Secondary battery and electrical device

Abstract

A secondary battery comprising a positive electrode plate, a negative electrode plate, a separator, and an electrolyte, characterized in that the positive electrode plate comprises a positive current collector and a layer of positive active material arranged on at least one surface of the positive current collector, the layer of positive active material comprises a positive active material, and the positive active material comprises a phosphate material, wherein a charging curve can be obtained by performing a charging test on the secondary battery at 25 °C at a rate of 2 C in a voltage range of 2.5 - 4.25 V, the charging curve having three charging plateaus with different potentials, namely a first plateau, a second plateau, and a third plateau in the order from a low potential to a high potential; The potential difference between the first plateau and the second plateau is represented by U in units of V; When the potential of the secondary battery is on the first plateau, a lithium-ion diffusion coefficient of a corresponding negative electrode plate r in units of × 10 -8 cm 2 / s is; and The secondary battery satisfies the following relationship: 0.06 ≤ U × r ≤ 0.189.

Description

TECHNICAL AREA

[0001] The present application relates to the field of electrochemical technology, in particular a secondary battery and an electrical device. BACKGROUND

[0002] Lithium-ion batteries are used in many fields such as 3C electronic products, electric vehicles and energy storage stations due to their high energy density, low self-discharge, lack of memory effect and long cycle life, and currently represent a research focus in new energy storage and conversion systems.

[0003] The material used for the positive electrode has a significant impact on the battery's performance and cost. Lithium manganese iron phosphate (LMFP) with an olivine structure offers a level of safety comparable to that of lithium iron phosphate due to the olivine structure of phosphate materials. Furthermore, the addition of manganese greatly enhances the reactivity of LMFP. Consequently, the market share of LMFP in the power battery market has steadily increased in recent years.

[0004] However, the LMFP material of the positive electrode is subject to some limitations during fast charging when using these batteries. At the initial charging stage, the positive electrode potential is relatively high, and during high-rate charging, the rapid increase in the positive electrode potential further promotes a rapid decrease in the negative electrode potential. This rapid potential change significantly shortens the fast-charging stage, which is detrimental to the battery's charging efficiency and increases the overall charging time.

[0005] Therefore, there is a need to develop a secondary battery with a higher fast-charging capability. SUMMARY OF THE INVENTION

[0006] The objective of the present application is to overcome the shortcomings of the prior art and to provide a secondary battery and an electrical device which reduces the charging time of the battery and improves the fast-charging cycle life by controlling the potential difference between two charging plateaus at a low SOC under charging conditions of 2 C and a lithium-ion diffusion coefficient of the corresponding negative electrode plate when the battery potential is at a first plateau, and the secondary battery exhibits excellent fast-charging capability.

[0007] To solve the above problem, in a first aspect of the present application a secondary battery is provided which has a positive electrode plate, a negative electrode plate, a separator and an electrolyte, wherein the positive electrode plate has a positive current collector and a layer of the positive active material arranged on at least one surface of the positive current collector, the layer of the positive active material has a positive active material, and the positive active material has a phosphate material; A charging curve can be obtained by performing a charging test on the secondary battery at 25 °C at a rate of 2 C in a voltage range of 2.5 - 4.25 V; the charging curve exhibits three charging plateaus with different potentials, namely a first plateau, a second plateau, and a third plateau in the order from a low potential to a high potential; the potential difference between the first plateau and the second plateau is represented by U in units of V. When the potential of the secondary battery is on the first plateau, a lithium-ion diffusion coefficient of the corresponding negative electrode plate divided by r in units of × 10 -8 cm 2 / s is shown; The secondary battery satisfies the following relationship: 0.06 ≤ U × r ≤ 0.189.

[0008] In a preferred embodiment of the present application, the secondary battery satisfies the following relationship: 0.124 ≤ U × r ≤ 0.152.

[0009] In a preferred embodiment of the present application, a value of U lies in the range of 0.07 to 0.19 V.

[0010] In another preferred embodiment of the present application, the value of U is in the range of 0.13 to 0.16 V.

[0011] In a preferred embodiment of the present application, a value of r lies in the range of 0.7 × 10 -8 up to 1.28 × 10 -8 cm 2 / s.

[0012] In another preferred embodiment of the present application, the value of r is in the range of 0.9 × 10 -8 up to 1.05 × 10 -8 cm 2 / s.

[0013] In a preferred embodiment of the present application, the phosphate material comprises lithium manganese iron phosphate (LMFP) and lithium iron phosphate (LFP).

[0014] In a preferred embodiment of the present application, the particle size Dn50 of the lithium iron phosphate (LFP) is 0.6 - 1.5 µm.

[0015] In a preferred embodiment of the present application, the particle size Dn50 of lithium manganese iron phosphate (LMFP) is 60 - 200 µm.

[0016] In a preferred embodiment of the present application, the mass ratio between lithium manganese iron phosphate (LMFP) and lithium iron phosphate (LFP) is (1.5 - 19): 1.

[0017] In a further preferred embodiment of the present application, the mass ratio between lithium manganese iron phosphate (LMFP) and lithium iron phosphate (LFP) is (2 - 6): 1.

[0018] In a preferred embodiment of the present application, the negative electrode plate comprises a negative current collector and a layer of the negative active material arranged on at least one surface of the negative current collector. The layer of the negative active material comprises a negative active material, comprising one consisting of natural graphite, synthetic graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, SiO₂. x , silicon-carbon composite material and / or lithium titanate is selected.

[0019] In a second aspect of the present application, the present application provides an electrical device which includes the aforementioned secondary battery.

[0020] Advantageous effects of the present application: The present application provides a secondary battery and an electrical device. The present application improves the fast-charging performance of the secondary battery, reduces the charging time of the secondary battery, and improves the fast-charging cycle life by controlling the potential difference between two charging plateaus at lower potentials under charging conditions of 2C and the lithium-ion diffusion coefficient of the negative electrode plate under specific conditions. BRIEF DESCRIPTION OF THE DRAWINGS Fig. Figure 1 is a diagram showing a charging curve of the lithium-ion battery of embodiment 1. Fig. Figure 2 is a diagram of a dQ / dV-V curve of the lithium-ion battery of embodiment 1. DETAILED DESCRIPTION

[0021] To clarify the purpose, technical solutions, and advantages of the embodiments of the present application, the technical solutions in the embodiments of the present application are described clearly and completely below. It is obvious that the described embodiments represent only a subset of the embodiments of the present application and not all embodiments. All further embodiments that can be derived by a person skilled in the art from the embodiments of the present application without inventive effort fall within the scope of protection of the present application.

[0022] In the present application, closed technical solutions composed of the listed features and open technical solutions containing the listed features are included for technical features that are described in an open manner.

[0023] In this application, unless otherwise specified, with regard to numerical ranges, the values ​​within the above numerical ranges are considered continuous and include the minimum and maximum values ​​of the range, as well as any value between these minimum and maximum values. If the range refers to integers, any integer between the minimum and maximum values ​​of the range is also included. If several ranges are provided to describe features or characteristics, these ranges may be combined. In other words, all ranges specified herein are to be understood as covering all subranges contained therein, unless otherwise stated.

[0024] The present application contains no specific restrictions with regard to specific dispersion and stirring treatment processes.

[0025] The reagents or instruments used in the present application are, without specified manufacturers, conventional products that can be purchased on the market.

[0026] In one embodiment of the present application, a secondary battery is provided comprising a positive electrode plate, a negative electrode plate, a separator, and an electrolyte. The positive electrode plate comprises a positive current collector and a layer of the positive active material arranged on at least one surface of the positive current collector, wherein the layer of the positive active material contains a positive active material and the positive active material comprises a phosphate material.

[0027] A charging curve is obtained by performing a charging test on the secondary battery at 25 °C at a rate of 2 C within a voltage range of 2.5–4.25 V. The charging curve includes three charging plateaus at different potentials, namely a first plateau, a second plateau, and a third plateau in the order from a low potential to a high potential; where the potential difference between the first plateau and the second plateau is represented by U in units of V. When the potential of the secondary battery is at the first plateau, the lithium ion diffusion coefficient of the corresponding negative electrode plate is given by r in units of x 10 -8 cm 2 / s displayed; The secondary battery satisfies the following relationship: 0.06 ≤ U × r ≤ 0.189.

[0028] In the fast-charging technology of secondary batteries, the battery's charging performance is closely linked to the material properties of the electrode materials and the operating state of the electrode plates. In the present application, it has been found that under charging conditions of 2C, comprehensive control of the potential difference (U) between the two charging plateaus of the secondary battery at a lower potential and of the lithium-ion diffusion coefficient (r) of the corresponding negative electrode plate when the battery potential is at the first plateau is key to improving the fast-charging performance of the secondary battery.

[0029] The battery's fast-charging mechanism employs a high-rate charging process in the initial charging stage, followed by a gradual reduction until full charge is achieved. During the initial charging stage, the negative electrode exhibits the highest lithium affinity and can accommodate a large number of lithium atoms, thus enabling high-rate charging in this initial phase. When the potential difference (U) is low, the polarization of the positive electrode can be enhanced during the high-rate charging stage. This effectively prevents an excessively rapid voltage drop at the negative electrode, ensuring a sustained high-rate charging period, reducing the overall charging time, and improving fast-charging performance.

[0030] The lithium-ion diffusion coefficient r of the negative electrode reflects the lithium ionization capacity of the negative electrode. If U and r satisfy the relationship 0.06 ≤ U × r ≤ 0.189, the battery's fast-charging capability is significantly improved, not only with relatively higher fast-charging rates but also with a better cycle life under fast-charging conditions.

[0031] If the value of U × r exceeds 0.189, the battery's potential difference at low potential plateaus is too large, and the lithium-ion diffusion coefficient of the negative electrode is too high. During the initial charging stage, when the battery has low remaining power (i.e., a low state of charge) and a high charging rate due to increased current density, a large number of lithium ions accumulate on the surface of the negative electrode. This leads to a blockage of lithium intercalation into the mass phase of the negative electrode, resulting in a poor fast-charging rate. This accumulation of lithium ions not only affects normal lithium intercalation in the negative electrode but can also cause structural damage to the negative electrode material, thus impacting the battery's stability and cycle life.Furthermore, at a high state of charge (SOC), the positive active material carries a higher current density, and a high charge makes it more difficult to polarize the positive electrode, thus hindering the deintercalation of lithium ions from the positive electrode and extending the fast-charging time. This not only reduces the battery's charging efficiency but can also increase thermal hazards during high-rate charging and reduce the battery's cycle life during fast charging.

[0032] If the value of U × r is less than 0.06, the battery's potential difference at low potential plateaus is too small to effectively improve its fast-charging capability; the lithium-ion diffusion coefficient of the battery's negative electrode is low, which may indicate that the charge transfer resistance (Rct) of the negative electrode plate is too high at the first plateau potential, and the increased impedance limits the diffusion of lithium ions at the negative electrode interface, thus hindering effective lithium-ion intercalation through the negative electrode. This results in a shortened charging time at a high rate under low state-of-charge (SOC) conditions during the initial charging stage, a deteriorated overall battery charging rate, and an extended charging time.

[0033] For example, the value of U × r in the present application can be 0.060, 0.070, 0.080, 0.090, 0.095, 0.100, 0.110, 0.150, 0.180, 0.189.

[0034] In one embodiment, the secondary battery satisfies the following relationship: 0.124 ≤ U × r ≤ 0.152.

[0035] If the product of U and r is within the range above, the secondary battery will have better fast-charging capability, a shorter fast-charging time, and a relatively higher cycle life when fast-charging.

[0036] In the secondary battery of the present application, the potential of the first plateau is generally between 3.4 and 3.6 V, and the potential of the second plateau is generally between 3.6 and 3.8 V.

[0037] In one embodiment, U is in the range of 0.07 to 0.19 V.

[0038] In a preferred embodiment, U is in the range of 0.13 to 0.16 V.

[0039] In the present application, it has been found that the fast-charging capability and cycle performance of the battery are significantly better when U is within a suitable range. If the value of U is too high, this indicates that the potential difference between the first and second plateaus is too large, and in this case, the electrode polarization increases when fast charging at a high state of charge (SOC), resulting in a longer charging time. In particular, if the potential of the second plateau is too high, a rapid decrease in the potential of the negative electrode is promoted, resulting in poor fast-charging performance. Furthermore, an excessively high value of U can indicate that the potential of the first plateau is too low.In LMFP batteries, the loss of active lithium from the negative electrode is the primary factor contributing to a decrease in cycle capacity, resulting in a drop in the capacity of the lower potential plateau of the positive electrode at the end of discharge. Furthermore, the lower the potential of the first plateau, the greater the risk of this drop, thus reducing the cycle capacity retention rate. If the voltage (U) is too low, the potential difference between the first and second plateaus is too small. When the battery is charged at a low state of charge (SOC), the corresponding potential of the negative electrode decreases rapidly until it reaches the cutoff potential. This results in a very short high-rate charging phase without any significant improvement in the battery's fast-charging rate.

[0040] The value of U is related to factors such as the type, composition, morphology (or shape / profile), and electrochemical properties of the phosphate materials in the positive active material. The value of U can be adjusted by controlling the composition, chemical element content, particle morphology, crystal structure, and processing technology of the phosphate materials in the positive active material.

[0041] In the present application, the value of U can be obtained from the charging curve diagram of the secondary battery.

[0042] In particular, U can be measured using the following method: (1) Capacity formation: After allowing the secondary battery to stand for 120 minutes at 25 °C, the secondary battery is discharged at a constant current of 0.33 C to 2.5 V; after allowing it to stand for 20 minutes, the secondary battery is charged at a constant current of 0.33 C to 4.25 V, charged at a constant current of 0.05 C, and discharged at a constant current of 0.33 C to 2.5 V; after repeating the above steps once, the charge capacity Q0 of the second cycle is obtained; (2) Plotting the charging curve: After standing for 120 minutes at 25 °C, the secondary battery is charged with a constant current of 2 C up to the upper limit of the voltage of 4.25 V, obtaining data of the charging capacity Q and the voltage V; (3) The following step is carried out: the derivatives of the above QV data are calculated, then dQ is divided by dV to obtain dQ / dV; the dQ / dV-V curve is plotted with dQ / dV as the ordinate and the voltage V as the abscissa; (4) In the dQ / dV-V curve, the peak position of the characteristic peak of the abscissa voltage with the range of 3.4 V - 3.6 V represents the potential U1 of the first plateau; the peak position of the characteristic peak of the abscissa voltage with the range of 3.6 V - 3.8 V represents the potential U2 of the second plateau; the potential difference U between the first plateau and the second plateau is U2-U1 in units of V.

[0043] In one embodiment, r lies in the range of 0.7 × 10 -8 up to 1.28 × 10 -8 cm 2 / s.

[0044] In one embodiment, r lies in the range of 0.9 × 10 -8 up to 1.05 × 10 -8 cm 2 / s.

[0045] During the charging process of lithium-ion batteries, the lithium-ion diffusion coefficient (r) of the negative electrode at the first plateau potential directly influences the charging efficiency and stability of the battery. The value of r reflects the transport rate and intercalation rate of lithium ions into the negative electrode of the battery. When r is within a suitable range, the negative electrode exhibits good lithium-ion transport and intercalation / deintercalation characteristics, and the solid electrolyte interface (SEI film) on the surface of the negative electrode exhibits good stability, resulting in both a better fast-charge rate and improved fast-charge cycle performance.If the value of r is too high, exceeding the preferred range described above, lithium ions are transported very rapidly into the bulk phase of the negative electrode. At this point, the layered structure of the negative electrode expands very rapidly, exposing numerous active sites and easily causing rupture of the SEI film. This induces severe side reactions at the interface and degrades high-temperature stability. If the value of r is relatively high, the limit of lithium intercalation is reached not only in the bulk phase but also at the interface of the negative electrode, even though the transport rate of lithium ions in the bulk phase is increased. Therefore, the fast-charging performance of the battery is not significantly improved at this point.If transport in the bulk phase occurs more rapidly, the exposure of active sites caused by structural expansion can induce interfacial side reactions and instead lead to a reduction in interfacial transport, thereby risking a deterioration of fast-charging performance. If the value of r is too small, below the preferred value mentioned above, the diffusion rate of lithium ions within the negative electrode is low, resulting in increased polarization of the negative electrode. Consequently, active lithium at the interface cannot be trapped in the bulk phase in a timely manner, leading to the risk of lithium plating, which impairs fast-charging performance and results in a longer charging time.

[0046] The value of r is influenced by several factors, such as the negative active material in the negative electrode plate, the design of the negative electrode plate, and the electrolyte. The value of r can be controlled to meet the requirements of the technical solution of the present application by adjusting the type, starting materials, processing technology, morphology of the negative active material, and the content of each component in the layer of the negative active material. The present application does not impose any restrictions on the method for determining r, and those skilled in the art can determine the ion diffusion coefficient of the negative electrode plate at the potential of the specific first plateau using conventional technical means, such as an electrochemical impedance spectroscopy (EIS) test.

[0047] For example, r can be determined using the following procedure: (1) The positive electrode plate and the negative electrode plate are removed from the secondary battery and reassembled, forming a single-layer battery, a PE separator is used, there are no special restrictions regarding the electrolyte components, and it is ensured that free electrolyte is present when the battery is charged to the upper voltage limit; and a copper wire is attached as a third electrode on the negative side; (2) After assembly of the single-layer battery, the single-layer battery is left to stand at 25 °C for 120 minutes, first charged with a constant current of 0.03 C to 4.25 V, then discharged with a constant current of 0.3 C to 2.5 V, charged with a constant current of 0.33 C to 4.25 V, then charged with a constant voltage to 0.05 C, left to stand at 25 °C for 10 minutes, then discharged with a constant current of 0.33 C to 2.5 V; after this process is repeated twice, the third electrode is plated with lithium, the positive electrode being used at 0.01 C for 6 hours; after completion of the plating, a charge is carried out again at 0.33 C to adjust the voltage to that of the first plateau; followed by a 30-minute stand at 25 °C, continuing with an EIS test to monitor the negative electrode and the third electrode at a test frequency of 0.01 - 106 Hz; (3) After the test, EIS data are obtained, the low-frequency range with a slanted line is selected, the curve with the real part Z' of ω -0,5 The impedance is plotted, the slope σ of the straight line in the region of the lowest frequency is selected; this slope is used in the formula: DLi + =(R 2 T 2 ) / (2A 2 n 4 F 4 C 2 σ 2 ) used, thereby enabling DLi + is obtained as the diffusion coefficient (r) of the lithium ion; where R is the gas constant in J / mol / K, T is the absolute reaction temperature in K, and A is the area of ​​the negative electrode material immersed in the electrolyte in cm². 2 where n is the number of electrons involved in the reaction, F is the Faraday constant in C / mol, and C is the molar concentration of lithium ions in mol / cm³. 3 is.

[0048] In one embodiment, the phosphate material comprises lithium manganese iron phosphate (LMFP) and lithium iron phosphate (LFP).

[0049] In the present application, the phosphate material comprises a mixture of lithium iron phosphate (LFP) and lithium manganese iron phosphate (LMFP). LFP and LMFP exhibit different material characteristics, in particular different charging and discharging characteristics, and a suitable combination of LFP and LMFP contributes to the secondary battery of the present application achieving better fast-charging capability.

[0050] During the initial stage of fast charging, the decrease in the negative electrode potential is influenced by the intercalation of lithium ions and their own interfacial and mass-phase impedances. Furthermore, the oxidation reaction of the positive electrode at a high potential further hinders the decrease in the negative electrode potential. If the phosphate material is a mixture of LFP and LMFP, the added LFP is delithiated before the LMFP, creating an oxidation plateau at a lower potential. This mitigates the decrease in the negative electrode potential and increases the intercalation space for lithium ions at the negative electrode. Additionally, the dissolution of metal from the positive electrode and its deposition on the negative electrode catalyzes the formation of an SEI film at the negative electrode, thus influencing the interfacial impedance of the negative electrode.In the present application, it has been found that the impedance of the SEI film of the negative electrode can be reduced by appropriately dissolving manganese from LMFP. Therefore, the combination of LFP and LMFP contributes to achieving improved fast-charging capability of the secondary battery.

[0051] In one embodiment, the mass ratio between lithium manganese iron phosphate (LMFP) and lithium iron phosphate (LFP) is (1.5 - 19): 1.

[0052] In a preferred embodiment, the mass ratio between lithium manganese iron phosphate (LMFP) and lithium iron phosphate (LFP) is (2 - 6): 1.

[0053] Within the preferred range above, the combination of LFP and LMFP has a better effect, resulting in a more significant improvement in the secondary battery's fast charging capability and a more balanced improvement in the fast charging rate and fast charging cycle life.

[0054] In one embodiment, the particle size Dn50 of the lithium iron phosphate (LFP) is 90 - 200 nm.

[0055] In a preferred embodiment, the particle size Dn50 of the lithium iron phosphate (LFP) is 150 - 180 nm.

[0056] In one embodiment, the particle size Dn50 of the lithium manganese iron phosphate (LMFP) is 50 - 180 nm.

[0057] In one embodiment, the particle size Dn50 of the lithium manganese iron phosphate (LMFP) is 90 - 120 nm.

[0058] The particle sizes of LFP and LMFP, as morphological features of the positive active material, influence not only the U-value but also the overall kinetic performance and stability of the battery. Combining LFP and LMFP with suitable particle sizes contributes to shortening the lithium ion transport path and ensures an adequate contact area between the positive active material and the electrolyte, thereby improving the battery's kinetic performance while avoiding excessive interface side reactions. Furthermore, the particles of the positive active material undergo some volume expansion and contraction during repeated charging and discharging cycles, particularly under fast-charging conditions where positive active materials are subjected to relatively higher internal stress.By combining materials with specific particle sizes, the mechanical stability of positive active materials can be improved, thereby increasing the fast-charging cycle life.

[0059] The particle sizes of lithium iron phosphate and lithium manganese iron phosphate can be controlled by adjusting the selection of starting materials and the process for producing lithium iron phosphate and lithium manganese iron phosphate.

[0060] In the present application, there are no restrictions regarding the test procedure for particle sizes of lithium iron phosphate and lithium manganese iron phosphate, and those skilled in the art can determine the particle sizes of lithium iron phosphate and lithium manganese iron phosphate using conventional technical means.

[0061] For example, the particle sizes of lithium iron phosphate and lithium manganese iron phosphate can be determined by the following method: A charge-free positive electrode plate is removed and soaked for 4 hours in a dimethyl carbonate (DMC) solution at room temperature. After soaking, the positive electrode plate is removed and dried in a vacuum environment, and the powder of the positive active material is scraped from the surface of the positive electrode plate using a ceramic knife. The scraped powder of the positive active material is uniformly dispersed in ethanol, followed by the performance of a SEM (scanning electron microscopy) test, whereby the element is isolated in the SEM observation field by means of EDS (energy-dispersive X-ray analysis) spot scans to identify lithium iron phosphate particles and lithium manganese iron phosphate particles;

[0062] The size of lithium iron phosphate and lithium manganese iron phosphate particles is measured in SEM images using MEARSURE NANO software. Particle sizes are obtained using the diagonal line method. After isolating more than 100 samples, the particle size distribution is analyzed, and the Dn50 particle size of lithium iron phosphate and lithium manganese iron phosphate is calculated, where Dn50 represents the particle size corresponding to 50% of the cumulative quantity in the quantity-based distribution.

[0063] The present application contains no restrictions regarding the method for producing LMFP, whereby skilled persons can produce LMFP using conventional technical means.

[0064] For example, the process for manufacturing LMFP may include the following steps: A source of manganese, a source of iron, a source of phosphorus, a source of lithium and a source of carbon (if present) are mixed in specific molar ratios and dispersed in a solvent for a reaction, resulting in a liquid mixture; The above liquid mixture is spray-dried, resulting in a powder; The spray-dried powder is sintered in an atmosphere with an oxygen concentration of less than 150 ppm; The sintered material is crushed and sieved, resulting in LMFP.

[0065] In particular, the process for manufacturing LMFP may include the following steps: The source of manganese, the source of iron, the source of phosphorus, and the source of lithium are mixed in a specific molar ratio and dispersed in deionized water; the concentration of reactive ions is controlled to be 1–8 M; then the source of carbon for the reaction is added, resulting in a liquid mixture; The above liquid mixture is spray-dried, resulting in a powder; The spray-dried powder is sintered in an atmosphere with an oxygen concentration of less than 150 ppm; The sintered material is crushed and sieved, resulting in LMFP.

[0066] The process for manufacturing LFP may include the following steps: The source of iron, the source of phosphorus, the source of lithium and the source of carbon (if present) are mixed in a specific molar ratio for mixing and sand milling; The mixed and sand-ground product is sintered in an atmosphere with an oxygen concentration of less than 150 ppm; The sintered material is crushed and sieved, resulting in LFP.

[0067] If necessary, the process for producing LFP after the sintering step is supplemented by a sand grinding (or ball grinding) step after the sintering of the finished product.

[0068] In particular, the process for manufacturing LFP may include the following steps: The source of iron, the source of phosphorus, the source of lithium and the source of carbon (if present) are mixed in a specific molar ratio for a 2- to 7-hour mixing and sand milling process; the linear speed for mixing and sand milling is 3-10 m / s; The sand-ground product is sintered in an atmosphere with an oxygen concentration of less than 150 ppm; The mixed and sand-ground product is sintered in an atmosphere with an oxygen concentration of less than 150 ppm; The sand milling (or ball milling) step after sintering is carried out with the sintered material, with the linear speed for the 2- to 6-hour sand milling after sintering being 8-15 m / s; After sand milling and sintering, the product is crushed and sieved, resulting in LFP.

[0069] The source of lithium may include lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate and / or lithium acetate.

[0070] The source of phosphorus may include diammonium hydrogen phosphate, lithium dihydrogen phosphate, ammonium phosphate and / or lithium phosphate.

[0071] The source of iron may include iron(II) oxalate, iron hydroxide, iron(II) hydroxide, iron phosphate, iron(II) phosphate, iron acetate, iron(II) acetate, iron carbonate, iron(II) carbonate, iron(III) oxide, iron(III,II) oxide and / or iron oxalate.

[0072] The source of manganese may include manganese carbonate, manganese sulfate, manganese nitrate, manganese chloride, manganese oxalate and / or manganese acetate.

[0073] The source of carbon can include glucose and / or sucrose.

[0074] Manganese iron phosphate can be selected to serve simultaneously as a source of manganese, iron, and phosphorus; iron phosphate can be selected to serve simultaneously as a source of manganese, iron, and phosphorus; the source of lithium can include lithium hydroxide, lithium carbonate, lithium nitrate, lithium oxalate, lithium dihydrogen phosphate, lithium citrate, and / or lithium acetate.

[0075] In the production of LMFP and / or LFP, a specific amount of dopant sources, such as a source of vanadium (vanadium pentoxide), a source of tungsten (ammonium metatungstate), a source of titanium (titanium oxide), a source of magnesium (magnesium carbonate), etc., can be mixed with the source of manganese (if present), a source of iron, a source of phosphorus, a source of lithium as required, thereby obtaining LMFP and / or LFP containing specific amounts of dopant elements.

[0076] The manganese content in LMFP can be controlled by adjusting the amounts added to the manganese source, the iron source, and phosphoric acid.

[0077] The particle size of LMFP or LFP can be controlled by adjusting the amount and type of carbon source added, the ball milling conditions, the sintering conditions, or by changing the comminution conditions and controlling the sieving conditions.

[0078] In addition to the above positive active materials, the positive active material layer may also include a conductive agent and a binder.

[0079] The conductive material only needs to exhibit suitable electronic conductivity without causing adverse chemical changes in the battery, and there are no specific restrictions regarding the type of conductive material in the present application. In particular, the conductive material may include carbon nanotubes, carbon black, and / or graphene.

[0080] The binder serves to improve adhesion between particles of the positive active material and between the positive active material and the current collector. The binder can be a conventional option used in batteries. In particular, the binder can include polyvinylidene fluoride (PVDF), polytetrafluoroethylene (PTFE), polyvinyl alcohol (PVA), styrene-butadiene rubber (SBR), polyacrylonitrile (PAN), polyimide (PI), polyacrylic acid (PAA), polyacrylate, polyolefin, sodium carboxymethylcellulose (CMC), and / or sodium alginate.

[0081] In the present application, the positive current collector is not subject to any special restriction as long as it has conductivity and does not cause adverse chemical changes in the battery, and it may consist, for example, of: stainless steel, aluminum, nickel, titanium, burnt carbon; or aluminum or stainless steel that has undergone a surface treatment with a coating of carbon, nickel, titanium, silver, etc.

[0082] In the present application, the positive electrode plate can be produced according to conventional methods in the field. For example, the positive active material, the conductive agent, and the binder are dispersed in the solvent, forming a uniform positive slurry. The positive slurry is applied to the positive current collector, followed by drying, rolling, and other processes, thereby obtaining the positive electrode plate.

[0083] In one embodiment, the negative electrode plate comprises a negative current collector and a layer of negative active material arranged on at least one surface of the negative current collector. The layer of negative active material comprises a negative active material consisting of natural graphite, synthetic graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, or SiO₂. x , silicon-carbon composite material and / or lithium titanate is selected.

[0084] The separator is located between the positive and negative electrode plates and is designed to separate them, thus preventing contact and short circuits. The separator can be made of various materials suitable for the separator membranes of the electrochemical energy storage device in this field. Specifically, the separator may include polyethylene, polypropylene, polyvinylidene fluoride, aramid, polyethylene terephthalate, polytetrafluoroethylene, polyacrylonitrile, polyimide, polyamide, polyester, and / or a natural fiber.

[0085] The electrolyte of the present application can be various electrolytes suitable for electrochemical energy storage devices in this field. The electrolyte includes an electrolyte salt and a solvent, and the electrolyte salt can typically include a lithium salt.

[0086] Specifically, the lithium salt includes lithium hexafluorophosphate (LiPF6), lithium tetrafluoroborate (LiBF4), lithium perchlorate (LiClO4), lithium hexafluoroarsenate (LiAsF6), lithium bis(fluorosulfonyl)imide (LiFSI), lithium bis(trifluoromethanesulfonyl)imide (LiTFSI), lithium trifluoromethanesulfonate (LiTFS), lithium difluoro(oxalato)borate (LiDFOB), lithium bis(oxalato)borate (LiBOB), lithium difluorophosphate (LiPO2F2), lithium difluorobis(oxalato)phosphate (LiDFOP), and / or lithium tetrafluoro(oxalato)phosphate (LiTFOP). The electrolyte concentration in the electrolyte solution can range from 0.5 to 5 mol / L.

[0087] In particular, the solvent includes ethylene carbonate (EC), propylene carbonate (PC), ethyl methyl carbonate (EMC), diethyl carbonate (DEC), dimethyl carbonate (DMC), dipropyl carbonate (DPC), methyl propyl carbonate (MPC), ethyl propyl carbonate (EPC), butylene carbonate (BC), fluoroethylene carbonate (FEC), methyl formate (MF), methyl acetate (MA), ethyl acetate (EA), propyl acetate (PA), methyl propionate (MP), ethyl propionate (EP), propyl propionate (PP), methyl butyrate (MB), ethyl butyrate (EB), γ-butyrolactone (GBL), sulfolane (SF), dimethyl sulfone (MSM), ethyl methyl sulfone (EMS) and / or diethyl sulfone (ESE).

[0088] In one embodiment of the present application, an electrical device is provided which includes the aforementioned secondary battery.

[0089] The secondary battery serves as a power supply for the electrical device.

[0090] The term "electrical device" refers to any device that can utilize electrical energy and convert it into mechanical energy, thermal energy, light energy, or other forms of energy, such as an electric motor, electric heater, electric light source, etc. The term "electrical device" may specifically include, but is not limited to, mobile devices, electric vehicles, electric trains, ships, satellites, energy storage systems, etc. Mobile devices may include mobile phones, laptops, drones, robotic vacuum cleaners, electronic cigarettes, etc.; electric vehicles may include pure electric vehicles, hybrid electric vehicles, plug-in hybrid electric vehicles, electric bicycles, electric scooters, electric golf carts, electric trucks, etc. The present application is further illustrated by specific embodiments below. Design 1

[0091] In embodiment 1, a lithium-ion battery is provided which is manufactured using the following method: (1) Production of a positive electrode plate (1.1) Preparation of the positive active material

[0092] Production of LMFP: Lithium hydroxide, manganese sulfate, iron chloride, potassium dihydrogen phosphate are reacted according to the molar ratio of the elements Li, Mn, Fe, P in the chemical formula LiMn₂ a Fe bPO4 (where the value a / b is 72 / 25) is weighed and added to deionized water, followed by stirring until complete dissolution and adjusting the amount of deionized water to control the concentration of the reacting ion (or the concentration of the reacting ions) to 1.5 M. The mixture is then heated to 65 °C and held at pH 7 for 3 hours, yielding a reaction precursor. Then, 20 wt% glucose, based on the weight of the reaction product LiMn, is added. aFe3PO4, weighed out, is added to glucose, followed by continuous stirring and dispersion at 500 rpm for 2 hours. This mixture is spray-dried to obtain a dried powder. The dried powder is then sintered under a protective atmosphere. The temperature of the tube furnace is started at room temperature and increased uniformly at 5 °C / min to 400 °C, held for 5 hours, then increased to 600 °C and held for 3 hours, after which it is allowed to cool naturally to room temperature. After classification and sieving, LMFP with a particle size Dn50 of 122 nm is obtained as the final LMFP product.

[0093] Production of LFP: Iron(II) oxalate, diammonium hydrogen phosphate, and lithium carbonate are weighed out as required in a molar ratio of Li, Fe, and P of 1:1:1 for mixing and sand milling. Additionally, 10 wt% sucrose, based on the weight of the LFP product, is weighed out. The above materials are added to the sucrose for 5 hours of mixing and sand milling at a linear velocity of 7 m / s. The sand milled material is sintered under a protective atmosphere. The temperature of the tube furnace is started at room temperature and rises uniformly at 5 °C / min to 250 °C, held at this temperature for 2 hours. The temperature increase continues until a sintering platform of 700 °C is reached, and the temperature is held at this platform for 6 hours. The material is then allowed to cool naturally to room temperature.The resulting material is subjected to sand milling after sintering for 4 hours at a linear speed of 10 m / s, then, after classification and sieving, LFP with a particle size Dn50 of 320 nm is obtained as the LFP end product. (1.2) LMFP and LFP are mixed in a mass ratio of 2.6:1, resulting in a positive active material; The positive active material is uniformly mixed with the binder (PVDF), the conductive agent (SP) and the conductive agent (CNT) in a mass ratio of 96:2:1.5:0.5 in NMP, then the mixed positive slurry is uniformly applied to the aluminum foil, followed by drying in a vacuum oven at 100 °C, and then the resulting product is rolled, thus obtaining the positive electrode plate. (2) Production of a negative electrode plate

[0094] The negative active material (artificial graphite) is mixed with a binder (carboxymethylcellulose, CMC) and a conductive agent (SP) in a mass ratio of 96:2.5:1.5, dispersed in deionized water, blended, and uniformly dispersed to produce a negative slurry. The negative slurry is uniformly applied to the negative current collector (copper foil). The negative current collector, coated with the slurry, is then placed in a vacuum environment in a 100 °C oven, where it is dried for 12 hours. It is then rolled to obtain a negative electrode plate. (3) Production of an electrolyte

[0095] Ethylene carbonate (EC) and ethyl methyl carbonate (EMC) are mixed in a weight ratio of 3:7, giving an organic solvent, and then the thoroughly dried lithium salt LiPF6 is dissolved in the organic solvent mixture, producing the electrolyte with a concentration of 1.15 mol / l. (4) Production of a separator

[0096] A polyethylene (PE) separator is used. (5) Manufacturing a battery

[0097] The positive electrode plate, separator, and negative electrode plate produced above are assembled, resulting in an unencapsulated cell without electrolyte filling; the unencapsulated cell is placed in an outer packaging film, the electrolyte produced above is injected into the dried unencapsulated cell, and the lithium-ion battery is obtained after vacuum packaging, standing, formation, inspection, and other procedures. Embodiments 2 - 21 and comparative examples 1 - 4

[0098] In embodiments 2-21 and comparative examples 1-4, a lithium-ion battery is provided in each case, the manufacturing process being essentially the same as in embodiment 1 with the following exceptions: During the production of a positive electrode plate: at step (1.1) for the production of LMFP:

[0099] The value of a / b in the chemical formula LiMn a Fe b PO4 corresponds to the representation in Tables 1-1 and 1-2; the amount of deionized water is adjusted so that the concentration of reaction ions is controlled to correspond to Tables 1-1 and 1-2; the particle size Dn50 of LMFP corresponds to Tables 1-1 and 1-2; For the production of LFP:

[0100] The linear speed of mixing and sand milling and the linear speed of sand milling after sintering correspond to the values ​​in Tables 1-1 and 1-2; the temperature of the sintering platform is controlled according to the values ​​in Tables 1-1 and 1-2; the particle size Dn50 of the LFP particles corresponds to Tables 1-1 and 1-2; in step (1.2) LMFP and LFP are mixed in the mass ratio shown in Tables 1-1 and 1-2; in the production of a negative electrode plate: The mass ratio of the negative active material, the binder and the conductive material is set according to the information in Tables 1-1 and 1-2. Table 1-1 LMFP LFP away Dn50 (nm) Ion concentration of the reaction (M) Dn50 (nm) Linear speed of grinding and sand grinding (m / s) Linear speed of sand grinding after sintering (m / s) Temperature of the sintering platform (°C) Mass ratio of mixed LMFP and LFP Mass ratio of negative active material, binder and conductive agent Design 1 75 / 25 93 1,5 160 7 10 700 2,6:1 96:2,5: 1,5 Design 2 75 / 25 115 1,2 152 7 12 680 4:1 96:2,6: 1,4 embodiment 3 70 / 30 105 1,3 164 8 11 700 2,6:1 96:2,4: 1,6 Design 4 85 / 15 99 1,5 166 8 10 710 2:1 95,8:2,7: 1,5 Design 5 75 / 25 91 1,5 151 5 12 710 3,5:1 95,9:2,5:1,6 Design 6 70 / 30 51 1,7 105 7 10 700 3:1 95,9:2,4:1,7 Model 7 65 / 35 155 1,3 135 7 12 680 2,6:1 96:2,3:1,7 Design 8 65 / 35 107 1,4 92 8 13 730 6:1 96:2,5: 1,5 Design 9 80 / 20 175 1,6 197 9 10 680 2,8:1 96:2,7:1,3 Design 10 55 / 45 99 1,6 156 5 12 710 2,6:1 96:2,3:1,7 Design 11 85 / 15 102 1,3 180 7 10 700 2,3:1 96:2,7:1,3 Design 12 65 / 35 115 1,4 177 7 12 680 3,5:1 95,8:2,3:1,9 embodiment 13 75 / 25 104 1,4 161 8 13 730 3:1 96:2,9:1,1 embodiment 14 85 / 15 100 1,8 163 9 10 680 1,5:1 96:2,5: 1,5 Design 15 50 / 50 113 1,6 175 7 12 680 19:1 96:2,3:1,7 Table 1-2 LMFP LFP away Dn50(nm) Ion concentration of the reaction (M) Dn50(nm) Linear speed of grinding and sand grinding (m / s) Linear speed of sand grinding after sintering (m / s) Sintering platform temperature (°C) Mass ratio of mixed LMFP and LFP Mass ratio of the negative active material, the binder and the conductive agent Design 16 65 / 35 107 1,5 160 8 13 730 9:1 95,8:2,7: 1,5 embodiment 17 75 / 25 101 1,5 157 9 10 690 2,3:1 96:2,3:1,7 Design 18 70 / 30 118 1,6 167 7 12 720 2,8:1 96:2,7:1,3 Design 19 50 / 50 95 1,4 163 7 12 680 2,8:1 95,7:3,3:1,0 Design 20 50 / 50 100 1,3 175 8 13 730 3,8:1 96:1,9:2,1 Design 21 90 / 10 97 1,5 159 7 9 730 3:1 95,5:3,5:1,0 Comparative example 1 40 / 60 92 1,4 151 7 12 680 5,5:1 95,5:3,5:1,0 Comparative example 2 75 / 25 135 1,7 178 8 13 730 5:1 96:2,0:2,0 Comparative example 3 90 / 10 167 1,5 213 7 12 680 4,5:1 96:2,1:1,9 Comparative example 4 60 / 40 61 1,6 107 8 13 730 4:1 96: 1,6:2,4

[0101] The methods for determining U and r of each embodiment and each comparative example are as follows: Procedure for determining U: (1) Capacity formation: The secondary battery is left to stand at 25 °C for 120 min, followed by a discharge with a constant current from 0.33 C to 2.5 V; the secondary battery is left to stand for 20 min, followed by a charge with a constant current from 0.33 C to 4.25 V, a charge with a constant voltage to 0.05 C, a discharge with a constant current from 0.33 C to 2.5 V; after a single repetition of the above steps, the charge capacity Q0 of the second cycle is obtained; (2) Plotting the charging curve: the secondary battery is left at 25 °C for 120 min, followed by charging with a constant current of 2 C up to the upper limit of the voltage of 4.25 V, so that data for the charge capacity Q and the voltage V are obtained; (3) The derivative is calculated using the QV data above, then dQ is divided by dV to obtain dQ / dV; the dQ / dV-V curve is plotted with dQ / dV as the ordinate and the voltage V as the abscissa; (4) In the dQ / dV-V curve, the peak position of the characteristic peak of the abscissa voltage with the range of 3.4 V - 3.6 V represents the potential U1 of the first plateau; the peak position of the characteristic peak of the abscissa voltage with the range of 3.6 V - 3.8 V represents the potential U2 of the second plateau; the potential difference U between the first plateau and the second plateau is U2-U1 in units of V.

[0102] Test procedure for r: (1) The positive electrode plate and the negative electrode plate are removed from the secondary battery and reassembled to form a single-layer battery, a PE separator is used, there are no special restrictions regarding the electrolyte components, and it is ensured that free electrolyte is present when the battery is charged to the upper voltage limit; a copper wire is attached as a third electrode on the negative side; (2) After assembly of the single-layer battery, the single-layer battery is left to stand at 25°C for 120 minutes, followed by charging at a constant current of 0.03C to 4.25V, then discharging at a constant current of 0.3C to 2.5V, charging at a constant current of 0.33C to 4.25V, then charging at a constant voltage to 0.05C, standing at 25°C for 10 minutes, and then discharging at a constant current of 0.33C to 2.5V; after repeating the above steps twice, the third electrode is plated with lithium at 0.01C for 6 hours using the positive electrode; after completion of the plating, it is charged again at 0.33C to adjust to the voltage of the first plateau; after standing at 25°C for 30 minutes, an EIS test is performed; The negative electrode and the third electrode are tested at a frequency of 0.01 - 10 6 Hz monitored; (3) After the test, EIS data are obtained, the low-frequency range with a slanted line is selected, the curve with the real part Z' of ω -0,5 Impedance is plotted, the slope σ of the straight line in the region of the lowest frequency is selected; this slope is entered into the formula: DLi + =(R 2 T 2 ) / (2A 2 n 4 F 4 C 2 σ 2 ) used, thereby enabling DLi + is obtained, where is the diffusion coefficient (r) of the lithium ion; where R is the gas constant in J / mol / K, T is the absolute reaction temperature in K, A is the area of ​​the material of the negative electrode immersed in the electrolyte in cm² 2 where n is the number of electrons involved in the reaction, F is the Faraday constant in C / mol, and C is the molar concentration of lithium ions in units of mol / cm³. 3 is.

[0103] Fig.Figure 1 is a diagram showing the charging curve of the lithium-ion battery of embodiment 12, where SOC (%) represents the charging capacity Q. Fig. 2 is the dQ / dV-V curve of the lithium-ion battery of embodiment 12.

[0104] The test results for each embodiment and each comparison example are shown in Table 2. Table 2 U (in units of V) R (in units of × 10 -8 cm 2 / s) U × r Design 1 0,150 0,98 0,147 Design 2 0,156 0,9 0,140 embodiment 3 0,145 1,05 0,152 Design 4 0,16 0,94 0,150 Design 5 0,13 0,96 0,125 Design 6 0,15 1,01 0,152 Model 7 0,138 1,03 0,142 Design 8 0,147 0,97 0,143 Design 9 0,158 0,91 0,144 Design 10 0,122 1,03 0,126 Design 11 0,164 0,92 0,151 Design 12 0,097 1,28 0,124 embodiment 13 0,158 0,82 0,130 embodiment 14 0,146 0,99 0,145 Design 15 0,131 1,04 0,136 Design 16 0,155 0,94 0,146 embodiment 17 0,153 1,03 0,158 Design 18 0,132 0,91 0,120 Design 19 0,072 0,83 0,060 Design 20 0,148 1,28 0,189 Design 21 0,19 0,71 0,135 Comparative example 1 0,075 0,71 0,053 Comparative example 2 0,19 1,22 0,232 Comparative example 3 0,241 1,18 0,284 Comparative example 4 0,137 1,96 0,269

[0105] Performance tests regarding the fast charging time and fast charging cycle life of the lithium-ion batteries were conducted using the following specific procedures: (1) Fast charging time for a SOC of 8% - 80% at room temperature: The lithium-ion battery is discharged with a constant current of 0.05 C to 2 V, disassembled without charge, maintaining room temperature and low humidity during disassembly; after disassembly, the positive and negative electrode plates are immediately sealed in aluminum-plastic bags to insulate them from external moisture and air; the electrode plates are transferred to a glovebox; after complete evaporation of the electrolyte, cutting into pieces, and weighing, a complete battery is assembled, a copper wire is attached to the surface of the negative electrode plate; then electrolyte is injected, and the resulting product is left to stand at room temperature for 24 hours, thus obtaining a complete battery; The above battery is fully charged at 0.05C to 4.25V, discharged at a constant current of 0.33C to 2.5V; after a 10-minute standstill, the battery is recharged at a constant current of 0.33C to 4.25V, charged at a constant voltage until it is cut off at 0.05C, and after a 10-minute standstill, the battery is discharged at a constant current of 0.33C to 2.5V. Using the charging capacity from the last cycle as a standard, the battery is charged at 0.33C up to an 8% state of charge (SOC). It is then charged with a constant current in the sequence 2C-1.8C-1.6C-1.4C-1.2C-1C-0.8C-0.6C-0.4C-0.3C-0.2C-0.1C-0.05C until a voltage of 4.25V is reached and the negative electrode potential (relative to lithium) reaches 0mV. This is the cutoff condition until either 100% SOC is reached or the current drops to 0.05C. The charging time is recorded from 8% to 80% SOC. (2) Capacity retention rate for a fast charge cycle of 100 cycles at room temperature: A charge-discharge cycle test is performed on the above lithium-ion battery at 25 °C using a battery charge-discharge tester under the following charge-discharge conditions: discharge with a constant current of 0.33 C to 2.5 V, stand for 10 minutes, charge with a constant current of 0.33 C to 4.25 V, then charge with a constant voltage until cut-off at 0.05 C, stand for 10 minutes, charge with a constant current of 0.33 C to 4.25 V; Repeat the above charge-discharge cycle twice, then charge at 25 °C with a constant current of 1 C up to a constant voltage of 4.3 V, then discharge with a constant current of 1 C down to 2.5 V, repeat the above charge and discharge cycles at 1 C for 100 cycles, record the discharge capacity of the first cycle as Q1, the discharge capacity of the 100th cycle as Q100, capacity retention rate for 100 cycles = (Q2 / Q1) × 100 %.

[0106] The test results are shown in Table 3. Table 3 Fast charging time (min) Capacity retention rate for one fast charging cycle of 100 cycles (%) Design 1 21,8 97,8 Design 2 22,1 98,1 embodiment 3 20,8 97,5 Design 4 21,2 97,1 Design 5 21,9 97,2 Design 6 22,2 96,7 Model 7 22,7 96,6 Design 8 22,1 96,9 Design 9 22,6 96,8 Design 10 23,1 96,4 Design 11 24,1 95,9 Design 12 24,3 96,2 embodiment 13 23,9 96,3 embodiment 14 24,8 97 Design 15 23,2 95,8 Design 16 23,5 96,1 embodiment 17 25,1 95,2 Design 18 25,5 95,6 Design 19 26,5 94,8 Design 20 26,1 95 Design 21 26,9 94,3 Comparative example 1 28,9 93,2 Comparative example 2 29,2 93,1 Comparative example 3 31,8 91,5 Comparative example 4 33,2 90,2

[0107] According to the test results in Table 3, the lithium-ion batteries produced according to various embodiments of the present application all exhibit good fast charging performance with a fast charging time ≤26.9 min and good fast charging cycle stability with a capacity retention rate ≥94.3 % after 100 fast charging cycles.

[0108] From embodiments 1-4, 10-13, and 17-21, it is evident that the lithium-ion battery exhibits a shorter fast-charging time and a higher capacity retention rate after 100 fast-charging cycles when the product of the potential difference between the first plateau and the second plateau and the lithium-ion diffusion coefficient of the corresponding negative electrode plate at the potential of the first plateau is 0.125 ≤ U × r ≤ 0.152. 2 / s is located, which has better fast charging performance.

[0109] From embodiments 6 - 9 and embodiments 14 - 16, it can be seen that with the lithium-ion battery, if the particle size Dn50 of LFP is in the range of 90 - 200 nm, the particle size Dn50 of LMFP is in the range of 50 - 180 nm and the mass ratio of LFP to LMFP is (1.5 - 19):1, a comprehensively good fast charging performance can be achieved.

[0110] According to comparative examples 1-4, the fast-charging performance of the lithium-ion battery is still comparatively poor, with either an excessively long fast-charging time or an excessively low capacity retention rate after fast charging, if the value of U × r of the lithium-ion battery exceeds the range of the technical solution of the present application, even if the value of U is within 0.11-0.19 V and the value of r is 0.7 × 10 -8 -1.25 × 10 -8 cm 2 / s fulfilled.

[0111] Finally, it should be noted that the above embodiments are used only to illustrate the technical solutions of the present application, rather than to limit the scope of protection of the present application. Although the present application has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions of the technical solutions of the present application can be made without altering the content and scope of the technical solutions of the present application.

Claims

[1] Secondary battery comprising a positive electrode plate, a negative electrode plate, a separator and an electrolyte, characterized by , that the positive electrode plate has a positive current collector and a layer of positive active material arranged on at least one surface of the positive current collector, the layer of positive active material has a positive active material and the positive active material has a phosphate material, wherein a charging curve can be obtained by performing a charging test on the secondary battery at 25 °C at a rate of 2 C in a voltage range of 2.5 - 4.25 V, the charging curve having three charging plateaus with different potentials, which are a first plateau, a second plateau and a third plateau in the order from a low potential to a high potential; The potential difference between the first plateau and the second plateau is represented by U in units of V; When the potential of the secondary battery is on the first plateau, a lithium-ion diffusion coefficient of a corresponding negative electrode plate r in units of × 10 -8 cm 2 / s is; and The secondary battery satisfies the following relationship: 0.06 ≤ U × r ≤ 0.

189. [2] Secondary battery according to claim 1, characterized by , that the secondary battery satisfies the following relationship: 0.124 ≤ U × r ≤ 0.

152. [3] Secondary battery according to claim 1 or 2, characterized by , that the value of U is in the range of 0.07 V to 0.19 V. [4] Secondary battery according to claim 3, characterized by , that the value of U is in the range of 0.13 V to 0.16 V. [5] Secondary battery according to claim 1 or 2, characterized by , that a value of r in the range of 0.7 × 10 -8 cm 2 / s to 1.28 × 10-8 cm 2 / s lies. [6] Secondary battery according to claim 5, characterized by , that the value of r is in the range of 0.9 × 10 -8 cm 2 / s to 1.05 × 10 -8 cm 2 / s lies. [7] Secondary battery according to claim 1 or 2, characterized by , that the phosphate material contains lithium manganese iron phosphate (LMFP) and lithium iron phosphate (LFP). [8] Secondary battery according to claim 7, characterized by , that the particle size Dn50 of lithium iron phosphate (LFP) is 90 - 200 nm. [9] Secondary battery according to claim 7, characterized by , that the particle size Dn50 of lithium manganese iron phosphate (LMFP) is 50 - 180 nm. [10] Secondary battery according to claim 7, characterized by , that the mass ratio between lithium manganese iron phosphate (LMFP) and lithium iron phosphate (LFP) is (1.5 - 19):

1. [11] Secondary battery according to claim 10, characterized by, that the mass ratio between lithium manganese iron phosphate (LMFP) and lithium iron phosphate (LFP) is (2 - 6):

1. [12] Secondary battery according to any one of the preceding claims, characterized by that the negative electrode plate has a negative current collector and a layer of negative active material arranged on at least one surface of the negative current collector, the layer of negative active material containing a negative active material, the negative active material comprising at least one material consisting of natural graphite, synthetic graphite, mesocarbon microbeads (MCMB), hard carbon, soft carbon, silicon, SiO₂ x , silicon-carbon composite material and lithium titanate is selected. [13] Electrical device, characterized by that the electrical device comprises the secondary battery according to any one of claims 1 to 12. [14] Electrical device according to claim 13, characterized bythat the electrical device is a mobile device, an electric vehicle, an electric train, a ship, a satellite or an energy storage system. [15] Electrical device according to claim 14, characterized by that the mobile device is a mobile phone, a laptop, a drone, a robotic vacuum cleaner, or an electronic cigarette. [16] Electrical device according to claim 14, characterized by that the electric vehicle is a pure electric vehicle, a hybrid electric vehicle, a plug-in hybrid electric vehicle, an electric bicycle, an electric scooter, an electric golf cart or an electric truck.

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