Patent ID: 12218318

DETAILED DESCRIPTION

The invention will be described more fully hereinafter with reference to the accompanying drawings, in which exemplary embodiments are shown. This invention may, however, be embodied in many different forms, and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like reference numerals refer to like elements throughout.

It will be understood that when an element is referred to as being “on” another element, it can be directly on the other element or intervening elements may be therebetween. In contrast, when an element is referred to as being “directly on” another element, there are no intervening elements present.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting. As used herein, the singular forms “a,” “an,” and “the” are intended to include the plural forms, including “at least one,” unless the content clearly indicates otherwise. “Or” means “and/or.” As used herein, the term “and/or” includes any and all combinations of one or more of the associated listed items. It will be further understood that the terms “comprises” and/or “comprising,” or “includes” and/or “including” when used in this specification, specify the presence of stated features, regions, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, regions, integers, steps, operations, elements, components, and/or groups thereof.

Furthermore, relative terms, such as “lower” or “bottom” and “upper” or “top,” may be used herein to describe one element's relationship to another element as illustrated in the Figures. It will be understood that relative terms are intended to encompass different orientations of the device in addition to the orientation depicted in the Figures. For example, if the device in one of the figures is turned over, elements described as being on the “lower” side of other elements would then be oriented on “upper” sides of the other elements. The exemplary term “lower,” can therefore, encompasses both an orientation of “lower” and “upper,” depending on the particular orientation of the figure. Similarly, if the device in one of the figures is turned over, elements described as “below” or “beneath” other elements would then be oriented “above” the other elements. The exemplary terms “below” or “beneath” can, therefore, encompass both an orientation of above and below.

“About” or “approximately” as used herein is inclusive of the stated value and means within an acceptable range of deviation for the particular value as determined by one of ordinary skill in the art, considering the measurement in question and the error associated with measurement of the particular quantity (i.e., the limitations of the measurement system).

Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. It will be further understood that terms, such as those defined in commonly used dictionaries, should be interpreted as having a meaning that is consistent with their meaning in the context of the relevant art and the disclosure, and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Hereinafter, exemplary embodiments of the invention will be described in detail with reference to the accompanying drawings.

FIG.1shows a flowchart of a battery charging method according to an exemplary embodiment.

In an exemplary embodiment, the battery is charged based on the multi-stage constant current charging scheme. Referring toFIG.1, in an exemplary embodiment, a battery charging device checks a charged amount (a state of charge or a charging voltage) of the battery, and selects a charging section corresponding to a residual charged amount (S110).

According to an exemplary embodiment, a plurality of charging sections for charging a battery are determined based upon a relationship between a state of charge (“SOC”) and an open circuit voltage (“OCV”) of an anode material of the battery. The charging section according to an exemplary embodiment will now be described in detail with reference toFIG.2andFIG.3.

FIG.2shows a graph of a relationship between an SOC of a battery and an OCV of an anode according to an exemplary embodiment, andFIG.3shows a functional relation between an SOC of a battery and an OCV of an anode, and a charging section determined by the functional relation.

InFIG.2, the x-axis indicates an SOC of the battery, and the y-axis represents an OCV of an anode of the battery. The SOC of the battery is determined by a ratio of Li in the anode. Referring toFIG.2, the OCV of the anode decreases as the SOC increases. In such an embodiment, when the charging is performed, a potential (phis) of an anode active material (a solid matter) decreases, and on the contrary, a potential (phil) of an electrolyte (a liquid) increases because of supplying of lithium positive ions. In such an embodiment, when the potential of the anode active material becomes equal to the potential of the electrolyte (phis=phil), lithium positive ions may be deposited. Therefore, a lithium-plating (Li-plating) phenomenon may be effectively prevented by analyzing a change of reduction of the OCV caused by a Li concentration in the anode active material. The lithium plating phenomenon represents a phenomenon that lithium positive ions (Li+) supplied to the anode are not quickly absorbed at the anode, but are accumulated and thereby deposited as a lithium metal, which is one of the most undesired aspect that have to be considered when the battery is charged by applying a high charging rate (i.e., a high current rate (high charging rate)). When the lithium plating phenomenon occurs, non-uniform lithium dendrites (Li-dendrite) may be formed, the battery may become shorted. Accordingly, the life-span of the battery may be reduced, and the battery may be exploded. The lithium plating phenomenon occurs when the battery is charged and a difference between the potential of the anode active material and the potential of the electrolyte is close to zero (0). Therefore, the lithium plating may be estimated by the change of potential of the anode according to the concentration of lithium in the anode active material.

According to an exemplary embodiment, a plurality of charging sections for charging the battery may be determined or distinguished depending on a point at which a pattern of an OCV reduction (e.g., a slope of an SOC-OCV graph or a dOCV/dSOC graph) of the anode changes. In one exemplary embodiment, for example, the charging section may be determined or distinguished with reference to the point where a slope of the OCV of the anode is analyzed with respect to the SOC (or time), and a difference of slopes becomes a predetermined value.

According to an exemplary embodiment, a peak point is determined based on a differential graph (shown by a single dash-dot line) having differentiated a functional relation of the OCV with respect to the SOC. When there is a minimum (a point at which the differential value changes from a negative value to a positive value) in the differential graph, the charging section is determined based on the minimum as a reference. Referring toFIG.3, a point P1and a point P2on the differential graph correspond to the minimums. A window (a window in the (+) direction) with a height of S0is applied with reference to the respective minimums.

According to an exemplary embodiment, the window has a predetermined height S0, and a width of the window is determined by a point where one of an upper side and a lower side of the window meets the differential graph. The height S0of the window is a predetermined value, e.g., a value that is not greater than 0.6 according to a complexity of a charging process. In one exemplary embodiment, for example, when the height S0is determined to be high, a width of the window increases to increase a length of the charging section and reduce a number of charging sections included in the charging process. When the height S0is determined to be low, the width of the window reduces to reduce the length of the charging section and increase the number of charging sections included in the charging process. Therefore, in a case where the charging process is desired to be simply controlled, the height S0of the window is predetermined as a relatively greater value. In another case, where the charging process is desired to be precisely controlled, the height S0of the window is predetermined as a relatively less value.

Referring toFIG.3, when the window with the height S0is applied to the point P1, a right border of the second charging section is determined, and when the window with the height S0is applied to the point P2, respective borders of the fifth charging section are determined. A left border of the point P1may be determined by a maximum (a point at which the differential value changes from a positive value to a negative value) since the maximum exists in the window applied to the point P1.

The window with the height S0is applied with reference to the maximum. Referring toFIG.3, points P3and P4on the differential graph correspond to the maximum. The window (a window in a (−) direction) with the height S0is applied with respect to a y-axis value of the maximum. Accordingly, a left border of the second charging section and a left border of the fourth charging section are determined. InFIG.3, the right border of the first charging section is equal to the left border of the predetermined second charging section, and the respective borders of the third charging section are equal to the right border of the predetermined second charging section and the left border of the fourth charging section. That is, according to an exemplary embodiment, a border of the charging section (the third charging section) that monotonically increases or monotonically decreases may be determined by a border of another charging section. In such an embodiment, in the section (the sixth charging section) with a small variation of the OCV, the charging sections may not be divided although there exists a minimum or a maximum. In such an embodiment, the last charging section (e.g., the sixth charging section) of the charging sections is a constant voltage section, and the last charging section may be determined according to another reference.

In such an embodiment, when the minimum and the maximum are within a predetermined range (i.e., when gaps of the minimum and the maximum is smaller than a predetermined value), it may be omitted to determine the border by the maximum. In one exemplary embodiment, for example, inFIG.3, when the minimum P1and the maximum P4are included in a predetermined range, respective borders of the second charging section may be determined by the window (a window in the (+) direction) with the height S0with respect to the minimum P1, or the right border of the second charging section may be determined by the window (a window in the (+) direction) with the y-axis value that is greater than the minimum P1by S0, and the left border of the second charging section may be determined by the window (a window in the (−) direction) with the y-axis value that is less than the minimum P1by S0.

According to an exemplary embodiment, when the height S0indicating the difference between the slope corresponding to the border and the slope of one of the minimum and the maximum is set to be a relatively big value (e.g., 0.3), a section length of respective charging sections becomes longer and the number of charging sections reduces so the charging process may be simplified. Alternatively, when the height S0is set to be a relatively small value (e.g., 0.05), the section length of respective charging sections becomes shorter and the number of charging section increases so the battery may be further precisely charged. In one exemplary embodiment, S0indicating the height of the window for determining a charging section may be determined to be less than a predetermined value (e.g., 0.5).

Referring toFIG.3, the slope of the SOC-OCV graph in each section is maintained to be relatively constant (a changing rate of the slope in the section≈0) or at a substantially constant value, but average slopes of respective sections have different values. That is, the changing rate of the slope of the border of each section has a relatively big value than the changing rate of the slope in each section (the changing rate of the slope of the border of the section>>0). In the section in which the changing rate of the slope is maintained at a relatively small value, the battery charging device may relatively easily process the lithium-plating phenomenon. Therefore, a plurality of charging sections for charging the battery may be determined by the slope of the SOC-OCV graph or the changing rate of the slope, and the borders of respective charging sections when the battery is charged may be distinguished according to the charging time or the charging voltage.

Referring back toFIG.1, the battery charging device charges the battery for the selected charging section with the charging rate (a first charging rate) corresponding to the selected charging section (the first charging section) (S120). In an exemplary embodiment, the first charging section may be an m-th (m<n) charging section from among n charging sections. Here, the charging rate (also known in the art as C-rate) represents a value for indicating the ratio of the charging current with respect to the capacity of the battery. Accordingly, when the size (or value) of the charging current corresponds to the capacity of the battery, for example, the charging rate is 1C.

The size of the charging rate corresponding to the respective charging sections is determined to be the maximum size for preventing the lithium plating phenomenon. According to an exemplary embodiment, the sizes of the charging rates corresponding to the respective charging sections are determined by a potential difference (dphisl) between the solid matter and the liquid of the anode and a surface of a separation layer. The potential difference (dphisl) between the solid matter and the liquid satisfies the following Equation 1.
dphis1=phis−phi1  (Equation 1)

In Equation 1, phis denotes a solid potential, that is, an anode potential, and phil denotes a liquid potential, that is, an electrolyte potential. The dphisl is desired to be maintained to be always greater than 0, and it is determined in consideration of a design/manufacturing condition and stability of the battery cell. The dphisl of the battery is provided to be close to zero (0) at an end point of each charging section. When the dphisl of the battery reaches a predetermined dphisl value U0(e.g., 2×10−6), the battery charging stage is changed to a next charging section, and the charging rate with a different size is applied to the battery in the next charging section. In such an embodiment, when the first charging section ends, the battery charging device charges the battery with a second charging rate corresponding to a second charging section during a time duration of the second charging section that is the next charging section of the first charging section. In such an embodiment, the charging rate of the next charging section is less than the charging rate of a previous charging section.

FIG.4shows a flowchart of a method for determining charging rates for respective charging sections according to an exemplary embodiment.

Referring toFIG.4, in an exemplary embodiment, the size of the initial charging rate of a specific charging section is randomly selected before a battery charging simulation is performed (S410). In such an embodiment, the size of the initial charging rate may be selected to be greater than 10. A battery charging simulation for a specific charging section is performed based on the initial charging rate (S420), and the dphisl on a border of the specific charging section is checked (S430).

When the dphisl of the border of the specific charging section is greater than U0, the size of the charging rate is increased to perform the battery charging simulation (S440) because the fact that the dphisl is greater than U0means that the battery may endure the high current rate charging. In such an embodiment, when the dphisl of the border of the specific charging section is less than U0, the size of the charging rate is reduced to perform the battery charging simulation (S450) because the fact that the dphisl is less than the U0means that an excessive charging rate is applied to the battery, which may generate a lithium plating. When the dphisl becomes equal to U0, the size of the charging rate at that time is determined to be the charging rate in the corresponding charging section, and the stages starting from S410begins to determine the charging rate of the next charging section (S460).

FIG.5shows a graph for charging rates and dphisl for respective charging sections according to an exemplary embodiment.

Referring toFIG.5, the x-axis represents the time, and the y-axis indicates the charging rate and the size of dphisl. Here, the charging rate represents a relative current size with reference to the current size of discharging the battery for one hour.FIG.5shows that the dphisl is quickly reduced in the initial charging section to which a high-level charging rate is applied.

In such an embodiment, the first charging section may be the last n-th charging section (m=n) from among n-numbered charging sections, or the second charging section may be the last charging section. When the current charging section is the last charging section (S130), the battery charging device charges the battery with the n-th charging rate corresponding to the n-th charging section, and monitors the charging voltage of the battery to check if the charging voltage of the battery has reached a predetermined voltage value for the charging section (S140). In such an embodiment, the predetermined voltage value may be expressed with a predetermined ratio (e.g., 99%) for a maximum charging voltage (Vmax), and the predetermined ratio and the maximum charging voltage are determined by considering the cathode, the anode, and the physical property of the electrolyte. In an exemplary embodiment, the battery charging device may adaptively lower the predetermined ratio according to a worn-out degree of the battery or an elapsing time.

When the charging voltage of the battery has reached a predetermined voltage value, the battery charging device may stop applying of a constant current and may apply the maximum charging voltage to the battery (a constant voltage stage) (S150). In such an embodiment, it may be determined whether to enter the constant voltage stage based on design variables of the battery cell and an available maximum range of the SOC. When the constant voltage is applied, the battery charging device may terminate the constant voltage stage with reference to the lowest current value (generally O.O5C). When the charging of the battery is finished as the constant voltage stage is terminated, the current applied to the battery is intercepted by a current control device. When the constant voltage stage is omitted, the battery charging device may control the size of the n-th charging rate so that the charging voltage may not exceed the maximum charging voltage. That is, the size of the charging rate may be controlled so that the charging voltage of the battery may reach the maximum charging voltage when the desired charging SOC is achieved.

FIG.6shows a graph of charging rates applicable at an actual charging time, dphisl, and changes of charging voltages according to an exemplary embodiment.

Referring toFIG.6, when the battery is charged with a constant charging rate in each charging section, the dphisl is maintained to be greater than a predetermined value dphisl0 in the entire section, and the charging voltage rapidly increases. The charging section and the charging rate determined according to the above-described method represent values determined according to the characteristic of the anode material, and when the optimized algorithm for the charging section and the charging rate determined by a numerical modeling is applied to the actual battery, a length of the charging section or the size of the charging rate may be controlled in detail to reduce an error caused by a processing deviation of the battery.

FIGS.7A and7Bshow graphs of a charging section and a charging rate applied to an LCO/Ni—Sn battery cell according to an exemplary embodiment,FIG.8shows a comparison graph of changes of charging voltages of an LCO/Ni—Sn battery cell according to an exemplary embodiment, andFIG.9shows a graph of changes of a thickness of an SEI thin film of an LCO/Ni—Sn battery cell according to an exemplary embodiment.

InFIGS.7A and7B, the x-axis represents SOC, and the y-axis indicates OCV or size of the charging. InFIG.8, the x-axis indicates time, and the y-axis denotes charging voltage of the battery cell. InFIG.9, the x-axis shows time, and the y-axis represents a thickness of a thin film of a solid electrolyte interface (SEI).

Referring toFIGS.7A and7BandFIG.8, the battery cell (capacity of 800 Wh/L for each volume) adopting cathode LCO (LiCoO2)-anode Ni—Sn (Ni3Sn4) is charged according to an exemplary embodiment of the charging method (mCC-CV). The OCV of the anode is estimated from a result of a low-rate charging (0.1C of a half cell) experiment using an Ni—Sn anode. Referring toFIG.7A, six charging sections are determined based on the changing rate of the slope of the anode OCV, and the ending point of the final sixth charging section becomes a point of the constant voltage section. The battery begins being charged in the third charging section by the initial condition (3.0 volts (V), SOC=0,085) of the battery. In an exemplary embodiment, as shown inFIG.7B, the charging rates of 18.25C, 9.87C, 3.44C and 1.4C are sequentially applied in the charging sections, and the constant voltage of 4.2 V is finally applied. The finishing condition of the constant voltage section is less than the current of 0.05C. The dphisl is predetermined to be 2×10−6V.

Referring toFIG.8, battery charging voltages when the voltages are charged in the same battery cell according to the CC-CV scheme are compared. The maximum charging rate within which the lithium plating is not generated in the LCO/Ni—Sn battery cell is 1.41C which is estimated through a simulation, and the charging voltage when the LCO/Ni—Sn battery cell is charged with this charging rate is shown as a comparison embodiment (1.41C CC-CV).

Referring toFIG.8, when the battery charging method according to an exemplary embodiment is applied, the charging time is reduced by equal to or greater than 58% (i.e., 47.8 minutes to 20 minutes) compared to when a charging method according to the conventional constant current charging scheme is applied.

Referring toFIG.9, the thickness of the SEI thin film (i.e., an SEI increment) that is an index for detecting a degradation of a life-span of the battery cell in an exemplary embodiment is 0.9 nanometer (nm), is substantially similar to the thickness of the SEI thin film of 0.92 nm when the conventional CC-CV charging scheme is applied. Therefore, such an embodiment of the battery charging method is expected to have a similar cycle life-span characteristic to the conventional CC-CV charging scheme.

FIG.10shows a graph of a charging section applied to an LCO/graphite battery cell according to an exemplary embodiment, andFIG.11shows a graph of a comparison result of capacity retentions of an LCO/graphite battery cell according to an exemplary embodiment.

Referring toFIG.10, the charging section determined by the change of the OCV of the battery cell using the graphite that is mesoporous carbon micro beads (“MCMB”) as the anode material is shown (S0: 0.45). The CC-CV charging scheme is used to find capacity retention after a charging/discharging cycle of the battery cell is repeated. A charging start voltage 3.0 V and SOC of 0.044 are applied as the initial state of the battery, the charging rates corresponding to the respective charging sections are sequentially 2.47C, 1.9C, 1.58C, 1.24C, 1.06C and 0.94C, and the constant voltage of 4.4 V is applied to the battery in the seventh charging section.

InFIG.11, the x-axis represents the charging/discharging cycles of the battery cell, and the y-axis indicates capacity retention of the cell measured by an experiment of the battery. Cases to which the charging rates of 1C, 2C and 3C are applied are used as a control group. Referring toFIG.11, the battery charging method according to an exemplary embodiment has shown improved capacity retention (equal to or greater than 90%) compared to 2C and 3C after fourteen cycles are performed. In the case of 1C, compared to the charging time of 120 minutes, the battery charging method according to an exemplary embodiment (OPT.1 or OPT.1′) has the charging time of 80 minutes, thereby showing the 33.3% of improvement than 10 from the viewpoint of the charging time.

FIG.12AtoFIG.12Cshow graphs of changes of dphisl with respect to charging section, charging rate, and time of an LCO/graphite battery cell according to an exemplary embodiment,FIG.13shows a graph of comparison of changes of a charging voltage of an LCO/graphite battery cell according to an exemplary embodiment, andFIG.14shows a graph of changes of a thickness of an SEI thin film of an LCO/graphite battery cell according to an exemplary embodiment.

InFIG.12A, the x-axis is SOC, and the y-axis shows the size of OCV. InFIG.12BandFIG.12C, the x-axis represent time, and the y-axis indicates the charging rate and the size of dphisl. InFIG.13, the x-axis is time, and the y-axis is the charging voltage of a battery cell. InFIG.14, the x-axis indicates time, and the y-axis is the thickness of an SEI thin film.

Referring toFIG.12AtoFIG.12C,FIG.13, andFIG.14, the battery cell (capacity of 800 Wh/L for each volume) adopting cathode LCO (LiCoO2)-anode graphite is charged according to an exemplary embodiment of the charging method. Referring toFIG.12A, six charging sections are determined (S0: 0.6) based on the changing rate of the slope of the anode OCV, and the ending point of the final or sixth charging section becomes a point of the constant voltage section. The battery begins being charged in the second charging section by the initial condition (3.0 V, SOC=0,035) of the battery. The charging rates sequentially are 8.25C, 4.92C, 3.73C, 2.75C, 2.335C, 1.63C and 1.25C in the respective charging sections, and the constant voltage of 4.4 Vis finally applied. The dphisl is predetermined to be 2×10−6V.

Referring toFIG.13, battery charging voltages when the voltages are charged in the same battery cell according to the CC-CV scheme, and the battery charging voltage according to a pulse charging scheme are compared. The maximum charging rate, within which the lithium plating does not occur, in the LCO/graphite battery cell is 1.35C which is estimated or determined through a simulation, and the charging voltage when the LCO/graphite battery cell is charged with the charging rate of 1.35C is shown as a comparison embodiment. The pulse charging scheme represents the result of local optimization determined by performing the numerical experiment more than 20 times.

Referring toFIG.13, when the battery charging method according to an exemplary embodiment is applied, the charging time is reduced by equal to or greater than 38% (reduced form 47.7 minutes to 29.5 minutes) compared to the conventional constant current charging scheme, and the charging time is reduced by about 14% (reduced from 34.3 minutes to 29.5 minutes) compared to the pulse charging scheme.

Referring toFIG.14, the thickness of the SEI thin film is 2.14 nm, which is similar to the thickness of 1.91 nm in a case of the conventional CC-CV charging scheme is used and the thickness of 2.03 nm in a case of the pulse charging scheme. Therefore, such an embodiment is expected to have a similar cycle life-span characteristic to the conventional CC-CV charging scheme and the pulse charging scheme.

FIG.15shows a block diagram of a battery charging device according to an exemplary embodiment.

Referring toFIG.15, an exemplary embodiment of the battery charging device1500includes a processor1510, a memory1520, and a charging interface1530.

The memory1520may be connected to the processor1510to store various kinds of information for driving the processor1510or at least one program to be performed by the processor1510. The processor1510may realize functions, processes, or methods proposed in the exemplary embodiments of the disclosure. That is, an operation of the battery charging device1500according to an exemplary embodiment of the battery charging method may be realized by the processor1510. The charging interface1530may be connected to the battery in a wired or wireless manner to monitor the charging amount (a SOC or a charging voltage) of the battery according to control by the processor1510and apply the current and the voltage for charging the battery to the battery.

While this invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.