Lithium ion battery and energy storage device

Abstract

The present application relates to the technical field of battery, and particularly relates to a lithium ion battery and energy storage device. The lithium ion battery comprises a pole piece with active material, the active material has a spatial distribution coefficient η in the pole piece, η = a * γ / ζ; a = 100, γ = Dn50 / (Dn100 - Dn00), Dn00, Dn50 and Dn100 are sizes of the active material when the quantity proportion of the active material is 0%, 50% and 100%, and the unit is μm; ζ = 1 - D tap / D true , D tap and D true are tap density and true density of the active material, and the unit is g / cm 3 ; the pole piece comprises a positive pole piece with positive active material and a negative pole piece with negative active material, the positive active material is lithium iron phosphate, the positive active material has a first spatial distribution coefficient η 正 in the positive pole piece, the negative active material has a second spatial distribution coefficient η 负 in the negative pole piece, and 1.5 <= η 正 / η 负 <= 3.3.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of batteries, in particular to a lithium ion battery and an energy storage device. BACKGROUND

[0002] 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 whole 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

[0003] In order to solve the above technical problems, the embodiments of the present application 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, the lithium ion battery with excellent cycle stability can be more efficiently and simply obtained.

[0004] In a first aspect, the embodiments of the present application 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;

[0005] Wherein, the a = 100;

[0006] Wherein, the γ = Dn50 / (Dn100 - Dn00), the Dn00 is the size of the active material corresponding to the number percentage of 0% of the active material, unit: μm, the Dn100 is the size of the active material corresponding to the number percentage of 100% of the active material, unit: μm, the Dn50 is the size of the active material corresponding to the number percentage of 50% of the active material, unit: μm;

[0007] The ζ = 1 - D tap / D true , the D tap is the tap density of the active material, unit: g / cm 3 , the D true is the true density of the active material, unit: g / cm 3 ;

[0008] The pole piece includes a positive pole piece having a positive active material, a negative pole piece having a negative active material, the positive active material being lithium iron phosphate, the positive active material having a first spatial distribution coefficient η 正 in the positive pole piece, the negative active material having a second spatial distribution coefficient η 负 in the negative pole piece, 1.5≤η 正 / η 负 ≤3.3.

[0009] Further, 1.5≤η 正 / η 负 ≤2.8.

[0010] Further, for the negative active material, 0.7 μm≤Dn00≤1.2 μm, 1.5 μm≤Dn50≤2.5 μm, 20 μm≤Dn100≤50 μm.

[0011] Further, the tap density of the negative active material satisfies 1.0 g / cm 3 ≤D tap ≤1.3 g / cm 3 .

[0012] Further, the true density of the negative active material satisfies 2.0 g / cm 3 ≤D true ≤2.3 g / cm 3 .

[0013] Further, for the positive active material, 0.10 μm≤Dn00≤0.30 μm, 0.70 μm≤Dn50≤1.0 μm, 3.4 μm≤Dn100≤5.0 μm.

[0014] Further, the tap density of the positive active material satisfies 0.8 g / cm 3 ≤D tap ≤1.4 g / cm 3 .

[0015] Further, the true density of the positive active material satisfies 3 g / cm 3 ≤Dtrue≤3.8 g / cm 3 .

[0016] Further, the negative active material includes one or more of graphite, hard carbon, silicon-carbon, silicon negative electrode, carbon microspheres; and / or,

[0017] The positive active material is prepared by a lithium iron phosphate solid phase method, a red iron process solid phase method, a ferrous oxalate process method, or a liquid phase method; and / or,

[0018] The negative electrode active material is graphite, which is obtained by grinding, sieving, shaping, granulating and graphitizing carbon-based raw materials. The graphite is primary particles and / or secondary particles.

[0019] Thirdly, this application provides an energy storage device, which includes a battery separator as described in the first aspect, or the energy storage device includes a battery separator prepared by the method described in the second aspect.

[0020] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0021] This application addresses two parameters that significantly influence the contact area of ​​the active material with the electrolyte: particle size distribution and pore size distribution. It constructs a spatial distribution coefficient η = a*γ / ζ for the active material and limits the ratio of the positive and negative electrode spatial distribution coefficients to satisfy: 1.5 ≤ η. 正 / η 负 A coefficient ≤3.3 offers several advantages: First, it ensures a high degree of matching in the transport rate of lithium ions between the positive and negative electrodes, resulting in excellent cycle stability for lithium-ion batteries. Second, since the spatial distribution coefficient can be determined through the quantity, particle size distribution, and pore distribution of the active material, the stability of the cycle performance of lithium-ion batteries can be determined more efficiently and easily, without requiring the electrodes to be assembled into a battery for testing. Third, because it fully considers the kinetic performance matching between the positive and negative electrodes, it avoids situations where improving one electrode significantly enhances kinetics while the other electrode remains unimproved, leading to kinetic mismatch and an inability to effectively improve cycle stability. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic diagram of the structure of a residential energy storage system according to an embodiment of this application;

[0024] Figure 2 This is a schematic diagram of the structure of an energy storage system according to an embodiment of this application.

[0025] Reference numerals: 100, energy storage system; 10, energy storage device; 20, power conversion device; 30, first user load; 40, second user load; 50, high-voltage cable; 60, first power conversion device; 70, second power conversion device. DETAILED DESCRIPTION

[0026] In the present application, the terms "upper", "lower", "left", "right", "front", "back", "top", "bottom", "inner", "outer", "middle", "vertical", "horizontal", "transverse", "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 to better describe the present application and its embodiments, and are not intended to limit the indicated devices, elements or components to have a specific orientation, or to be constructed and operated in a specific orientation.

[0027] 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 application can be understood according to the specific circumstances.

[0028] In addition, the terms "mount", "set", "provided with", "connected", "connected" should be broadly understood. 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 directly connected, or indirectly connected through an intermediate medium, or internal communication between two devices, elements or components. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0029] 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 intended 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.

[0030] The technical solutions of the present application will be further described below in conjunction with the embodiments.

[0031] The positive electrode sheet and the negative electrode sheet are the core components of the lithium ion battery, and their material performance has a decisive influence on the cycle stability of the lithium ion battery. The related technology often only focuses on the performance improvement of a single electrode sheet, but the lithium ion battery has two kinds of electrode sheets, positive electrode sheet and negative electrode sheet. The two kinds of electrode sheets interact with each other during charging and discharging. 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 difficult to efficiently and simply determine whether the lithium ion battery has excellent cycle stability only by the structure characteristics of a single electrode sheet and its active material.

[0032] On the basis of deeply analyzing the problems existing in the prior art, the application provides a lithium ion battery and an energy storage device, and through 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.

[0033] In a first aspect, the embodiments of the application provide a lithium ion battery, comprising a pole piece having an active material, the active material having a spatial distribution coefficient η in the pole piece, η = a * γ / ζ;

[0034] Wherein, a = 100;

[0035] Wherein, γ = Dn50 / (Dn100 - Dn00), Dn00 is the size of the active material corresponding to the number percentage of 0% of the active material, in units of μm, Dn100 is the size of the active material corresponding to the number percentage of 100% of the active material, in units of μm, Dn50 is the size of the active material corresponding to the number percentage of 50% of the active material, in units of μm;

[0036] ζ = 1 - D tap / D true , D tap is the tap density of the active material, in units of g / cm 3 , D true is the true density of the active material, in units of g / cm 3 ;

[0037] 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 having a first spatial distribution coefficient η 正 in the positive pole piece, and the negative active material having a second spatial distribution coefficient η 负 in the negative pole piece, 1.5 ≤ η 正 / η 负 ≤ 3.3.

[0038] 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.

[0039] The lithium ion battery of the embodiments of the application controls the first spatial distribution coefficient η 正 of the positive active material and the second spatial distribution coefficient η 负The ratio between them is in the range of 1.5-3.3, which can well match the kinetic performance of the positive and negative electrode sheets, so that the lithium ion transmission between the positive and negative electrodes is more balanced. In this way, the problems of lithium precipitation and serious side reactions at the interface of the negative electrode sheet caused by the mismatch of lithium ion transmission rate can be avoided, the diffusion capacity of lithium ion between the positive and negative electrode sheets is accurately controlled, and the cycle stability of the lithium ion battery is improved.

[0040] The spatial distribution coefficient η of the active material in the electrode sheet can reflect the lithium ion diffusion capacity of the positive and negative electrode sheets, which determines the transmission rate of lithium ion between the electrode sheets. The stronger the lithium ion diffusion capacity is, the faster the transmission rate is. When η 正 / η 负 When controlled in the range of 1.5-3.3 in the embodiments of the present application, the lithium ion diffusion capacity 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 capacity of lithium ion between the positive and negative electrode sheets, a lithium ion battery with good cycle stability can be obtained.

[0041] When η 正 / η 负 When <1.5, it indicates that the lithium ion transmission rate on the positive electrode sheet side is higher than that on 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 on the negative electrode sheet side, which is prone to interface lithium precipitation, and eventually leads to cycle performance degradation. When η 正 / η 负 When >3.3, it indicates that the lithium ion transmission rate on the positive electrode sheet side is lower than that on 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 on the negative electrode sheet side and the electrolyte, and further leads to serious and irreversible lithium loss, and eventually leads to the deterioration of the cycle performance of the battery.

[0042] In addition, in the embodiments of the present application, the spatial distribution coefficient η=a*γ / ζ, where a is a constant, γ=Dn50 / (Dn100-Dn00), and ζ=1-D tap / D trueIt can be seen that the space distribution coefficient of the embodiment of the present application 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 application 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*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.

[0043] As can be seen from the above, the embodiment of the present application constructs the space distribution coefficient η=a*γ / ζ of the active material with respect to the two parameters of the active material which have important influence on the contact area of the electrolyte, i.e. the number particle size distribution and the pore distribution, and limits the ratio of the positive and negative space distribution coefficients to satisfy: 1.5≤η 正 / η 负 ≤3.3. Firstly, it makes the transmission rate of lithium ions between the positive electrode plate and the negative electrode plate have 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 dynamic performance matching between the positive electrode and the negative electrode is fully considered, the situation that the dynamic performance of a single electrode plate is greatly improved after improvement, but the other electrode plate is not improved, and the dynamic performance is not matched, thereby the cycle stability cannot be effectively improved, does not occur.

[0044] Therefore, the embodiment of the present application can screen and determine the dynamic 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.

[0045] Further, 1.5≤η 正 / η 负 ≤2.8.

[0046] 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. Therefore, the embodiments of the present application can further optimize the η 正 / η 负 The ratio range is 1.5-2.8, which can obtain better cycle stability.

[0047] 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.

[0048] 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.

[0049] 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, but it will make the yield of active material low, the production cost of lithium ion battery high, and also not conducive to actual production.

[0050] It should be noted that, in the embodiments of the present application, 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 present application embodiment controls the parameter of the maximum pore volume ratio ζ formed when the active material is stacked, thereby limiting the balance matching of the positive and negative electrode sheets to the lithium ion transmission rate through the cooperation of the number particle size distribution and the pore distribution, which is more intuitive and simple. In addition, compared with the volume particle size distribution, the present application embodiment selects 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, so by the cooperation of the number particle size distribution and the pore distribution, it is beneficial to more accurately regulate and control the lithium ion transmission efficiency.

[0051] 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 .

[0052] Further, the tap density of the negative active material satisfies 1.0 g / cm 3 ≤D true ≤1.3 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 .

[0053] 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 .

[0054] 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 .

[0055] 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.

[0056] 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.

[0057] 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:

[0058] 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.

[0059] 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.

[0060] 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:

[0061] 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.

[0062] It should be noted that the active material of the embodiments of the present application can also be prepared by other conventional methods in the art, and the present application does not limit the preparation method of the positive active material (such as lithium iron phosphate) and the negative active material (such as graphite).

[0063] 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, etc., 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 the existing manufacturing process and equipment of lithium ion batteries, thus making it difficult to directly apply such a solution in actual production.

[0064] The positive active material and the negative active material used in the present application, especially the preferred lithium iron phosphate and graphite, can all be selected from the commonly used positive active material and negative active material in the art, without the need for further structural modification of the material. In this way, the embodiments of the present application do not require complex structural design of 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 application, 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 application more suitable for actual industrial application.

[0065] In a second aspect, the embodiments of the present application also provide a energy storage device 10, which comprises the battery separator film of the first aspect or the second aspect.

[0066] Taking electrochemical energy storage as an example, the embodiments of the present application 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.

[0067] Current energy storage applications are widely used, including energy storage on the power generation side, the power grid side, and the power consumption side. The corresponding types of energy storage devices 10 include:

[0068] (1) Large-scale energy storage power stations applied in wind power and photovoltaic power stations can assist renewable energy power generation to meet grid connection requirements and improve renewable energy utilization. As high-quality active / reactive power regulation power sources on the power supply side, energy storage power stations can 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, and have great significance in power grid system backup, peak load power supply pressure relief, and peak regulation;

[0069] (2) Energy storage containers applied in the power grid can mainly function as peak regulation, frequency regulation, and peak regulation for relieving power grid congestion, and can realize peak clipping and valley filling of power consumption, i.e., charging energy storage batteries during low power consumption load valleys and releasing stored power during high power consumption load peaks, thereby balancing power production and consumption;

[0070] (3) Small-scale energy storage cabinets applied in power consumption can mainly function as power self-generation and self-use, peak-valley price arbitrage, capacity cost management, and improved 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, which are generally used with distributed photovoltaic power. Industrial and commercial users can use energy storage for peak-valley price arbitrage and capacity cost management. In the electricity market implementing peak-valley electricity prices, the energy storage system 100 is charged during low electricity prices and discharged during high electricity prices to realize peak-valley price arbitrage and reduce electricity costs. In addition, industrial enterprises using two-part electricity prices can use the energy storage system 100 to store energy during low power consumption and discharge during peak load, thereby reducing peak power and the maximum demand amount reported, achieving the purpose of reducing capacity electricity costs. Household photovoltaic power storage can improve the level of power self-generation and self-use. Due to high electricity prices and poor power supply stability, household photovoltaic power demand is driven. Considering that photovoltaic power is generated during the day and users generally have high load at night, configuring energy storage can better utilize photovoltaic power, improve the level of self-generation and self-use, and reduce electricity costs. In addition, communication base stations and data centers need to configure energy storage for backup power.

[0071] Please refer to Figure 1 , Figure 1is a structural schematic diagram of a household energy storage system 100 according to an embodiment of the present application. The present application 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.

[0072] Please refer to Figure 2 , Figure 2 is a structural schematic diagram of an energy storage system 100 according to an embodiment of the present application. The present application Figure 2 The embodiment takes a power generation / distribution side shared energy storage scenario as an example for description. The energy storage device 10 according to the present application is not limited to the power generation / distribution side energy storage scenario.

[0073] The present application 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 application. In a power generation condition, 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, so as to reduce the wind and light curtailment rate and improve the new energy power generation consumption problem. When the electric load is high, the power grid issues an instruction, the energy storage device 10 stores the electric energy, and the high-voltage cable 50 transmits the electric energy in a grid-connected mode to supply the electric load for use, thereby providing peak shaving, frequency modulation, backup, and other services for the power grid operation, fully playing the role of the power grid peak shaving, promoting the power grid peak shaving and valley filling, and relieving the power grid power supply pressure.

[0074] 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.

[0075] 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.

[0076] 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 application can be, but is not limited to, the listed products, and can also be other application forms. The embodiments of the present application do not strictly limit the application form of the energy storage device 10. The embodiments of the present application only take the energy storage device 10 as a multi-core battery as an example for description. 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.

[0077] The scheme of the present application will be further introduced below in combination with specific examples and experimental data.

[0078] Example 1

[0079] The present embodiment provides a lithium ion battery, which is obtained by the following method.

[0080] Preparation of the positive electrode sheet: lithium iron phosphate, conductive carbon black and polyvinylidene fluoride are dispersed into N-methylpyrrolidone 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.

[0081] Preparation of the negative electrode sheet: graphite, conductive carbon black, sodium carboxymethyl cellulose and butadiene-styrene 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.

[0082] Preparation of the electrolyte: in an argon atmosphere glove box with water content ≤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.

[0083] Separator: a polyethylene separator with a thickness of 16 μm is used.

[0084] 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. After winding, a bare cell is obtained. After connecting the tab, the cell is assembled into an outer package, the above electrolyte is injected, and the cell is packaged, placed, formed, shaped, capacity tested, etc. Finally, a lithium ion battery is prepared.

[0085] Examples 2-6

[0086] The difference between Examples 2-6 and Example 1 is that the structural parameters of the positive active material and the negative active material are different, as shown in Table 1. The total mass of the negative active material in Example 6 is the same, and the mass of the hard carbon accounts for 2%.

[0087] Comparative Examples 1-2

[0088] The difference between Comparative Examples 1-2 and Example 1 is that the structural parameters of the positive active material and the negative active material are different, as shown in Table 1.

[0089] <Performance Test>

[0090] (1) Particle size distribution test of active material: The positive active material and the negative active material of Examples 1-6 and Comparative Examples 1-2 were taken and a laser particle size analyzer (Model Malvern Mastersizer 3000) was used to test Dn00, Dn50, and Dn100 according to the particle size distribution laser diffraction method (GB / T19077-2016).

[0091] (2) Tap density test of active material

[0092] 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 active material / negative active material after tapping was calculated.

[0093] (3) True density test of active material

[0094] 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 equilibrium 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 active material / negative active material was calculated.

[0095] (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.

[0096] The constant power charging is carried out at the charging power of 1P in the environment of 25℃ until reaching the upper limit voltage 3.65V and then the constant voltage charging is carried out, and then the constant power discharging is carried out at the discharging power of 1P until the final voltage is 2.5V, and the first cycle discharge capacity of the battery is recorded; and then 500 cycles of charging and discharging are carried out, and the discharge capacity of the 500th cycle is recorded. The capacity retention rate is calculated according to the formula: the capacity retention rate after the 500th cycle = (the discharge capacity after the 500th cycle / the first cycle discharge capacity) x 100%.

[0097] Table 1 structure parameters and test results of examples 1-6 and comparative examples 1-2

[0098]

[0099]

[0100] According to the above test results, η 正 / η 负 is 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 is too small, and in comparative example 2, η 正 / η 负 is too large, reflecting that the transmission rate of lithium ions between the positive electrode sheet and the negative electrode sheet is not matched, which is prone to problems such as interface lithium precipitation, serious side reactions, etc., resulting in decreased cycle performance.

[0101] The above technical solutions of the embodiments of the present application are described in detail, and the principles and implementation modes of the present application are described by applying specific examples. The above example is only used to help understand the technical solutions and core ideas of the present application. Meanwhile, for those skilled in the art, according to the idea of the present application, the specific implementation mode and application range will be changed, and the above description should not be understood as a limitation of the present application.

Claims

1. A lithium-ion battery, characterized in that, The lithium-ion battery includes an electrode with active material, wherein the active material has a spatial distribution coefficient η in the electrode, η=a*γ / ζ; Where a = 100; Wherein, γ = Dn50 / (Dn100-Dn00), Dn00 is the size of the active substance when the proportion of the active substance is 0%, in μm; Dn100 is the size of the active substance when the proportion of the active substance is 100%, in μm; and Dn50 is the size of the active substance when the proportion of the active substance is 50%, in μm. The ζ=1-D tap / D true The D tap The tap density of the active material is expressed in g / cm³. 3 The D true The true density of the active substance is expressed in g / cm³. 3 ; The electrode includes a positive electrode with a positive active material and a negative electrode with a negative active material. The positive active material is lithium iron phosphate, and the positive active material has a first spatial distribution coefficient η in the positive electrode. 正 The negative electrode active material has a second spatial distribution coefficient η in the negative electrode sheet. 负 1.5≤η 正 / η 负 ≤3.

3.

2. The lithium-ion battery according to claim 1, characterized in that, 1.5≤η 正 / or 负 ≤2.8。 3. The lithium-ion battery according to claim 1, characterized in that, For the negative electrode active material, 0.7 μm≤Dn00≤1.2 μm, 1.5 μm≤Dn50≤2.5 μm, and 20 μm≤Dn100≤50 μm.

4. The lithium-ion battery according to claim 1, characterized in that, The tap density of the negative electrode active material satisfies 1.0 g / cm³. 3 ≤D tap ≤1.3 g / cm 3 .

5. The lithium-ion battery according to claim 1, characterized in that, The true density of the negative electrode active material is 2.0 g / cm³. 3 ≤D true ≤2.3 g / cm 3 .

6. The lithium-ion battery according to claim 1, characterized in that, For the positive electrode active material, 0.10 μm≤Dn00≤0.30 μm, 0.70 μm≤Dn50≤1.0 μm, and 3.4 μm≤Dn100≤5.0 μm.

7. The lithium-ion battery according to claim 1, characterized in that, The tap density of the positive electrode active material satisfies 0.8 g / cm³. 3 ≤D tap ≤1.4 g / cm 3 .

8. The lithium-ion battery according to claim 1, characterized in that, The true density of the positive electrode active material satisfies 3 g / cm³. 3 ≤D true ≤3.8 g / cm 3 .

9. The lithium-ion battery according to claim 1, characterized in that, The negative electrode active material includes one or more of graphite, hard carbon, silicon carbide, silicon negative electrode, and carbon microspheres.

10. The lithium-ion battery according to claim 9, characterized in that, The negative electrode active material is graphite, which is obtained by grinding, sieving, shaping, granulating and graphitizing carbon-based raw materials. The graphite is primary particles and / or secondary particles.

11. The lithium-ion battery according to claim 1, characterized in that, The positive electrode active material is prepared by solid-phase method of ferric phosphate, solid-phase method of iron oxide red process, ferrous oxalate process or liquid-phase method.

12. An energy storage device, characterized in that, The energy storage device includes a lithium-ion battery as described in any one of claims 1 to 11.

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