage and discharge rate described in S4 to the correlation model described in S3 to calculate the charge capacity of the lithium primary battery.

[0071] In this embodiment, the relationship between the discharge capacity and the open-circuit voltage of the lithium primary battery under different rate conditions is calculated using formulas (1) and (2), and the relationship is fitted. Then, using the discharge rate as a parameter, a correlation model is established between the discharge rate, open-circuit voltage, and charge. In the correlation model, the current charge of the lithium primary battery is quickly estimated by uploading the battery open-circuit voltage and discharge rate.

[0072] To further understand the invention's content, features, and effects, the following embodiments are provided for detailed explanation.

[0073] Example:

[0074] The embodiment of this invention patent selects a lithium-metal oxide battery system, and the experimental temperature is selected as room temperature 25℃±3℃.

[0075] (1) Three lithium-metal oxide single-cell battery samples that have completed aging and are to be assembled were selected and labeled as Y-1, Y-2 and Y-3 respectively. Under normal temperature conditions, the open circuit voltage of the three selected single-cell batteries was tested and recorded using a four-probe internal resistance tester as the open circuit voltage data before the first discharge.

[0076] (2) Under normal temperature conditions, the three samples were discharged at rates of 0.1C, 0.2C and 0.5C respectively. The initial discharge capacity was set to Q1, where Q1 = 3Ah, that is, the discharge of a single cell was stopped after 3Ah.

[0077] (3) After an interval of ≥5 days, test the open-circuit voltage of each sample cell and record it as the open-circuit voltage data of the cell before the second discharge. Perform the second discharge on the selected cells according to the method in step (2), with a discharge capacity of Q2, where Q2 = Q1 = 3Ah, that is, stop discharging the cell after the second discharge of 3Ah.

[0078] (4) Repeat steps (2) and (3) cyclically, recording the discharge capacity as Qi each time, where i represents the number of discharges, until the capacity of a single cell is completely discharged. The sign that the capacity of a single cell is completely discharged is the last discharge to the set cutoff voltage. For the lithium-metal oxide battery system selected in this invention, the discharge cutoff voltage is set to 2.0V, the total number of discharges of a single cell is recorded as n, and the capacity of the last discharge is recorded as Qn, where Q1=Q2=Q3=…Qi…=Q(n-1)=3Ah, Qn≤Q1=3Ah, and the measured value of Qn is recorded according to the discharge conditions.

[0079] (5) Calculate the total capacity of each individual battery cell according to the formula in this step. The total capacity is denoted as Q. Y-X The total capacity of a single battery cell is the sum of its capacity after n discharge cycles, i.e.

[0080]

[0081] Where X represents the sample number, and Q... Y-X Qi represents the total discharge capacity, Qi represents the discharge capacity set value, and n represents the number of discharges.

[0082] (6) Calculate the SOC (State of Charge) of a single cell before each discharge at different discharge rates using the formulas in this step. The battery charge before the first discharge is 100%. The calculation method for the SOC of a single cell at different discharge rates is as follows:

[0083]

[0084] Where SOC represents the battery charge, Q Y-X Qi represents the total discharge capacity, Qi represents the discharge capacity set value, and n represents the number of discharges.

[0085] (7) Obtain the first relationship curve between the battery open-circuit voltage and the calculated SOC under different discharge rates from the aforementioned steps, and establish a fitting model based on the first relationship curve.

[0086] (8) Using the discharge rate as a parameter, the established fitting model is modeled using MATLAB software to establish a correlation model between the discharge rate, open-circuit voltage, and charge. In this embodiment, the correlation model obtained for the lithium-metal oxide system battery is as follows:

[0087] f(x,y)=p00+p10*x+p01*y+p11*x*y+p02*y^2(R-square=0.9779)

[0088] Where f(x,y) represents the charge of the lithium primary battery, x represents the discharge rate, y represents the open circuit voltage, p00 = 65.88, p10 = -0.5825, p01 = 35.32, p11 = 0.4284, p02 = -9.95.

[0089] (9) For lithium primary batteries of the same system, upload the battery open circuit voltage y and discharge rate x to the correlation model in step (8) to quickly estimate the current charge (SOC) of the selected lithium primary battery system.

[0090] The lithium primary battery charge estimation method provided by this invention has practical significance in practical engineering applications, especially in situations where there is no BMS system to monitor the power consumption of lithium primary batteries. It helps to determine the remaining capacity of lithium primary batteries, improve the reliability and safety of actual battery applications, and prevent safety accidents caused by over-discharge of lithium primary batteries.

[0091] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A method for estimating the state of charge (SOC) of a lithium primary battery based on the open-circuit voltage-charge characteristic curve, characterized in that, The method includes the following steps: Selected lithium primary battery system; The lithium primary battery was discharged at different discharge rates under certain temperature conditions to obtain the discharge capacity of the lithium primary battery at different discharge rates. Regularly test the open-circuit voltage of lithium primary batteries; Establish the first relationship curve between the open-circuit voltage and the battery charge of a lithium primary battery under different discharge rates; A fitting model is established based on the first relationship curve; Discharge rate was selected as a parameter factor, and a correlation model between discharge rate, open circuit voltage and charge was established using MATLAB based on the fitting model. In the aforementioned correlation model, the battery charge is calculated by uploading the open-circuit voltage and discharge rate. The expression for the association model is: f(x,y) = p00 + p10*x + p01*y + p11*x*y + p02*y^2; Where f(x,y) represents the charge of the lithium primary battery, x represents the discharge rate, y represents the open circuit voltage, p00 = 65.88, p10 = -0.5825, p01 = 35.32, p11 = 0.4284, p02 = -9.95; The current battery charge can be obtained by uploading the open-circuit voltage and discharge rate values ​​in the correlation model.

2. The method for estimating the state of charge (SOC) of a lithium primary battery based on the open-circuit voltage-charge characteristic curve according to claim 1, characterized in that, The selected lithium primary battery system is one or more of the following: lithium-carbon fluoride battery, lithium-metal oxide battery, and lithium-iron disulfide battery.

3. The method for estimating the state of charge (SOC) of a lithium primary battery based on the open-circuit voltage-charge characteristic curve according to claim 1, characterized in that, The battery discharge ambient temperature is 25℃±3℃, and the interval discharge time is ≥5 days.

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