Lithium-ion battery and energy storage apparatus

Abstract

The present disclosure relates to the technical field of batteries, and in particular, to a lithium-ion battery and an energy storage apparatus. The lithium-ion battery comprises electrode sheets each having an active substance, wherein the active substance has a spatial distribution coefficient η in the electrode sheet, and η=a×γ / ζ; a=100, and γ=Dn50 / (Dn100-Dn00), Dn00, Dn50, and Dn100 being the size of the active substance when the amount proportion of the active substance is 0%, 50%, and 100%, and the unit being μm; and ζ=1-Dtap / Dtrue, Dtap and Dtrue being the tap density and true density of the active substance, and the unit being g / cm3. The electrode sheets comprise a positive electrode sheet having a positive electrode active substance and a negative electrode sheet having a negative electrode active substance. The positive electrode active substance is lithium iron phosphate. The positive electrode active substance has a first spatial distribution coefficient ηpositive in the positive electrode sheet, and the negative electrode active substance has a second spatial distribution coefficient ηnegative in the negative electrode sheet, wherein 1.5≤ηpositive / ηnegative≤3.3.

Description

Lithium ion battery and energy storage device

[0001] Related Cross-Reference

[0002] The present disclosure claims priority to the Chinese patent application No. 2024113753760, filed on September 29, 2024, entitled "Lithium ion battery and energy storage device", the entire content of which is incorporated herein by reference. TECHNICAL FIELD

[0003] The present disclosure relates to the technical field of battery, and relates to a lithium ion battery and an energy storage device. BACKGROUND

[0004] In the research of lithium ion batteries, the cycle stability of lithium ion batteries is a key performance index, which is directly related to the service life and reliability of lithium ion batteries. At present, only the positive electrode sheet or only the negative electrode sheet is improved to try to improve the overall performance of the lithium ion battery through the performance improvement of a single electrode sheet. However, the influence of the performance improvement of a single electrode sheet on the cycle stability of the entire battery still needs to be tested after being assembled into a lithium ion battery, and then the cycle stability of the lithium ion battery can be confirmed. It can be seen that the current technology cannot efficiently and simply determine whether the lithium ion battery has excellent cycle stability. SUMMARY

[0005] In order to solve the above technical problems, the embodiments of the present disclosure provide a lithium ion battery and an energy storage device, by providing a lithium ion battery with kinetic performance of a positive electrode sheet and a negative electrode sheet matched, a lithium ion battery with excellent cycle stability can be more efficiently and simply obtained.

[0006] In a first aspect, the embodiments of the present disclosure provide a lithium ion battery, the lithium ion battery comprising an electrode sheet with an active material, the active material having a spatial distribution coefficient η in the electrode sheet, η = a × γ / ζ;

[0007] wherein the a = 100;

[0008] wherein the γ = Dn50 / (Dn100 - Dn00), the Dn00 is a size of the active material corresponding to a quantity proportion of the active material of 0%, unit: μm, the Dn100 is a size of the active material corresponding to a quantity proportion of the active material of 100%, unit: μm, and the Dn50 is a size of the active material corresponding to a quantity proportion of the active material of 50%, unit: μm;

[0009] the ζ = 1 - D tap / D true , the D tapthe tap density of the active material, g / cm 3 , the D true the true density of the active material, g / cm 3 ;

[0010] The pole piece includes a positive pole piece having a positive active material, and a negative pole piece having a negative active material, the positive active material being lithium iron phosphate, the positive active material having a first space distribution coefficient η 正 in the positive pole piece, the negative active material having a second space distribution coefficient η 负 in the negative pole piece, 1.5≤η 正 / η 负 ≤3.3.

[0011] In a second aspect, the present disclosure provides an energy storage device, which includes the lithium ion battery according to the first aspect.

[0012] Compared with the prior art, the present disclosure has the following advantages:

[0013] The embodiments of the present disclosure are directed to two parameters of the active material, i.e., the number particle size distribution and the pore distribution, which have important influences on the contact area of the active material and the electrolyte, and a space distribution coefficient η=a×γ / ζ of the active material is constructed, and the ratio of the positive space distribution coefficient to the negative space distribution coefficient is limited to satisfy: 1.5≤η 正 / η 负 ≤3.3, which has the following advantages: first, the transmission rate of lithium ions between the positive pole piece and the negative pole piece has higher matching, thereby making the lithium ion battery have excellent cycle stability; second, since the space distribution coefficient can be determined by the number particle size distribution and the pore distribution of the active material, the stability of the cycle performance of the lithium ion battery can be determined more efficiently and simply without the need of testing the cycle stability after the pole piece is assembled into a battery; third, since the dynamic performance matching between the positive pole piece and the negative pole piece is fully considered, the situation that the dynamic performance of a single pole piece is greatly improved after improvement, but the other pole piece is not improved, and the dynamic performance is not matched, thereby failing to effectively improve the cycle stability, does not occur. BRIEF DESCRIPTION OF DRAWINGS

[0014] In order to more clearly illustrate the technical solutions in the embodiments of the present disclosure, the drawings used in the embodiments will be briefly introduced as follows. Obviously, the drawings in the following description are only some embodiments of the present disclosure, and other drawings can be obtained by those skilled in the art without creative effort based on these drawings.

[0015] FIG. 1 is a structural schematic diagram of a household energy storage system according to an embodiment of the present disclosure.

[0016] Fig. 2 is a structural schematic diagram of an energy storage system according to an embodiment of the present disclosure.

[0017] Reference signs: 100, energy storage system; 10, energy storage device; 20, electric energy conversion device; 30, first user load; 40, second user load; 50, high-voltage cable; 60, first electric energy conversion device; 70, second electric energy conversion device. DETAILED DESCRIPTION

[0018] In the present disclosure, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "lateral", "longitudinal", and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings. These terms are mainly used for better description of the present disclosure and its embodiments, and are not used to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0019] In addition, in addition to being used to indicate the orientation or positional relationship, the above-mentioned partial terms can also be used to indicate other meanings, for example, the term "upper" can also be used to indicate a certain dependent relationship or connection relationship in some cases. For those skilled in the art, the specific meaning of these terms in the present disclosure can be understood according to the specific circumstances.

[0020] In addition, the terms "mount", "set", "provided with", "connected", "connected to" should be understood broadly. For example, it can be a fixed connection, a detachable connection, or an integral structure; it can be a mechanical connection, or an electrical connection; it can be a direct connection, or an indirect connection through an intermediate medium, or an internal communication between two devices, elements or components. For those skilled in the art, the specific meaning of the above-mentioned terms in the present disclosure can be understood according to the specific circumstances.

[0021] In addition, the terms "first", "second", and the like are mainly used to distinguish different devices, elements or components (the specific types and structures can be the same or different), and are not used to indicate or imply the relative importance and quantity of the indicated devices, elements or components. Unless otherwise stated, the meaning of "multiple" is two or more.

[0022] The technical solutions of the present disclosure will be further described below in conjunction with the embodiments.

[0023] The positive electrode sheet and the negative electrode sheet are core components of a lithium ion battery, and the material properties thereof have a decisive influence on the cycle stability of the lithium ion battery. The related art often only focuses on the performance improvement of a single electrode sheet, but the lithium ion battery has two kinds of electrode sheets, namely, the positive electrode sheet and the negative electrode sheet, and the two kinds of electrode sheets interact with each other in the charging and discharging process. Therefore, the performance improvement of a single electrode sheet has an influence on the performance of the entire battery, and the cycle stability of the battery also needs to be tested after being assembled into a lithium ion battery. It is also reflected that it is difficult to efficiently and simply determine whether the lithium ion battery has excellent cycle stability only by the structural characteristics of a single electrode sheet and the active material thereof.

[0024] On the basis of in-depth analysis of the problems existing in the prior art, the present disclosure provides a lithium ion battery and an energy storage device. By exploring the kinetic performance matching between the positive active material and the negative active material, the lithium ion can be efficiently and simply made to have excellent cycle stability.

[0025] In a first aspect, the embodiments of the present disclosure provide a lithium ion battery, comprising an electrode sheet having an active material, the active material having a spatial distribution coefficient η in the electrode sheet, η = a x γ / ζ;

[0026] wherein a = 100;

[0027] wherein γ = Dn50 / (Dn100 - Dn00), Dn00 is the size of the active material corresponding to an active material quantity proportion of 0%, in units of μm, Dn100 is the size of the active material corresponding to an active material quantity proportion of 100%, in units of μm, and Dn50 is the size of the active material corresponding to an active material quantity proportion of 50%, in units of μm;

[0028] ζ = 1 - D tap / D true , D tap is the tap density of the active material, in units of g / cm 3 , and D true is the true density of the active material, in units of g / cm 3 ;

[0029] The electrode sheet comprises a positive electrode sheet having a positive active material and a negative electrode sheet having a negative active material, the positive active material having a first spatial distribution coefficient η 正 in the positive electrode sheet, and the negative active material having a second spatial distribution coefficient η 负 in the negative electrode sheet, 1.5 ≤ η 正 / η 负 ≤ 3.3.

[0030] wherein 1.5 ≤ η 正 / η 负≤3.3 includes any point value in the above ratio range, for example, η 正 / η 负 is 1.5, 1.8, 2, 2.2, 2.5, 2.8, 3, or 3.3.

[0031] The lithium ion battery of the embodiments of the present disclosure can well match the kinetic performance of the positive electrode sheet and the negative electrode sheet by controlling the ratio between the first spatial distribution coefficient η 正 of the positive electrode active material and the second spatial distribution coefficient η 负 of the negative electrode active material in the range of 1.5-3.3, so that the lithium ion transmission between the positive electrode and the negative electrode is more balanced. In this way, the problems of lithium precipitation at the interface of the negative electrode sheet and serious side reactions caused by the mismatch of lithium ion transmission rate can be avoided, the diffusion ability of lithium ion between the positive electrode sheet and the negative electrode sheet is accurately controlled, and the cycle stability of the lithium ion battery is improved.

[0032] The spatial distribution coefficient η of the active material in the electrode sheet can reflect the lithium ion diffusion ability of the positive electrode sheet and the negative electrode sheet, which determines the transmission rate of lithium ion between the electrode sheets. The stronger the lithium ion diffusion ability, the faster the transmission rate. When η 正 / η 负 is controlled in the range of 1.5-3.3 of the embodiments of the present disclosure, the lithium ion diffusion ability of the positive electrode sheet side and the negative electrode sheet side has good matching, so that the lithium ion transmitted from the positive electrode sheet to the negative electrode sheet can be properly embedded into the negative electrode sheet, and there will be no excessive lithium ion precipitated at the interface of the negative electrode sheet, nor will it cause excessive side reactions at the negative electrode sheet. As can be seen, by accurately controlling the diffusion ability of lithium ion between the positive electrode sheet and the negative electrode sheet, a lithium ion battery with good cycle stability can be obtained.

[0033] When η 正 / η 负 <1.5, it indicates that the lithium ion transmission rate of the positive electrode sheet side is higher than that of the negative electrode sheet side, which makes the number of lithium ions transmitted from the positive electrode sheet to the negative electrode sheet exceed the capacity of the negative electrode sheet to receive and store lithium ions, and further leads to the excess of lithium ions at the negative electrode sheet side, which is prone to interface lithium precipitation, and eventually leads to cycle performance degradation. When η 正 / η 负 >3.3, it indicates that the lithium ion transmission rate of the positive electrode sheet side is lower than that of the negative electrode sheet side, which makes the number of lithium ions transmitted from the positive electrode sheet to the negative electrode sheet insufficient to fully utilize the lithium ion storage capacity of the negative electrode sheet. At this time, the negative electrode sheet side has high kinetics, which leads to serious side reactions between the materials and electrolyte at the negative electrode sheet side, and further leads to serious and irreversible lithium loss, and eventually leads to the deterioration of the cycle performance of the battery.

[0034] In addition, the space distribution coefficient η in the embodiment of the present disclosure is η = a x γ / ζ, where a is a constant, γ = Dn50 / (Dn100 - Dn00), and ζ = 1 - D tap / D true It can be seen that the space distribution coefficient of the embodiment of the present disclosure can be jointly defined by the number particle size distribution and the pore distribution of the active material, thereby more efficiently, simply and intuitively reflecting the diffusion ability of lithium ions in the active material. Wherein, γ = Dn50 / (Dn100 - Dn00) is the number distribution coefficient of the active material, and ζ is the maximum pore ratio formed when the active material is most densely packed. The above two parameters mainly affect the contact area of the positive and negative active materials with the electrolyte, and then affect the diffusion ability of lithium ions in the positive and negative electrodes. It can be understood that, since the space distribution coefficient η of the present disclosure includes the first space distribution coefficient η 正 of the positive active material in the positive electrode plate and the second space distribution coefficient η 负 of the negative active material in the negative electrode plate, both η 正 and η 负 satisfy a x γ / ζ. Wherein, the first space distribution coefficient is determined by the number particle size distribution and the pore distribution of the positive active material, and the second space distribution coefficient is determined by the number particle size distribution and the pore distribution of the negative active material.

[0035] As can be seen from the above, the embodiment of the present disclosure constructs the space distribution coefficient η = a x γ / ζ of the active material with respect to the two parameters of the number particle size distribution and the pore distribution of the active material which have important influence on the contact area of the electrolyte, and by limiting the ratio of the positive and negative space distribution coefficients to satisfy: 1.5 ≤ η 正 / η 负 ≤ 3.3, firstly, the transmission rate of lithium ions between the positive electrode plate and the negative electrode plate has higher matching, thereby making the lithium ion battery obtain excellent cycle stability; secondly, since the above space distribution coefficient can be determined by the number particle size distribution and the pore distribution of the active material, it is not necessary to test the cycle stability after assembling the electrode plate into a battery; thirdly, since the kinetic performance matching between the positive electrode and the negative electrode is fully considered, the situation that the kinetic performance of a single electrode plate is greatly improved after improvement, but the other electrode plate is not improved, and the kinetic performance is not matched, thereby the cycle stability cannot be effectively improved, does not occur.

[0036] Therefore, the embodiment of the present disclosure can screen and determine the kinetic performance matching degree of the positive and negative electrode plates after the positive and negative electrode plates are made, which is helpful to efficiently and simply determine the cycle stability performance of the lithium ion battery, and then is conducive to quickly screening and optimizing the adaptation degree of the used positive and negative electrode plates, and obtaining the lithium ion battery with excellent cycle stability.

[0037] Further, 1.5≤η 正 / η 负 ≤2.8.

[0038] Since the spatial distribution coefficient η of the active material is closely related to the diffusion ability of lithium ions, it can intuitively reflect the influence of the positive and negative active materials on the diffusion balance and diffusion efficiency of lithium ions, and therefore the embodiments of the present disclosure can obtain better cycle stability by further optimizing the η 正 / η 负 ratio range of 1.5-2.8.

[0039] Further, for the negative active material, 0.7 μm≤Dn00≤1.2 μm, 1.5 μm≤Dn50≤2.5 μm, and 20 μm≤Dn100≤50 μm. Exemplarily, for the negative active material, Dn00 is 0.7 μm, 0.8 μm, 0.9 μm, 1.0 μm, 1.1 μm, or 1.2 μm, Dn50 is 1.5 μm, 1.6 μm, 1.8 μm, 2.0 μm, 2.2 μm, or 2.5 μm, and Dn100 is 20 μm, 25 μm, 30 μm, 35 μm, 40 μm, 45 μm, or 50 μm.

[0040] Further, for the positive active material, 0.10 μm≤Dn00≤0.30 μm, 0.70 μm≤Dn50≤1.0 μm, and 3.4 μm≤Dn100≤5.0 μm. Exemplarily, for the positive active material, Dn00 is 0.10 μm, 0.12 μm, 0.15 μm, 0.20 μm, 0.25 μm, or 0.30 μm, Dn50 is 0.70 μm, 0.75 μm, 0.80 μm, 0.85 μm, 0.90 μm, 0.95 μm, or 1.0 μm, and Dn100 is 3.4 μm, 3.8 μm, 4.0 μm, 4.2 μm, 4.5 μm, 4.8 μm, or 5.0 μm.

[0041] When the number particle size distribution of the negative active material and the positive active material is within the above range, it is more conducive to control the number particle size distribution of the active material with a suitable γ range, and further obtain a lithium ion battery with excellent cycle stability. The wider the γ range, the more the number of large and small particle active materials, and the increase in the number of small particle active materials will exacerbate the degree of side reactions. The narrower the γ range, the less the number of large and small particle active materials, although this is conducive to further improving the cycle stability of the lithium ion battery, it will make the yield of active material low, the production cost of the lithium ion battery high, and also not conducive to actual production.

[0042] It should be noted that, in the embodiments of the present disclosure, by controlling the above-mentioned number particle size distribution range of the positive active material and the negative active material, the uniformity of the active material as a whole can be better reflected, and the stability of the electrode sheet structure can be maintained by the uniform particle size, thereby also being conducive to improving the cycle stability of the lithium ion battery. As for the actual space occupied by the active material particles in the electrode sheet, the embodiments of the present disclosure control the parameter of the maximum pore volume ratio ζ formed when the active material is stacked, so as to limit by the cooperation of the number particle size distribution and the pore distribution, so as to more intuitively and simply predict the balanced matching of the positive and negative electrode sheets to the lithium ion transmission rate. In addition, compared with the volume particle size distribution, the embodiments of the present disclosure select the number particle size distribution to regulate and control the kinetic performance of the positive and negative electrode sheets, because the number particle size distribution better reflects the role of small particle active materials, and therefore by the cooperation of the number particle size distribution and the pore distribution, the lithium ion transmission efficiency can be more accurately regulated and controlled.

[0043] Further, the tap density of the negative active material satisfies 1.0 g / cm 3 ≤D tap ≤1.3 g / cm 3 . Exemplarily, the tap density D tap of the negative active material is 1.0 g / cm 3 , 1.1 g / cm 3 , 1.2 g / cm 3 or 1.3 g / cm 3 .

[0044] Further, the tap density of the negative active material satisfies 1.0 g / cm 3 ≤D true ≤2.3 g / cm 3 . Exemplarily, the tap density D true of the negative active material is 1.0 g / cm 3 , 1.1 g / cm 3 , 1.2 g / cm 3 or 1.3 g / cm 3 .

[0045] Further, the tap density of the negative active material satisfies 1.0 g / cm 3 ≤D tap ≤1.4 g / cm 3 . Exemplarily, the tap density D tap of the negative active material is 1.0 g / cm 3 , 1.1 g / cm 3 , 1.2 g / cm 3 or 1.3 g / cm 3 .

[0046] Furthermore, the true density of the positive electrode active material satisfies 3 g / cm³. 3 ≤D true ≤3.8g / cm 3 For example, the true density D of the positive electrode active material. true 3g / cm 3 3.2g / cm 3 3.5g / cm 3 3.6g / cm 3 Or 3.8g / cm 3 .

[0047] By controlling the tap density and true density of the positive and negative electrode active materials within the above range, it is beneficial to better control the pore distribution range of the active materials with a suitable ζ range under the condition of the densest packing. This avoids the difficulty of electrolyte wetting due to too small pores, or the difficulty of improving the compaction density of the electrode due to too large pores, which in turn affects the capacity level and energy density of the lithium-ion battery.

[0048] Optionally, the positive electrode active material includes one or more of lithium iron phosphate, lithium manganese iron phosphate, and lithium-rich manganese-based materials. Preferably, the positive electrode active material is lithium iron phosphate. Lithium iron phosphate is prepared by solid-phase method with iron phosphate, solid-phase method with iron oxide red process, ferrous oxalate process, or liquid-phase method.

[0049] For example, in one optional embodiment, when lithium iron phosphate is used as the positive electrode active material, the preparation method of lithium iron phosphate includes the following steps:

[0050] A solid-state process is employed, in which precursor iron, lithium, and carbon sources are ground and mixed in a specific ratio, followed by spray granulation, sintering, and pulverization to produce lithium iron phosphate (LFP) finished products. During this process, the particle size of the precursor can be adjusted by changing the grinding time of the raw materials. The primary particle size of the final product is controlled by the sintering temperature and time. Finally, a pulverization process breaks the sintered material into finished powder with a specific particle size distribution. The particle size distribution of the powder is mainly controlled by the sintering temperature and time. Crushing breaks up agglomerated secondary particles to form dispersed primary particles. The tap density and true density are determined by the primary particle size of the powder; a smaller primary particle size often reduces the tap density and true density of the powder material.

[0051] Optionally, the negative electrode active material includes one or more of graphite, hard carbon, silicon carbide, silicon anode, and carbon microspheres. Preferably, the negative electrode active material is graphite. Graphite is obtained by grinding, sieving, shaping, granulating, and graphitizing carbon-based raw materials, and the graphite is in the form of primary particles and / or secondary particles.

[0052] For example, in one optional embodiment, when graphite is used as the negative electrode active material, the method for preparing graphite includes the following steps:

[0053] The raw material low-sulfur coke or medium-sulfur coke is ground, screened, shaped, granulated, and graphitized to obtain the desired graphite. The particle size distribution of the raw material during grinding, screening, shaping, and granulation is the main factor affecting the particle size distribution and tap density of the graphite. In addition, the tap density is also affected by the graphitization degree. The true density of the graphite is related to the type of raw material and the graphitization process, and generally there is no significant difference in the true density of the graphite after complete graphitization of the same type of raw material.

[0054] It should be noted that the active material of the embodiments of the present disclosure can also be prepared by other conventional methods in the art, and the present disclosure does not limit the preparation method of the positive active material (such as lithium iron phosphate) and the negative active material (such as graphite).

[0055] The related art often focuses on structural modification of the active material in the pole piece, such as functional coating design of the core-shell structure of the positive active material, and the like, to improve the performance of the positive pole piece. However, such modified materials often require a complex synthesis process, and there is a risk of poor structural stability such as cracking or film peeling during use, and often are not compatible with existing lithium-ion battery manufacturing processes and equipment, thus making it difficult to directly apply such a solution in actual production.

[0056] The present disclosure uses the above-mentioned positive active material and negative active material, especially the preferred lithium iron phosphate and graphite, which can select the positive active material and negative active material commonly used in the art, without further structural modification of the material. In this way, the embodiments of the present disclosure do not need to perform complex structural design on the active material, but only need to make the number particle size distribution and pore distribution of the conventional active material satisfy the space distribution coefficient η = a × γ / ζ of the present disclosure, and ensure that η 正 / η 负 In the range of 1.5-3.3, the lithium-ion battery has excellent cycle stability. This material selection feature makes the lithium-ion battery of the embodiments of the present disclosure more suitable for actual industrial application.

[0057] In a second aspect, the embodiments of the present disclosure also provide a energy storage device 10, which comprises the battery separator film of the first aspect or the second aspect.

[0058] Taking electrochemical energy storage as an example, the embodiments of the present disclosure provide an energy storage device 10, which is provided with a group of chemical batteries, mainly using chemical elements in the battery as energy storage medium. The charging and discharging process is accompanied by chemical reaction or change of the energy storage medium. In simple terms, the electrical energy generated by wind and solar energy is stored in the chemical battery, and when the use of external electrical energy reaches a peak, the stored electrical energy is released for use, or transferred to a place where electrical energy is in short supply for use.

[0059] The current energy storage (i.e., energy storage) application scenarios are relatively wide, including energy storage on the power generation side, energy storage on the power grid side, and energy storage on the power consumption side, and the corresponding types of energy storage devices 10 include:

[0060] (1) Large-scale energy storage power stations applied on the side of wind power and photovoltaic power stations, which can assist renewable energy power generation to meet grid connection requirements and improve renewable energy utilization rate; as high-quality active / reactive power regulation power sources on the power supply side, energy storage power stations realize load matching in time and space, enhance renewable energy consumption capacity, reduce instantaneous power changes, reduce the impact on the power grid, improve new energy power generation consumption problems, and have great significance in power grid system backup, relieving peak load power supply pressure, and peak regulation;

[0061] (2) Energy storage containers applied on the power grid side, the main functions of which are peak regulation, frequency regulation, and relieving power grid congestion, which can realize peak clipping and valley filling of power consumption, i.e., charging energy storage batteries when power consumption load is low, and releasing stored power during power consumption load peak period, so as to realize the balance between power production and consumption;

[0062] (3) Small energy storage cabinets applied on the power consumption side, the main functions of which are power self-generation and self-use, peak-valley price difference arbitrage, capacity cost management, and improvement of power supply reliability. According to different application scenarios, power consumption side energy storage can be divided into industrial and commercial energy storage cabinets, household energy storage devices 10, and energy storage charging piles, etc., which are generally used with distributed photovoltaic power. Industrial and commercial users can use energy storage for peak-valley price difference arbitrage and capacity cost management. In the electricity market implementing peak-valley electricity price, through charging the energy storage system 100 at low price and discharging the energy storage system 100 at high price, peak-valley price difference arbitrage is realized, and the electricity cost is reduced. In addition, industrial enterprises suitable for two-part electricity price can use the energy storage system 100 to store energy during low power consumption and discharge during peak load, so as to reduce the maximum demand amount and achieve the purpose of reducing capacity electricity cost. Household photovoltaic power storage can improve the level of power self-generation and self-use. Due to high electricity price and poor power supply stability, household photovoltaic power demand is increased. Considering that photovoltaic power is generated during the day and users generally have high load at night, through the configuration of energy storage, photovoltaic power can be better utilized, the level of self-generation and self-use is improved, and the electricity cost is reduced. In addition, communication base stations, data centers, and other fields need to configure energy storage for backup power supply.

[0063] Please refer to FIG. 1, which is a structural schematic diagram of a household energy storage system 100 according to an embodiment of the present disclosure. The present disclosure provides a household energy storage system 100, which comprises an electric energy conversion device 20 (a photovoltaic panel), a first user load 30 (a street lamp), a second user load 40 (for example, a household appliance such as an air conditioner), and an energy storage device 10. The energy storage device 10 is a small energy storage box, which can be installed on an outdoor wall by a wall-mounted manner. Specifically, the photovoltaic panel can convert solar energy into electric energy during a low electricity price period, and the energy storage device 10 is used to store the electric energy and supply the street lamp and the household appliance for use during a high electricity price period or during a power grid outage.

[0064] Please refer to FIG. 2, which is a structural schematic diagram of the energy storage system 100 according to an embodiment of the present disclosure. The embodiment of FIG. 2 is used to illustrate a power generation / distribution side shared energy storage scenario. The energy storage device 10 according to the present disclosure is not limited to the power generation / distribution side energy storage scenario.

[0065] The present disclosure provides an energy storage system 100, which comprises a high-voltage cable 50, a first electric energy conversion device 60, a second electric energy conversion device 70, and an energy storage device 10 provided by the present disclosure. In a power generation situation, the first electric energy conversion device 60 and the second electric energy conversion device 70 are used to convert other forms of energy into electric energy, are connected with the high-voltage cable, and supply a power distribution network for use. When the electric load is low, the first electric energy conversion device 60 and the second electric energy conversion device 70 generate excess electricity, which is stored in the energy storage device 10, thereby reducing the curtailment rate of wind power and solar power and improving the problem of new energy power generation consumption. When the electric load is high, the power grid issues an instruction to transmit the electric energy stored in the energy storage device 10 in a grid-connected mode together with the high-voltage cable 50 to supply the electric load for use, thereby providing various services such as peak shaving, frequency modulation, and backup for the power grid operation, fully playing the role of peak shaving of the power grid, promoting the peak shaving and valley filling of the power grid, and relieving the power supply pressure of the power grid.

[0066] Optionally, the first electric energy conversion device 60 and the second electric energy conversion device 70 can convert at least one of solar energy, light energy, wind energy, heat energy, tidal energy, biomass energy, and mechanical energy into electric energy.

[0067] The number of the energy storage devices 10 can be multiple, and the multiple energy storage devices 10 are connected in series or in parallel with each other and are supported and electrically connected by an isolation plate (not shown in the figure). In the embodiment, “multiple” means two or more. The energy storage device 10 can further be provided with an energy storage box outside for accommodating the energy storage device 10.

[0068] Optionally, the energy storage device 10 can include, but is not limited to, a battery module, a battery pack, a battery system, etc. The actual application form of the energy storage device 10 provided by the embodiments of the present disclosure can be, but is not limited to, the listed products, and can also be other application forms, and the embodiments of the present disclosure do not strictly limit the application form of the energy storage device 10. The embodiments of the present disclosure only take the energy storage device 10 as an example of a multi-core battery. When the energy storage device 10 is a single battery, the energy storage device 10 can be at least one of a cylindrical battery, a square battery, etc.

[0069] The scheme of the present disclosure will be further introduced below in combination with specific embodiments and experimental data.

[0070] Embodiment 1

[0071] The present embodiment provides a lithium ion battery, which is obtained by the following method.

[0072] Preparation of the positive electrode sheet: lithium iron phosphate, conductive carbon black and polyvinylidene fluoride are dispersed into N-methyl pyrrolidone in a mass ratio of 95:3:2 to mix uniformly to obtain a positive electrode slurry, and the positive electrode slurry is uniformly coated on a positive electrode current collector. After drying, cold pressing, slitting and sheet cutting, a positive electrode sheet is obtained. The structure parameters of the positive electrode active material lithium iron phosphate are shown in Table 1.

[0073] Preparation of the negative electrode sheet: graphite, conductive carbon black, sodium carboxymethyl cellulose and butadiene rubber are dispersed into a solvent in a mass ratio of 96:1.5:1.5:1 to mix uniformly to obtain a negative electrode slurry, and the negative electrode slurry is coated on a negative electrode current collector. After drying, cold pressing, slitting and sheet cutting, a negative electrode sheet is obtained. The structure parameters of the negative electrode active material graphite are shown in Table 1.

[0074] Preparation of the electrolyte: in an argon atmosphere glove box with a water content of ≤1 ppm, ethylene carbonate (EC), methyl ethyl carbonate (EMC) and dimethyl carbonate (DMC) are mixed in a volume ratio of 1:1:1 to obtain a mixed solvent, and dry lithium salt LiPF6 is added to the mixed solvent to prepare an electrolyte with a concentration of 1 mol / L.

[0075] Separator: a polyethylene separator with a thickness of 16 μm is used.

[0076] Assembly of the lithium ion battery: the above positive electrode sheet, separator and negative electrode sheet are stacked in order, so that the battery separator is in the middle of the positive electrode and the negative electrode, and the positive electrode sheet and the negative electrode sheet are separated, and after winding, a bare cell is obtained. After connecting the tab, the cell is assembled into an outer package, the electrolyte is injected, and the cell is packaged, placed, formed, shaped, capacity tested, etc., and finally a lithium ion battery is prepared.

[0077] Embodiments 2-6

[0078] The difference between Examples 2-6 and Example 1 is that the structural parameters of the positive electrode active material and the negative electrode active material are different, as shown in Table 1. The total mass of the negative electrode active material in Example 6 is the same, and the mass of the hard carbon accounts for 2%.

[0079] Comparative Examples 1-2

[0080] The difference between Comparative Examples 1-2 and Example 1 is that the structural parameters of the positive electrode active material and the negative electrode active material are different, as shown in Table 1.

[0081] <Performance Test>

[0082] (1) Particle size distribution test of active material: The positive electrode active material and the negative electrode active material of Examples 1-6 and Comparative Examples 1-2 were tested by laser particle size analyzer (Model Malvern Mastersizer 3000) according to particle size distribution laser diffraction method (GB / T19077-2016) to obtain Dn00, Dn50 and Dn100.

[0083] (2) Tap density test of active material

[0084] The prepared sample was placed in a graduated cylinder, and the graduated cylinder was fixed on a mechanical vibration device (instrument model Dandong Baiter BT-313). The vibration motor drove the mechanical vibration device to vibrate vertically up and down. The graduated cylinder containing the sample vibrated with the mechanical vibration device in a rhythmic manner. When the vibration frequency reached the set frequency, the mechanical vibration device stopped vibrating, and the volume of the graduated cylinder was read. According to the definition of density: mass divided by volume, the tap density of the positive electrode active material / negative electrode active material after tapping was calculated.

[0085] (3) True density test of active material

[0086] When measuring the sample, the instrument (instrument model Baisi De 3H-2000TD) automatically collected the pressure P1 and volume V1 of the reference cavity and recorded them. A sample with an unknown volume V was placed in a sample testing cavity with a known volume V2. A certain amount of gas was injected into the reference cavity, and the stable pressure P2 was recorded. The sample testing cavity was connected to the reference cavity, and the stable pressure P3 was recorded. According to the balanced stable pressure value and the related known volumes V1 and V2, the sample volume Vsample was calculated. According to the definition of density: mass divided by volume, the true density of the positive electrode active material / negative electrode active material was calculated.

[0087] (4) Cycle stability test of battery: The lithium ion batteries of Examples 1-6 and Comparative Examples 1-2 were tested for charge and discharge cycles on a charge and discharge instrument.

[0088] The constant power charging was carried out at 1P of the charging power in an environment at 25℃ until reaching the upper limit voltage 3.65V and then the constant voltage charging was carried out after that, and then the constant power discharging was carried out at 1P of the discharging power until the final voltage was 2.5V, and the first cycle discharge capacity of the battery was recorded; and then 500 cycles of charging and discharging were carried out, and the discharge capacity of the 500th cycle was recorded. The calculation formula of the capacity retention rate was: the capacity retention rate after the 500th cycle = (the discharge capacity after the 500th cycle / the first cycle discharge capacity) x 100%.

[0089] Table 1 structure parameters and test results of examples 1-6 and comparative examples 1-2

[0090] According to the above test results, η 正 / η 负 When controlled in the range of 1.5-3.3, the capacity retention rate is higher, reaching more than 95.12%. Especially when controlled in the range of 1.5-2.8, the capacity retention rate can be further improved to more than 96.46%, indicating that the transmission rate matching degree of lithium ions between the positive electrode sheet and the negative electrode sheet is higher, so that the lithium ion battery has high level of cycle stability performance. While in comparative example 1, η 正 / η 负 The ratio is small, and in comparative example 2, η 正 / η 负 The ratio is large, reflecting that the transmission rate of lithium ions between the positive electrode sheet and the negative electrode sheet is not matched, and problems such as interface lithium precipitation, serious side reactions, etc. are prone to occur, resulting in decreased cycle performance.

[0091] The above describes the technical solutions disclosed by the embodiments of the present disclosure in detail, and the principles and implementation manners of the present disclosure are described by applying specific examples. The above description of the embodiments is only to help understand the technical solutions of the present disclosure and the core idea thereof. Meanwhile, for those skilled in the art, according to the idea of the present disclosure, the specific implementation manners and application ranges will be changed, and the above description of the specification should not be understood as a limitation of the present disclosure.

Claims

1. A lithium-ion battery, wherein, The lithium ion battery comprises a pole piece with an active substance, the active substance has a spatial distribution coefficient η in the pole piece, η = a × γ / ζ; Wherein, the a = 100; Wherein, the γ = Dn50 / (Dn100 - Dn00), the Dn00 is the size of the active substance corresponding to the number ratio of 0%, unit: μm, the Dn100 is the size of the active substance corresponding to the number ratio of 100%, unit: μm, the Dn50 is the size of the active substance corresponding to the number ratio of 50%, unit: μm; said ζ = 1 - D tap / D true , said D tap is the tap density of the active substance in g / cm 3 , said D true is the true density of the active substance in g / cm 3 ; The electrode sheet includes a positive electrode sheet having a positive electrode active material, the positive electrode active material being lithium iron phosphate, the positive electrode active material having a first spatial distribution coefficient η 正 in the positive electrode sheet, a negative electrode sheet having a negative electrode active material, the negative electrode active material having a second spatial distribution coefficient η 负 in the negative electrode sheet, and 1.5 ≤ η 正 / η 负 ≤ 3.

3.

2. The lithium-ion battery of claim 1, wherein, 1.5 < η 正 / η 负 ≤ 2.

8.

3. The lithium-ion battery of claim 1, wherein, For the negative active substance, 0.7 μm ≤ Dn00 ≤ 1.2 μm, 1.5 μm ≤ Dn50 ≤ 2.5 μm, 20 μm ≤ Dn100 ≤ 50 μm.

4. The lithium-ion battery of claim 1, wherein, The tap density of the negative electrode active material satisfies 1.0 g / cm 3 ≤D tap ≤1.3 g / cm 3 .

5. The lithium-ion battery of claim 1, wherein, The true density of the negative electrode active material satisfies 2.0 g / cm 3 ≤D true ≤2.3 g / cm 3 .

6. The lithium-ion battery of claim 1, wherein, For the positive active substance, 0.10 μm ≤ Dn00 ≤ 0.30 μm, 0.70 μm ≤ Dn50 ≤ 1.0 μm, 3.4 μm ≤ Dn100 ≤ 5.0 μm.

7. The lithium-ion battery of claim 1, wherein, The tap density of the positive electrode active material satisfies 0.8 g / cm 3 ≤ D tap ≤ 1.4 g / cm 3 .

8. The lithium-ion battery of claim 1, wherein, The true density of the positive electrode active material satisfies 3 g / cm 3 ≤D true ≤3.8 g / cm 3 .

9. The lithium-ion battery of claim 1, wherein, The negative active substance comprises one or more of graphite, hard carbon, silicon carbon, silicon negative electrode, carbon microspheres; and / or, The positive active substance is prepared by a solid phase method of iron phosphate, a solid phase method of iron red process, a ferrous oxalate process method or a liquid phase method; and / or, The negative active substance is graphite, the graphite is obtained by grinding, screening, shaping, granulating and graphitizing carbon-based raw materials, and the graphite is primary particles and / or secondary particles.

10. An energy storage device, wherein, The energy storage device comprises the lithium ion battery according to any one of claims 1 to 9.

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