Method for controlling battery cell assembly and battery management system (BMS)

Abstract

According to exemplary embodiments, a method for controlling a battery cell assembly is provided. The method comprises a step for controlling a battery cell assembly including battery cells so that the battery cells operate in a first voltage range at a first temperature, and the battery cells operate in a second voltage range different from the first voltage range at a second temperature lower than the first temperature.

Description

Method for controlling a battery cell assembly and BMS (BATTERY MANAGEMENT SYSTEM)

[0001] The present invention relates to a method for controlling a battery cell assembly and a Battery Management System (BMS). The present application claims the benefit of Korean application No. 10-2025-0004205, filed on January 10, 2025, which is incorporated herein by reference in its entirety.

[0002] Unlike primary batteries, secondary batteries can be charged and discharged multiple times. Secondary batteries are widely used as energy sources for various wireless devices such as handsets, laptops, and cordless vacuum cleaners. Recently, as the manufacturing cost per unit capacity of secondary batteries has decreased dramatically due to improved energy density and economies of scale, and as the driving range of BEVs (battery electric vehicles) has increased to a level equivalent to that of fuel vehicles, the primary use of secondary batteries is shifting from mobile devices to mobility.

[0003] Recently, research has been focusing on LFP (lithium iron phosphate) batteries. This is because LFP batteries offer advantages over NCM (nickel-cobalt-manganese) batteries in terms of stability, cost, lifespan, and environmental impact.

[0004] Key research challenges for LFP batteries include overcoming low energy density, improving low-temperature performance, enhancing conductivity, improving charge / discharge rates, addressing volume expansion and contraction issues, developing recycling and disposal processes, and improving high-temperature stability.

[0005] The problem that the technical concept of the present invention aims to solve is to provide a method for controlling a battery cell assembly with improved low-temperature performance and a BMS configured to perform the same.

[0006] According to exemplary embodiments of the present invention for solving the above-described problem, a method for controlling a battery cell assembly is provided. The method comprises the step of controlling a battery cell assembly including battery cells to operate the battery cells in a first voltage range at a first temperature, and to operate the battery cells in a second voltage range different from the first voltage range at a second temperature lower than the first temperature.

[0007] The length of the second voltage range is different from the length of the first voltage range.

[0008] The second voltage range is longer than the first voltage range.

[0009] The first voltage range is included in the second voltage range.

[0010] The first upper limit of the first voltage range is the same as the second upper limit of the second voltage range.

[0011] The first lower limit of the first voltage range is different from the second lower limit of the second voltage range.

[0012] The first lower limit of the first voltage range is greater than the second lower limit of the second voltage range.

[0013] The first lower limit of the first voltage range above is 2.5V.

[0014] The second lower limit of the above second voltage range is 2.5V or less.

[0015] The second lower limit of the above second voltage range is 2.3V or less.

[0016] The second lower limit of the above second voltage range is 1.5V or higher.

[0017] The second lower limit of the above second voltage range is 1.8V or higher. The second lower limit of the above second voltage range is 2.0V.

[0018] The above first temperature is 5℃ or higher.

[0019] The above second temperature is less than 5℃.

[0020] Each of the above battery cells contains lithium iron phosphate.

[0021] According to exemplary embodiments of the present invention, the operating range of lithium iron phosphate battery cells can be extended at low temperatures. Accordingly, the degradation of the capacity of lithium iron phosphate battery cells at low temperatures can be mitigated, and the low-temperature performance of the lithium iron phosphate battery can be improved.

[0022] The effects obtainable from the exemplary embodiments of the present invention are not limited to those mentioned above, and other unmentioned effects can be clearly derived and understood by those skilled in the art to which the exemplary embodiments of the present disclosure belong from the following description. That is, unintended effects resulting from the implementation of the exemplary embodiments of the present disclosure can also be derived by those skilled in the art from the exemplary embodiments of the present disclosure.

[0023] FIG. 1 is a block diagram illustrating a battery device according to exemplary embodiments.

[0024] FIG. 2 is a flowchart illustrating a method for manufacturing a secondary battery according to exemplary embodiments.

[0025] FIG. 3 is a graph illustrating the effect of a method for controlling a battery cell assembly according to exemplary embodiments.

[0026] Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the attached drawings. Prior to this, terms and words used in this specification and claims should not be interpreted as being limited to their ordinary or dictionary meanings. Instead, based on the principle that the inventor can appropriately define the concepts of terms to best describe his invention, they should be interpreted in a meaning and concept consistent with the technical spirit of the present invention.

[0027] Therefore, the embodiments described in this specification and the configurations illustrated in the drawings are merely the most preferred embodiments of the present invention and do not represent all of the technical ideas of the present invention; thus, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

[0028] In addition, in describing the present invention, if it is determined that a detailed description of related known components or functions may obscure the essence of the invention, such detailed description is omitted.

[0029] Since embodiments of the present invention are provided to more fully explain the invention to those skilled in the art, the shapes and sizes of the components in the drawings may be exaggerated, omitted, or schematically depicted for clearer explanation. Accordingly, the size or proportion of each component does not entirely reflect the actual size or proportion.

[0030]

[0031] (1st and 2nd embodiments)

[0032] FIG. 1 is a block diagram illustrating a battery device (10) according to exemplary embodiments.

[0033] Referring to FIG. 1, the battery device (10) may include a battery pack (100), a Power Distribution Unit (PDU) (200), and a Vehicle Controller Unit (VCU) (300).

[0034] The battery pack (100) may include a plurality of battery cell assemblies (120) and a master BMS (Battery Management System) (130). The battery pack (100) is the final form of a battery system mounted on mobility, etc. The battery pack (100) may further include a pack housing that provides space for mounting the plurality of battery cell assemblies (120) and the master BMS (130).

[0035] Each of the plurality of battery cell assemblies (120) may include a plurality of battery cells (121) and a slave BMS (123). Each of the plurality of battery cells (121) may include an electrode assembly, an electrolyte, and a case. Each of the plurality of battery cells (121) may be any one of a cylindrical battery cell, a prismatic battery cell, and a pouch-type battery cell. The electrode assembly of the cylindrical battery cell is embedded in a cylindrical metal can. The electrode assembly of the prismatic battery cell is embedded in a prismatic metal can. The electrode assembly of the pouch-type battery cell is embedded in a pouch case containing an aluminum laminate sheet.

[0036] An electrode assembly includes an anode, a cathode, and a separator interposed between the anode and the cathode. A jelly roll type electrode assembly is formed by winding an anode, a cathode, and a separator interposed between them. A stack type electrode assembly includes a plurality of anodes, a plurality of cathodes, and a plurality of separators interposed between them, which are stacked sequentially.

[0037] The positive electrode may include a positive current collector and a positive active material. The thickness of the positive current collector may be in the range from about 3 μm to about 500 μm. The positive current collector may not cause chemical changes in the secondary battery finally manufactured and may have high conductivity. The positive current collector may include, for example, any one of stainless steel, nickel, titanium, calcined carbon, and aluminum. The positive current collector may also include stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The surface of the positive current collector may include a micro-irregular structure to increase the adhesion of the active material. The shape of the positive current collector may include any one of a film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0038] The positive electrode active material is a material capable of causing an electrochemical reaction. The positive electrode active material may be a lithium transition metal oxide. The positive electrode active material is, for example, with the chemical formula Li 1+x M 1-y M' y PO 4-z X z It may include any one of the olivine-based lithium metal phosphates represented by (where M is a transition metal, more specifically one of Fe, Mn, Co, and Ni; M' is one of Al, Mg, and Ti; X is one of F, S, and N; -0.5≤x≤+0.5; 0≤y≤0.5; and 0≤z≤0.1). The cathode active material may include, for example, lithium iron phosphate. The cathode active material is Li 1+x M 1-y M'yO 2-z X z It may further include a lithium metal oxide represented by (where M is a main metal one of Fe, Mn, Co, and Ni, M' is a substitutional metal element different from M among Fe, Mn, Co, and Ni, and X is a substitutional non-metal element or defect). The positive electrode active material may include, for example, lithium iron oxide.

[0039] The negative electrode may include a negative current collector and a negative active material. The thickness of the negative current collector may be in the range of about 3 μm to about 500 μm. The negative current collector may not cause chemical changes in the secondary battery finally manufactured and may have high conductivity. The negative current collector may include any one of copper, stainless steel, aluminum, nickel, titanium, calcined carbon, and aluminum-cadmium alloy. The negative current collector may also include stainless steel surface-treated with carbon, nickel, titanium, silver, etc. The surface of the negative current collector may include a micro-roughness structure to increase the adhesion of the active material. The shape of the negative current collector may include any one of a film, sheet, foil, net, porous material, foam, and nonwoven fabric.

[0040] The negative electrode active material may include carbon, for example, non-graphitizable carbon, graphite-based carbon, etc. The negative electrode active material is, for example, Li x Fe2O3(0≤x≤1), LixWO2(0≤x≤1), Sn x Me 1-x Me y O z (wherein Me is any one of Mn, Fe, Pb, and Ge, and Me' is any one of Al, B, P, Si, Group 1, Group 2, and Group 3 elements of the periodic table, and halogens; 0 <x≤1이고; 1≤y≤3 이며; 1≤z≤8) 등의 금속 복합 산화물을 포함할 수 있다. 음극 활물질은, 예컨대, 리튬 금속; 리튬 합금; 규소계 합금; 및 주석계 합금 중 어느 하나를 포함할 수 있다. 음극 활물질은, 예컨대, SnO, SnO2, PbO, PbO2, Pb2O3, Pb3O4, Sb2O3, Sb2O4, Sb2O5, GeO, GeO2, Bi2O3, Bi2O4및 Bi2O5등의 금속 산화물을 포함할 수 있다. 음극 활물질은, 예컨대, 폴리아세틸렌 등의 도전성 고분자; Li-Co-Ni 계 재료 등을 포함할 수도 있다.

[0041] The cell case may include a cup-shaped receiving portion. The receiving portion may be formed by a pouch forming process. An electrode assembly may be received in the receiving portion. The cell case may be any one of a pouch case, a cylindrical can, and a rectangular can.

[0042] The electrolyte may be any one of a non-aqueous electrolyte, an aqueous electrolyte, an ionic electrolyte, and a gel electrolyte. The electrolyte may also be a solid electrolyte. The non-aqueous electrolyte may include organic solvents such as ethylene carbonate and dimethyl carbonate, and lithium salts such as LiPF6 and LiBF4 dissolved in organic solvents. The non-aqueous electrolyte may also include ethylene carbonate dissolved in tetraethylammonium salts. The aqueous electrolyte may include sodium sulfate solution, sulfuric acid solution, hydrochloric acid solution, or sodium hydroxide solution. The ionic electrolyte is an ionic compound that is in a liquid state at room temperature, such as ethylmethylimidazolidium bis(trifluoromethylsulfonyl)amide, and has high thermal stability. The gel electrolyte may be provided by treating the liquid electrolyte using polyacrylonitrile and PVA, etc. The solid electrolyte may include a polymer material doped with a lithium salt (e.g., polyethylene oxide (PEO)) and a ceramic electrolyte composed of ceramic materials such as NASICON and LLZO.

[0043]

[0044] According to exemplary embodiments, a plurality of battery cells (121) may form a plurality of banks. A plurality of banks may include one or more parallel-connected battery cells (121). A plurality of banks may be connected in series with each other. The number of battery cells (121) included in each of the plurality of banks and the number of banks connected in series with each other may be determined according to the voltage and current to be output through each of the battery cell assemblies (120).

[0045]

[0046] The master BMS (130) may be configured to perform monitoring, balancing, and control of the battery pack (100). Monitoring of the battery pack (100) may include measuring the voltage and current of specific nodes within the battery cell assemblies (120) and measuring the temperature of set locations within the battery pack (100). The battery pack (100) may include sensors for measuring the voltage, current, and temperature described above.

[0047] Each of the master BMS (130) and each of the slave BMS (123) of the plurality of battery cells can be implemented using an MCU (Micro Controller Unit) and an MPU (Micro Processor Unit).

[0048] Balancing of the battery pack (100) is an operation that reduces deviations between battery cell assemblies (120). Control of the battery pack (100) includes preventing overcharging, over-discharging, and overcurrent. Through monitoring, balancing, and control, the battery pack (100) can operate under optimal conditions, and accordingly, the shortening of the lifespan of each battery cell assembly (120) can be prevented.

[0049] The electrical components may further include a cooling device, a Power Relay Assembly (PRA), a safety plug, etc. The cooling device may include a cooling fan. The cooling fan can prevent overheating of each of the battery cell assemblies (120) by circulating air inside the battery pack (100). The PRA may be configured to supply or cut off power from the high-voltage battery to an external load (e.g., a vehicle motor). The PRA can protect the battery cell assemblies (120) and the external load (e.g., a vehicle motor) by cutting off power supply to the external load (e.g., a vehicle motor) in situations where abnormal voltage occurs, such as a voltage surge.

[0050] The master BMS (130) can be connected to the vehicle's VCU (Vehicle Controller Unit) (300) via the PDU (200). The VCU (300) may be a vehicle control unit. The VCU (300) may be configured to integrally control the vehicle's power controller. The PDU (200) may be configured to distribute power supplied from a power supply unit, including a battery pack (100), to the vehicle's loads and electrical components.

[0051]

[0052] The master BMS (130) may be configured to control the operating range of the voltage of each of the plurality of battery cells (121) of each of the plurality of battery cell assemblies (120). The master BMS (130) may be configured to set an upper limit for the charging of each of the plurality of battery cells (121) of each of the plurality of battery cell assemblies (120).

[0053] For example, if some of the multiple battery cells (121) of the multiple battery cell assemblies (120) reach a charging limit, the master BMS (130) may be configured to block the charging of the battery cells (121) that have reached the charging limit.

[0054] The upper limit of charging may be the maximum safe voltage, but is not limited thereto. The maximum safe voltage may be the maximum allowable voltage set to prevent damage due to overcharging during the charging of multiple battery cells (121), and in the case of LFP cells, the maximum safe voltage may generally be around 3.8V. When multiple battery cells (121) are overcharged, the electrodes and electrolytes react irreversibly, reducing the performance and lifespan of the battery. In particular, when multiple battery cells (121) are LFP cells, overcharging of multiple battery cells (121) causes lithium deposition on the electrode surfaces of multiple battery cells (121), which may increase the possibility of an internal short circuit of multiple battery cells (121).

[0055] For example, if some of the multiple battery cells (121) of the multiple battery cell assemblies (120) reach a lower limit of discharge, the master BMS (130) may be configured to block the discharge of the battery cells (121) that have reached the lower limit of discharge.

[0056] The lower limit of discharge may be a minimum safe voltage, but is not limited thereto. The minimum safe voltage may be a lower limit of the operating voltage of multiple battery cells (121) to prevent damage to the cells, reduction of available capacity, or thermal runaway due to over-discharge. If the voltage of multiple battery cells (121) becomes excessively low due to over-discharge of multiple battery cells (121), the active material of the electrode may be damaged and the reversible capacity may be reduced. In particular, in the case of LFP cells, the electrolyte may deteriorate due to over-discharge. Furthermore, over-discharge can cause imbalance between cells and increase internal resistance, which may increase the possibility of thermal runaway in the long term. Accordingly, it is important to appropriately set a lower limit of the operating voltage for the efficient and safe operation of the battery pack (100).

[0057] According to exemplary embodiments, a master BMS (130) may be configured to control a plurality of battery cell assemblies (120) depending on the temperature inside the battery pack (100) or the temperature around the battery pack (100). The master BMS (130) may be configured to generate a signal for controlling the plurality of battery cell assemblies (120) based on the temperature inside the battery pack (100) or the temperature around the battery pack (100), and to transmit said signal to the plurality of battery cell assemblies (120). The temperature inside the battery pack (100) or the temperature around the battery pack (100) may be detected by a temperature sensor of the plurality of battery cell assemblies (120), by a temperature sensor of the master BMS (130), by a temperature sensor of the battery pack (100) located outside the master BMS (130), or by a temperature sensor included in the VCU (300).

[0058] The master BMS (130) may be configured to control the plurality of battery cell assemblies (120) so that the plurality of battery cells (121) of the plurality of battery cell assemblies (120) operate in a first voltage range when the temperature inside the battery pack (100) or the temperature around the battery pack (100) is above a critical temperature.

[0059] The first voltage range may include a first upper limit and a first lower limit. That the plurality of battery cells (121) of the plurality of battery cell assemblies (120) operate in the first voltage range means setting the upper limit of charging of the plurality of battery cells (121) of the plurality of battery cell assemblies (120) to the first upper limit, and setting the lower limit of discharging of the plurality of battery cells (121) of the plurality of battery cell assemblies (120) to the first lower limit.

[0060] The master BMS (130) may be configured to control the plurality of battery cell assemblies (120) so that the plurality of battery cells (121) of the plurality of battery cell assemblies (120) operate in a second voltage range when the temperature inside the battery pack (100) or the temperature around the battery pack (100) is below a critical temperature.

[0061] The second voltage range may include a second upper limit and a second lower limit. That the plurality of battery cells (121) of the plurality of battery cell assemblies (120) operate in the second voltage range means setting the upper limit of charging of the plurality of battery cells (121) of the plurality of battery cell assemblies (120) to the second upper limit, and setting the lower limit of discharging of the plurality of battery cells (121) of the plurality of battery cell assemblies (120) to the second lower limit.

[0062]

[0063] According to exemplary embodiments, the critical temperature may be in the range of about 0°C to about 10°C. According to exemplary embodiments, the critical temperature may be about 5°C.

[0064] The first voltage range may differ from the second voltage range. The first voltage range may be included within the second voltage range. The length of the first voltage range may differ from the length of the second voltage range. The length of the first voltage range may be shorter than the length of the second voltage range. The length of the first voltage range may be the difference between the first upper limit and the first lower limit. The length of the second voltage range may be the difference between the second upper limit and the second lower limit.

[0065] The first upper limit may be substantially the same as the second upper limit. The first lower limit may be different from the second lower limit. The first lower limit may be greater than the second lower limit. The first upper limit and the second upper limit may each be in the range of about 3.5V to about 4.0V. The first upper limit and the second upper limit may each be about 3.8V. The first lower limit may be about 2.5V.

[0066] The second lower limit may be less than or equal to 2.5V. The second lower limit may be less than or equal to 2.4V. The second lower limit may be less than or equal to 2.3V. The second lower limit may be less than or equal to 2.2V. The second lower limit may be less than or equal to 2.1V. The second lower limit may be greater than or equal to approximately 1.5V. The second lower limit may be greater than or equal to approximately 1.6V. The second lower limit may be greater than or equal to approximately 1.7V. The second lower limit may be greater than or equal to approximately 1.8V. The second lower limit may be greater than or equal to approximately 1.9V. The second lower limit may be greater than or equal to approximately 2.0V.

[0067]

[0068] (2nd Example)

[0069] FIG. 2 is a flowchart illustrating a method for manufacturing a secondary battery according to exemplary embodiments.

[0070] Referring to FIGS. 1 and 2, in P110, the temperature inside the battery pack (100) or the temperature around the battery pack (100) can be detected. The temperature inside the battery pack (100) or the temperature around the battery pack (100) can be detected by any one of the temperature sensor of the battery pack (100), the temperature sensor of the plurality of battery cell assemblies (120), and the temperature sensor of the master BMS (130).

[0071] In P120, if the detected temperature is above the critical temperature, in P131, the master BMS (130) can control the plurality of battery cell assemblies (120) so that the plurality of battery cells (121) of the plurality of battery cell assemblies (120) operate in a first voltage range.

[0072] In P120, if the detected temperature is below the threshold temperature, in P133, the master BMS (130) can control the plurality of battery cell assemblies (120) so that the plurality of battery cells (121) of the plurality of battery cell assemblies (120) operate in a second voltage range.

[0073]

[0074] FIG. 3 is a graph illustrating the effect of a method for controlling a battery cell assembly (120) according to exemplary embodiments. In FIG. 3, hollow square dots represent the available capacity of the battery cells according to temperature when using a discharge lower limit of 2.5V. Also in FIG. 3, solid square dots represent the available capacity of the battery cells according to temperature when using a discharge lower limit of 2.0V.

[0075] Referring to FIG. 3, the capacity of LFP battery cells can be rapidly degraded due to a rapid increase in charge transfer resistance under low temperature conditions. According to exemplary embodiments, when the discharge lower limit is changed from about 2.5V to about 2.0V, the discharge capacity at 0°C can be increased by 11%p from about 70% to about 81%, the discharge capacity at -10°C can be increased by 14%p from about 50% to about 64%, and the discharge capacity at -20°C can be increased by 17%p from about 20% to about 37%.

[0076] According to exemplary embodiments, by lowering the range of the discharge lower limit based on the temperature inside the battery pack (100, see FIG. 1) or the temperature around the battery pack (100, see FIG. 1), the discharge capacity at low temperatures (e.g., an environment where the temperature inside the battery pack (100, see FIG. 1) or the temperature around the battery pack (100, see FIG. 1) is less than 5°C) can be increased and the low-temperature performance of the LFP battery cells can be improved.

[0077]

[0078] The present invention has been described in more detail above through drawings and embodiments. However, the configurations described in the drawings or embodiments described in this specification are merely one embodiment of the present invention and do not represent all technical concepts of the present invention; therefore, it should be understood that various equivalents and modifications that can replace them may exist at the time of filing this application.

Claims

1. A method for controlling a battery cell assembly comprising the step of controlling the battery cell assembly including the battery cells to operate the battery cells in a first voltage range at a first temperature, and to operate the battery cells in a second voltage range different from the first voltage range at a second temperature lower than the first temperature.

2. In Paragraph 1, A method for controlling a battery cell assembly characterized in that the length of the second voltage range is different from the length of the first voltage range.

3. In Paragraph 1, A method for controlling a battery cell assembly characterized in that the second voltage range is longer than the first voltage range.

4. In Paragraph 1, A method for controlling a battery cell assembly characterized in that the first voltage range is included in the second voltage range.

5. In Paragraph 1, A method for controlling a battery cell assembly characterized in that the first upper limit of the first voltage range is the same as the second upper limit of the second voltage range.

6. In Paragraph 1, A method for controlling a battery cell assembly characterized in that the first lower limit of the first voltage range is different from the second lower limit of the second voltage range.

7. In Paragraph 1, A method for controlling a battery cell assembly characterized in that the first lower limit of the first voltage range is greater than the second lower limit of the second voltage range.

8. In Paragraph 1, A method for controlling a battery cell assembly characterized in that the first lower limit of the first voltage range is 2.5V.

9. In Paragraph 1, A method for controlling a battery cell assembly characterized in that the second lower limit of the second voltage range is 2.5V or less.

10. In Paragraph 1, A method for controlling a battery cell assembly characterized in that the second lower limit of the second voltage range is 2.3V or less.

11. In Paragraph 1, A method for controlling a battery cell assembly characterized in that the second lower limit of the second voltage range is 1.5V or higher.

12. In Paragraph 1, A method for controlling a battery cell assembly characterized in that the second lower limit of the second voltage range is 1.8V or higher.

13. In Paragraph 1, A method for controlling a battery cell assembly characterized in that the second lower limit of the second voltage range is 2.0V.

14. In Paragraph 1, A method for controlling a battery cell assembly characterized in that the first temperature is 5°C or higher.

15. In Paragraph 1, A method for controlling a battery cell assembly characterized in that the second temperature is less than 5℃.

16. In Paragraph 1, A method for controlling a battery cell assembly characterized in that each of the above battery cells comprises lithium iron phosphate.

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