Battery system

Abstract

To improve an estimation accuracy of a SOC.SOLUTION: A non-aqueous electrolyte secondary battery contains: a positive electrode; a negative electrode; and an electrolyte. At least one of the positive electrode and the negative electrode contains a two-phase coexistence type active material. The two-phase coexistence type active material contains two or more particle groups. In a single test, a discharge curve of each particle group includes a potential flatness part. In each particle group, a potential in the potential flatness part is actually equal. In each particle group, a specific capacity corresponded to the potential flatness part is different from each other.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] This disclosure relates to non-aqueous electrolyte secondary batteries and battery systems. [Background technology]

[0002] Japanese Patent Publication No. 2010-027409 (Patent Document 1) discloses a two-phase coexistence type active material. [Prior art documents] [Patent Documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2010-027409 [Overview of the project] [Problems that the invention aims to solve]

[0004] Non-aqueous electrolyte secondary batteries containing two-phase coexistence active materials (hereinafter sometimes abbreviated as "batteries") have been developed. In two-phase coexistence active materials, discharge proceeds through a two-phase coexistence reaction (also referred to as a "two-phase separation reaction"). The discharge curve of two-phase coexistence active materials tends to exhibit very high flatness in the potential plateau. Because the voltage change of the battery is small, a stable output can be expected throughout. However, the voltage change can be used as information to estimate the State of Charge (SOC) of the battery. Because the voltage change is small, it may be difficult to estimate the SOC.

[0005] To improve the accuracy of SOC estimation, for example, it has been proposed to mix multiple types of two-phase coexisting active materials (see Patent Document 1). Multiple types of two-phase coexisting active materials have different ion diffusion coefficients. That is, multiple types of two-phase coexisting active materials have different reactivity. Due to the difference in reactivity, a step appears in the discharge curve. The SOC can be estimated from the position of the step. However, the position of the step can change significantly depending on the magnitude of the charge-discharge rate. There is room for improvement in the accuracy of SOC estimation.

[0006] An object of the present disclosure is to improve the estimation accuracy of the state of charge (SOC).

Means for Solving the Problems

[0007] 1. A non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and an electrolyte. At least one of the positive electrode and the negative electrode includes a two-phase coexisting active material. The two-phase coexisting active material includes two or more particle groups. In a single-pole test, the discharge curve of each particle group has a potential plateau portion. The potentials of each particle group at the potential plateau portion are substantially equal. The specific capacities corresponding to the potential plateau portion of each particle group are different from each other.

[0008] Hereinafter, the "potential at the potential plateau portion" is also referred to as "plateau potential". The "specific capacity corresponding to the potential plateau portion" is also referred to as "plateau capacity". The two or more particle groups are each a two-phase coexisting active material. The two or more particle groups have substantially equal plateau potentials. The two or more particle groups have different plateau capacities from each other.

[0009] FIG. 1 is a first schematic diagram showing the generation principle of a step. The horizontal axis in FIG. 1 is the state of charge (SOC). The SOC takes values from 0 to 100%. As the horizontal axis goes to the right, the SOC becomes smaller. The vertical axis in FIG. 1 is the reaction potential. As an example, a combination of three particle groups is described. The first active material has a first plateau potential P1. The second active material has a second plateau potential P2. The third active material has a third plateau potential P3. The relationship of "P0 = P1 = P2 = P3" is satisfied. The first active material has a first plateau capacity C1. The second active material has a second plateau capacity C2. The third active material has a third plateau capacity C3. The relationship of "C3 < C2 < C1" is satisfied. In FIG. 1, as an example, the relationships of "C2 / C1 = 0.8 (80%)" and "C3 / C1 = 0.5 (50%)" are satisfied.

[0010] Figure 2 is a second schematic diagram illustrating the principle of step generation. As discharge progresses, the State of Charge (SOC) decreases. Due to the decrease in SOC, the third active material is the first to reach a fully discharged state. Once the third active material reaches a fully discharged state, it stops accepting carrier ions. Therefore, it is thought that the distribution of carrier ions to the second and first active materials increases. This increase in distribution is essentially an increase in the rate. The increase in load generates an increase in overpotential ΔV1. This increase in overpotential is thought to shift the reaction potential toward the less vicious side. As a result, the first step S1 may be formed at the position corresponding to the third plateau capacity C3. Further discharge leads to the second active material reaching a fully discharged state. An increase in overpotential ΔV2 occurs. The second step S2 may be formed at the position corresponding to the second plateau capacity C2. The position of each step can serve as information to aid in SOC estimation. The position of the steps due to the difference in plateau capacities is thought to be less dependent on the charge-discharge rate. Therefore, an improvement in the accuracy of SOC estimation can be expected.

[0011] During charging, the reaction potential may shift towards a nobler direction due to an increase in overvoltage. It is thought that a step similar to that in the discharge curve may be observed in the charging curve. The steps in the discharge and charging curves may be detected, for example, as peaks in the dV / dQ curve.

[0012] 2. The non-aqueous electrolyte secondary battery described in "1" above may include, for example, the following configuration: The two-phase coexistence type active material has the composition of the following general formula. Li x Fe y M z PO4 M is at least one element selected from the group consisting of Al, Co, Cr, Cu, Mg, Mn, Mo, Nb, Ni, Ti, V, W, and Zr. The relationships 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, and 0 ≤ z ≤ 1 are satisfied.

[0013] In the two-phase coexistence type active material represented by the above general formula, for example, the plateau capacity can change while the plateau potential is maintained, depending on the type of M and the values ​​of x, y, and z.

[0014] The non-aqueous electrolyte secondary battery described in the above "1" or "2" may include, for example, the following configuration. Among all types of particle groups, the particle group with the maximum specific capacity has a mass fraction of 50 to 90% with respect to the total of all types of particle groups.

[0015] When the mass fraction of the particle group having the maximum plateau capacity is 50 to 90%, it is expected that detection of an increase in overvoltage becomes easy while maintaining a desired energy density.

[0016] The non-aqueous electrolyte secondary battery described in any one of the above "1" to "3" may include, for example, the following configuration. The discharge curve of the non-aqueous electrolyte secondary battery has two or more voltage plateau portions. The number of voltage plateau portions is equal to the number of types of particle groups. There is a step between each voltage plateau portion. The step indicates an increase in overvoltage.

[0017] The battery system includes the non-aqueous electrolyte secondary battery described in the above "4", and a control device. The control device is configured to perform SOC estimation. The SOC estimation includes the following (a) to (e). (a) Calculate a first estimated value for estimating the current SOC from the total amount of current flowing through the non-aqueous electrolyte secondary battery. (b) Calculate a second estimated value for estimating the SOC at which overvoltage should increase from the first estimated value and the specific capacity of each particle group. (c) By detecting an increase in overvoltage, obtain an actual measured value of the SOC when overvoltage actually increases. (d) When the second estimated value is larger than the actual measured value, calculate a third estimated value by adding a correction value to the first estimated value. (e) When the second estimated value is less than or equal to the actual measured value, calculate a third estimated value by subtracting a correction value from the first estimated value.

[0018] For example, the estimated value of the current SOC may be corrected based on the SOC when overvoltage increases. The correction value may be, for example, the absolute difference between the second estimated value and the actual measured value. Improvement in estimation accuracy is expected by the correction.

[0019] Embodiments of the present disclosure (which may be abbreviated as “Embodiments”) and examples of the present disclosure (which may be abbreviated as “Examples”) are described below. However, these embodiments and examples do not limit the technical scope of the present disclosure. These embodiments and examples are illustrative in all respects. These embodiments and examples are non-limiting. The technical scope of the present disclosure includes all modifications within the meaning and scope equivalent to the claims. For example, it is intended from the outset that any configuration may be extracted from these embodiments and examples and combined in any way.

[0020] Numerical ranges such as "m to n%" include both ends unless otherwise specified. That is, "m to n%" indicates a numerical range of "m% or more and n% or less". "m% or more and n% or less" includes "greater than m% and less than n%". "Greater than or equal to" and "less than or equal to" are represented by the equals sign inequality "≦". "Greater than" and "less than" are represented by the equals sign inequality "<". A number arbitrarily selected from within a numerical range may be used as a new upper or lower limit. For example, a new numerical range may be set by arbitrarily combining a number within a numerical range with a number listed in another part of this specification, in a table, in a figure, etc.

[0021] In this disclosure, the term "DOD (Depth of Discharge)" may be used instead of "SOC". 100% SOC corresponds to 0% DOD. 0% SOC corresponds to 100% DOD. [Brief explanation of the drawing]

[0022] [Figure 1] This is the first schematic diagram illustrating the principle of step generation. [Figure 2] This is the second schematic diagram illustrating the principle of step generation. [Figure 3] This is a conceptual diagram showing an example of a non-aqueous electrolyte secondary battery in this embodiment. [Figure 4] This is a conceptual diagram showing an example of an electrode in this embodiment. [Figure 5] This is a conceptual diagram showing the battery system in this embodiment. [Figure 6] This is a schematic flowchart illustrating an example of SOC estimation in this embodiment. [Figure 7] This is the discharge curve for No. 1. [Figure 8] This is the dV / dQ curve No. 1. [Figure 9] This is a table showing the blending ratios. [Figure 10] This is the discharge curve for No. 3. [Figure 11] This is the dV / dQ curve for No. 3. [Modes for carrying out the invention]

[0023] 1.Non-aqueous electrolyte secondary battery This embodiment can be applied to any non-aqueous electrolyte secondary battery. The non-aqueous electrolyte secondary battery may be, for example, a lithium-ion battery or a sodium-ion battery.

[0024] Figure 3 is a conceptual diagram showing an example of a non-aqueous electrolyte secondary battery in this embodiment. The battery 100 includes a power generation element 50 and an outer casing 60. The outer casing 60 houses the power generation element 50. The power generation element 50 includes a positive electrode 11, a negative electrode 12, and an electrolyte 20. The electrolyte 20 may be a liquid electrolyte, a gel electrolyte, or a solid electrolyte. The liquid electrolyte may include, for example, an electrolyte solution, an ionic liquid, etc. The liquid electrolyte may be impregnated in a separator (porous membrane).

[0025] Figure 4 is a conceptual diagram showing an example of an electrode in this embodiment. Electrode 10 may be either a positive electrode 11 or a negative electrode 12. Electrode 10 may include, for example, an active material layer 5 and a current collector foil 6. The active material layer 5 is disposed on the surface of the current collector foil 6. The active material layer 5 contains an active material. The active material layer 5 may further contain a conductive material and a binder, etc. The active material layer 5 may, for example, contain, by mass fraction, 0-20% conductive material, 0-20% binder, and the remainder active material.

[0026] The active material layer 5 contains a two-phase coexisting active material. The two-phase coexisting active material is, for example, LiFePO4 (a positive electrode active material for a lithium-ion battery), LiMnPO4 (a positive electrode active material for a lithium-ion battery), LiCoPO4 (a positive electrode active material for a lithium-ion battery), Li4Ti5O 12 (a negative electrode active material for a lithium-ion battery), NaFeO2 (a positive electrode active material for a sodium-ion battery), or Na 0.6 Ni 0.22 Al 0.11 Mn 0.66 O2 (a positive electrode active material for a sodium-ion battery), etc. may be used. In the two-phase coexisting active material, charge and discharge proceed by a two-phase coexistence reaction. As an example, in the two-phase coexistence reaction of LiFePO4, it is considered that the LiFePO4 phase and the FePO4 phase coexist.

[0027] The two-phase coexisting active material contains two or more kinds of particle groups. The number of types of particle groups may be, for example, three or more, four or more, or five or more. The number of types of particle groups may be, for example, ten or less, five or less, four or less, or three or less. The active material layer 5 may, for example, contain a first particle group 1, a second particle group 2, and a third particle group 3. The first particle group 1, the second particle group 2, and the third particle group 3 have substantially equal plateau potentials. "Substantially equal plateau potentials" indicates that the plateau potentials may be different as long as they do not affect the basic and novel characteristics of the disclosed technology. For example, in two or more kinds of particle groups, the following relationship may be satisfied.

[0028] 0.95 ≦ P i / P u ≦ 1.05 P i : The plateau potential of any one kind of particle group alone (P i = P1, P2, P3, ···) P u : The arithmetic mean of the plateau potentials of all kinds of particle groups

[0029] "P i / P u" can be any of the following: 0.96 or higher, 0.97 or higher, 0.98 or higher, 0.99 or higher, 0.999 or higher, or 0.9999 or higher. i / P u " may be any of the following: 1.04 or less, 1.03 or less, 1.02 or less, 1.01 or less, 1.001 or less, or 1.0001 or less.

[0030] The first particle group 1, the second particle group 2, and the third particle group 3 have different plateau capacities. For example, the relationship in the following equation may be satisfied.

[0031] C3 <C2<C1 C1: Plateau capacity of particle group 1 C2: Plateau capacity of particle group 2 C3: Plateau capacity of particle group 3

[0032] For example, the following relationship may also be satisfied. 10% ≤ (C1 - C2) ≤ 30% 10% ≤ (C2 - C3) ≤ 30% The percentage is the value when C1 is considered to be 100%. "C1-C2" can be either 20% or more, or 20% or less, for example. "C2-C3" can be either 20% or more, or 20% or less, for example.

[0033] For example, the following relationship may also be satisfied. 60% ≤ C2 / C1 ≤ 90% 30% ≤ C3 / C1 ≤ 60% "C2 / C1" can be any of the following: 70% or more, 80% or more, 80% or less, or 70% or less. "C3 / C1" can be any of the following: 40% or more, 50% or more, 50% or less, or 40% or less.

[0034] For example, the first particle group 1, the second particle group 2, and the third particle group 3 may all be two-phase coexisting active materials having the composition of the following general formula. Li x Fe yM z PO4 M is at least one element selected from the group consisting of Al, Co, Cr, Cu, Mg, Mn, Mo, Nb, Ni, Ti, V, W, and Zr. The relationships 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, and 0 ≤ z ≤ 1 are satisfied.

[0035] In the two-phase coexistence type active material represented by the above general formula, the plateau capacity can change while the plateau potential remains constant, for example, depending on the type of M and the values ​​of x, y, and z. For example, in the first particle group 1, the second particle group 2, and the third particle group 3, at least one of M, x, y, and z may be different from each other.

[0036] In the first particle group 1, second particle group 2, and third particle group 3, the first particle group 1 has the largest plateau capacity (C1). The mass fraction of the first particle group 1 relative to the whole may be, for example, 50 to 90%. The whole represents the sum of the first particle group 1, second particle group 2, and third particle group 3. It is expected that detecting an increase in overpotential will be easier if the mass fraction of the first particle group 1 is 90% or less. It is expected that the desired energy density will be maintained if the mass fraction of the first particle group 1 is 50% or more. The mass fraction of the first particle group 1 may be, for example, 80% or less, 70% or less, or 60% or less. The mass fraction of the first particle group 1 may be, for example, 60% or more, 70% or more, or 80% or more.

[0037] The discharge curve of battery 100 has two or more voltage flats. The number of voltage flats is equal to the number of particle group types. For example, when the active material layer 5 contains a first particle group 1, a second particle group 2, and a third particle group 3, three voltage flats may be formed. There are steps between each voltage flat. These steps are voltage drops during discharge or voltage increases during charging. These steps indicate an increase in overvoltage. This increase in overvoltage can occur due to differences in plateau capacitance.

[0038] The step size (increase in overvoltage) may be, for example, 0.01V or more, 0.025V or more, 0.05V or more, 0.075V or more, 0.1V or more, 0.15V or more, or 0.2V or more. The step size may also be, for example, 0.2V or less, 0.15V or less, 0.1V or less, 0.075V or less, 0.05V or less, or 0.025V or less.

[0039] The "number of voltage flats," "number of steps," and "size of steps" are observed in the discharge curve at a rate of 0.1C. "C" is a symbol representing the rate (time rate). A rate of 1C means that the rated capacity of a 100L battery is discharged in 1 hour.

[0040] 2. Battery System Figure 5 is a conceptual diagram showing the battery system in this embodiment. The battery system 1000 includes a battery 100 and a control device 200. Details of the battery 100 are as described above. The control device 200 may include, for example, an arithmetic unit, a memory device, an input / output interface, a voltage sensor, a current sensor, etc. The control device 200 is configured to perform SOC estimation.

[0041] Figure 6 is a schematic flowchart showing an example of SOC estimation in this embodiment. SOC estimation includes, for example, "(a) calculation of the first estimate," "(b) calculation of the second estimate," "(c) acquisition of measured values," "(d) addition correction," and "(e) subtraction correction." Note that the execution order of the steps in Figure 6 is just one example. For example, multiple steps may be executed simultaneously. For example, one or more steps may be executed in a sequential order.

[0042] In (a), a first estimated value is calculated from the total amount of current that has flowed through battery 100. The first estimated value is an estimated value of the current SOC. The total amount of current (integrated) includes the total amount of discharge current and the total amount of charge current. For example, the current SOC may be estimated from the capacity at the time of the previous full charge, the total amount of discharge current thereafter, and the total amount of charge current thereafter.

[0043] In (b), a second estimate is calculated from the first estimate and the plateau capacity of each particle group. The second estimate is the estimated SOC at which the overpotential should increase.

[0044] In (c), an increase in overvoltage is detected. An increase in overvoltage can be detected, for example, by a voltage drop during discharge or a voltage rise during charging. For example, a peak in the dV / dQ curve may be detected. The dV / dQ curve is derived by differentiating the voltage with respect to capacitance. Compared to the discharge curve, the increase in overvoltage is expected to be clearer in the dV / dQ curve. The SOC when the overvoltage actually increases is recorded. That is, the measured value of SOC is obtained. The measured value is compared with the second estimated value.

[0045] In (d), the second estimate is greater than the measured value. The third estimate is calculated by adding a correction value to the first estimate. The correction value may be, for example, the absolute difference between the second estimate and the measured value.

[0046] In (e), the second estimated value is less than or equal to the measured value. The third estimated value is calculated by subtracting the correction value from the first estimated value. [Examples]

[0047] 3. Experiment A slurry was prepared by mixing positive electrode active material, conductive material, binder, and dispersion medium. The mass ratio of solids was "positive electrode active material:conductive material:binder = 8:1:1". An active material layer was formed by coating the surface of the current collector foil with the slurry. After drying the slurry, the basis weight of the active material layer was 10 mg / cm². 2 This resulted in the production of a cathode raw material. A sample was taken from the cathode raw material by punching. The sample was disc-shaped (diameter: 16 mm).

[0048] The following materials were used in this experiment. Cathode active material: LiFePO4 (hereinafter also referred to as "LFP(1)"). Conductive material: Acetylene black Binder: Carboxymethylcellulose Dispersion medium: water Current collector foil: Al foil (thickness: 12 μm)

[0049] The test cell was assembled. The test cell for this experiment had the following configuration. Positive electrode: Sample prepared as described above Negative electrode: Li metal Separator: Microporous polypropylene membrane Electrolyte (electrolyte solution): Solute "LiPF6 (1.1 ml / L)", Solvent composition (volume ratio) "Ethylene carbonate:Dimethyl carbonate:Ethyl methyl carbonate = 3:4:3", Injection volume: 10 μL Outer shell: Coin-shaped (2032 size, 20mm diameter, 3.2mm thickness) Rated capacity: 2.5mAh

[0050] The test cell was charged and discharged under room temperature conditions. The current was 10 mA. 10 mA corresponds to a 4C rate. Figure 7 shows the discharge curve of No. 1. Figure 8 shows the dV / dQ curve of No. 1.

[0051] In the discharge curve of No. 1, a single potential flat region was observed (see Figure 7). In the dV / dQ curve of No. 1, no peak was observed (see Figure 8). This is thought to be because No. 1 uses only one type of active material.

[0052] LFP(2) was prepared. The percentage of the plateau capacity of LFP(2) to the plateau capacity of LFP(1) was 60%. In No. 2 to No. 6, a mixture of LFP(1) and LFP(2) was used as the positive electrode active material. Except for this, the test cells were prepared in the same manner as No. 1. Figure 9 is a table showing the blend ratios.

[0053] Figure 10 shows the discharge curve for No. 3. Figure 11 shows the dV / dQ curve for No. 3. In the discharge curve for No. 3, a voltage drop due to overvoltage was observed. When the charge / discharge rate is 10 mA, the capacity of the test cell is 1.1 mAh. The voltage drop was observed at 60% of 1.1 mAh. In the dV / dQ curve for No. 3, the voltage change (peak) was more clearly observed. The dV / dQ curve is considered suitable for detecting increases in overvoltage.

[0054] As shown in Figure 9, when the proportion of LFP(2) was 10% or more, the clarity of the peak in the dV / dQ curve was good. However, the energy density tends to decrease as the proportion of LFP(2) increases. Energy density is a value per unit mass. The energy density in Figure 9 is a relative value with the energy density of No. 1 set to 100%. For example, the blend ratio may be considered by taking into account the relationship in the following equation.

[0055] x ≤ (1-r) / (1-α) x: Blend ratio of LFP(2) to the total of LFP(1) and LFP(2) α: Ratio of the plateau capacity of LFP(2) to the plateau capacity of LFP(1) r: The ratio of the energy density of an electrode with an arbitrary blend ratio to the energy density of an electrode with a ratio of 100% LFP(1). 0 ≤ r ≤ 1.

[0056] Considering particle size effects and solubility gaps, two-phase coexistence reactions are likely to proceed when the State of Composite (SOC) is between 20% and 80%. Therefore, for example, the relationship 0.2 ≤ α ≤ 0.8 may be satisfied. However, α is arbitrary as long as a flat plateau can be formed over a given range. For example, the relationship 0.02 ≤ α ≤ 0.98 may be satisfied. For example, the range of α may expand as the particle size increases.

[0057] From the relationship in the above equation, when α is 0.8 or less, x is 0.5 or less. Therefore, when the ratio of LFP(2) is between 10 and 50%, it is expected that the desired energy density will be maintained while the peak of the dV / dQ curve becomes clear. That is, when the ratio of LFP(1) is between 50 and 90%, it is expected that the desired energy density will be maintained while the peak of the dV / dQ curve becomes clear.

[0058] Note that r in the above formula can be any of the following values: 0.7 or greater, 0.8 or greater, 0.9 or greater, or 0.95 or greater. For example, when r = 0.9, an energy density of 90% or more can be expected. [Explanation of symbols]

[0059] 1 First particle group, 2 Second particle group, 3 Third particle group, 5 Active material layer, 6 Current collector foil, 10 Electrode, 11 Positive electrode, 12 Negative electrode, 20 Electrolyte, 50 Power generation element, 60 Outer casing, 100 Battery, 200 Control device, 1000 Battery system, C1 First plateau capacity, C2 Second plateau capacity, C3 Third plateau capacity, P0 Plateau potential, S1 First step difference, S2 Second step difference.

Claims

1. A non-aqueous electrolyte secondary battery, and Includes control device, The aforementioned non-aqueous electrolyte secondary battery includes a positive electrode, a negative electrode, and an electrolyte. At least one of the positive electrode and the negative electrode includes a two-phase coexistence type active material. The aforementioned two-phase coexistence type active material includes two or more particle groups, In the unipolar test, the discharge curve of each particle group has a potential flat section. Each of the aforementioned particle groups is 0.95≦P i / P u ≦1.05 Satisfying the relationship, The Pi indicates the potential of the single potential flat region of any one of the particle groups, The Pu represents the arithmetic mean of the potentials of the potential flat region of the entire group of particles, Each of the particle groups has a different specific capacity corresponding to the potential flat portion. The aforementioned specific capacity is a relative value in which the capacity of the particle group having the largest capacity corresponding to the potential flat portion is set to 100% among all types of particle groups. The difference in specific volume between different groups of particles is 10% or more and 50% or less. The discharge curve of the aforementioned non-aqueous electrolyte secondary battery has two or more voltage flat sections. The number of voltage flat sections is equal to the number of types of particle groups. There is a step between each of the aforementioned voltage flat sections, The aforementioned step indicates an increase in overvoltage. The control device is configured to perform SOC estimation, The aforementioned SOC estimation is, (a) Calculate a first estimated value of the current SOC from the total amount of current that has flowed through the non-aqueous electrolyte secondary battery. (b) Calculate a second estimated value obtained by estimating the SOC at which the overpotential should increase, from the first estimated value and the specific capacity of each particle group. (c) By detecting the increase in the overvoltage, obtain the measured value of the SOC when the overvoltage actually increases. (d) When the second estimated value is larger than the measured value, the third estimated value is calculated by adding a correction value to the first estimated value, and (e) When the second estimated value is less than or equal to the measured value, the third estimated value is calculated by subtracting the correction value from the first estimated value. including, Battery system.

2. The aforementioned two-phase coexistence type active material has the general formula: Li x Fe y M z PO 4 Having the composition, In the above general formula, M is at least one selected from the group consisting of Al, Co, Cr, Cu, Mg, Mn, Mo, Nb, Ni, Ti, V, W, and Zr, and the relationships 0 ≤ x ≤ 1, 0 ≤ y ≤ 1, and 0 ≤ z ≤ 1 are satisfied. The battery system according to claim 1.

3. Of all the particle groups, the particle group with the largest specific volume has a mass fraction of 50 to 90% of the total mass of all the particle groups. The battery system according to claim 1 or claim 2.

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